CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

Any example answers to questions taken from past question papers, practice questions, accompanying marks and mark
schemes included in this resource have been written by the authors and are for guidance only. They do not replicate
examination papers. In examinations the way marks are awarded may be different.

Coursebook answers
Biology
Chapter B1 A multicellular organism is made of many
cells – for example, a human or a plant.
Before you start B1.04 The animal cells do not have any coloured
1 excretion, sensitivity, growth, reproduction, parts, which makes them difficult to see
movement, nutrition, respiration without a stain, but the plant cells contain
green chloroplasts. Also, the plant cell
2 You could look for cell walls, which all plant walls stand out because they are much
cells have, but no animal cell does. You could thicker than the animal cell membranes.
also look for chloroplasts – if the cell has
these, it is a plant cell. However, if it does not B1.05 a ribosome
have chloroplasts it could still be a plant cell. b nucleus
In a multicellular organism, different c chloroplast
cells can become specialised to carry out d cell wall
particular functions.
e vacuole
Science in context B1.01 f cell membrane
In a multicellular organism, different B1.06 ribosome, nucleus, cell membrane
cells can become specialised to carry out B1.07 For example:
particular functions.
Bacterial cell Animal cell Plant cell
Questions has cell has cell has cell
B1.01 Although plants might appear to be still membrane membrane membrane
and unable to respond to changes in their has cell wall, no cell wall cell wall
environment, they demonstrate sensitivity but not made made of
and can move, albeit much more slowly of cellulose cellulose
than animals. They also show the other key has cytoplasm has cytoplasm has cytoplasm
characteristics of living things: they respire,
no nucleus has a nucleus has a nucleus
reproduce, grow, excrete waste gases, and
gain nutrition through photosynthesis. DNA is DNA is not DNA is not
circular circular circular
B1.02 The responses from learners will vary, and forms and forms
depending on the organisms they choose. chromosomes chromosomes
It is important that the responses clearly
has has has
identify the characteristics of living things
ribosomes ribosomes ribosomes
that are carried out all the time by their
chosen organisms (such as respiration does has has
and excretion), and the characteristics not have mitochondria mitochondria
that only happen at certain times (such as mitochondria
growth and reproduction). does does may have
not have not have chloroplasts
B1.03 A unicellular organism is made of
chloroplasts chloroplasts
a single cell – for example, bacteria.

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B1.08 1000 • ribosome – where proteins are made

B1.09 a actual length in Figure B1.10 is 83 mm • mitochondrion – site of aerobic
respiration / releases energy
b 83 mm = 83 × 1000 = 83 000 μm from glucose[6]
c Real size = 83 000 ÷ 20 000 = 4.15 μm
6 a nucleus[1]
d 1 mm = 1000 μm. So you could fit
1000 ÷ 4.15 = 240.96. Rounded up, b Any six from:
this is 241 mitochondria. • protein synthesis requires energy
Practice questions • B is a mitochondrion; mitochondria
1 C[1] provide energy (do not accept
produce energy)
2 a 
taking in substances from the
environment; and using them • by aerobic respiration; which releases
for energy, growth and development[2] energy from glucose

b By detecting chemicals on the gills • C is a ribosome

of a fish, the tongue-eating louse is • ribosomes are the site of
demonstrating sensitivity. protein synthesis[6]
By crawling into the fish’s
c Any one from:
mouth, the tongue-eating louse is
demonstrating movement.[2] • has a nucleus
c i the processes that make new • has mitochondria
organisms; of the same species[2]
• has vesicles[1]
ii Possible reasons include: short life
cycle; spends very little time Chapter B2
outside the host organism;
rare in the wild.[1] Before you start
3 B[1] • The particles are far apart and rarely collide
with each other. – gas
4 B[1]
• The particles vibrate on the spot. – solid
5 a Magnification = image size ÷ actual size.
• The particles are close to one another but can
Width of jellyfish in the photo is 89 mm. move around. – liquid
Actual width of jellyfish is 50 mm.
• The particles move freely in all directions. – gas
So magnification is 89 ÷ 50 = ×1.78.
Round up to 2 significant figures: ×1.8[3] • The particles stay in contact and slide past one
another as they move. – liquid
(one mark for stating correct equation;
one mark for correct substitution into • The particles are in fixed positions, close to
equation; one mark for correct statement of one another. – solid
magnification, with a × sign and no unit)
Science in context B2.01
b Any three of the following pairs, two
marks per pair: 1 Learners cannot be expected to know any
detail about transplants or availability of
• cell membrane – partially permeable / organs and should be encouraged to put
controls what enters and leaves the cell forward any suggestions that they have.
• cytoplasm – where many metabolic The real reasons are: the body will reject an
reactions take place organ that is from a person with a different
tissue type, so it is very difficult to find a
• nucleus – contains DNA / kidney that will be accepted by the recipient’s
chromosomes / information about body; there are never enough donated
which proteins the cell makes

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kidneys to go around – they need to come Experimental skills B2.02

from a healthy person who has recently died,
or from a close relative who is willing to 1 The answers provided by the learner will
donate one. depend upon which of the three variables is
chosen for investigation.
2 This question looks ahead to factors that
affect the rate of diffusion, and to the concept 2 The independent variable is the variable
of a diffusion gradient. Learners may be that is changed by the learner. The answer
able to work out for themselves that keeping provided by the learner will depend upon
the fluid flowing through will make sure that which of the three variables is chosen
the harmful substances do not build up in the for investigation.
dialysis fluid, and may also be able to see that 3 The answer provided by the learner will
this would stop the substances from diffusing depend upon which of the three variables
out of the blood and into the fluid. is chosen for investigation. However, it will
be important for the learner to identify a
Activity B2.01 sufficient range of values to show a pattern or
The ‘particles’/people have diffused to fill the space trend in the results.
available by moving around and bumping into
4 The dependent variable is the variable that is
each other (or in this case, avoiding bumping into
measured by the learner. This is the time taken
each other).
for the cubes to completely change colour.
This can then be used to calculate the rate
Questions of diffusion.
B2.01 a 
Diffusion requires particles to
spread out. 5 The answer provided by the learner will
depend upon which of the three variables is
b For diffusion to occur, particles chosen for investigation. However, it will be
must spread out from a region of important for the learner to identify a method
high concentration to a region of by which the dependent variable can be
lower concentration. measured in a straightforward way.
c Diffusion depends on the movement 6 The answer provided by the learner will
of particles in all directions so that depend upon the nature of their investigation.
they can spread out effectively. However, it will be important for the
learner to provide a comprehensive list of
B2.02 the cell membrane variables to keep constant (standardised),
and to describe how this will be achieved in
Experimental skills B2.01 each case.
1 The cubes had an alkali in them. As the acid
7–9  The answers provided by the learner will
diffused into the agar jelly cubes, it neutralised
depend upon which of the three variables is
the alkali, so the indicator changed colour.
chosen for investigation.
2 The total volume was the same.
Questions
3 The surface area of the eight small cubes was
double/larger than the surface area of the B2.03 Water is the solvent and sugar is
large cube. the solute.

4 The time taken for the eight small cubes to B2.04 The water molecules are small enough to
completely change colour was shorter than the pass through the holes in the membrane,
time for the one single cube. This is because but the sugar molecules are too big.
the surface area of the small cubes was greater B2.05 from the dilute solution to the
than that of the single cube. concentrated solution
5 The conclusion will depend on the results but B2.06 The dilute solution has the higher water
is likely to be: the greater the surface area, the potential, because it contains more
faster diffusion takes place. water molecules.

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B2.07 When an animal cell is placed in pure b to allow time for the dye solutions to
water, water enters the cell by osmosis come to the same temperature as the
through the partially permeable water-baths[1]
cell membrane.
c Any two from:
B2.08 Plant cells have a strong cell wall • the concentration of the dye solution
surrounding the cell membrane,
which stops the cell bursting. • the volume of the dye solution

B2.09 Water moves out of the cell through the • the volume of the jelly cubes
partially permeable cell membrane. • the surface area of the jelly cubes[2]
The cytoplasm and vacuole shrink. d i the value at 20 °C, time 4.5 minutes;
The cell membrane is pulled away from because the time is shorter than the
the cell wall. time at 30 °C[2]

B2.10 The same solution that the cell is ii As the temperature increases, the
immersed in. The only thing between the time to change colour decreases.[1]
external solution and space X is the cell
iii At higher temperatures, kinetic
wall, which is fully permeable.
energy of particles increases; so,
B2.11 The cells will take up water by osmosis, particles move faster / diffusion
because the water potential of the water happens more quickly.[2]
outside the cell is greater than the water
4 a 
the net movement of water molecules;
potential of the solution inside the cell.
from a higher water potential to a
The vacuole and cytoplasm will increase
lower water potential / down a water
in volume, so the cell membrane will be
potential gradient; through a partially
pushed back against the cell wall, into its
permeable membrane[2]
normal position.
b Any six from:
Experimental skills B2.03
• both animal cell and plant cell take
1 Learners should find that they got longer. up water by osmosis
2 Each cell in the piece of potato gained water • because there is a water potential
by osmosis, because the solution inside the cell gradient from outside the cell to inside
was more concentrated (had less water, or a
lower water potential) than the water outside. • the volumes of both cells increase
As each cell swelled up, this increased the size • the animal cell bursts but the plant
of the potato strip. cell does not
3 Learners should find that they got shorter.
• because the plant cell has a cell wall
4 Each cell in the piece of potato lost water by (but the animal cell does not)
osmosis, because the solution inside the cell
• the plant cell becomes turgid
was less concentrated (had more water, or
a higher water potential) than the solution • as the contents of the cell push
outside. As each cell lost water and shrank, outwards on the cell wall
this decreased the size of the potato strip.
• which is called turgor pressure[6]
Practice questions 5 a 
more potassium in the plant cells
1 D[1] than in the water; more sodium in the
water than in the plant cells; use of
2 B[1] comparative figures[3]
3 a 
diffusion; random/net movement of b active transport; if diffusion then
particles; down a concentration gradient[3] concentrations in the cells and the
water would be the same[2]

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c Any four from: Experimental skills B3.02

• cells use energy 1 Answers will depend on the foods that
learners tested.
• from respiration
2 A sensible answer will refer to the degree of
• to move potassium ions into the cell /
cloudiness of the emulsion. The clearer the
move sodium ions out of the cell
solution (the less the emulsion), the less fat/oil
• against their concentration gradients is present.

• reference to transport / carrier Question

proteins[4]
B3.04 nitrogen
Chapter B3 Experimental skills B3.03
Before you start 1 Answers will depend on the foods that
1 a O2 learners tested.

b a molecule 2 The method could ensure that the mass

of each food tested for protein is equal.
c an element This would make the comparisons of the
2 a carbon, hydrogen, oxygen food types more valid.

b C6H12O6 Practice questions

c a compound 1 B[1]

Science in context B3.01 2 A[1]

The conditions are not right. There is a different 3 a starch[1]
mix of chemicals in the atmosphere and the oceans.
b carbon, hydrogen and oxygen[1]
This is a big and very wide topic, and some learners
might like to research further into modern theories c made up of many glucose molecules;
about the origin of life. joined in a long chain[2]

Experimental skills B3.01 d Add Benedict’s solution to the liquid;

heat; colour change from blue to
1 Answers will depend on the foods that green / yellow / orange / red
learners tested. indicates glucose.[3]
2 Learners should find that all the foods 4 a i The mixture should not be heated.[1]
containing starch and reducing sugar are of
plant origin. If they are processed foods with ii The colour change is from blue to
several ingredients, then at least some of these purple or violet.[1]
ingredients will have come from plants. b i Cut the food into very small pieces;
mix with ethanol; pour some of the
Questions ethanol into distilled water.[3]
B3.01 glucose
ii a milky emulsion[1]
B3.02 The fat layer acts as an insulator.
It reduces heat loss from the animal’s Chapter B4
body to its environment.
Before you start
B3.03 Birds don’t want to carry any more weight The incorrect statements are:
than necessary, or they would waste a lot
of energy when they fly long distances. • In a chemical reaction, atoms of one element
Storing energy in fat allows them to keep are rearranged to make atoms of other
their weight much lower than if they elements. This is incorrect, because atoms do
stored it as carbohydrate. not change in a chemical reaction. Atoms can

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be arranged to make new compounds, or new 7 Answers will depend on the learner’s
substances, but not new atoms. experience as they did the experiment.
They are likely to include:
• Products are changed to reactants. This is the
wrong way round – reactants are changed • variables other than pH affecting the time
to products. for the paper to rise to the top: for example,
differences in how much celery extract was
Science in context B4.01 absorbed onto the paper; differences in
The production of the enzyme lactase, which is a the sizes of the pieces of paper; differences
protein, requires the use of amino acids and energy in how the paper behaved (it might have
by the cell. In many adults, especially a long time flipped round sideways or hit the side of
ago in our history, milk was not a fluid that was the tube on its way up); these are all very
consumed after they had passed a young age. So, difficult to standardise, and learners may
the production of lactase in older children and suggest a different method of measuring
adults would have been a waste of cellular resources how much oxygen is released, such as
and energy. collecting in a gas syringe and measuring
the volume collected
Questions • difficulty in measuring the time precisely:
B4.01 biological because they are made by it is difficult to improve this, as it is
organisms; catalysts because they increase almost impossible to standardise the
the rate of chemical reactions moment at which the paper is placed
at the bottom of the beaker, and also
B4.02 a carbohydrase exactly when it reaches the surface of
the liquid.
b lactose
B4.03 As temperature increases from 0 to 37 °C, Experimental skills B4.02
the rate of reaction increases. The increase 1 The liquid was alkaline, and the indicator
is exponential. As temperature increases (thymolphthalein) is blue in alkaline
above 37 °C, the rate of reaction conditions. (Learners may also explain
decreases and reaches 0 at 58 °C. that the liquid is alkaline because sodium
This decrease is steeper than the increase carbonate solution has been added to it.)
at lower temperatures.
2 Lipase digested the fat in the milk, breaking it
B4.04 a 2 down to fatty acids. These are acidic, and so
b 7 they reduced the pH. This caused the indicator
to change from blue to colourless.
c between pH 5.6 and 10.4
3–4  These answers will depend on the
learner’s results.
Experimental skills B4.01
5 The colour change does not take place
1 hydrogen peroxide catalase
 → water + oxygen
instantaneously. It is impossible to judge
2 There was catalase on the filter paper, because precisely when the colour change occurs. It is
it had been dipped into the celery extract. tricky even to judge this to the nearest second,
When the paper was put into the hydrogen and it certainly cannot be done to the nearest
peroxide solution, the catalase broke down 0.1 or 0.01 s.
the hydrogen peroxide, releasing oxygen.
6 This will depend on what the learner
The oxygen collected as bubbles on the paper,
experienced as they did the experiment.
which made it rise upwards.
The most likely suggestions for sources of
3–5  These answers depend on the error and improvements are:
learner’s results. • difficulty in deciding on the time of colour
6 The experiment could be done again, this time change: it would help to have a set of
using a range of pH values clustered around tubes with different pH values and the
the value that gave the fastest times in the indicator, for reference
original experiment.

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• difficulty in measuring volumes b i 

Amylase works most quickly at pH 7
of liquids accurately: syringes and / its optimum is pH 7. Four minutes
measuring cylinders could be replaced by is the shortest time. Amylase does
graduated pipettes not work at all / is denatured at pH 4
or pH 11.[3]
• the possibility of unrecognised anomalous
results: the chance of this could be ii Any three from:
reduced by having replicates, perhaps
• the concentration of
three at each temperature.
amylase solution
Questions • the concentration of
B4.05 Explanations should refer to: starch solution

• the increase in kinetic energy of • the volume of amylase solution

enzyme and substrate molecules as • the temperature.[3]
temperature increases
5 a Any five points from:
• therefore, an increase in the frequency
of collisions • activity of both enzymes increases
with temperature at first
• the loss of shape of the active site of
the enzyme as temperature increases • maximum activity of enzyme A is at
above optimum, so that the substrate 40 °C (the optimum temperature for A)
no longer fits into it
• maximum activity of enzyme B is at
• denaturation. 70 °C (the optimum temperature for B)
B4.06 Explanations should refer to: • beyond the optimum temperature, the
• the active site of the enzyme only activity of both enzymes decreases to 0
having its ‘correct’ shape within a • enzyme A is denatured at 58 °C
narrow range around pH 7
• enzyme B is denatured at 92 °C
• the loss of shape of the active site
of the enzyme as pH decreases or • for both enzymes, activity decreases
increases from the optimum, so that more rapidly than it increased.[5]
the substrate no longer fits into it
b i Between 40 °C and 60 C, activity
• denaturation. increases rapidly; as temperature
increases, kinetic energy of enzyme
Practice questions and substrate molecules also
1 A[1] increases; so molecules move more
quickly and collide with each other
2 a proteins; metabolic; active[3] more frequently.[3]
b They increase the reaction rate ii Between 70 °C and 90 C, activity
(of metabolic reactions); so that these decreases rapidly; as temperature
work well enough to sustain life.[2] increases above the optimum (70 °C),
the kinetic energy of the enzyme
3 P: substrate; Q: active site; R: enzyme–
causes the active site to lose its shape;
substrate complex; S: products[4]
so substrate molecules can no longer
4 a 
The iodine went blue–black at the start fit into the active site / the active site
because the solution contained starch; is no longer a complementary shape
it stayed brown at the end because the to the substrate molecules; so the
solution no longer contained starch; reaction cannot take place / the
because the amylase broke down enzyme is denatured.[4]
the starch.[3]

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Chapter B5 Questions
Before you start B5.04 Starch is a storage material, and if you
are storing something you need to be able
1 carbohydrates and fats (and to get it back again when required. Plants
occasionally proteins) need to be able to break down starch to
2 sunlight glucose, so they can use it in respiration
to provide energy. Cellulose, however, is a
3 through photosynthesis in plants, which use structural material, used to make cell walls.
energy from sunlight to make carbohydrates It needs to stay there, not be broken down,
or the cell walls would easily break apart.
Science in context B5.01
B5.05 glycogen
Carbon dioxide is a significant greenhouse gas
contributing to global warming and climate B5.06 Some parts of a plant are not exposed to
change. The process of photosynthesis uses carbon light (e.g. roots) and some parts do not
dioxide, so large-scale artificial photosynthesis have chloroplasts (e.g. flowers). These
could help to reduce the concentration of carbon parts cannot photosynthesise and make
dioxide in the atmosphere, helping to slow down their own carbohydrates, so they must
climate change. have sucrose delivered to them.
B5.07 Element nitrogen magnesium
Questions
B5.01 Animals get all of their energy from Mineral nitrate ions magnesium
organic substances, which they are not salt ions
able to synthesise themselves. Plants Why to make to make
synthesise organic substances from needed amino chlorophyll
inorganic ones, using sunlight as an acids,
energy source. and then
proteins
B5.02 Chlorophyll absorbs energy from sunlight.
(Do not accept ‘attracts sunlight’.) Deficiency weak yellowing
The energy enables carbon dioxide and growth, of leaves,
water to react to produce carbohydrates. yellow often
leaves especially
B5.03 two between
the veins
Activity B5.01
B5.08 (Learners may differ in the knowledge
1 The model shows that six molecules of carbon they already have about plant
dioxide and six molecules of water produce reproduction; this is covered in more
one molecule of glucose and six molecules detail in Chapter B11.) Pollination is
of oxygen. essential for sexual reproduction in plants.
2 Accept any sensible suggestions. Nectar attracts insects to the flower, and
For example, some pieces of orange card the insects transfer pollen to another
could be used to represent energy in sunlight, flower, allowing fertilisation to take place.
and a learner could hand some to the learners B5.09 A: upper epidermis
who are building the glucose molecule.
The cards can be placed in the carton with the B: palisade mesophyll layer
glucose molecule, showing that the energy is
C: spongy mesophyll layer
incorporated into it.
D: stomata (surrounded by guard cells)
3 The oxygen that is released in photosynthesis
comes from water molecules, not carbon B5.10 It has a large number of chloroplasts,
dioxide. All the carbon and oxygen in where photosynthesis takes place.
the carbon dioxide becomes part of the
glucose molecule.

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This means that there is a lot of Experimental skills B5.05

chlorophyll, which transfers energy from
sunlight to energy in carbohydrates. 1 The plant releases oxygen as bubbles,
which we can see and count.
The cells are tall and thin, so many can
be packed into a small area, with few cell 2 As light intensity increases, the rate of
walls for sunlight to pass through to reach photosynthesis increases.
all of the chloroplasts. 3 Without the heat shield, temperature would
B5.11 They receive less sunlight than other be an uncontrolled variable, so it would not be
tissues in the leaf. possible to say whether changes to the rate of
photosynthesis were due to light intensity or
Experimental skills B5.01 temperature.

1 Learners should find that the leaf becomes 4 The bubbles released may be different sizes.
blue- black, indicating that it contains starch. It is also not easy to count them reliably.
Measuring volume will give a more reliable
2 Boiling breaks down cell membranes. indication of the quantity of oxygen released
The membranes around the chloroplasts and, therefore, the rate of reaction.
and around the cell need to be broken down
to allow the iodine to come into contact with Experimental skills B5.06
the starch, which is inside the chloroplasts
inside the leaf cells. 1 Graph will depend on the learner’s results but
should show:
3 To allow any change in colour to be seen
• independent variable (temperature or
more clearly.
mass of sodium hydrogencarbonate
added) on the x-axis
Experimental skills B5.02
• dependent variable (number of bubbles
1 Learners should find that only the green parts
per minute) on the y-axis
contained starch.
• good scales on both axes, going up in
2 Chlorophyll is needed for photosynthesis. sensible and regular intervals, and using at
least half of the grid provided
Experimental skills B5.03
• points plotted accurately, as neat crosses
1 If the plant was not destarched, we would not
know whether any starch we found had been • lines drawn with a ruler between points.
made during the experiment or before.
2–4  These answers will depend on the learner’s
2 To give the plant time to photosynthesise and results, and their experience in carrying out
make starch. their planned investigation.

3 Light is necessary for photosynthesis. Practice questions

Experimental skills B5.04 1 D[1]

1 Either leaf could be said to be the control. 2 D[1]

One has carbon dioxide and one does not;
3 a i palisade mesophyll[1]
it is justifiable to say that either one is the
experiment, and the other is the control. ii Any two from:
The essential point is that you need both, • cells contain many chloroplasts
in order to compare the results.
• in which photosynthesis
2 This was to control a variable. The only takes place
difference between the two flasks is that one
has a liquid that absorbs carbon dioxide, • (chloroplasts) contain a lot
and the other has a liquid that does not. of chlorophyll

3 Carbon dioxide is necessary for • which transfers energy from light

photosynthesis. to energy in carbohydrates

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• cells are tall and narrow c Graph should show:

• allowing sunlight to reach • independent variable (concentration
chloroplasts without having to of sodium hydrogencarbonate
pass through many cell walls[2] solution) on the x-axis
b Any two from B, E, I, H (do not allow A, F • dependent variable (distance moved
or G, as these are not cells or tissues).[2] by meniscus) on the y-axis
c It can change shape; to open or close • good scales on both axes, going up
the stoma.[2] in sensible and regular intervals,
and using at least half of the grid
d Water moves up through the xylem provided
vessels in structure E; then into a
palisade cell in layer C by osmosis • points plotted accurately, as
and into a chloroplast.[2] neat crosses
4 a 
for photosynthesis; idea that • lines drawn with a ruler
photosynthesis takes place between points. [1]
inside chloroplasts[2]
d distance moved by meniscus/
b A; it does not contain any chloroplasts[2] rate of photosynthesis increases
as concentration of sodium
c B[1] hydrogencarbonate solution increases[2]
d Any two from: e i 
Accept any two sensible suggestions,
• it absorbs energy from light (do not for example:
allow ‘attracts’)
• leakage of air into or out of
• the energy is used to make carbon the syringes
dioxide and water react together
• variation in the plants
• chlorophyll transfers energy from (size, activity)
sunlight to energy in carbohydrates/
glucose [2] • difficulty in reading the position
of the meniscus precisely against
5 a 
carbon dioxide and water; react to produce the scale on the ruler
glucose and oxygen; using energy from
sunlight; absorbed by chlorophyll[4] (do not accept anything that sounds
like a mistake made by the learners,
b Any two of these pairs: such as not ensuring their eye is
• glucose; used to release energy parallel with the meniscus)[2]
in respiration ii Accept any two sensible suggestions
• starch; as an energy store relating to the answers in i, for example:
• cellulose; to make cell walls • use petroleum jelly to make the
syringe plungers airtight
• sucrose; for transport
• use plant pieces of identical mass
• nectar; to attract pollinators
to flowers[4] • use a glass tube with a scale
on it[2]
6 a 
independent variable is concentration
of sodium hydrogencarbonate solution
(or carbon dioxide concentration); Chapter B6
dependent variable is distance Before you start
moved by meniscus after 30 minutes[2]
1 Starch is a carbohydrate.
b sunlight provides the energy for
photosynthesis; bright sunlight ensures 2 It is made of many glucose molecules
light intensity is not a limiting factor[2] linked together.

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3 Protein molecules are made of amino acids anus. There are also other organs in the
linked together. digestive system, such as the gall bladder.
4 Lipase digest fats to fatty acids and glycerol. B6.03 Any two from: liver, pancreas, gall
bladder, salivary gland
5 It is an enzyme. All enzymes are
protein molecules. B6.04 mouth, oesophagus, stomach, (duodenum,
ileum, colon, rectum), anus. The
Science in context B6.01 bracketed terms can also be summarised
Carnivores such as lions and hyenas may eat meat as ‘small intestine, large intestine’.
that is not fresh, and is therefore likely to contain B6.05 a mouth and/or oesophagus
large numbers of potentially harmful bacteria.
The strong acid in their stomachs helps to kill b mouth, stomach, duodenum
these bacteria, preventing infection. It is also c ileum, colon
possible that the acid helps with the digestion of
proteins from the meat in the stomach, where the d anus
enzyme pepsin requires acidic conditions to work. B6.06 mouth and duodenum

Questions B6.07 stomach and duodenum

B6.01 For example: B6.08 a pancreas

Nutrient Main dietary Uses in the b duodenum

sources body B6.09 To emulsify fat means to break up large
carbohydrate grains and for energy, drops of fat into tiny droplets which
foods made which is disperse through the water contents of
from them released in the duodenum. This increases the surface
– e.g. rice, respiration area of fat that lipase can contact, and so
pasta, bread; lipase can break the fats into fatty acids
potatoes; and glycerol more quickly.
sweet foods
fat cooking for energy, Practice questions
oil, meat, released in 1 C[1]
eggs, dairy respiration;
products, to make cell 2 D[1]
oily fish membranes; 3 a G: large intestine / colon; J: liver[2]
as an
insulator, b A and D[2]
preventing c E[1]
heat loss; as
a protective d Any six from:
layer around • secretes protease enzymes
body organs
• which digest protein
protein meat, fish, making
eggs, dairy new cells, • to amino acids
products, for growth; • reference to chemical digestion
pulses (peas, making
beans, proteins • secretes hydrochloric acid
lentils), nuts such as • which provides a suitable pH
and seeds haemoglobin for enzymes
and
antibodies • kills microorganisms
• churns food
B6.02 The alimentary canal is part of the
digestive system. It is the tube that food • reference to physical digestion[6]
moves through, from the mouth to the

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Chapter B7 B7.04 to absorb water and mineral ions from

the soil
Before you start
B7.05 It is long and thin, and therefore has a
In the case of the plant cell, learners may show:
relatively large surface area. This increases
• carbon dioxide / water / glucose / oxygen / the rate at which it can absorb water and
other nutrients entering the cell mineral ions.

• carbon dioxide / water leaving the cell. B7.06 The solution in the soil has a relatively
low concentration of solutes compared
They should remember from the previous chapter with the solution inside the root hair
that water is moved around the plant through cell. These solutions are separated from
xylem vessels, while glucose is transported (as each other by the partially permeable
sucrose) through phloem vessels. Carbon dioxide cell membrane. Water moves into the
and oxygen diffuse in from air spaces in the plant, cell through this membrane by osmosis,
while waste water vapour diffuses out of cells. from a dilute solution to a more
In the case of the animal cell, learners may show: concentrated solution.

• oxygen / glucose / water / other nutrients B7.07 Water moves from an area of high water
entering the cell potential in the soil into the lower water
potential inside the root hair cell, down a
• carbon dioxide / urea leaving the cell. water potential gradient. It continues to
They may know that these substances are brought move from cell to cell towards the centre
to and from the cell in the blood. They may also of the root, by osmosis, down the water
give other detail, such as that oxygen enters the potential gradient.
blood in the lungs, or that nutrients enter the
blood in the small intestine. Experimental skills B7.01
1 xylem
Science in context B7.01
2 the vascular bundles (veins)
Learners may suggest osmosis. They will later
find that this is also how water reaches individual 3 Temperature is the variable to be changed.
cells in plants that do have xylem, and how it first A suitable range would be between 0 °C and
enters the plant and moves across the root into the perhaps 80 °C, with intervals of 10 °C or 20 °C.
xylem vessels. This could be done using water-baths. The
most important variables to be kept constant
Questions include the size of the celery stalk and the
concentration of the dye.
B7.01 support; transport of water and
mineral ions If the dye can be seen in the stalk without
having to cut it, learners could measure the
B7.02 transport of sugars and amino acids
distance travelled by the dye in a set time
B7.03 In roots, both types of vessels are found period – for example, every two minutes. If it
in the vascular bundles. The xylem is cannot be seen, they will need to have several
found in the centre, whereas the phloem is stalks at each temperature, and cut one of
arranged around it. them across at a set distance (e.g. 10 cm)
after a set time – say every two minutes – to
In stems, both types of vessels are found determine how long it takes the dye to travel
in the vascular bundles that are studded this distance.
around the middle of the stem. The
xylem is found on the inner side of each The main safety risk is the sharp blade used to
of these bundles, with the phloem on the cut the stalks. Learners should describe how
outer side. they will avoid cutting themselves or someone
else with the blade.
In leaves, both types of vessels are found
in the vascular bundles that pass through
the midrib of the leaf.

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Questions B7.14 As it passes through the body organs

other than the lungs; oxygen diffuses out
B7.08 root hair cells, root cortex cells, xylem, of the blood into the body cells, where it
mesophyll cells is used in aerobic respiration.
B7.09 a liquid B7.15 Learners may start with any chamber of
b liquid the heart but the order must be as follows:
left atrium, left ventricle, right atrium,
c gas
right ventricle
Experimental skills B7.02 B7.16 left atrium and left ventricle
1 Answers will depend on the learner’s B7.17 away from
experience as they used the potometer.
B7.18 towards
2 Water vapour is lost from the leaves of a plant
by evaporation (transpiration). This water is B7.19 The muscles in the walls of the ventricles
replaced by water that moves out of the xylem contract, squeezing inwards and reducing
vessels in the leaves. As water leaves the top the volume inside the heart. This increases
of the xylem vessels, more water is drawn into the pressure inside the heart and pushes the
the bottom of the xylem vessels (transpiration blood out.
pull). This draws water in at the cut end of the B7.20 In the heart wall / on the outside of the
shoot, causing the air/water meniscus to move heart. They provide oxygen and nutrients
up the potometer. for the heart muscle.
3 The line graphs should have: B7.21 Any two of: Using an ECG, measuring
• time / minutes on the x-axis, with a pulse rate (e.g. by placing your fingers
suitable scale that uses at least half of the over an artery and counting, or by using a
graph paper provided phone app or smart watch) or listening to
the sounds of the valves closing.
• distance moved by meniscus / mm
(or cm) on the y-axis, with a suitable B7.22 The septum separates oxygenated blood
scale that uses at least half of the graph from deoxygenated blood, ensuring that
paper provided all of the blood that enters the aorta
is fully oxygenated. The bicuspid valve
• points plotted as neat crosses or
is between the left atrium and the left
encircled dots
ventricle. It prevents blood flowing back
• lines drawn from point to point with a into the left atrium as the left ventricle
ruler or best fit lines contracts, so that all the blood is forced
out into the aorta. There is another valve
• lines clearly labelled, either directly on the
at the entrance to the aorta, to prevent
graph or using a key.
blood flowing back into the left ventricle
Questions when the heart relaxes again. These valves
ensure that blood flows forwards in the
B7.10 Leaves are a source, and the trunk and aorta at high pressure.
roots are sinks.
B7.11 Trunk and roots are sources, and the
Experimental skills B7.03
growing buds and leaves are sinks. 1 The line graph will depend on the
learner’s results.
B7.12 Transpiration happens at the top of the
xylem vessels, reducing the pressure at 2 Answers will depend on the learner’s
this point. The pressure is always lower results. They are likely to find that heart
at the top of the xylem vessels than at the rate fluctuated a little before exercise,
bottom, so water always flows upwards. then increased rapidly during exercise and
decreased slowly after exercise ended.
B7.13 The left side contains oxygenated
blood, and the right side contains
deoxygenated blood.

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3 Muscle contraction needs energy, which is ii root hairs absorb water from the soil;
obtained from aerobic respiration. As muscles a large surface area increases the rate
work harder, they need more energy and at which this happens[2]
therefore aerobic respiration needs to happen
more quickly. The muscles therefore need more c phloem transports sucrose and amino
oxygen, which is supplied to them by the blood. acids but xylem does not; phloem
A faster heart rate moves blood more quickly, transports in both directions (by
supplying oxygen to the muscles more quickly. translocation) but xylem transports only
upwards (by transpiration)[2]
Questions 3 a 
Carbon dioxide reacts with water; during
B7.23 a artery b capillary photosynthesis / to make glucose / to
make carbohydrates.[2]
c vein
b Any two from: it is produced during
B7.24 a in the lungs photosynthesis; it evaporates from
b in the body organs mesophyll cells; into the air spaces
in leaves[2]
c pulmonary artery
c i Any five from:
B7.25 The blood pulses as it is forced through
the arteries – it is at high and fluctuating • percentage hydration decreases
pressure. The elastic tissue in artery walls (over time)
allows them to expand as a high-pressure • from 100% at day 1 to 30%
pulse of blood flows through, rather at day 5
than bursting. They can then recoil to
their normal diameter in between pulses. • percentage hydration fluctuates
This helps to even out the blood pressure. each day
Veins, on the other hand, carry blood • drops during the day and
that has already been through capillaries increases at night
and has lost most of its pressure, and is
not pulsing. • drops more quickly than
it increases
B7.26 A white blood cell has a nucleus.
• drops by a greater amount than
B7.27 A phagocyte normally has a lobed it increases[5]
nucleus, whereas a lymphocyte has a large,
ii Any four from:
round nucleus that almost fills the cell.
• percentage hydration of the
B7.28 Blood plasma is the liquid part of the soil drops
blood. It is mostly water but it also contains
dissolved substances, including dissolved • (so) less water can be taken in by
nutrients, hormones, dissolved gases, and osmosis through root hairs
excretory substances such as urea. • water lost by transpiration cannot
be (completely) replaced
Practice questions
• during daylight, it is hotter /
1 C[1] stomata are open, so water loss
2 a 
number of stomata in 0.06 mm2 is 20 exceeds water uptake
(allow 18, 19 or 21); so, number in 1 mm2 • at night, it is cooler / stomata are
is 333 (to nearest whole number; allow 300 closed, so water uptake exceeds
(for 18 stomata in image), 317 (for 19 in water loss[4]
image), or 350 (for 21 in image))[2]
iii it has wilted; leaves have collapsed /
b i 
mesophyll cells have a large surface other suitable description; leaf cells
area in contact with the air spaces; have lost their turgidity / become
from which water evaporates; filling flaccid[3]
the air spaces with water vapour that
can diffuse out through stomata[3]

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4 plasma[1] c 60 ÷ 0.75 = 80 beats per minute;

(allow error carried forward from b)[2]
5 S and R[1]
d The plotted line should have the same
6 a Any two from: shape as the existing line, but would
• white blood cell is larger at all times be lower. [2]

• white blood cell has a nucleus 9 a i A: nucleus; B: mitochondrion[2]

• white blood cell has a less ii Any two from:

regular shape • to allow substances to move
• white blood cell does not contain quickly/easily
haemoglobin[2] • between the capillary and
b diameter of cell in diagram is 20 mm surrounding cells

(magnification = image size ÷ actual size) • by diffusion

actual size is 0.007 mm • any two examples of substances:
magnification = 20 ÷ 0.007 = ×2860 oxygen / carbon dioxide / named
(to 3 s.f.)[3] nutrients[2]

c Any three from: iii red blood cell is transporting

oxygen; reduces distance for oxygen
• (take up oxygen) when oxygen to diffuse, out of the capillary / to
concentration is high surrounding cells[2]
• at the alveoli / in the lungs b Any three from:
• oxygen combines with haemoglobin / • suitable description of
forms oxyhaemoglobin shape difference
• carried in blood (from lungs) to rest • red blood cell has no nucleus /
of body structure A
• release oxygen when oxygen • red blood cell has no mitochondria /
concentration is low[3] structure B
d Any one from: fight pathogens / • red blood cell contains
produce antibodies / phagocytosis / haemoglobin[3]
clear up dead body cells[1]
c plasma[1]
7 a Any two from:
• measuring pulse rate Chapter B8
• ECG Before you start
There is a very wide variety of sentences that
• listening to valves closing[2]
learners could write. For example:
b (activity of heart) increases when Bacteria and viruses are pathogens, which are
exercising; beats faster and harder; destroyed inside our body by antibodies produced
decreases gradually when by white blood cells.
exercise finishes[3]
8 a 
A: just starting to contract; B: just Science in context B8.01
starting to relax[2] 1 Learners may be aware that some parents
b (time between A and next corresponding think vaccinations are harmful to health.
position on the graph is) 0.75 s There is a lot of misinformation on the
(accept 0.74–0.76)[1] internet, and it is worth listening to what
learners themselves have picked up about the
effects of vaccines. In some countries, this

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has become a political or religious issue, so Even if there are harmful bacteria on
it is important to take care when chairing the food, when their numbers remain
this discussion. small there is less chance of getting ill
if you eat them.
2 There is no correct answer to this question.
Opinions may be divided between those who B8.07 An antigen is a molecule on a cell that is
think it is a parent’s right to decide whether not normally found in the body – such as
or not to have their child vaccinated, and a pathogen – and that the body recognises
those who think that the health of the school as ‘foreign’. An antibody is a protein
community should take precedence over that secreted by lymphocytes, which can bind
of an individual. These are not easy decisions to its complementary antigen.
to make, and learners should be encouraged to
look at both points of view. B8.08 The antigen and antibody have
complementary shapes, so that they fit
Questions together precisely. They do not have the
same shape.
B8.01 A disease that can be passed from one
person (or other organism) to another. B8.09 a 
It takes time for the lymphocytes that
Transmissible diseases are caused can make the appropriate antibody
by pathogens. for this pathogen to make contact
with the antigen on the pathogen,
B8.02 Unbroken skin is a physical barrier that then to divide and produce a clone of
stops most pathogens moving through to identical cells, which can then make
the underlying tissues. If skin is broken, a large quantities of the antibody.
blood clot seals the wound and prevents
pathogen entry. b The number rises rapidly between
day 0 and day 1, and then decreases
B8.03 The acid kills bacteria in food, preventing more slowly, reaching 0 at the end of
infection by pathogens that might cause day 3. The number of bacteria is able
food poisoning or other infections. to increase rapidly at first, because
there are no antibodies to stop them
B8.04 Water that is not clean contains
dividing. But as the quantity of
microorganisms, and some of these are
antibodies increases, the bacteria are
pathogens. If you drink water containing
immobilised or killed, and the rate
pathogens or use it in ways that allow
at which they die becomes greater
the pathogens to get from the water
than the rate at which they reproduce.
into your eyes, nose or mouth, or into
Their numbers therefore fall.
cuts or grazes on the skin, it can cause
serious illness. B8.10 The body now contains memory cells,
which are able to react immediately to the
B8.05 The water in a deep well comes from deep
presence of the bacteria and very rapidly
underground, where it is less likely to have
produce large quantities of the specific
been contaminated with urine or faeces. It
antibody that binds with the antigen on
is therefore less likely to contain pathogens
these bacteria. The number of bacteria
from the body of an infected person.
therefore has time to increase only very
B8.06 a 
Covering food keeps animals such as slightly, and is reduced to 0 by the end
houseflies away from it. Houseflies of day1.
transfer pathogens on their feet or in
B8.11 The response would look like the first
their saliva. If the food is in a warm
graph because the antigens on this
place, these pathogens can breed
new bacterium would be different.
quickly, so that by the time someone
The memory cells produced from the
eats the food there are large numbers
first infection give no protection against
of pathogens, which could cause food
any other type of pathogen.
poisoning or other illnesses.
b Keeping the food cold reduces the
rate at which bacteria can multiply.

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B8.12 Through having a transmissible disease 5 a genetic material / DNA / RNA[1]

and recovering from it; by receiving
a vaccination containing dead or b Any five from:
inactivated pathogens. • proteins in virus coat are antigens
B8.13 The pathogen is unable to breed in a • lymphocytes make antibodies
person who has been vaccinated. If
enough people have been vaccinated, this • which have complementary shape
greatly reduces the number of people who to antigens
can be a host for the pathogen, making it • produce memory cells
much less easy for the pathogen to spread
through the population. • which can produce antibodies quickly
on next exposure to the same antigen
Practice questions
• these antibodies cannot bind with
1 C[1] other antigens
2 D[1] • so cannot protect against new strains
of the virus[5]
3 a pathogens; host; mucus[3]
b i 
idea that skin is a barrier to entry of Chapter B9
pathogens through it; blood clots to
seal wounds[2] Before you start
The exact response provided will differ between
ii hydrochloric acid; is secreted by the
learners. Most will find that the breathing depth
stomach; killing microorganisms
and rate increase after this moderate exercise.
in food[3]
4 a Any five from: Science in context B9.01
• introduction of dead / There is no ‘right’ answer for this – it is intended as
weakened pathogens an intriguing issue to encourage learners to think
separately about their breathing rate and heart rate.
• (antigens on pathogens are) One possible answer is that we use breathing for
recognised by (specific) lymphocytes purposes other than ‘staying alive’ – such as talking.
• antibodies produced We have therefore evolved to have some control
over this process, whereas there is no advantage in
• antibodies are specific to
being able to consciously control heart rate.
pathogen / antigen
• memory cells produced Questions
• which respond quickly on second B9.01 mouth or nose; trachea; bronchi;
entry of same pathogen[5] bronchioles; alveoli; wall of alveolus; wall
of capillary
b i Any three from:
• increased B9.02 The arrow for oxygen goes into a red
blood cell, because oxygen is transported
• from 15 000 to 76 000 (allow some in combination with haemoglobin in red
leeway with figures) blood cells. The arrow for carbon dioxide
• fluctuated comes from the blood plasma, because
most carbon dioxide is transported in
• maximum number of cases was solution in the plasma.
76 000 in 1957 / 1958[3]
B9.03 The arrows in the bronchiole represent
ii rapid decrease in number of cases; mass flow. The arrows showing carbon
to 0 by 1991; many children now dioxide and oxygen moving into and out
immune to measles; reference to of the blood represent diffusion.
herd immunity / few hosts for
measles virus[4]

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B9.04 Emphysema leads to a reduction of the • clean, clear, ruled lines that join precisely
surface area of the alveoli. As a result, less at the centres of the crosses.
oxygen is able to diffuse into the blood
in a given time. This reduces the oxygen 2 Answers will depend on the learner’s results.
supply to cells, which therefore cannot 3 Answers will depend on the learner’s results.
undergo aerobic respiration as rapidly, However, suggestions may include the fact
and cannot release as much energy as that the learner’s ability to do intense activity
normal. The person may therefore find will vary from day to day, in light of the
it difficult to exercise. (In addition, temperature, food they have eaten, and so on.
the removal of waste products from
respiration is less efficient, because the Questions
diffusion of carbon dioxide from the
blood into the alveoli is less efficient.) B9.07 The reactants in aerobic respiration
are the products of photosynthesis.
Experimental skills B9.01 The reactants in photosynthesis are the
products of aerobic respiration.
1 When you breathe out, air moves into the
short tube in A and the long tube in B. B9.08 every cell
Expired air therefore only bubbles through the B9.09 During photosynthesis in plants,
limewater in B. chlorophyll captures energy from sunlight
When you breathe in, air is drawn from the and transfers it to glucose molecules.
end of the short tube in A, causing air to be
pulled into the limewater in A through the Practice questions
long tube. This leads to bubbles in A only. 1 C[1]
2 Learners should find that the limewater goes 2 C[1]
cloudy more quickly in tube B. This shows
that there is more carbon dioxide in expired glucose + oxygen → carbon dioxide +
3 a 
air than in inspired air. water
(one mark for reactants; one mark
Questions for products)[2]
B9.05 The inner surface of the alveoli is moist.
b Any three from:
Water from this surface evaporates and is
breathed out with expired air. • muscle contraction
B9.06 The percentage is 78%. As nitrogen gas • making protein molecules /
is not used in the body, the nitrogen protein synthesis
concentration in the blood remains the
same as in the air in the lungs, because • cell division
nitrogen molecules diffuse between the air • active transport
and blood until equilibrium is reached.
• growth
Experimental skills B9.02
• passage of nerve impulses
1 Look for:
• maintenance of a constant
• axes the right way round, and fully body temperature[3]
labelled with units
4 a i 12[1]
• suitable scales on both axes – they should
go up in regular intervals and use at least ii 0.5 dm3[1]
half of the grid provided b i 21[1]
• points correctly plotted as small, ii 1.1 dm3[1]
neat crosses

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c Any four from: is that no one has ever responded in less than 0.1 s,
and most reaction times are well above this value.
• brain senses the pH of blood
(If learners research this issue, they will find that
• pH decreases during exercise measured reaction times have steadily reduced
• because more carbon dioxide / lactic since 2004, but this is thought to be a reflection of
acid is dissolved in the blood plasma changes in the sensors and measuring technology,
rather than in the athletes themselves.)
• brain responds by sending more
frequent nerve impulses to the Questions
breathing muscles (diaphragm and
intercostal muscles) B10.01 They have a cell membrane, nucleus,
cytoplasm, mitochondria and ribosomes.
• so they contract harder and
more frequently[4] B10.02 They have long, thin fibres of cytoplasm
stretching out from the cell body / they
d Any five from: have a very long axon, along which
impulses can travel long distances quickly.
• muscles need more energy
for contraction B10.03 It coordinates electrical impulses
travelling through the nervous system;
• deeper / more rapid breathing brings
it receives impulses from different
more fresh air into the lungs
receptors and sends impulses to
• more oxygen can diffuse into the appropriate effectors.
blood more quickly
B10.04 a 
in a small swelling just outside the
• more oxygen is supplied to spinal cord
the muscles
b in the spinal cord
• so aerobic respiration can
c in the spinal cord
happen faster
B10.05 Sensory neurones have long cytoplasmic
• releasing more energy from glucose[5]
extensions on either side of the cell
5 a 
5 minutes[1] body, whereas motor neurones have only
one long extension and relay neurones
b • during exercise not enough oxygen have none.
was supplied to muscles
B10.06 There is a very wide variety of possible
• so they respired anaerobically (as well answers. Look for genuine reflex actions
as aerobically) that happen automatically, not reactions
• producing lactic acid that are decided on.

• which is broken down by combining Activity B10.01

with oxygen (when exercise finished)
1 Divide the time by the number of people, to
• reference to paying back the find the mean reaction time.
oxygen debt[5]
2 People generally respond faster as the
experiment is repeated. This is because
Chapter B10 learning is taking place.
Before you start 3 Usually, the squeeze travels more slowly
eyes: light; ears: sound; skin: temperature, when it is sent in the opposite direction.
pressure; tongue: chemicals (taste); nose: This is because the people in the circle have
chemicals (smell) to ‘unlearn’ what they have just learnt and
start again.
Science in context B10.01
Reaction times in sprint races have been measured
in thousands of races over the years. The evidence

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4 Answers will depend on the sites that the glucose from the blood; some of
learner finds. There is no ‘correct’ answer this glucose is used for respiration in
to which method is best. We have no way liver cells, and some is converted into
of knowing whether the time given on the insoluble glycogen and stored. This
website is correct or not. However, it is likely reduces the concentration of glucose
to be very reliable. in the blood.
d Blood glucose concentration is
Questions
regulated by negative feedback.
B10.07 pancreas: insulin (and glucagon); adrenal The pancreas will not stop secreting
glands: adrenaline; testes: testosterone; insulin until it detects that blood
ovaries: oestrogen glucose concentration levels have
fallen below the ideal concentration.
B10.08 They travel in the blood plasma, usually
Then it will release glucagon, which
in solution.
causes blood glucose concentration to
B10.09 Any situation in which a person is rise again.
frightened or angry – i.e. any fight or
B10.13 Proteins are made by joining amino acids
flight situation. Adrenaline is also secreted
together on the ribosomes. The process
when we are nervous, such as before an
requires energy, which is provided by
interview or examination.
aerobic respiration in mitochondria.
B10.10 It increases breathing rate and heart rate, As the islet cells in the pancreas make
which provides more oxygen to muscle a lot of proteins, they need a lot of
cells so they can release more energy for these structures.
contraction, by aerobic respiration. It
makes the pupils wider, to allow more Practice questions
light into the eyes for better vision of the 1 C[1]
perceived danger. It also causes the liver
to release glucose into the blood, allowing 2 D[1]
muscles to respire more quickly and
3 a i 
chemical substance made by a gland;
release more energy.
carried in the blood; which alters
B10.11 They are made by an endocrine gland activity of target organs[3]
(the pancreas), are transported in the
ii adrenal (glands)[1]
blood, and affect target organs (in this
case, the liver). iii pancreas[1]
B10.12 a 
Her blood glucose concentration b the action is slower; the effect
begins at 85 mg per 100 cm3 and lasts longer[2]
does not change until 20 minutes
after eating. It then rises until 4 a i 
by amylase; in the mouth; and in
1 hour 20 minutes after eating, to the small intestine / duodenum[3]
a maximum of 105 mg per 100 cm3. ii small intestine / ileum[1]
After this, it falls until 4 hours after
eating, reaching a minimum of 79 mg b Any two from:
per 100 cm3. Finally, it rises again to
• the contents of the cells would
85 mg per 100 cm3 at 5 hours.
be more dilute than the solution
b It took time for the starch in the around them
food to be digested by amylase and
• so they would lose water by osmosis
maltase, producing glucose. The
glucose then had to be absorbed. • metabolic reactions in the cells
cannot take place if they lose too
c The pancreas detected the increase
much water[2]
in blood glucose concentration and
secreted a hormone called insulin.
Insulin causes the liver to absorb

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c i pancreas[1] • water around B’s body warms up

(as heat is lost from his body to
ii reduces blood glucose the water)
concentration[1]
• heat transfers from hot object to
5 a 
for respiration; which supplies energy; colder object
for any named process (e.g. active
transport, movement)[3] • more heat lost from A’s body
than B’s body[3]
b pancreas[1]
c i 
starch broken down to glucose; by Chapter B11
amylase (and maltase); absorbed into
the blood from the ileum[3] Before you start
In the image on the left, the strawberry plant
ii used by cells for respiration; insulin is producing runners – a method of asexual
secreted; which causes the liver to reproduction. In the image on the right, the
take up glucose; glucose stored in the strawberry plant is producing fruits – a method of
liver as glycogen[4] sexual reproduction.
d sensors in pancreas detect blood glucose
concentration; if it is too high, insulin Science in context B11.01
is secreted and brings the concentration There is a range of answers to this question.
down; if it is too low, glucagon is secreted Accept sensible ideas, for example, that there were
and increases the concentration[3] no plausible alternative ideas at the time.
e c urve rises at same time as original
curve; to a higher level; remains
Questions
high for longer[3] B11.01 14
6 a A: 37.4 °C; B: 37.5 °C[2] B11.02 a 14
b Any four from: b 28
• homeostasis B11.03 The flower has brightly coloured petals, to
attract insects. The petals have guide-lines,
• humans are endothermic / maintain a
to guide the insect to the centre of the
constant body temperature
flower. The anthers and stigma are within
• body produces more heat to maintain the petals. They are arranged so that the
body temperature insect has to brush past them to reach the
nectar in the base of the flower.
• reference to shivering
B11.04 a 
The stamens dangle out of the flower,
• reference to vasoconstriction so that the anthers can swing in the
• reference to increased metabolism[4] wind and release their pollen. The
stigmas are feathery and stick out
c Any two from: of the flower, so that they can easily
catch pollen blowing on the wind.
• air is more insulating than water
There are no petals to obstruct
• heat lost more easily from the body in the wind or movement of pollen.
water than in air by conduction[2]
b Wind-pollinated flowers produce
d Any three from: much more pollen than insect-
pollinated flowers. Their pollen is also
• person A was moving but person B much lighter, so it is more likely to
remained still be floating in the air, where it can be
• idea that ‘new’ cold water was breathed in by a person.
constantly coming into contact with
A’s skin

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Experimental skills B11.01

1 Water: to provide a solvent in which substances in the cells can dissolve, so that metabolic reactions can
take place. Oxygen: for aerobic respiration, to release energy from glucose to drive energy-requiring
metabolic reactions, or for active transport. A warm temperature: to ensure that reacting molecules,
and enzymes catalysing their reactions, have sufficient kinetic energy to collide frequently and react.
2 If the seeds germinated when there was only a little light, they would not be able to photosynthesise
once they had grown into plants with leaves, and would die. Waiting for a tree to fall, letting light
through to the forest floor, means they have a better chance of obtaining light and being able to
grow successfully.

Questions
B11.05 eggs: in follicles, in ovaries; sperm: in the testis
B11.06 a the prostate gland
b an oviduct
c the lining of the uterus
B11.07 For example:

Egg Sperm Explanation

haploid haploid at fertilisation, a diploid zygote is formed
eggs need to be large to provide space for stored
relatively large
small cell nutrients; sperm need to be small to reduce the
cell
energy required for swimming
the nutrients in an egg provide for the zygote and
contains stored
no stored nutrients embryo before implantation; sperm use nutrients in
nutrients
semen (secreted by the prostate gland)
has a jelly coat no need for a jelly coat prevents entry of more than one sperm
has a flagellum, sperm cell requires energy for swimming, provided
does not have a
containing many by aerobic respiration in mitochondria; flagellum
flagellum
mitochondria provides propulsion
has an acrosome,
does not have an enzymes make a pathway through the egg’s jelly
containing digestive
acrosome coat, allowing the sperm head to enter
enzymes

B11.08 Eggs are moved by the cilia and muscles in the wall of the oviducts – they do not move themselves.
In contrast, sperm swim actively, using their flagella.
B11.09 Testosterone – any one from: stimulates sperm production; causes facial and pubic hair to develop;
causes shoulders to broaden; causes the voice to break. Oestrogen – any one from: causes pubic
hair to develop; causes the breasts to develop; causes the hips to broaden; helps to control the
menstrual cycle.
B11.10 a An egg is developing in a follicle.
b The egg continues to develop until it is released from the follicle during ovulation.
c The follicle from which the egg was released has changed into a corpus luteum.

Practice questions
1 A[1]
2 A[1]

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3 a Tube A B C D E [2] b haploid nucleus, to produce a diploid

zygote when it fuses with an egg nucleus;
Water ✗ ✓ ✓ ✓ ✓ acrosome containing digestive enzymes,
Oxygen ✓ ✓ ✗ ✓ ✓ to make a pathway into the egg for the
Warm ✓ ✓ ✓ ✓ ✗ head of the sperm; long flagellum for
temperature propulsion to the egg; many mitochondria
to release energy by aerobic respiration,
Light ✓ ✓ ✓ ✗ ✓
for swimming[4]
(all correct for two marks; with one c haploid nucleus, to produce a diploid
mistake one mark; with two mistakes no zygote when it fuses with a sperm nucleus;
marks) food stores to provide for zygote and
embryo until implantation; jelly coat to
b B and D[2] prevent entry of more than one sperm[3]
c i 
a male nucleus from a pollen grain; 8 a 
increases from 1990 to 1999; falls from
fuses with a female nucleus from 1999 to 2017; change in figures quoted,
an ovule[2] e.g. from 2 million in 1990 to 3.2 million
ii ovule[1] in 1999[3]

4 a asexual[1] b HIV infection does not produce

symptoms immediately; people can be
b produces new banana plants that are infected and not know[2]
identical to the parent (so the bananas
will be exactly the same variety); c HIV enters white blood cells /
predictable yields / flavour / other lymphocytes; destroys them / reduces their
named attribute[2] numbers; so immune system cannot attack
pathogens / cancerous cells successfully;
c all new plants will be genetically identical; allowing other infections to develop;
if the parent did not have resistance to the increasing risk of cancer developing[5]
disease then nor will the offspring[2]
d number of people living with HIV/AIDS
5 a 
pin-eyed has stigma above anthers; is increasing, but number of deaths from
thrum-eyed has anthers above stigma[2] HIV/AIDS is decreasing; comparative
b i thorax or mid-section[1] figures quoted; use of antiretrovirals;
allows people to live normal lives even
ii abdomen or rear section[1] when infected; prevents AIDS developing
after HIV infection[5]
c i abdomen or rear section[1]
ii thorax or mid-section[1] Chapter B12
6 a urethra[1] Science in context B12.01
b prostate[1] 1 It is likely that coat colour in the chinchillas is
controlled by genes.
c testosterone[1]
2 Other characteristics of chinchillas, such
7 a as body mass, are likely controlled by
acrosome nucleus mitochondrion genes but also some environmental factors
– for example, how much food is eaten by
an individual.
cell membrane
flagellum cytoplasm Questions
B12.01 nucleus
[3] B12.02 gene; DNA molecule; chromosome;
nucleus; cell
(one mark for any two correct)

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B12.03 All humans have the same genes (genes B12.13 a T

for the same characteristics), but every
b T and t
individual has a different combination of
alleles of those genes. c t
B12.04 32 B12.14 TT

B12.05 This is so that, when the cell divides B12.15 Tt

by mitosis, each daughter cell gets an B12.16 TT and Tt
identical set of alleles – so that the new
cells are genetically identical. This is Activity B12.02
required for growth, repair of damaged Answers will depend on what was used for the
tissues, replacement of cells and asexual ‘alleles’, and how the learner did their experiment.
reproduction. For example, perhaps the learner did not pick out
B12.06 With 46 chromosomes in the cell, there the different beads randomly – maybe one bead
is a lot of potential for them to become was larger than the other, and more likely to be
tangled up together. If the two identical picked up.
copies of each chromosome are held
together, it is easier for them to separate in
Questions
an orderly way as the cell divides. B12.17 a NN normal wings, Nn normal wings,
nn vestigial wings
B12.07 The new cells produced have a reduced
number of chromosomes (half as many b
chromosomes), compared with the Parents’ phenotypes normal wings normal wings
parent cell.
Parents’ genotypes NN Nn
B12.08 14 Gametes N N n
B12.09 During sexual reproduction, two gametes Offspring genotypes N n
fuse – one from each parent – to form and phenotypes
NN Nn
a zygote. If the gametes were formed
by mitosis, they would each have the N normal normal
diploid number of chromosomes and the wings wings
zygote would have double this number of All the offspring would have normal wings.
chromosomes. For the zygote to have the
correct diploid number of chromosomes,
each gamete must have half the normal B12.18 Although the predicted ratio is 3 brown:
number (the haploid number) – so 1 red, this is only a probability so these
gametes must be formed by meiosis. two parents could have three red and two
brown offspring.
B12.10 a 
any upper case and lower case letter
Parents’ phenotypes brown hair brown hair
– e.g. B for brown eyes and b for
green eyes Parents’ genotypes Bb Bb

b BB brown, Bb brown and bb green Gametes B b B b

c BB and bb are homozygous, Bb Offspring genotypes B b

and phenotypes
is heterozygous. BB Bb
B
B12.11 The allele for round leaves is dominant, brown hair brown hair
because this is the phenotype shown by a Bb bb
heterozygous plant. b
brown hair red hair
B12.12 For letters like S or C, it is difficult to tell
the upper and lower case (capital and
small) letters apart. For letters like A or B, Practice questions
it is easy to tell the upper and lower case 1 B[1]
letters apart.
2 B[1]

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3 a heterozygous[1] environment. Genes could determine the

maximum length to which fingers can grow,
b phenotype[1] while environment could affect whether or not
c recessive[1] they reach this potential length.

d allele[1] Questions
4 a i ee[1] B13.01 a discontinuous
ii EE[1] b continuous
b c continuous
E e
d discontinuous
EE Ee
E
indented indented B13.02 a genes alone
Ee ee b genes and environment
e
indented smooth
c genes and environment
[3] d genes alone
(one mark if all offspring genotypes B13.03 a discontinuous
correct; one mark if phenotypes correctly
matched to genotypes; one mark if b It is caused entirely by genes.
expected ratio of 3 : 1 indented to smooth The recessive allele codes for green
is roughly equivalent to the actual seeds – call it g. The dominant allele
numbers of 302 : 99) codes for yellow seeds – G. Seeds
with the genotype gg are green
Chapter B13 and are therefore homozygous and
pure-breeding. Yellow seeds can be
Before you start heterozygous, Gg, and can therefore
A gene is a region of DNA that encodes a protein. produce some yellow and some green
An allele is a particular type of a gene. They are seeds when they are crossed.
passed between parents and offspring during the
B13.04 a discontinuous; the kernels are either
process of reproduction.
white or brown.

Science in context B13.01 (Note: learners may see that there are
some dark brown kernels and some
1 The stichius form of the butterfly imitates the
light brown ones, and not be sure
poisonous common rose swallowtail butterfly,
whether to count these as brown or
because predators avoid eating the poisonous
white. Accept either interpretation.)
butterfly. This imitation only gives the
mormon butterfly an advantage in areas where b The ratio of 302 : 99 is approximately
the common rose swallowtail butterfly is equal to 3 : 1.
found and predators have learned to avoid it.
In other areas, the bright colouring would be c If learners consider that all the
a disadvantage because it makes the mormon brown kernels are the same, then
butterfly more visible. they are likely to suggest that the
allele for white is dominant, and the
2 Female butterflies may carry eggs, and male allele for brown is recessive. Accept
butterflies might be more common than females. any symbols that use upper case for
white and lower case of the same
Experimental skills B13.01 letter for brown – for example, B and
b. The parents could have had the
1, 2 These answers will depend on the
genotypes Bb and Bb, which would
learner’s results.
give a 3 : 1 ratio of white : brown in the
3 Learners should recognise that finger length offspring phenotypes.
could be affected by both genes and the

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B13.05 1 Variation: in the peppered moth B13.08 a 

Choose an individual wheat plant
population, most peppered moths from a variety that has some
were pale but a few were dark. resistance to rust, and another
2 Overproduction: peppered moths that has high yield. Transfer pollen
produce many offspring, most of which from one to the stigma of the other.
do not survive. Only a small proportion Collect the seeds, sow them and grow
survive long enough to reproduce. the plants to their full size. Expose
3 Best-adapted individuals are more them all to rust, and select those that
likely to survive and reproduce: when the are most resistant, and that have the
environment is polluted, dark moths are highest yield, to breed. Continue for
better camouflaged than pale ones on tree many generations. You could also
trunks. The pale moths are more likely bring in new individuals at some
to be eaten by birds, while the dark ones stage, for example a different high-
have a better chance of evading capture, yielding parent could be used to breed
surviving and reproducing. with the best rust-resistant offspring
4 Alleles that confer useful adaptations in generation 2 or 3.
are more likely to be passed on: the allele
for dark wings is therefore more likely to b The rust undergoes natural selection.
be passed on to the next generation than There will be variation among the
the allele for pale wings. rust individuals, and some may have
alleles that allow them to infect
B13.06 With less air pollution, more lichen grows the resistant wheat plants. These
on tree trunks. Now pale moths are better individuals have a selective advantage
camouflaged than dark moths, so they are – they are more likely to survive and
more likely to survive, reproduce and pass reproduce, as they have access to
on their alleles for pale wings. Over time, more food than the rust individuals
the pale wing allele gradually becomes that can only grow on non-resistant
more common in the population of wheat plants. The alleles for the
peppered moths, so most moths now have ability to infect resistant wheat plants
pale wings and few have dark wings. are therefore more likely to be passed
on to the next generation of rust
Activity B13.01 fungus. Over time, more and more
rust fungi in a population are likely to
1 The reliability of an investigation is improved
have these alleles and be able to infect
by taking repeats. This was done here for the
previously resistant wheat plants.
different types of beak, and also the different
types of food.
Practice questions
2 Answers will depend on the instruments used, 1 D[1]
but should focus on the size, the ability to pick
up small objects, and the ability to manipulate 2 C[1]
the instruments.
3 a species[1]
3 Answers will depend on the instruments used.
Accept sensible alternatives. b discontinuous[1]
c continuous[1]
Questions
4 a  ny two from: mean milk yield increased;
A
B13.07 The breeder should measure the methane no change in the first two years; relatively
output of all the sheep. Select a female steady change from then on; total change
and a male with low methane output is 366 kg per cow[2]
and breed them together. Measure the
methane output of the lambs and select b Any two from: select cows that produce
a male and a female with the lowest most milk and bulls whose female
methane output to breed together. relatives produce most milk; breed them
Continue for many generations. together; select offspring that produce
most milk; repeat for many generations[2]

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c breeder can simply choose animals that b creosote bush

produce most milk; selection is done
on phenotype, not genotype[2] c primary consumer: kangaroo rat;
secondary consumer: kit fox; tertiary
d breeder was not selecting for protein consumer: coyote
content / perhaps cows that produce
more milk have always had less protein in d Kangaroo rats are herbivores. Kit
their milk[1] foxes and coyotes are carnivores.

5 a 
Any two from: they rise and then fall; e
maximum number is in 2006; overall grasshopper tarantula
change is from about 40 cases in 1993
to about 260 cases in 2012[2] creosote kangaroo kit
coyote
bush rat fox
b 1650 cases out of 2150 = 76.7%[1]
c Any two of the following pairs jackrabbit
(allow other suitable and biologically
correct suggestions): B14.02 Look for a correct and plausible food
chain, with arrows in the correct
• reducing use of antibiotics – reduces direction. Producer, primary consumer,
selection pressure on the bacteria secondary consumer and so on should be
• better hygiene when treating patients correctly labelled.
/ description of this (e.g. washing B14.03 Energy is lost to the environment at each
hands more carefully after touching level in a food chain. By the fifth step in
one patient before touching another) a food chain, there is not enough energy
– avoiding transmission of bacteria to support a population of consumers at
between individuals this level.
• finding new antibiotics that kill B14.04 People can eat soya beans. A great deal of
MRSA – so people infected with it energy is lost as it is transferred from soya
are less likely to die[4] beans to cattle, so humans get less energy
6 a 
change in base sequence in DNA; by eating the cattle than they would have
random[1] done by eating the soya directly. (Some
learners may also appreciate the high
b ionising radiation / named example of energy costs of transporting the soya
ionising radiation; chemicals / named beans to this area, and the difficulties
mutagenic chemical[2] in supplying water to the cattle in a
desert region.)
Chapter B14 B14.05 a 
photosynthesis
Science in context B14.01 b respiration and combustion
1 Accept sensible suggestions. These will include
B14.06 For example: The lion dies. Its body
observations of animal behaviour in the wild,
is decomposed, and some of the
and inspecting the faeces or pellets of animals
carbon atoms in it become part of the
to determine what they had eaten.
decomposers. They respire, and some
2 In order to suggest food chains that existed of the carbon atoms return to the air as
in communities in the distant past, scientists carbon dioxide. This is taken into a grass
would need to judge the behaviour of animals plant and used in photosynthesis to make
from their anatomy and body structures, from glucose in the plant cells.
the fossil record.
Practice questions
Questions 1 B[1]
creosote bush → kangaroo rat →
B14.01 a 
2 A[1]
kit fox → coyote

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3 a the transfer of energy[1] Science in context B15.01

b grass / ladysmock[1] There are many reasons why it is important to
maintain species diversity and prevent extinction.
c ladysmock → caterpillar → Learners might suggest examples relating to
robin → kestrel conservation, medicine and the importance of
or maintaining existing ecosystems.

ladysmock → caterpillar → short-tailed Questions

field vole → kestrel
B15.01 Each species has adaptations that increase
or its ability to survive and reproduce in its
habitat. If that habitat is destroyed, the
ladysmock → caterpillar → short-tailed species may not be able to survive and
field vole → fox[2] reproduce in another habitat.
(one mark for the organisms, one mark B15.02 Coral reefs and rainforests provide a very
for arrows in the correct direction) wide variety of different habitats, which
d less grass eaten by voles; so more means that many different species can
food for rabbits and their population live there. A monoculture provides a very
increases; fewer voles for foxes to eat; narrow range of habitats, so only a few
so foxes eat more rabbits and the rabbit species can live there.
population decreases[4] B15.03 Any five from: reduced biodiversity;
4 a approximately 0.04% (allow 0.03–0.05)[1] habitat loss; risk of extinction of plant
and animal species; increased soil erosion;
b stomata[1] increased risk of flooding; increased
c photosynthesis[1] carbon dioxide concentration in the air;
decreased transpiration so less water
d decomposition / decomposing[1] vapour in the air
e respiration[1] B15.04 Any five from: climate change; habitat
destruction; hunting; pollution;
f Any four from: if there is not enough
overharvesting; introduced species (some
oxygen; dead plants and animals do not
learners may also have other suitable
decompose; over millions of years, heat
suggestions)
and pressure transform them to fossil
fuels; which contain the carbon from the B15.05 The new species may be a predator of
bodies of the organisms; when fossil fuels some of the native species, or it may
are burnt, carbon is returned to the air; as compete with them for scarce resources,
carbon dioxide[4] such as food or nesting sites.
B15.06 Captive breeding is breeding animals in
Chapter B15 captivity, such as in zoos. If the captive
Before you start breeding programme is successful,
numbers of the endangered species can be
There is only one species of plant growing in this increased. Eventually, it may be possible
field. Other, wild plants have been either removed to return some of them to the wild.
or their growth has been prevented. This means
that animals that feed on other species of plant B15.07 Genetic diversity increases the chances
will not be able to live there. There are also areas that a population of organisms will
of bare land between the rows of plants. Perhaps be able to adapt to changes in their
the land has been treated with pesticides to prevent environment, such as climate change. It
other plants (weeds) or animals from growing and also reduces the chances of two harmful
competing with these crops. This has limited the recessive alleles being brought together in
diversity of the species that can live on this land. the offspring of a breeding pair.

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Practice questions b i so that proper care can be provided;

example of suitable care, for example,
1 A[1] providing a suitable place to give
2 C[1] birth / isolating from other animals /
providing suitable food[1]
3 a 
the number of different species
that live in an area[1] ii Any three from:

b carbon dioxide / CO2[1] • idea that you cannot tell she is

pregnant until the 5th / 6th week
c they become endangered (or words of pregnancy
to that effect; accept ‘they could
become extinct’)[1] • concentration of PGFM rises
at week 5
d it increases / is enhanced[1]
• can predict birth as likely to
4 a 
a species whose numbers have fallen so take place three weeks after the
low; that it is likely to become extinct[2] rise begins
b Any three from: • can predict birth as likely to take
• loss of habitat place when the level reaches 1.4
arbitrary units[3]
• people use sandy beaches for pleasure
iii Any three from:
• pollution (of the sea or beach)
• to prevent closely related animals
• (pollution) could reduce food supply breeding together
/ poison the turtles / increase risk
of disease • to maintain genetic diversity

• climate change • which reduces chances of

harmful recessive alleles coming
• causing sea level rise so beaches now together in offspring
covered by water
• increases ability of the
• turtles do not begin to breed until population to adapt to changes
they are 30 years old in their environment[3]
• so unable to increase the population 6 store seeds (in controlled conditions) for long
quickly if it starts to fall periods of time; maintain a population of a
species that is threatened in the wild; some
• alternative valid points[3]
(stored) seeds germinated to provide fresh
5 a Any two from: seeds; collect seeds from different places to
ensure genetic diversity; maintain / increase,
• deforestation genetic diversity by breeding individuals with
• use of land for mining different alleles together (to produce more
seeds for storage); if habitat is restored then
• use of land for building roads plants can be returned to the wild[6]
• use of land for building homes /
factories
• pollution[2]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

Any example answers to questions taken from past question papers, practice questions, accompanying marks and mark
schemes included in this resource have been written by the authors and are for guidance only. They do not replicate
examination papers. In examinations the way marks are awarded may be different.

Chemistry
Chapter C1 C1.04 a If iodine is heated strongly then
the temperature rises very quickly.
Science in context C1.01 The melting and boiling points are
close together, so the liquid stage is
1 Jupiter and Saturn are the biggest of the
not seen as it boils quickly.
planets in our solar system and are made of
hydrogen and helium in the gaseous state. b You would need to heat the solid
There is a progression outwards from the Sun slowly so that the temperature does
in terms of the structure of the planets. Those not rise too quickly. You could use an
nearest the Sun are rocky and relatively small; electric heater to control temperature
beyond Mars the planets are gaseous. more carefully, or you could use an
oil bath to heat the solid and carefully
2 Hydrogen molecules are the smallest of all
control the temperature so it is kept
the elements and therefore the forces between
between the melting point (114 °C)
them are very small. The gas needs to be
and boiling point (184 °C) of iodine.
highly compressed (so that the molecules are
close together) and at a very low temperature
(so that the molecules are moving slowly) in
Experimental skills C1.01
order for it to condense into a liquid. 1 Substance B is a pure substance as the curve is
flat while the substance melts. Substance A is
Questions a mixture as there is no single melting point –
that region of the curve is sloped.
C1.01 a freezing
2 Take temperature readings at shorter time
b boiling
intervals (e.g. every 30 s). Using a digital
c condensation thermometer would give more accurate
readings. Using a temperature sensor linked
C1.02 a methane to a computer would allow the readings to be
b Ethanol and mercury; they taken continuously and enable the graph to
have melting points below room be plotted as the readings were being taken.
temperature, but boiling points above The samples can be re-heated and cooled
room temperature. again, allowing duplicate sets of data to
be collected.
c The impurity alters the freezing point
of the liquid, often meaning melting Questions
occurs over a range of temperatures.
C1.05 A = solid; B = energy released;
C1.03 a Volatility describes how easily a liquid C = energy absorbed
evaporates. A volatile liquid is one
that evaporates easily; it has a low C1.06 A = solid; B = liquid; C = liquid and gas
boiling point. (vapour); D = gas

b e thanol > water > ethanoic acid; Experimental skills C1.02

ethanol is the most volatile, ethanoic
1 silver iodide
acid is the least volatile
silver potassium silver potassium
c  ; Both the melting point and boiling
B 2 + → +
nitrate iodide iodide nitrate
point are above room temperature;
therefore, it is a solid at room 3 the rates of diffusion of silver and iodide ions
temperature.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

4 because the rates of diffusion of the ions are 5 a 

evaporation of the liquid; and
not the same; silver ions are less heavy and so diffusion of the gas particles[2]
diffuse slightly more quickly
b Particles moved more slowly;
Questions because the temperature was lower.[2]

C1.07 Evaporation of bromine takes place as 6 a A solid; is cooling down.[2]

molecules escape from the surface of the b They are moving more slowly;
liquid. The gaseous bromine molecules and getting closer together.[2]
then spread throughout the gas jar
to completely fill the container. This c Heat comes from the formation of
occurs because the molecules are moving bonds (interactive forces) between
randomly and there are collisions with air the particles.[1]
molecules. Thus, bromine molecules move
7 a A
 mmonia, which is alkaline, reached
from a region of high concentration to low
the indicator first to change its colour;
concentration until they are completely
because it moved more quickly;
mixed with the air and at the same
because it was lighter.[3]
concentration throughout.
b Around 50 s; Rate of diffusion is inversely
C1.08 a 
Methylamine molecules have a greater
related to the molecular mass; heavier
mass than ammonia molecules and
molecules, such as HCl here, diffuse
so diffuse more slowly. The white
more slowly than lighter molecules. [2]
smoke ring will be more central than
for ammonia/hydrochloric acid,
slightly to the right of centre as Chapter C2
methylamine diffuses slightly faster Before you start
than hydrochloric acid.
1 ‘H’ and ‘O’ are the chemical symbols for
b hydrobromic acid or hydroiodic acid a hydrogen atom and an oxygen atom,
respectively. Water consists of two hydrogen
C1.09 In Figure C1.19a the liquid levels are
atoms chemically bonded to one oxygen atom.
the same because there is air both inside
When atoms join together like this, they form
and outside the porous pot cylinder.
a molecule. A molecule must have more than
In b, hydrogen diffuses into the pot more
one atom in it.
quickly than air molecules diffuse out
because hydrogen molecules have less mass 2 You may have heard of protons, neutrons and
than the air molecules. This produces an electrons; these are subatomic particles, and
increase in pressure inside the pot and so they come together to make the many different
the liquid level is pushed down on the left types of atom.
(and up on the right).
Science in context C2.01
Practice questions
1 The rings are made up of carbon atoms
1 D[1] (not many elements can form rings like
this). Carbon is the basis of the molecules
2 B[1]
of life because it can form so many
3 A[1] different structures.
4 a moving slowly; close to each other[2] 2 There are 19 atoms in all (count all the
corners), arranged in five hexagonal rings.
b They vibrate more quickly.[1]
c evaporation[1] Questions
d changing from liquid to solid[1] C2.01 neutron = 1, electron = 0 (or 1/1840)
C2.02 15 protons, 16 neutrons, 15 electrons

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

C2.03 An element is a substance that cannot C2.10 6 electrons (the number of electrons
be broken down into anything simpler does not change between isotopes of the
by chemical means. Atoms are the same atom)
particles that make up all substances.
An atom is the smallest particle of an C2.11 All the atoms of an element contain the
element that shows the properties of that same number of protons (and the same
element. Atoms can join together to make number of electrons).
molecules. C2.12 D
Each element has its own type of atom C2.13 C
and the atoms of an element all have the
same number of protons and electrons. C2.14 C

C2.04 Protons are positively charged and C2.15 C

would therefore repel each other/the C2.16 a LiF
presence of the neutrons counteracts
this repulsion and means that the nucleus + –

can hold together. Li+ F–

Experimental skills C2.01
b NaBr
1 The metal present is responsible for
–
determining the colour seen in the flame.
+
The non-metal present is the same in all cases
and so cannot be responsible for the change.
2 The salt which produces light of the greatest
energy is the one which gave the most violet/
blue flame colour. The results will depend on sodium ion, Na+ bromide ion, Br–
which salts you tested.
c KCl
Questions
+ –
C2.05 a first shell, maximum 2: second shell,
maximum 8
b 2,8,8,2
c 8 in both cases
C2.06 A nitrogen atom has 7 protons potassium ion, K+ chloride ion, Cl–
(positively charged) and 7 electrons
C2.17 A
(negatively charged).
C2.18 A
C2.07 a A, C: they have 4 electrons in their
outer shells C2.19 C
b D: it has 8 electrons in its outer shell
Practice questions
c B: it has 7 electrons in its outer shell 1 C[1]
d C, D: they have 3 shells of electrons 2 a the number of protons in the nucleus
e 14: the number of electrons must of an atom[1]
equal the number of protons in b mass number is protons + neutrons;
an atom. argon has two more neutrons[2]
C2.08 B
C2.09 Cl-35 has 18 neutrons whereas Cl-37 has
20 neutrons.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

c because delocalised electrons between

the layers of atoms are free to move.[2]
Particle Charge Mass Position
b Graphite has layers which can slide
in atom
over each other; diamond has a
proton + 1 in the three-dimensional lattice in which
nucleus all the atoms are bonded.[2]
neutron 0 1 in the
nucleus Chapter C3
electron − 1 orbiting Before you start
1840 the nucleus
There are no right/wrong answers here as the
[5] questions are written by individual learners.
Examples of questions could include: What
d hydrogen[1] compound is represented by H2O? (water) Is CO2
an element or a compound? (compound) What
e They both have full/complete
elements are present in sulfuric acid? (hydrogen,
outer shells.[1]
sulfur, oxygen) Common formulae that they may
3 a C-14 has more neutrons in the nucleus; it come up with that should be checked are O2, CO2,
has 8 neutrons compared with 6 in C-12[2] H2O, NH3, HCl, H2SO4 and HNO3.

b 2,6[1] Science in context C3.01

c i 4[1] 1 Other costs: energy costs / safety costs in terms
ii 4[1] of the physical plant / level of manpower
needed / cost of unwanted by-products.
4 It is the outer electrons of an atom that give
rise to its chemical properties. The isotopes 2 Marketing should consider uses for the by-
have the same number of electrons in the products and then convincingly ‘sell’ their
outer shell.[2] usefulness.

5 a C[1] Questions
b The structure shown is of an ionic C3.01 a iron + oxygen → iron(III) oxide
compound; potassium bromide is the sodium sulfuric sodium
only ionic compound in the list.[2] b + → + water
hydroxide acid sulfate
6 a Potassium has lost an electron; sodium
chlorine has gained an electron.[2] c sodium + water → + hydrogen
hydroxide
b diagram showing 1 shared pair of
electrons between atoms/3 pairs non- C3.02 a 2Cu + O2 → 2CuO
bonding electrons on each atom[2]
b N2 + 3H2 → 2NH3
c 4Na + O2 → 2Na2O
Cl Cl
d 2NaOH + H2SO4 → Na2SO4 + 2H2O

c covalent[1] e 2Al + 3Cl2 → 2AlCl3

d KCl high melting point/Cl2 low melting f 3Fe + 4H2O → Fe3O4 + 4H2
point (or b.p.); OR KCl is a solid at room
C3.03 a H2 + Cl2 → 2HCl
temperature and Cl2 is a gas; OR KCl
conducts electricity when dissolved or b 2Cu + O2 → 2CuO
molten/Cl2 does not conduct electricity[1]
c Mg + ZnCl2 → MgCl2 + Zn
7 a Graphite has a high melting point because
it has strong covalent bonds between the
atoms in the layers/conducts electricity

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

C3.04 Solid sodium carbonate reacts with d the sum of the relative atomic masses of
hydrochloric acid solution to give sodium the atoms present in a ‘formula unit’ of
chloride solution and carbon dioxide gas. a substance[1]
Water, a liquid, is also produced.  1.2 
e   × 21 = 4.2 g[2]
 6 
C3.05 a Ag+(aq) + Cl−(aq) → AgCl(s)
(partial calculation = 1 mark)
b Ba2+(aq) + SO42−(aq) → BaSO4(s)
4 a C3H8 + 5O2 → 3CO2 + 4H2O[2]
C3.06 a HCl(aq) + KOH(aq) → KCl(aq) +
H2O(l) (1 mark for correct formulae; 1 mark
for balancing)
H+(aq) + OH−(aq) → H2O(l)
b volume ratio of propane to carbon
b 2HCl(aq) + CuCO3(s) → CuCl2(aq) + dioxide is 1 : 3; 100 × 3 = 300 cm3[2]
H2O(l) + CO2(g)
(Wrong answer to part a can be carried
2H+(aq) + CO32−(s) → H2O(l) + through to gain marks here.)
CO2(g)
c 50 cm3 of methane forms 50 cm3 of
C3.07 a covalent carbon dioxide; water condenses at
b ionic room temperature and pressure so not
counted; excess of oxygen is 50 cm3
c CH4, NaI, C3H6, ICl3, BrF5, HBr so total is 100 cm3[3]
C3.08 a 32 b 17 5 a C2H4O[1]
c 98 d 119 b 88[1]
e 188 c Mg(s) + 2C3H7COOH(aq) →
Mg(C3H7COO)2(aq) + H2(g)[4]
C3.09 100
(1 mark for state symbols; 1 mark for
C3.10 a 0.02 moles formula of magnesium butanoate;
b 2 moles 1 mark for balancing; 1 mark for
correct substances)
c 0.07 moles
d The sum of the relative atomic masses
C3.11 a 36 000 cm3 of the elements in a compound[2]
b 1440 cm3 (1 mark if only the simpler terms,
c 12 000 cm3 masses or atomic masses are used)
e magnesium butanoate (or any
Practice questions ionic compound) is not made up
1 A[1] of molecules and so cannot have a
molecular mass[1]
2 D[1]
3 a H3PO4 (order of elements not critical)[1] Chapter C4
b magnesium carbonate (s) + phosphoric Before you start
acid (aq) → magnesium phosphate (aq) + 1 Wiring is most often made of copper (due to
carbon dioxide (g) + water (l) its high conductivity and flexibility).
(1 mark for substances; 1 mark for 2 Wiring is usually covered in plastic coating to
state symbols)[2] insulate the wires to ensure that the electricity
c 24 + 12 + (3 × 16) = 84 is conducted to where it is intended to go.

(partially correct calculation = 1 mark)[2] Plastic is used as the insulator because it is

generally flexible. This is helpful as it can be
easily manipulated and will not crack.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

3 Liquid metals do conduct electricity. Other Questions

liquids that conduct include molten and
aqueous solutions of ionic substances. C4.04 a h
 ydrogen at cathode and chlorine
at anode
Science in context C4.01 b potassium at cathode and chlorine
1 Ions within the substances need to be free to at anode
move. In a solid they are fixed in a lattice but C4.05 Metal is formed at the cathode and a non-
when in solution or molten, the ions are free metal at the anode.
to move.
C4.06 a 2Br−(l) → Br2(g) + 2e−
2 Ions are Na+, Cl–, H+, OH–; products are
chlorine, hydrogen and sodium hydroxide, all b A dark red-brown gas would
of which have industrial uses. be produced at one electrode
(the anode). A ball of molten lead
3 (1) makes Al – used in a variety of processes would be formed in the container/at
e.g. in aircraft manufacture the other electrode/at the cathode.
(2) electroplating is used in a wide range C4.07 2H2(g) → 4H+(aq) + 4e−
of applications – means products are more
attractive/last longer C4.08 fuel cells: a, d, e; petrol cars: b, c, f

(3) products of electrolysis all have Practice questions

applications in fuels (H2) or the
chemical industry. 1 C[1]
2 A[1]
Questions
3 a E[1]
C4.01 a i, iii, iv and v conduct electricity.
b F[1]
b iii and v are electrolytes (aqueous
solutions of ionic compounds). c D[1]
C4.02 a T
 he ionic solid does not conduct d C[1]
as the ions present cannot move
about (they can only vibrate at 4 a i cathode[1]
fixed positions). ii electrolyte[1]
b Melt it or dissolve it in water. b arrows pointing (clockwise) away
C4.03 W
 hen a metal conducts electricity it is from negative and towards positive
the delocalised electrons present in the terminals of power supply[1]
structure that move through the metal to c dilute sulfuric acid[1]
carry the charge. In aqueous solutions of
ionic compounds it is the ions present that d carbon/graphite or platinum[1]
move to carry the charge.
5 a i mass of cathode increases[1]
Experimental skills C4.01 ii mass of anode does not change[1]
1 Depends on the equipment available but a b the blue colour would fade
reliable power pack to adjust the voltage to colourless[1]
applied is useful / use of an ammeter rather
than a light bulb to detect flow of current. c 4OH− → O2 + 2H2O + 4e−[2]

2 The electrodes would need to be thoroughly (1 mark for correct substances; 1 mark
cleaned with sandpaper / washed in propanone for balancing)
and then dried / weigh the electrodes on as d i the anode would lose mass /
accurate a balance as is available. copper anode dissolves to form
ions; cathode increases in mass /
copper deposited on cathode[4]

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ii the solution colour would not change / C5.03 The energy of the reactants is lower than
concentration of copper ions in the energy of the products / upwards
solution remains the same[2] arrow.
e movement of copper ions; from anode C5.04 Bond breaking is endothermic.
to cathode[2]
C5.05
6 a produce water as the only product of
reaction rather than NO2 and CO2

Enthalpy / kJ/mol
which are harmful to the environment[1]
2H2O2
b any two from hydrogen – large fuel
tank, infrequent filling stations, can be
renewable, expensive; petrol – smaller 2H2O + O2
fuel tank, frequent filling stations,
not renewable, cheaper; or other
relevant points[2] Progress of reaction

C5.06 For a reaction to take place, some bonds

Chapter C5 in the reacting substances must first be
broken. Bond breaking is an endothermic
Science in context C5.01 process and therefore there is always a
1 CFCs were very stable compounds and need for some energy to be supplied by the
were not degraded (broken down) until they surroundings to start off a reaction.
reached the upper atmosphere where they
released chlorine free radicals. These radicals Practice questions
reacted with the ozone layer protecting
1 B[1]
the Earth from harmful UV radiation.
‘Holes’ appeared in the upper atmosphere, 2
particularly over the Earth’s poles. CFCs were
banned by the Montreal Protocol. CFCs are Process Temperature Chemical
also greenhouse gases. change or physical
2 Use of refrigerants greatly improved food water vapour increase physical
storage and preservation and allowed for changing to
the long-distance transportation of foods. water
Air-conditioning made the workplace much salt solution to increase physical
more comfortable in regions of intense or salt and water
extreme climate.
magnesium plus increase chemical
hydrochloric
Questions
acid
C5.01 an endothermic reaction burning increase chemical
C5.02 a hydrogen to
form water
Zn(s) + CuSO4(aq) iron rusting increase chemical
Energy / kJ

ZnSO4(aq) + Cu(s)
[5]
3 a effervescence/fizzing/bubbles[1]
b bubbling stops[1]
c endothermic; because the
Progress of reaction temperature goes down[2]
b Enthalpy change is shown by d exothermic; products have less energy
the dotted green arrow. This will than the reactants[2]
be negative.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

4 C6.06 The rate of reaction slows over time as the

concentration of the reagents decreases.
Enthalpy / kJ

Ea C6.07 A catalyst is a substance that speeds up a

N2 + 3H2
chemical reaction but is not itself used up
ΔH 2NH3 in the course of the reaction.
C6.08 The presence of a catalyst decreases the
activation energy of a reaction.
Progress of reaction [2]
C6.09 a An increase in temperature means
that the particles are moving more
Chapter C6 quickly and therefore collide more
frequently. When they collide,
Science in context C6.01 more particles have energy greater
than the activation energy so there
1 carbon dioxide + water → glucose + oxygen
will be more collisions that result in
The photosynthesis reaction maintains a reaction.
the level of oxygen in the atmosphere and
b There will be more surface area of
removes carbon dioxide. The two biochemical
the solid exposed so there will be
processes of photosynthesis and respiration
more frequent collisions between the
maintain the balance between these two gases
reactant particles.
that are important for life. Other important
reactions include those involved in the making c Greater concentration means
of proteins and the copying of DNA. there are more reactant molecules
present and so there will be more
2 The key factors in industry are achieving
frequent collisions.
sufficient product as economically as possible.
The reaction processes used must give a yield C6.10 a A, B and D
at a reasonable rate as time is an economic
cost. The product must also be achieved in b A and B
a system that is safe and environmentally c reduction
sustainable.
Practice questions
Questions
1 B[1]
C6.01 a physical
2 a because the reaction is complete
b chemical (has stopped)[1]
c physical 20
b = 0.67; unit cm3/s[2]
30
d physical c gas syringe[1]
C6.02 a exothermic d any two from:
b exothermic • increase temperature;
c exothermic • use smaller pieces of
d endothermic calcium carbonate;

C6.03 A new substance(s) has been formed. • use more concentrated acid[2]

C6.04 a rate increases 3 a As the temperature increases the cross is

obscured (becomes hidden) in a shorter
b rate increases time / the reaction rate increases with
temperature.[2]
c rate increases
C6.05 The reactions that would spoil the food
are slowed down at the lower temperature.

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b As temperature increases, the particles C7.02 a An indicator changes its colour
move more quickly and so collide more depending on whether it is in an
frequently / the particles have more kinetic acidic or alkaline solution.
energy and so more collisions involve
energy greater than the activation energy / b i alkaline ii neutral
more collisions produce a reaction.[3] iii alkaline iv acidic
4 a Smaller particles have a larger surface C7.03 pH 1 is more acidic (1000 times more
area; so there are more collisions between acidic than pH 4).
reactant particles[1]
b At higher temperatures, collisions are Experimental skills C7.01
more frequent; and a higher proportion 1 You need to consider the effectiveness of the
have sufficient energy to produce a whole tablet and then the mass of powder
reaction.[2] used. You need to work out a value for how
much acid has been neutralised per unit mass
5 a C[1]
of the tablet.
b B[1]
2 For example:
6 a D[1]
magnesium hydrochloric magnesium
+ → + water
b A[1] hydroxide acid chloride

c C[1] calcium hydrochloric calcium carbon

+ → + + water
carbonate acid chloride dioxide
d D[1]
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
Chapter C7 3 To make the solid more accessible to the acid /
to increase the surface area of the solid and to
Science in context C7.01 speed up the reaction.
1 Many of these terms come from what
Questions
was an impressive age of Islamic science
and mathematics centred around the C7.04 a H2SO4 b HCl
Mediterranean (including southern Spain).
C7.05 a i CuO(s) + 2HNO3(aq) →
Modern terms such as algebra have an Arabic
Cu(NO3)2(aq) + H2O(l)
origin. The period was linked to the practice
of alchemy, which included some truly ii Zn(s) + 2HCl(aq) → ZnCl2(aq) +
experimental science together with the more H2(g)
mystical aspects and practices.
b Zn has lost electrons and H+ ions
2 Strong alkali needs to be removed from have gained electrons; Zn atoms have
soap because it causes skin burns and can be been oxidised.
particularly dangerous for the eyes. Modern
soaps do have an interestingly wide range of C7.06 a blue
pH. Most are not actually neutral (pH = 7.0). b S(s) + O2(g) → SO2(g)
It is worth investigating; some are slightly
acidic, while others are mildly alkaline. magnesium
c magnesium + oxygen →
oxide
Questions C7.07 An amphoteric oxide is one that will
C7.01 a A corrosive substance dissolves or neutralise either an acid or an alkali to
‘eats away’ other substances. give a salt and water only.

b citric acid Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) +

3H2O(l)
c ethanoic acid
Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) +
H2O(l)

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

C7.08 zinc hydroxide or aluminium hydroxide e If heated too strongly, the salt
zinc sodium sodium could dehydrate (lose water of
+ → + water crystallisation) or even decompose.
hydroxide hydroxide zincate
Zn(OH)2(s) + 2NaOH(aq) → C7.14 a method B
Na2ZnO2(aq) + 2H2O(l) b sulfuric acid
or zinc sulfuric zinc
c + → + water
aluminium sodium sodium oxide acid sulfate
+ → + water
hydroxide hydroxide aluminate C7.15 a Precipitation is the sudden formation
of a solid when either two solutions
Al(OH)3(s) + NaOH(aq) → NaAlO2(aq) +
are mixed, or a gas is passed into a
2H2O(l)
solution.
C7.09 a sulfuric acid
b A method in which an acid solution
b nitric acid and an alkali are reacted precisely
to produce a salt solution; the salt
c carbonic acid can be crystallised from the solution
C7.10 a sodium hydroxide and hydrochloric produced.
acid c An ionic equation includes only those
b calcium hydroxide and nitric acid ions and molecules that actually take
part in the reaction.
c ammonia (ammonium hydroxide) and
sulfuric acid C7.16 A and C / silver iodide and lead(II)
chloride
C7.11 a nitric acid
C7.17 a sodium sulfate
b potassium sulfate and ammonium
nitrate b white

Experimental skills C7.02 Practice questions

1 D[1]
1 copper(II) + sulfuric → copper(II) + water
oxide acid sulfate
2 a red[1]
CuO + H2SO4 → CuSO4 + H2O
b calcium carbonate (s) + hydrochloric
2 That the copper oxide was present in acid (aq) → calcium chloride (aq) +
excess / this makes sure that all the acid is water (l) + carbon dioxide (g)[2]
reacted / this is important as the solution is
concentrated by heating after filtration, and (1 mark for compounds; 1 mark for
hot, concentrated acid is dangerous. state symbols)
c carbon dioxide is an acidic oxide
Questions (or simply acidic)[1]
C7.12 a magnesium chloride d test with universal indicator; note
b calcium nitrate colour change; compare with colour
chart to find pH value[3]
c zinc sulfate
3 B[1]
C7.13 a to make sure all the acid is reacted /
used up 4 a sodium chloride; sodium too reactive
and so unsafe[1]
b filtration
b sodium chloride[1]
c pipette, burette
c barium sulfate[1]
d yellow
d potassium carbonate[1]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

5 a bubbles / effervescence / fizzing[1] white solids, transition metal compounds

are coloured / alkali metals have relatively
b to ensure all the sulfuric acid was low melting and boiling points, transition
reacted / used up[1] metals have high melting and boiling
c fizzing would stop, or excess solid points; alkali metals are highly reactive,
remains[1] transition metals are less reactive.

d filter; heat to crystallisation point; C8.07 D

separate/dry crystals[3]
Practice questions
6 copper carbonate[1]
1 D[1]
7 a lead nitrate; sodium, potassium or
other soluble chloride[2] 2 B[1]

b mix solutions of the substances; 3 a iodine[1]

filter and keep the residue; wash the b lithium[1]
residue; dry the residue[4]
c bromine[1]
Chapter C8 d potassium; chlorine[2]

Science in context C8.01 4 a high densities[1]

1 Discuss the historic social and religious b metals[1]

attitudes to the role of women in society in
c Group VIII / noble gases[1]
different parts of the world – their role and
access to education; and opportunity to
pursue an independent career. Chapter C9
2 Consider the modern situation in different Science in context C9.01
cultures and the development of attitudes,
opportunities and perceptions. 1 The metallic nodules are rich in the metals
in demand and it would be relatively easy to
Questions extract the required metals. There are various
different sites in different regions of the ocean
C8.01 potassium hydroxide floor. The damage to the ocean floor itself
lithium through what is effectively open-cast mining
C8.02 lithium + water → + hydrogen would be significant, as would the damage to
hydroxide
the habitat of marine species about which we
C8.03 a approximately 40 °C (note that the know relatively little.
difference between one element and
the next is getting smaller as we go 2 The dependence on a single land-based source
down the group) is open to political and economic dangers.
It could lead to exploitation of the local
b Rubidium will react more strongly population and create socio-economic tensions.
with water than potassium.
C8.04 chlorine (of the options available in a Questions
school lab); also fluorine C9.01 a can be beaten into sheets / conducts
C8.05 They all have 8 electrons in their outer heat well / conducts electricity well /
shell, except for helium in the first period, can be drawn into wires
which has the maximum possible of 2. b is an insulator / poor thermal
They all have a full outer electron shell. conductor
C8.06 Any four from: alkali metals are soft, C9.02 a graphite
transition metals are hard / alkali metals
have low density, transition metals have b any two group I metals, e.g. lithium,
high density / alkali metal compounds are sodium, potassium, etc.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

c mercury Experimental skills C9.01

d diamond 1 The reaction would be exothermic, but the
rise in temperature would not be as great as
C9.03 All metals conduct electricity, while non-
that observed when zinc reacts with copper(II)
metals do not (except graphite); metals are
sulfate solution.
malleable and ductile while non-metals are
not; metals are good conductors of heat 2 Carry out the experiments in polystyrene
while non-metals are not (except diamond. cups or wrap the boiling tube in cotton wool
to prevent heat loss / take more frequent
Metals are formed from layers of positive
temperature readings to find the maximum
ions, surrounded by a ‘sea’ of delocalised
temperature reached more accurately.
electrons. These mobile electrons can move
through the structure, allowing metals
to conduct electricity. The attraction
Questions
between the positive metal ions and the C9.12
free electrons (metallic bonding) acts in copper(II) magnesium
magnesium+ → + copper
all directions, so the layers of positive ions sulfate sulfate
can slide over each other without breaking
the overall structure. This is why metals C9.13 Magnesium becomes coated with a
are malleable and ductile. layer of copper / the colour of the blue
solution fades.
C9.04 B
C9.14 Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)
C9.05 copper and silver
Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)
metal
C9.06 a 
metal + water → + hydrogen
hydroxide C9.15 This question is speculative – look at the
metal first letters of the metals in order and see
b metal + steam → + hydrogen if you can think of a phrase or sentence!
oxide

c i Mg + H2O → MgO + H2 C9.16 water and air (oxygen) / salt water or

acid rain
ii 3Fe + 4H2O → Fe3O4 + 4H2
C9.17 painting / oiling / greasing / coating with
C9.07 a D plastic
b brass (or steel) C9.18 Zinc is more effective because if the
surface layer is broken the zinc will still
C9.08 a any two from iron, chromium and
protect the steel beneath as it is more
nickel
reactive than iron (sacrificial protection)
b hardness and corrosion resistance / chromium will not protect if the layer is
broken as it is less reactive than iron.
C9.09 D
C9.10 a hydrogen Experimental skills C9.02
b potassium hydroxide 1 The formation of red–brown copper metal.

sodium 2 2CuO + C → 2Cu + CO2

c sodium+ water → +hydrogen
hydroxide
Questions
d 2K + 2H2O → 2KOH + H2
C9.19 To combine with the silicon(IV) oxide
C9.11 a strong and has a low density (sand/silica) and remove it as slag:
b Aluminium is coated with a very CaCO3(s) → CaO(s) + CO2(g)
thin oxide layer that protects it from
corrosion. C9.20 carbon monoxide
iron(III) carbon carbon
c copper + → iron +
oxide monoxide dioxide
Fe2O3 + 3CO → 2Fe + 3CO2

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

C9.21 silicon(IV) + calcium → calcium d aluminium[1]

oxide oxide silicate
e burning splint; pops[2]
SiO2 + CaO → CaSiO3
(glowing splint pops = 1 mark)
Practice questions 7 a aqueous copper sulfate or copper sulfate
1 D[1] solution[1]

2 C[1] b iron[1]

3 c Cu(s) + 2AgNO3(aq) →
Property Applies Applies to
Cu(NO3)2(aq)+ 2Ag(s)[3]
to most most non-
metals metals (1 mark for substances; 1 mark for
they conduct ✓ balancing; 1 mark for state symbols)
electricity d Copper becomes coated with silver
they react with ✓ ✓ coating; solution changes from
oxygen in the air colourless to blue.[2]

they are brittle ✓ e Zinc is more reactive than copper.[1]

they can easily be ✓ 8 a hematite[1]
bent and shaped
b carbon monoxide[1]
they have high ✓
melting points c because of the high temperature in
the furnace[1]
[6]
d calcium oxide/calcium carbonate; reacts
4 a its low density[1] with impurities/silica/silicon(IV) oxide in
b its resistance to corrosion[1] the ore[2]

c alloy; conductor; metal; mixture[4] 9 a the air[1]

d any two from: it does not rust/corrode; b It produces the heat needed in the furnace;
it is an alloy containing chromium and the carbon dioxide is then reduced in the
nickel; it is harder than pure iron[2] furnace to give carbon monoxide.[2]

5 a Layers of atoms / ions can slide over c It reacts with the silica (silicon dioxide)
each other.[1] impurity in the ore; forming calcium
silicate slag[2]
b The larger atoms prevent layers
sliding over each other.[1] 10 a stops air/water reaching the metal;
so rusting cannot occur[2]
c Yes; electrons are still free to move
around/between the metal ions.[2] b galvanisation[1]

6 a bubbles / fizzing / effervescence; c still protects even if the zinc layer is

zinc dissolves as it reacts[2] scratched or broken[1]

b no reaction[1] d the zinc or magnesium is more reactive

than iron; these metals lose electrons/
c iron, zinc, unknown metal, calcium[2] form positive ions more readily than iron;
so they are corroded rather than the iron /
(one out of order = 1 mark)
sacrificial protection[3]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

Chapter C10 C10.08 Rising sea levels so increased flooding

and faster rates of coastal erosion /
Science in context C10.01 changes to the life cycles and migratory
1 Possible reasons include population density patterns of animals and birds / more
(the greater the number of people, the higher severe droughts and crop failure / drying
the levels of pollution will tend to be), out of grasslands increases the frequency
presence of particular types of industry (living and severity of wildfires / more frequent
closer to large factories will generally mean and severe weather patterns, with
poorer air quality), impact of events such as associated problems such as flooding
forest/bush fires, government initiatives to and landslides / bleaching of coral reefs
reduce levels of airborne pollution, etc. and loss of marine life.

2 Factors that might encourage more Strategies include reducing use of fossil
environmentally friendly options include fuels for transportation and electricity
education (an understanding of the problems generation (e.g. by using renewable
caused to the environment), tax incentives sources of energy such as wind and
(reducing the cost of more environmentally solar) / phasing out of diesel and petrol
friendly solutions), cost savings (switching cars and replacing with electric or
off electrical equipment when not in use is hydrogen-powered cars / removing CO2
both good for the environment and saves from the atmosphere / reducing meat
money), etc. Factors that might prevent more consumption / improving separation of
environmentally friendly options include cost household waste / planting more trees.
(too expensive), habit (used to always using C10.09 Greenhouse gases absorb and re-emit
the car / not walking), inconvenience (easier the longer wavelength radiation reflected
to drive on a wet day than walk), lack of from the Earth’s surface.
education, etc.
C10.10 Cobalt chloride paper: colour change
Questions from blue to pink. Alternatively,
anhydrous copper(II) sulfate: colour
C10.01 nitrogen 78%, argon 0.9% and oxygen change from white to blue.
21%
C10.11 Measure melting or boiling point. For
C10.02 Harmful to life both on land and in the pure water, the melting point is 0 °C and
water / increased acidity levels in lakes the boiling point 100 °C.
can kill fish and other aquatic life / can
kill forests (many plants are extremely C10.12 Microplastics removed by filtration
sensitive to pH) / some building using a fine sand filter. Dissolved organic
materials will be damaged/corroded. compounds removed by an activated
carbon carbon filter. Microbes removed by
methane+ oxygen →
C10.03 a  + water disinfection using chlorine.
monoxide
b 2C6H14 + 13O2 → 12CO + 14H2O Practice questions
C10.04 Oxides of nitrogen are formed when 1 C[1]
nitrogen and oxygen from the air react at
a high temperature (e.g. in a car engine). 2 B[1]
They are linked to the formation of acid 3 a 78%[1]
rain and photochemical smog.
b any two from argon, carbon dioxide, other
C10.05 2CO + 2NO → 2CO2 + N2 noble gases (neon, krypton and helium)[2]
C10.06 Carbon dioxide: product of the c i B[1]
combustion of fossil fuels. Methane:
waste product from livestock (cattle) and ii A[1]
landfill sites. iii C and D[2]
C10.07 Increased use of fossil fuels. iv C[1]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

4 a oxides of nitrogen and sulfur cause C11.02

acid rain; this increases acidity of
lakes / rivers[2] H H H H H
H C H H C C C C H
b i not enough oxygen / air for
complete combustion[1] H H H H H

ii Carbon monoxide is toxic to humans methane butane

because it binds very strongly with
haemoglobin in red blood cells, carbon
C11.03 a 
propane + oxygen → + water
preventing them from carrying dioxide
oxygen around the body.[1]
b C3H8 + 5O2 → 3CO2 + 4H2O
c desulfurisation / scrubbing; using
C11.04
calcium oxide[2] H H

d the air[1] C C
5 a CO2 is produced from burning of fossil
fuels; needs to be reduced to reduce global H H
warming / reduce any sensible effect of
global warming[2]
C11.05 The bromine water is decolourised
b methane; livestock or decomposition in from orange–brown to colourless.
landfill sites[2] There would be no change if ethane was
bubbled through bromine water. The test
c They are greenhouse gases; allow short is for unsaturation (a carbon–carbon
wavelength energy from the Sun to reach double bond): ethene is unsaturated,
the Earth’s surface; but trap and re-emit but ethane is saturated.
longer wavelength radiation reflected from
the Earth.[3] C11.06 C2H 4Br 2
Br Br
Chapter C11 H C C H
Science in context C11.01 H H
1 The advantages of a space elevator are seen
in terms of the ease of transfer of astronauts C11.07 ethane → ethene + hydrogen
and goods to the space station without the
C2H6 → C2H4 + H2
need for rocket launches from the Earth.
Subsequent exploration from the space C11.08 a propene + hydrogen → propane
station would also be easier since there would
be no need for the technology to escape the b C4H8 + H2O → C4H9OH
Earth’s gravity. C11.09 a CH3CH(OH)CH3
2 These different forms of carbon all conduct b CH3CH=CHCH3
electricity because of the mobile, delocalised
electrons associated with their layered C11.10 Structural isomerism is a property
structure (see Chapter C2). of compounds that have the same
molecular formula but different
Questions structural formulae; the individual
compounds are known as structural
C11.01 methane, ethane, propane, butane / CH4,
isomers.
C2H6, C3H8, C4H10

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

C11.11 There is a steady increase in the boiling C11.18 a H H b H H

point of the alcohols with increasing
C C C C
number of carbon atoms.
H CH3 n H Cl n

C11.19 a a carbon–carbon double bond

150
b H H H H H H
Boiling point / °C

C C C C C C
C6H5 H C6H5 H C6H5 H

100 C11.20 a The monomers join together by a

reaction in which a small molecule
(usually water) is eliminated each
time a link is made.
b nylon; the amide link
(or peptide link)
50
0 1 2 3 4 5 6 C11.21 O O O O

Number of carbon atoms C C N N C C N N

H H H H

C11.12 a a carbon–carbon double bond, C=C

Practice questions
b –OH (a hydroxyl group)
1 B[1]
C11.13 a C2H4
2 C[1]
b as in Figure C11.06
3 a a compound that contains carbon
C11.14 a butane and hydrogen only[1]
b propene b no colour change / orange–brown colour
remains[1]
c propanol
c Ethene and steam are compressed
C11.15 bitumen: road surfacing; diesel: fuel to 6000 kPa and passed over a
in diesel engines; naphtha: chemical phosphoric acid catalyst at 300 °C.[3]
feedstock; gasoline: fuel in cars
d as a fuel; as a solvent[2]
C11.16 refinery gas, petrol, naphtha, diesel,
bitumen e (addition) polymerisation[1]

C11.17 Addition polymerisation takes place 4 a C[1]

when many molecules of an unsaturated b A and E[2]
monomer (e.g. ethene) join together to
form a long-chain polymer. c a carbon–carbon double bond, C=C[1]

H H H H d molecule must contain at least one

high pressure carbon–carbon double or triple bond[1]
n C C C C
heat, catalyst e C3H6[1]
H H H H n
ethene poly(ethene) 5 –40 °C[1]
6 a bitumen[1]
b bitumen[1]
c petrol (gasoline)[1]

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7 a hydrocarbons[1] 0.1
C12.03 Error in the mass is × 100% = 7.7%
1.3
b different boiling points[1]
0.5
c jet fuel (or heating systems)[1] Error in volume is ×100% = 5.0%
10.0
d i heat / catalyst[2] The larger error is in the mass. Random
errors could be reduced by repeating
ii hydrogen[1] the experiment several times, checking
for and removing anomalies and then
e C10H22 → C4H8 + 2C3H6 + H2[2]
calculating a mean average.

Chapter C12 Experimental skills C12.01

1 residue
Science in context C12.01
2 It will enable the material to dissolve
1 Portable distillation units. Strengths: provide
more quickly.
access to distilled water in remote areas
without need for large/expensive equipment 3 Salt is ionic and dissolves well in water. If the
/ may be powered by renewable sources. solution is concentrated by heat, then the
Weaknesses: if using solar power, the unit excess solid can be crystallised out. This would
will only operate under certain conditions / not be a good method for producing iodine
produce limited amounts of clean water / may crystals for several reasons. Iodine is toxic
be limited access to replacement parts if there and, unlike sodium chloride, it has covalent
is a failure / would need to be very robust if rather than ionic bonding so it is only partially
used in the field / may require training in safe soluble in water.
use / could be expensive.
Desalination units. Strengths: provide access Experimental skills C12.02
to drinking water in areas with access to 1 boiling points
seawater but limited freshwater / can be run
2 100 °C
continuously / proven technology. Weaknesses:
may be limited access to parts if there is 3 Distillation involves heating the liquid so
a failure / the waste product can be toxic that components start to evaporate. As they
to marine and coastal ecosystems / energy evaporate, they travel up through the
intensive as require high temperature and apparatus and into the condenser. In the
pressure / require training / could be expensive. condenser the temperature is lower and so
the gas will condense. Different fractions
2 The filter straw needs to remove particles of
separate at different temperatures due to
sand/silt/mud and harmful microbes such as
differences in their boiling points.
bacteria that can cause disease.
Questions
Questions
C12.04 The ink in this pen is a mixture of at
C12.01 The temperature should be recorded least two different dyes.
either with a thermometer or a digital
temperature probe and meter. The C12.05 A substance that remains on the baseline
volumes could be measured with a is insoluble in the solvent used. To
measuring cylinder or, for greater improve the experiment the learner
accuracy, a fixed volume could be needs to use an alternative solvent, e.g.
measured using a volumetric pipette and ethanol instead of water.
a variable volume by use of a burette. 2.3
C12.06 Rf = = 0.82 (to 2 d.p.)
2.8
C12.02 The teacher was not correct. The data distance moved by sample
have a narrow spread of results and Rf =
distance moved by solvent front
so are precise; however, they are not Distance moved by sample = Rf ×
accurate as the average of these results is distance moved by solvent front
not very close to the true value.
Distance moved by sample = 0.82 × 9.7
= 8.0 cm

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Experimental skills C12.03 Questions

1 Step a: The baseline needs to be drawn in C12.11 Iron(II) chloride would initially produce
pencil, not pen, as the ink in the pen could be a green precipitate. Iron(III) chloride
soluble. If the ink used to mark the baseline is would produce a brown precipitate.
soluble, it will also rise up the paper and affect
the results of the chromatogram. C12.12 When sodium hydroxide solution is
added to copper(II) sulfate solution, a
Step c: The solvent level should fall between light blue precipitate is formed. When
the bottom of the paper and the baseline; if it dilute ammonia solution is added to
covers the baseline, the samples will dissolve copper(II) sulfate solution, a light blue
into the solvent and not travel up the paper. precipitate is formed at first, but as more
Step d: The solvent should not travel all the ammonia solution is added this dissolves
way up but must be stopped just before it gets to produce a dark blue solution.
to the top of the paper. If this is not done, then C12.13 All acids release H+ ions in solution,
samples will continue to travel up the paper. and these ions react with carbonate ions
2 To reduce the amount of solvent lost through to produce carbon dioxide and water.
evaporation. In general, therefore, the reaction of
a carbonate with any acid produces
Questions carbon dioxide. Sodium carbonate
solution reacts with acids as follows:
C12.07 The nichrome wire probe is cleaned by
placing it alternately in a roaring flame Na2CO3(aq) + H2SO4(aq) → Na2SO4(aq)
and in concentrated acid. Once clean, + CO2(g) + H2O(l)
it is dipped in the acid and then into Na2CO3(aq) + 2HCl(aq) → 2NaCl +
the sample containing the sodium ions. CO2(g) + H2O(l)
Finally, the wire is held in a roaring
Bunsen flame. A yellow flame indicates Na2CO3(aq) + 2HNO3(aq) →
the presence of sodium ions. 2NaNO3(aq) + CO2(g) + H2O(l)
C12.08 The lilac flame indicates the presence C12.14 Acidified silver nitrate would produce a
of potassium ions. Potassium sulfate cream precipitate with the magnesium
is K2SO4. bromide and a white precipitate with the
magnesium chloride.
The red flame indicates the presence of
lithium ions. Lithium sulfate is Li2SO4. MgBr2(aq) + 2AgNO3(aq) →
The blue-green flame indicates the Mg(NO3)2(aq) + 2AgBr(s)
presence of copper ions. Copper sulfate MgCl2(aq) + 2AgNO3(aq) →
is CuSO4. Mg(NO3)2(aq) + 2AgCl(s)
C12.09 C and E C12.15 This would negate the results as the
C12.10 The use of state symbols in C shows sulfuric acid introduces sulfate ions and
that this is a precipitation reaction, so a white precipitate of barium sulfate
producing solid copper(II) hydroxide. is immediately produced.
C12.16 Al → Al3+ + 3e−
Experimental skills C12.04
C12.17 a Carbon dioxide was present.
1 A precipitate is an insoluble compound/salt
produced during a precipitation reaction (a b Ca(OH)2(aq) + CO2(g) → CaCO3(s)
reaction that produces an insoluble salt when + H2O(l)
solutions of two soluble salts are mixed).
C12.18 The gas is not carbon dioxide and it is
2 Iron(II) precipitates are green in colour; not oxygen.
iron(III) precipitates are brown in colour.
3 Ammonia is a base/an alkali.

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C12.19 The pieces of glassware are a volumetric Other valid methods should also
pipette that adds an accurate, fixed be accepted.[6]
volume of liquid and a burette, which
adds an accurate but variable volume 4 a to be able to measure the volume
of liquid. of the gas[1]

C12.20 Methyl orange and thymolphthalein b fully open the air hole at the base of
both produce clear colour changes at the the chimney[1]
end-point, universal indicator does not. c when crystals form around the edge
C12.21 Swirling ensures everything is mixed of the solution / when crystals form on the
and also ensures liquid that might have stirring rod[1]
splashed onto the sides of the flask is 5 D[1]
returned to the reaction, so the reaction
6
is complete.
Salt Flame Slowly adding Adding
C12.22 The mean titre would only use the test excess aqueous acidified
results within 0.10 cm3: i.e. mean titre = sodium silver
(12.15 cm 3 + 12.10 cm 3 + 12.10 cm 3 ) hydroxide nitrate
=
3 potassium lilac no reaction no
12.12 cm3
sulfate colour reaction
Practice questions copper blue– light blue cream
1 C[1] bromide green precipitate precipitate
colour formed
2 a tripod; and evaporating dish/basin; (the lithium red no reaction yellow
arrow also suggests a Bunsen burner)[2] iodide colour precipitate
b blue[1] [5]
c because copper oxide reacts with acid[1] 7 a add aqueous sodium hydroxide or
3 A maximum of 6 points from: Common aqueous ammonia slowly until in
starting process: excess; green precipitate which does
not redissolve[2]
• crush lump of malachite
b add acidified barium nitrate;
• with a pestle and mortar white precipitate[2]
Processes in method 1: (These two tests can be given in either order.)
• dissolve in acid 8 A maximum of 6 points from:
• named acid • a dd named volume of first vinegar
to a flask
• filter
• add a named indicator (methyl orange
• electrolyse filtrate
or thymolphthalein)
• recover copper from cathode
• slowly add from a burette
Processes in method 2:
• named alkali
• heat crushed powder • note volume needed for neutralisation
• to form copper oxide • repeat with same volume of second
• heat with charcoal vinegar

• wash with dilute acid • larger volume used (titre) = more

concentrated acid[6]
• filter and dry

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

Any example answers to questions taken from past question papers, practice questions, accompanying marks and mark
schemes included in this resource have been written by the authors and are for guidance only. They do not replicate
examination papers. In examinations the way marks are awarded may be different.

Physics
Chapter P1
Before you start P1.02 a • Fill a measuring cylinder with
enough water that it will cover
• Use a ruler to make the measurements and the steel block and the block of
multiply to find the volume. wood but not overspill.
• Divide the thickness by the number of sheets. • Gently immerse the steel block
• Use a piece of thread to follow the journey on and record the reading on the
the map, then measure the length of the string measuring cylinder. Raise the
using a ruler. steel block and allow any drips of
water to fall into the measuring
• Fill the cup with liquid and then pour the cylinder. Gently place the
liquid into a measuring cylinder. wooden block into the measuring
• Suspend the bag from a newtonmeter. cylinder. Lower the steel block
to immerse both the wooden and
• Pull a block across each surface using metal blocks.
a newtonmeter.
• Record the new reading on the
Science in context P1.01 measuring cylinder.

1 • Subtract the smaller reading from

the bigger reading to find the
Time Time / s Speed volume of the wooden block.
/ m/s
b 18 cm3
Spanish 3 years 94 608 000 0.42
ship P1.03 a 
0.1 mm
Jules Verne 80 days 6 912 000 5.79 b 3118.5 cm3 (or 3100 cm3 to 2 s.f.)
story
IDEC Sport 41 days 3 542 400 11.29 Experimental skills P1.01
balloon 13 days 1 123 200 35.61 1 Substances should be listed in order of density.
Virgin 3 days 259 200 154.32 2 13.5 g/cm3. This is much higher than the
Atlantic density of most liquids. Mercury is unusual
GlobalFlyer because it is a metal which is liquid at
Hypersonic 6.5 hours 23 400 1709 room temperature.
jet
Questions
2 If it travelled a longer route than the winner.
In this race, the boats need to find wind, so do P1.04 a 
4 g/cm3 b 40 000 kg
not necessarily follow the shortest route. P1.05 a 
0.215 m, 0.1025 m, 0.065 m
Questions b 1.43 × 10−3 m3
P1.01 a 
2 cm, 4.5 cm and 1 cm c 1958 kg/m3
b 9 cm3 P1.06 a 
9.71 × 10−2 g
b 0.22 cm3

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

c 0.44 g/cm3 P1.11 32.15 m/s

d Density is less than that of water P1.12 a 
C b B
(1.0 g/cm3) so a match will float.
P1.13 300 m/s
P1.07 50.4 mm3
P1.14 a 
114.3 km/h
P1.08 a Runner Time on Time on b 31.7 m/s
digital analogue
clock clock P1.15 5.36 × 1011 m = 5.36 × 108 km =
A 9.87 s 10 536 million km

B 10.34 s 10 P1.16 8 minutes

C 10.01 s 10 P1.17 a 400

Distance travelled / m
b All three runners record the same 300
time on the analogue clock, so the
winner cannot be determined. 200

P1.09 a 
Any random error with starting or 100
stopping the stopwatch would be
divided by 20. 0
0 20 40 60 80 100
b Time / s
Length Time for 20 Time for 1
of string oscillations oscillation
b 400 m
/m /s /s
0.00 0.0 0.000 c 100 seconds

0.20 18.1 0.905 d 4 m/s

0.40 25.1 1.255 P1.18 a 
40 km
0.60 28.3 1.415 b 5.0 km/h
0.80 39.4 1.970
c 2
1.00 40.5 2.025
d between C and D (between 5 p.m.
1.20 44.4 2.220
and 5.30 p.m.)
1.40 47.9 2.395
e between E and F (between 6 p.m. and
c How period of oscillation varies 7 p.m.)
with length of oscillator
f 6.15 km/h
oscillation / s

2.50
Period of

2.00 g 10 km/h between B and C

1.50
1.00 P1.19 a 
0.50 60
0.00
50
Distance / km
0
00

0
00

40

60

80

00

20

40

60
2
0.

0.

0.

0.

0.

1.

1.

1.

1.

40
Length of string / m
30
d 1 m, or correct reading from 20
student’s graph
10
P1.10 a 
10.44 m/s
0
0 10 20 30 40 50 60 70 80
b He started from rest and had to
Time / min
accelerate, so he ran slower than his
average speed which means he must
b Average speed = 72 km/h
also have run faster.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

P1.20 20 km/s c 16 + 48 = 64 m

1 1
P1.21 2.1 m/s2 d s =  (u + v)t =  (12 + 20) × 4 = 64 m
2 2
P1.22 0.2 m/s2
P1.27 a 
P1.23 a 
B, D, H
A = bh = 0.7 × 20 = 14 m
b A, C, G
c F 25

Speed / m/s
20
d E
15
P1.24
driver sees hazard 10
25
driver applies brakes
5
Speed / m/s

20 A = 12 bh
0 = 12 × 3.3 × 20 = 33 m
15 0 1 2 3 4
constant deceleration
10 Time / s

5 car stops vertical height

gradient =
horizontal width
0
0 1 2 3 4 –20 m/s
=
Time / s 3.3 s
= –6.1 m/s2
P1.25 a, b
b 6.1 m/s2 (see calculation above)
1 1
A= 2 bh = × 5 × 6 = 15 m
2
c thinking distance = 14 m;
braking distance = 33 m;
12 stopping distance = 47 m
10 (see calculation above)
Speed / m/s

A = bh = 5 × 12 = 60 m
8 P1.28 Mass Weight
6 scalar vector
4 unit = kilogram unit = newton
2 A = bh = 5 × 6 = 30 m measure of the value depends
amount of matter on local value of
0 in a body; does acceleration due
0 2 4 6 8 10
not change to gravity
Time / s
with position
c Total distance = 105 m measured with a measured with a
(top-pan) balance newton meter
P1.26 a, c
P1.29 a 
mass = 1 kg; weight is less than 9.8 N
25
b mass = 1 kg; weight is greater than
Speed / m/s

20
A= 1
2 bh
1
= × 4 × 8 = 16 m
2
9.8 N
15
P1.30 a i 686 N ii 70 kg
10
A = bh = 4 × 12 = 48 m iii 10.12 N iv 5000 kg
5
v 7.69 × 10−3 N/kg
0
0 1 2 3 4
b always the same
Time / s
c The force of gravity is much
v − u 20 −12
b a = = = 2 m/s2 (15 033 times) greater on Jupiter.
t 4

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

P1.31 a 
unbalanced; 20 N to left;
accelerate to left 18
b balanced; no acceleration 16
c unbalanced; 50 N downwards; 14
accelerate downwards 12

Load / N
P1.32 a 
500 N b 1.6 m/s 2
10
c 22 000 kg d 0.15 N 8
P1.33 a 
23.52 N b 23.52 N 6

c same; weight is a force 4

P1.34 66.7 m/s2 2
0
Experimental skills P1.03 0 0.05 0.1 0.15 0.2
Extension / m
Getting started
1 a to stop the apparatus toppling The load is between 10 and 12 N at the
limit of proportionality.
b to ensure the ruler is vertical
P1.39 moment of a force (Nm) = force (N) ×
2 100 g = 1 N
perpendicular distance from pivot to
3 independent: load applied, dependent: extension force (m)

Questions P1.40 a 
50 cm b 15 Nm
1 The line should pass through the origin. P1.41 a 
bigger
2 Where the force is proportional to the b further from
extension, the graph line is straight. Beyond
the limit of proportionality, load and c 90°
extension are not proportional and the line is P1.42 F3 will have the biggest turning effect,
no longer straight. because it acts at the equal largest
3 Values will depend on the learner’s results. distance and at 90° to the object. (F2 acts
at the same distance but will have a
4 No, once the spring was stretched beyond smaller turning effect because it does not
the limit of proportionality it remained act at 90° to the object.)
longer than its original length once the load
was removed. P1.43 A longer spanner will allow them to apply
a force at a greater distance from the
Questions pivot, so they can apply a smaller force to
achieve the same turning force.
P1.35 22 cm
P1.36 18 N P1.44 231.4 N

P1.37 35 N P1.45 3.3 m

P1.38 Load / N Length / m Extension / m Activity P1.02

0.0 1.396 0 1 a The worker needs to be able to do both
2.6 1.422 0.026 tasks and so the force which can be used
depends on the worker’s strength. If it was
5.3 1.448 0.052
much more difficult to push the bucket
7.9 1.475 0.079 down than to pull it up (or vice versa),
10.6 1.501 0.105 a worker might not be able to complete
13.2 1.536 0.140 both tasks.
15.9 1.579 0.183

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

b Without the shadoof, it would be harder Questions

to lift the bucket than to push it down.
With the shadoof, the bucket is lifted P1.46 a lines drawn connecting opposite
using the longer arm of the beam, so the vertices, cross in centre
moment of the force is increased. b cross in centre of circle
c lines drawn connecting each vertex
2 The figures given below are examples –
with the centre of the opposite side,
students may have estimated the arm lengths
cross in centre
differently. The important point is that the
counterweight arm is shorter than the water d cross in centre of inner circle
arm, and so the weight of water lifted is less P1.47 a Both buses would topple if tilted any
than the counterweight. further because their centres of mass
arm distance arm distance would be to the right of the ‘pivot’
(the right-hand wheel) which would
approx 3 m approx 0.5 m exert a clockwise moment.
counter b Stability reduces as the centre of mass
weight moves upwards. This means that the
fulcrum bus can be tilted through a smaller
angle before it topples over.
c This is to reproduce the worst-case
water scenario (most extreme situation).
150 N
weight
P1.48 a Wide tyres increase the surface area
and so decrease the pressure on the
ground. This means tractors can drive
25 N on soft ground without sinking in.
b A sharp knife edge has a smaller
Experimental skills P1.04 area, which increases the pressure and
Getting started makes cutting easier.

• Learners should draw the diagonals of the F

P1.49 p =
rectangle. The centre of gravity is where A
they cross. P1.50 pascal, Pa

• dependent on the shape chosen P1.51 200 N acting on 1.0 m2

• examples such as a doughnut shape P1.52 20 000 Pa

P1.53 1.88 × 106 N
Questions
1 Lines should intersect, or approximately Practice questions
intersect, depending on the accuracy of the
1 C[1]
learner’s work.
2 C[1]
2 Repeat the experiment.
3 0.8 cm[1]
3 Answer will depend on the learner’s response
to Q2. 4 300 N to the left[2]

4 Try to balance the shape with this point on 5 0.0043 m/s[1]

your fingertip. 6 a Object Mass Volume Density
5 Because the centre of gravity is the point /g / cm3 / g/cm3
from which the weight acts, and weight is a 1 160 200 0.8
downward force.
2 240 20 12
3 6400 800 8
4 540 45 12 [4]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

b 3[1]
c 3[1]
d 2 and 4[1]
7 a 1.744  s[1]
b 5.73 m/s[1]
c 10.58 m/s[1]
d 5.60 m/s2[1]
e 12.35 m/s[1]
8 increase (perpendicular) distance from the pivot; increase the applied force[2]
9 resultant force = zero
resultant moment = zero[2]
10 a W = mg; woman 588 N, elephant 49 000 N [3]
F
b p = [1]
A
c elephant: 3.77 × 105 Pa, woman: 2.35 × 107 Pa[2]
d If the woman puts all of her weight on one stiletto heel, she will exert a bigger pressure
than an elephant, because the area of the stiletto heel is so much smaller than the area of the
elephant’s foot.[1]

Chapter P2
Before you start
For example:

a torch switched on chemical (store) in light radiation (transfer) thermal (transfer)

battery from light bulb from light bulb
b wound up toy elastic/strain (energy kinetic (store) thermal (transfer)
store) / sound radiation
(transfer)
c radio-controlled car chemical (store) in kinetic (store); maybe thermal (pathway)
battery sound radiation
(transfer)
d Bunsen burner chemical (store) internal (store); thermal light radiation
(transfer) (transfer)
e loudspeaker in use electrical (pathway) sound radiation thermal (transfer)
from mains along wire (transfer)
to vibration (store) of
the diaphragm
f ringing bicycle bell vibration (store) sound radiation thermal (transfer)
(transfer)
g solar-powered battery light radiation chemical (store) thermal (transfer)
(pathway)
h hairdryer in use electrical (pathway) kinetic (transfer); sound radiation
thermal (transfer) (transfer)

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

Science in context P2.01 P2.05 Physical clue Which energy

1 The Moon has no fossil fuels. There is no life store is changing?
on the Moon, so biofuels are not an option. material changing elastic
The Moon does not have an atmosphere, so shape
wind power is impossible. There is no liquid object changes kinetic
water, so there cannot be any wave or tidal speed
energy – or coolant for nuclear power stations.
There is solar energy but a lunar day lasts chemical reaction chemical
four weeks and we do not have the (battery) change of internal / thermal
technology to store enough solar energy to temperature
power a lunar colony through two weeks of nuclear fission or nuclear
lunar night. fusion
2 Learner’s own answers, but they are likely
to be in favour. There are huge reserves of chemical (store) → thermal energy
P2.06 a 
thorium fuel available. Lifters produce tiny (transfer) → internal energy of
amounts of radioactive waste, an accidental surroundings (store)
meltdown would be impossible, and it would b electrical (transfer) → increases
be extremely difficult to make a nuclear bomb internal energy (store) of light bulb
using a lifter. → light radiation (transfer) + thermal
radiation (transfer)
Questions
c electrical energy (transfer) → kinetic
P2.01 kinetic energy
energy (store) + thermal energy
P2.02 an object can gain gravitational potential (transfer) + sound (transfer)
energy by being raised
Activity P2.01
P2.03 strain energy or elastic potential energy
Energy changes will depend on the devices
considered. They may be presented in a table as
P2.04 Store Examples
in the ‘Before you start’ section, or as an energy
a kinetic any moving object, flow diagram.
energy e.g. a train or a
runner Questions
b gravitational any high-up object,
P2.07 a 
60 J b 56 J
potential e.g. a bungee
energy jumper or a plane P2.08 a 
thermal b sound
c elastic any stretched,
P2.09 Energy is expensive, supplies are often
energy squashed or wound
limited, and our use of energy can
up object, e.g. a
damage the environment.
compressed spring
or a stretched P2.10 0.6 or 60%
bungee cord
P2.11 0.32 or 32%
d internal any warm object,
energy e.g. a cup of tea or P2.12 150 J
an iron
P2.13 a 
increasing
b remaining constant
c decreasing
P2.14 200 000 J (or 200 kJ)
P2.15 6200 J (to 2 s.f.)
P2.16 1600 J (to 2 s.f.)

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

P2.17 wasp P2.27 Advantages: a small amount of fuel

produces a large amount of energy; does
P2.18 any one from: wind, solar, waves, tidal, not produce greenhouse gases that lead to
geothermal, hydroelectric, biomass global warming
P2.19 any one from: fossil fuels, nuclear Disadvantages: not renewable; high costs
P2.20 because the resource is constantly being of decommissioning and dealing with
replaced / is not used up waste; accidents can be catastrophic

P2.21 chemical Activity P2.02

P2.22 When we burn biomass, we are releasing 1 any two from: burning biomass (wood from
energy that came from the Sun in the trees); using thermal energy from hot springs;
recent past. In the case of trees, the energy generating heat from solar panels
might have been captured ten or a hundred
years ago. Manure might be from food 2 burning biomass (wood from trees); solar
that captured energy a few days or months 3 Any sensible suggestion, such as: solar; wind;
before. When we burn coal, the energy hydroelectricity. It would be difficult to justify
released is from sunlight trapped by plants investing in the infrastructure for a small tidal
hundreds of millions of years ago. power station or a geothermal power station
Fossil fuels are the remains of organisms for a five-year study.
(plants and animals) that lived in the 4 Take rechargeable batteries to store energy
past. Many of the Earth’s coal reserves, or build a small dam and install a pumped
for example, formed from trees that lived storage HEP.
in the Carboniferous era, between 286
and 360 million years ago. Those trees 5 The woodland because, in the context of
captured sunlight by photosynthesis, a five-year mission, this a non-renewable
they grew and eventually they died. Their resource.
trunks fell into the swampy ground, but
they did not rot completely, because there 6 Learners’ own plans, with justification.
was insufficient oxygen. 7 Learner’s own answers, with justification.
P2.23 nuclear and geothermal 8 Learner’s own answers. This should prompt
P2.24 The Sun heats some parts of the Earth’s interesting discussion.
surface more than others. The surface
warms the air above it so that some parts
Questions
of the atmosphere are warmer than P2.28 Nuclear fusion is when the nuclei of
others. Heated air expands and moves – atoms fuse (join together) and fission is
this is a convection current (see Chapter when a heavy nucleus splits into two or
P3). This is the origin of winds. more smaller nuclei.
P2.25 Advantage: any one from: solar power is P2.29 c
becoming cheaper; it can be used in remote
locations (away from the electricity grid); it P2.30 the weight of the box; the height of
is renewable; there are no fuel costs; it does the stairs
not contribute to global warming P2.31 12.5 kJ
Disadvantage: any one from: unreliable / P2.32 a 
gravity; 1 N b 6 J
does not necessarily produce power when
you want it; diffuse (needs a large area c gravitational potential energy to
of land or roof space to generate power); kinetic energy
expensive initially P2.33 He could lift each brick more quickly
P2.26 Burning fossil fuels releases carbon or he could lift more than one brick at a
dioxide which contributes to global time. In other words, he could do more
warming, and sulfur dioxide which leads work or he could work more quickly.
to acid rain.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

P2.34 a 
1000 or 103 9 a 625  N[1]
b 1 000 000 or 106 b work done = force × distance
(in the direction of the force)[1]
P2.35 100 W
c 2 × 105 J[1]
P2.36 a 
10 450 000 J or 10.45 MJ
work done
d power = [1]
b 121 W time taken
e 349 W[1]
P2.37 144 kJ

Practice questions Chapter P3

1 A[1] Before you start
Learners may list elements or everyday
2 B[1] substances. Substances such as gels can be difficult
3 Energy cannot be created or destroyed – to categorise.
it can only be transferred from one energy We need liquid water to drink, irrigate crops, etc.
store to another.[1] Without water vapour there could be no rain so
4 renewable: any one from solar, wind, the water cycle would not happen. Without ice, all
waves, tidal, biofuel; non-renewable: the water currently in polar ice, glaciers, etc. would
any one from fossil fuels, nuclear[2] be liquid, with a consequent rise in sea levels.
Learners may consider many other aspects.
5 a work[1]
b more[1] Science in context P3.01
1 Sketch graph with axes labelled as shown.
c energy[1]
Density is at a maximum at 4 °C.
d less[1]
1000.1
6 a joule, J[1]
Density of freshwater / kg/m3

b joule, J[1] 1000.0

c watt, W[1]
999.9
1
7 a Ek =  mv2[1]
2
999.8
b 3.61 J[1]
c 3.61 J[1] 999.7
d gravitational potential energy = mgΔh[1]
999.6
e 7.69 × 10−2 m (7.69 cm)[2] 0 1 2 3 4 5 6 7 8 9 10
8 a Any one from: wind power is renewable / Temperature / ºC
does not contribute to global warming /
has no fuel costs.[1] 2 If water froze from the bottom up, fish would
be forced upwards by the ice and they would
b Wind is an unreliable source of energy die. All life in areas where the temperature
because the wind is not always blowing falls below freezing would be affected by
when there is demand for electricity. this effect.
There would need to be 1250 turbines
to generate the same power output as Questions
one coal-fired power station. This would
P3.01 solid, liquid, gas; volume; volume; space;
lead to a large area being covered
melts, liquid
with turbines[2]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

P3.02 A liquid takes the shape of its container P3.13

without its volume changing.
water vapour cools
P3.03 diagrams similar to those in Table P3.02 water vapour condenses

Temperature / °C
water cools
P3.04 a 
solid b gas 100
water solidifies
c gas
0
Time
P3.05 a B
 rownian motion is the motion ice cools
of small particles suspended
in a liquid or gas, caused by
molecular bombardment.
P3.14 a 
evaporation
b Kinetic theory says that the molecules
in a liquid or gas are constantly b fastest; cooler
moving. If small smoke particles (or P3.15 Unfolding the towel increases the surface
similar particles) are suspended in a area, sun increases the temperature and
liquid or gas, the moving liquid or wind provides a draught. These three
gas particles collide with the smoke factors all increase the rate of evaporation.
particles, causing them to change
direction repeatedly. P3.16 solids; hotter; cooler; an insulator;
polystyrene
c The particles would move more slowly
and change direction less frequently in P3.17 A metal spoon would conduct thermal
the colder experiment. This is because energy from the soup to your hand. The
the air molecules would be slower and wooden spoon does not conduct thermal
so would hit the smoke particles less energy, so it stays cool and easy to hold.
often and with less force.
P3.18 Marble is a better conductor than wood
P3.06 Molecules in liquids and gases are free to so more thermal energy would flow from
move, so we can push them aside as we your feet to the marble, cooling your
pass through. In a solid, the particles are feet down.
held together and so do not move apart.
P3.19 Air is a very poor conductor. The layer
P3.07 gas; pressure; faster; increases; increases of air trapped between two thin layers of
clothing will reduce the loss of thermal
P3.08 The air particles will move more slowly.
energy from the body.
They will hit the walls of the balloon with
less force and less often. The pressure P3.20 a 
Copper is a metal and so contains
inside the balloon will decrease and so it free electrons which carry thermal
will partially deflate. energy through the metal.
P3.09 a 
The speed increases. b Wood is solid, so the particles are close
and in fixed positions which allows
b They hit the walls more often.
vibrations to be passed on. Air is a gas,
c They hit the walls with more force. so its particles are far apart and do not
pass on thermal energy easily.
d The pressure increases.
P3.21 Arrow drawn above the heat source,
P3.10 expands; contracts; metals; bend pointing upwards, labelled ‘hot water’.
P3.11 When it is hot the bridge expands and the Arrow drawn on the opposite side of
rollers move to the right. In the cold it the pan, pointing downwards, labelled
contracts and the rollers move to the left. ‘cold water’.

P3.12 a 
ethanol P3.22 Arrows showing cold water sinking below
the ice and warm water rising at the sides.
b Ethanol expands most so will make
the thermometer easiest to read. It is
also safe if the thermometer is broken.

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P3.23 The water at the top will heat up and 2 Dull dark surfaces are better absorbers of
become less dense so it will stay at the top infrared radiation than light shiny surfaces.
and the water at the bottom will stay cold.
Questions
P3.24 a 
Diagram for hot gas shows fewer
particles than diagram for cold gas. P3.30 a 
The rollers are metal and are in
Particles in the hot gas have longer contact with the hot metal so are
arrows to indicate faster movement. heated by conduction.

b As the gas is heated its particles b The glowing metal is very hot so
gain energy and move faster and emits a lot of heat radiation which
further apart, so the gas expands. heats the worker’s face.
This decreases the density of the gas
c The hot metal heats the air around
so it rises.
it, causing convection currents which
P3.25 C heat the air in the building.

P3.26 Space is a vacuum which means there P3.31 a 

It is painted black to absorb the
are no particles. Both conduction and maximum amount of infrared
convection require particles for thermal radiation from the Sun.
energy to be transferred.
b The back is insulated to reduce heat
P3.27 The engine and the wheels are glowing loss by conduction.
yellow which means they are still hot.
c Cold water enters at the bottom so
P3.28 The shiny suit will reflect heat radiation that as it is heated, it will rise due
away, keeping the worker cool. to convection. It leaves from the
top because this is where the water
P3.29 A shiny teapot reflects the heat back into is hottest.
the tea/emits less radiation so the tea stays
hot for longer. The dark teapot emits Practice questions
a lot of heat radiation so the tea cools
more quickly. 1 A[1]
2 D[1]
Experimental skills P3.01
3 liquid; gas[2]
Getting started
The experiment is about heat loss by radiation, 4 When a fluid is heated it expands; this
so it is best to stop heat loss by other methods. causes its density to decrease; so it rises
The lids will prevent lots of the heat loss by above the colder denser fluid.[4]
convection, and the wooden or plastic surface will 5 Solid: particles are in fixed positions;
reduce heat loss by conduction. and only vibrate around these positions.
Liquids: particles are free to move; but
Experiment A
remain close together.
1 same size containers; same volume of water; Gas: particles are very spread out; and
same starting temperature move completely freely.[6]
2 Cooling curve graphs of learner’s results. 6 a conduction [1]
The black can will cool more quickly.
b Water at the bottom is heated and so
3 Dull dark surfaces are better emitters of it expands. The hot water rises; and
infrared radiation than light shiny surfaces. is replaced by cold water which is
then heated.[3]
Experiment B
c add insulation[1]
1 Graph of learner’s results. Temperature
should rise for both cans, but black can heats 7 a The particles move in a random
more quickly. manner / frequently change direction.[1]
b air molecules[1]

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c The kinetic model says the air molecules P4.02 a 

the same b different
are moving. The movement of the smoke
c dimmer
particles can be explained by them
being bombarded by air molecules.[2] P4.03 Wavelength marked from a point on one
wave to the same point on an adjacent
8 a So that there is only one independent
wave (e.g. crest to crest or trough to
variable – the surface.[1]
trough). Amplitude marked from rest
b Matte black: 71.2 °C; matt white: position to a crest or trough.
64.5 °C; shiny silver: 60.4 °C[3]
P4.04 340 m/s
c Zain’s results will be less precise OR
He will not be able to tell which of P4.05 a 
0.5 m b 10 Hz
shiny black or matte white would
emit more as both would be Experimental skills P4.01
recorded as 65 °C.[1] Getting started
9 a 6  cm3[1] Changing the speed of the motor changes the
frequency of the waves produced.
b The pressure increases; because the
particles are now hitting the walls of A small piece of cork placed in the water will
the syringe more frequently.[2] move up and down.

c The air molecules have heated up Questions

and so move faster; causing the gas 1 Diagram should show the waves being
to expand.[2] reflected at a 90° angle. The wavelength should
be unchanged.
Chapter P4
2 a Diagram should show the waves
Before you start continuing in the same direction
Examples of waves: water, light, sound, but with a shorter wavelength in the
microwaves and other electromagnetic waves, shallower water.
earthquake waves, waving your hand, a crowd b Diagram should show the waves bending
doing a Mexican wave. towards the normal, with a shorter
Learners may find the second part hard to wavelength in the shallower water.
answer – it is the main point of this chapter. 3 Line drawings similar to photos in
They may suggest vibrations or repeated Figure P4.12.
movements, or wave behaviour such as reflection.
4 Change the depth of the water.
Waves transfer information or energy, without
transferring matter. Questions
Science in context P4.01 P4.06 a 
waves reflect upwards; reflection

1 Both methods use reflected waves to calculate b waves get closer together; refraction
distance. Both methods make use of the c waves get closer together and bend
equation speed = distance/time. towards the normal; refraction
2 One method uses light waves and one uses d waves spread to make semicircles;
sound waves. diffraction
3 Sound waves cannot travel through the P4.07 a 
The waves diffract as they pass through
vacuum of space, and light waves would are the doorway, creating semicircular
refracted when travelling from air to water and waves which reach person B.
back again.
b longitudinal
Questions
P4.08 a 
so that it can easily be read in the
P4.01 a 
energy; matter rearview mirror of a car
b transverse; longitudinal b ECILOP

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P4.09 a 
30° (the angle of reflection for 60°). Questions
b She may have measured the angle to P4.15 1.52
the surface rather than to the normal
or misread her protractor. P4.16 a 
i = 50°, r = 31°

P4.10 Diagram similar to Figure 4.16 but with b 1.5

the angles of incidence and reflection both P4.17 Glass has a lower refractive index than
drawn and marked as 40°. diamond so the ray will bend away from
P4.11 a 
The first mirror reflects the light the normal as it passes from diamond
straight down to the second mirror to glass.
which reflects it towards the eye. P4.18 a 
34.7°
The light turns through 90° at
each mirror. b 197 000 000 m/s (to 3 s.f.)

b The light is reflected twice. The first P4.19 Total because all the light is reflected;
mirror inverts left to right and the internal because the reflection happens
second inverts it back. inside the material.

P4.12 a, b  Diagram should be similar to P4.20 No, because TIR only happens when
Figure 4.21d. the angle of incidence is greater than the
critical angle.
c 6 cm
P4.21 a 
x = angle of incidence, y = angle of
Experimental skills P4.02 reflection, z = angle of refraction

Getting started sin x

b x = y, = refractive index,
sin z
1 Mark dots along the ray and then remove the
apparatus and draw a line (using a pencil and x < critical angle
ruler) to join the dots. c As x increases, y will increase too and
2 Draw a line (using a pencil and ruler) to join these will have the same value. z will
up the lines on either side of the block. also increase. Eventually, when x is
equal to or greater than the critical
Questions angle for the material, the ray will be
totally internally reflected.
1 towards; refraction; incidence; away from
P4.22 any two from: endoscopy,
2 The ray passes straight through and is
communications, sensory play
not refracted.
P4.23 a T
 he light is not refracted because it
Questions enters the plastic along the normal.
P4.13 a 
Ray bends towards the normal. b 45°
b Ray bends away from the normal. c
P4.14 Diagram showing ray passing from glass
to air and bending away from the normal.
Incident and refracted rays and angles,
and the normal, all labelled.

Activity P4.03
sin i
The value of is not dependent on the angle of
sin r
incidence. It is a property of the material, known
as the refractive index. For a given material, the d The critical angle is less than 45°.
refractive index is constant.

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Activity P4.04 infrared is also used in the TV remote

control; radio waves carry the TV signal.
object
F P4.35 The radiographer is working with X-rays
F image all day so the cumulative effect would be
much greater than for the patient.
The image is real, diminished and inverted.
This is a camera. P4.36 vibrations
P4.37 drum: drumskin; flute: column of air;
violin: strings
F F
Activity P4.05
The image is real, enlarged and inverted. Answers should include:
This is a projector.
a microwaves are used to transit phone signals
P4.24 principal focus; focal length; shorter b ultraviolet rays can cause skin damage
P4.25 a 
Diagram shows rays converging at the c X-rays help doctors diagnose problems
principal focus on the right of the lens.
d telescopes like this can be used to detect radio
b Diagram shows rays converging at waves from space
the principal focus on the right of the
lens, but closer to the lens than for e infrared radiation can be used to cook food.
part a. Students should produce a poster, which will
c Diagram shows ray carrying on in a help reinforce their knowledge of the different
straight line through the lens. waves in the em spectrum, and their wavelengths,
frequencies, uses and dangers.
P4.26 refraction; less; dispersion
P4.38 The drummer hits the skin, causing it
P4.27 Diagram showing light refracting towards to vibrate. This makes the surrounding
the normal as it enters the prism and away air vibrate. The vibrations pass through
from the normal as it leaves. Emerging the air, causing the listener’s eardrum
light is dispersed and the colours red and to vibrate.
violet should be labelled.
P4.39 There are no particles to vibrate so sound
P4.28 red, orange, yellow, green, blue, cannot travel.
indigo, violet
P4.40 The bell is initially loud but as the air is
P4.29 Drawing of two waves, one with a longer pumped out the sound becomes quieter
wavelength than the other. The wave with until it cannot be heard as there are no
the longer wave should be labelled red and particles to carry the sound wave.
the other labelled violet.
P4.30 a 
gamma rays, X-rays, UV, visible light,
Experimental skills P4.03
IR, microwaves, radio waves Getting started
b radio waves, microwaves, IR, visible The longer the distance from the wall, the greater
light, UV, X-rays, gamma rays the time between hitting the blocks and hearing
the echo. This reduces the error due to the
P4.31 5.6 × 1014 Hz reaction time of the person starting and stopping
the stopwatch. It is difficult to measure the time
P4.32 infrared and microwaves
accurately because the reaction time is quite long
P4.33 X-rays and gamma rays compared with the time between hitting the blocks
and hearing the echo.
P4.34 Microwaves carry her mobile phone
signal; visible light lets her see the TV; Questions
infrared from the fire warms her and
1 330–350 m/s; learner’s own answer about how
this compares with their calcluated value.

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2 Time, because it is a very short time so c total internal reflection[1]

reaction time affects accuracy.
d a plane mirror[1]
Questions 9 a 
decreases[1]
P4.41 396 m b stays the same[1]
P4.42 The microphones record the sound c increases[1]
immediately, whereas a human with a
stopclock has a reaction time. d stays the same[1]

P4.43 a 
the number of vibrations per second 10 a 
300 000 000 m/s[1]

b Hertz (Hz) b 3 m[1]

c Sound B is louder and higher pitched Chapter P5

than sound A.
Before you start
Practice questions Mind map will depend on what learners have
1 D[1] retained from prior experience and will give a
good idea of where they are starting from.
2 B[1]
3 a 
P is infrared; Q is X-rays[2] Science in context P5.01
b frequency[1] 1 Learners should discuss the balance between
the need to keep experiments safe and the
4 a 
the number of vibrations or waves benefits of learning about a potentially
per second[1] hazardous phenomenon; the need to carry out
a risk assessment before proceeding; and the
b hertz / Hz[1]
possibility that some experiments are too risky
c ultrasound[1] and should not be undertaken.
5 a 
Light travels much faster than sound.[1] 2 If a scientific experiment affects the situation
it is trying to explain, then the results will be
b i 
transverse; at right angles to; can[3] invalid as they cannot be said to describe or
ii longitudinal; parallel to; cannot[3] explain the situation as it naturally occurs.

c 990 m; one mark for answer, Questions

one for unit[2]
P5.01 positive; negative; repel; attract
6 a 
2250 m; one mark for answer,
one for unit[2] P5.02 a F
 riction between the child and the
trampoline leads to a build up of
b 1.2 s; one mark for answer, static electricity. Electrons will be
one for unit[2] transferred either to or from the child.
c 5800 m/s[1] b The hairs must all have the
7 a 
focal length[1] same charge.

b Ray drawn from the top of the object P5.03 a ammeter

parallel to axis. This ray bends to b in series (in line)
pass through the principal focus on
the right. Inverted arrow drawn at the c a circle containing a capital A, as
point where rays cross.[3] shown in Figure P5.06

c diminished; inverted[2] P5.04 a C

 ircuit similar to Figure P5.06, with a
second ammeter on the left-hand side
8 a 
It is travelling along the normal.[1] of the circuit.
b The ray is reflected, turning through b They are the same.
90° so it travels vertically down.[1]

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P5.05 a ampere / amp / A P5.16 a 40 Ω

b 1000 c 1 000 000 b 16 Ω
C
P5.06 1 A = 1  P5.17 watts = volts × amps
s
P5.07 a 110  s P5.18 a 480 W b 5 A
b 5.33 mA c 30 V d 9.6 kW
c 270 C P5.19 72 W
d 77.1 s P5.20 0.21 A
P5.08 a voltmeter P5.21 8640 J
b Diagram as P5.09 with a voltmeter P5.22 a 5  kWh b 1.5 kWh
connected in parallel across the lamp.
c 0.5 kWh
P5.09 a potential difference
P5.23 3 days
b electromotive force or e.m.f.
P5.24 13 dirhams
c volts, V
P5.25 a 433  W b 21p
Experimental skills P5.01 c 1 hour d 14p
Getting started e 83 W f 16p
To measure voltage, use a voltmeter wired in
g 5 hours h 0.72p
parallel with the component you are measuring
the voltage through. To measure current, use an i 0.1 unit j 1.6p
ammeter wired in series with the component you
are measuring the current through. P5.26 iron, cobalt, nickel
P5.27 Unlike poles attract; like poles repel.
Question
No, the resistance stays the same. P5.28 See Table P5.07.
P5.29 Steel is a hard magnet but iron is a
Questions soft magnet.
P5.10 a 48  Ω b increase
P5.30 a Diagram should be like Figure P5.22.
P5.11 a 120  Ω b 4 mA
b The arrows point away from the
c 7.5 V d 1.5 Ω magnetic north pole.

P5.12 a 60  V b 120 V c The field is strongest where the field

lines are closest together.
P5.13 a 3  kΩ b 120 V
d at the poles
P5.14 3.75 mA
P5.31 a T
 he strength of an electromagnet can
P5.15 a long be changed and it can be switched on
b 5V
and off.
b a supply of electricity/electric current
A P5.32 Friction with the carpet causes you
to become charged. The charge flows
wire
through you and into the metal handle.

V P5.33 Any three insulators, such as plastic, glass,

wood, amber. Any three conductors, such
as copper, gold, aluminium.

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P5.34 a electrons; cloth; rod; negatively iv Continue this process, until you have
charged; positively charged moved round to the other pole of the
magnet or until you have gone off
b Diagram similar to Figure P5.27 the page.
but showing that the rod has
lost electrons and the cloth has Allow one mark for a basic answer
gained them. which will result in the drawing of
one correct field line. Allow two
c When an acetate rod is rubbed with marks for and an answer which will
a cloth, electrons move from the result in correctly plotting the shape
rod to the cloth. This means the rod of the field lines. Allow three marks
becomes positively charged and the for an answer which will result in a
cloth becomes negatively charged. correct field diagram with arrows
on the field lines.[3]
Practice questions
c A magnetically soft material loses its
1 D[1] magnetism easily, whereas a magnetically
2 D[1] hard material retains its magnetism.[1]

3 Any two of: iron, steel, cobalt, nickel[2] 8 a Negatively charged particles are
transferred from the hair to the comb.
4 a electrons[1]
One mark for negatively charge
b negative[1] particles; one mark for transfer
from hair to comb.[2]
5 4.08 J[1]
b electrons[1]
6 20 Ω[1]
c All his hairs have the same charge
7 a Diagram should be like Figure P5.06.
(positive); so they repel.[2]
Allow 1 mark for the correct shape of the
field lines and 1 mark for correct arrows 9 a 
showing the direction of the field lines.[2]
b You will need a bar magnet, plotting
compass, pencil and plain paper.
A
i Place a bar magnet in the centre of a
sheet of paper and draw round it.
ii Place a plotting compass near one of
the poles of the magnet. Mark dots 1 V
 [2]
and 2 on the paper to indicate the two
ends of the compass needle, as shown One mark for ammeter in series;
in the figure. one mark for voltmeter in parallel.
dot 2 b 4 Ω; one mark for answer, one
for unit[2]
c it will double[1]
10 a 2  160 000 J; one mark for answer,
dot 1
one for unit[2]
iii Move the compass away from the b 0.6 kWh; one mark for answer,
magnet and position it so that one one for unit[2]
end of its needle is marked by dot 2.
Mark dot 3 at the other end. c 5.2 A; one mark for answer,
one for unit[2]

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Chapter P6 P6.04 Each lamp can be controlled by its own

switch. If one lamp breaks and does not
Before you start allow current to flow, the other lamps will
1 To identify the type of circuit, trace the path still work. All the lamps will be brighter
of the current from the power supply all the for the same supply voltage.
way around the circuit until you return to the P6.05 Wire has resistance, like a resistor.
power supply. If there is only one possible A longer wire is like having resistors in
route around the circuit, it is a series circuit. series (i.e. a chain of resistors) whose total
If there is more than one possible route, it is a resistance is the sum of the resistors, so a
parallel circuit. longer wire has a higher resistance.
2 When two lamps are connected in series, P6.06 A thicker wire is like having resistors in
the total resistance is the sum of the parallel, whose combined resistance is less
individual resistances. If resistance increases, than the smallest resistance value.
current decreases.
P6.07 a 0.33  A
3 Learners may compare the resistance of thin
wires versus thick wires or explain using an b the 30.0 Ω resistor
analogy such as students walking along a P6.08 a 2.4  Ω
crowded corridor. Consider what would happen
if a parallel corridor was added – the result b 1 A (through 6 Ω resistor);
would be that the overall flow of students 1.5 A (through 4 Ω resistor)
would be faster.
c 2.5 A
Science in context P6.01 P6.09 multi-way bar extensions; block adapters
1 Students will probably notice that they P6.10 fuse
can list ten electrical appliances easily but
find the non-electrical ones more difficult. P6.11 It can lead to a fire.
These may include things such as tin opener,
P6.12 A fuse contains a thin section of wire that
carpet sweeper, scissors, or corkscrew.
melts and breaks the circuit if the current
2 Descriptions may refer to lack of passing through is too high.
entertainment appliances such as TV and
P6.13 5 A; a fuse of 3 A would melt every time
computers. They may also consider the
the hairdryer was switched on. Fuses
difficulty of life without washing machines,
rated higher than 5 A would allow too
etc. Some may consider the social benefits of
big a current to flow before melting and
a simpler lifestyle.
breaking the circuit.
3 This is an open question (there is no right
P6.14 a T
 his is to prevent too high a current
answer) and depends on whether humans can
entering the house where it could melt
control the behaviour of robots and other
the insulation on wiring, giving off
artificial intelligences.
poisonous fumes or causing a fire.
Questions b trip switch
P6.01 a c ircuit symbol for a resistor: P6.15 When the current gets too high, the
see Table P6.01 wires will overheat which can cause the
b circuit symbol for a variable resistor: insulation to give off poisonous fumes,
see Table P6.01 melt or catch fire.

P6.02 They are the same (1.4 A). P6.16 The earth wire provides a low resistance
electrical path to ground and reduces the
P6.03 90 Ω chances of a fatal electric shock.

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P6.17 If the fuse was connected to the earth for wire breaks, one mark for
or neutral wire, a person could still stops current[2]
be electrocuted when they touch the
d Water is a conductor, so this could lead
appliance.
to an electric shock.[1]
P6.18 Double insulation is where the electric
circuit for an electrical appliance is inside Chapter P7
a case made from an electrical insulator
(e.g. plastic), which is inside the outer case. Before you start
This means it is impossible for a live wire current (I): the rate at which electric charge passes
to touch the outer casing of the appliance. a point in a circuit; amps
potential difference (V): another name for the
Practice questions voltage between two points; volts
1 B[1]
resistance (R): a measure of the difficulty of
2 A and C[2] making an electric current flow through a device or
a component in a circuit; ohms
3 a 1: ammeter; 2: voltmeter[2]
energy (E): the capacity for doing work; joules
b 1: current; 2: voltage or p.d.[2]
power (P): the rate at which energy is transferred;
c 1: amps; 2: volts[2] watts
4 0.2 A[1] charge (Q): a property of an object which causes
it to attract or repel other objects with charge;
5 a decreases[1] coulombs
b increases[1] electromotive force (e.m.f.): the voltage across the
c increases[1] terminals of an electricity supply; volts
Equations
6 a 1 mark for correct placement of ammeter;
1 mark for correct placement of voltmeter Q = It E = IVt
V = IR E = QV
P = IV E
A P=
t
Science in context P7.01
1 Answers will depend on learner response
V but should help them to realise the effect
[2]
of motors on our lives, e.g. using a washing
b The lamp will be less bright.[1] machine instead of handwashing.
c 13.3 Ω; one mark for answer, 2 Again, dependent on learner response but
one for unit[2] could include antibiotics, plastics, planes, etc.
7 a A4 = 1.9 A; A5 = 2.6 A[2]
Questions
b A3 = 0.7 A; A4 = 0.7 A; A5 = 1.4 A[3] P7.01 current; circular; right-hand grip;
8 a A fuse is a safety device to stop bar magnet
dangerously high current which P7.02 an iron core
could cause a fire.[1]
P7.03 clockwise
b C[1]
P7.04 Energy transferred by electricity is
c A fuse contains a thin section of wire transferred to the kinetic energy store
which melts and breaks if the current of the motor and to the thermal energy
becomes too high; award one mark store of the surroundings by heating and
by sound.

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P7.05 a T
 urn the magnet round to reverse P7.16 step-down
the field. Swap the power supply
connections to reverse the current. P7.17 50 turns

b The motor effect only happens P7.18 a i 1000 A

when current flows across the field ii 10 A
(when the current cuts the magnetic
field lines). b Higher voltage means lower current
so less energy is lost as thermal energy
P7.06 direction of magnetic field in the wires.
(first finger); direction of current
(second finger); direction of force or P7.19 a 32 000 W
motion of wire (thumb) b 12.8 W
P7.07 a right P7.20 0.1 A. Assume the transformer is
b up 100% efficient.

c into the page Practice questions

P7.08 field, conductor (in either order); 1 D[1]
field strength, speed, number of turns
of wire (in any order); reversed 2 D[1]

P7.09 C 3 a Fleming’s left-hand rule[1]

P7.10 Move the wire. b out of the page[1]

P7.11 The magnet could be turned round so the 4 a primary[1]

opposite pole is moved in, or the original b decreases[1]
pole could be moved out of the coil.
c increases[1]
P7.12 With the cell, the current always flows
in one direction (d.c.). With the generator, 5 Any two from: use a stronger bar magnet;
the current constantly changes move the magnet faster; use a coil with
direction (a.c.). more turns.[2]

P7.13 a g rid; pylons; voltage; reduce; 6 a Fleming’s left-hand rule. Extend the
transformers thumb and first two fingers of the left
hand at right angles to each other, with
b A: primary coil; B: iron core; C: the first finger pointing in the direction of
secondary coil the field and the second in the direction
c Step-up. It has more turns on the of current, and the thumb will give the
secondary coil than on the primary coil. direction of force or motion.[2]

P7.14 a step-down b The commutator; it reverses the

connections to the battery so the motor
b 6 V spins continuously.[2]
P7.15 Np Ns Vp Vs Step-up c Any two from: increase the current;
or step- increase the strength of the field; increase
down? the number of turns on the coil.[2]
10 20 6 12 step-up 7 a Labels for: primary coil; secondary coil;
10 100 1.2 12 step-up soft iron core. More turns on secondary
2000 50 240 6 step- coil than on primary coil.[4]
down b A transformer will not work with
10 000 20 115 000 230 step- d.c. because the magnetic field in the
down transformer is unchanging.[1]

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

8 a A is a step-up transformer. It increases makes employers accountable for the safety

voltage to decrease energy losses in the of their workers. Also, the internet makes it
cables. B is a step-down transformer. It much easier for the workers to research safety
reduces the voltage to a safe level for use themselves. The women in the factories would
in homes.[4] have found it much more difficult to research
the properties of radium.
b 500 000 V; one mark for answer,
one for unit[2] Both these questions could lead on to discussion
of the need for people to be scientifically literate,
9 a The ammeter registers a current; because and the need for unbiased scientific research to be
the wire cuts through the field lines and available to all.
a current is induced.[2]
b i no current[1] Questions
P8.01 nucleus; protons; neutrons; mass; protons;
ii The current is bigger and in the
neutrons
same direction.[1]
P8.02 a 5
iii The current is the same as in the
first experiment.[1] b 12
iv The current is bigger and in the c 5 protons, 7 neutrons and 5 electrons
opposite direction.[1]
P8.03 a 27
10 a due to the high current[1]
b 60
27 Co
b 0.83 A
P8.04 a C
 arbon-12 has 6 protons, 6 electrons
One mark for calculating V1 = 240 V; and 6 neutrons. Carbon-14 has 6
one mark for calculating I1 = 0.83333; protons, 6 electrons and 8 neutrons.
one mark for rounding this to 2 s.f.
(I1 = 0.83333); one mark for getting b isotopes; proton; nucleon; chemical
both units correct.[4] P8.05 a 

Chapter P8 Nucleus Proton Neutron Nucleon

number Z number N number A
Before you start
Nu-1 6 6 12
1 False. Atoms contain protons, neutrons and Nu-2 7 6 13
electrons and these are all made up of even
smaller particles. Nu-3 7 7 14
Nu-4 6 8 14
2 False. There are 118 different atoms, though
many of the larger ones are unstable. Nu-5 5 6 11
Nu-6 6 7 13
3 True.
b Nu-1, Nu-4 and Nu-6
4 False. Atoms have no overall charge, but the
protons and electrons have charge. c Nu-2 and Nu-3

Science in context P8.01 d Nu-5 is boron; Nu-1, Nu-4 and

Nu-6 are carbon; Nu-2 and Nu-3
1 The answer to this is commercial rather are nitrogen.
than scientific. The owners would have
had to put in place safer working P8.06 Nu-1 +6, Nu-2 +7, Nu-3 +7, Nu-4 +6,
procedures if they had admitted the Nu-5 +5, Nu-6 +6
radium was dangerous and this would have P8.07 The radiation which we are exposed to all
cost money. the time from radioactive sources.
2 While it isn’t possible to say this could never
happen again, Health and Safety legislation

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P8.08 Natural, any three from: materials in the P8.20 a B

 eta particles or gamma rays would
ground, building materials, cosmic rays, penetrate through the smoke easily.
food and drink, gases in the atmosphere.
b Alpha particles are stopped by the
Artificial, any three from: medical uses, plastic casing or by a few centimetres
weapons testing, air travel, nuclear of air.
power stations. c A short half-life would mean the
P8.09 cosmic rays smoke detector would need to be
changed frequently.
P8.10 unstable; two protons; two neutrons;
electron; electromagnetic P8.21 More radiation would pass through the
sheet, increasing the count rate on the
P8.11 It comes from inside the nucleus. detector. This would lead to the rollers
being moved slightly further apart so the
P8.12 gamma rays
thickness would increase.
P8.13 The number of protons changes and this
P8.22 The radiation used is gamma which can
is what determines which element it is.
penetrate through plastic.
84 Po → 206
P8.14 a 210 82 Pb + 2 α + energy
4

Practice questions
b 84 = 82 + 2
1 D[1]
c 210 = 206 + 4
2 C[1]
P8.15 218
84 Po → 218
85 At + −1β
0

3 Natural: any one from: rocks and soil,

P8.16 a 800 b 200 cosmic rays, food and drink, gases in
the atmosphere[1]
P8.17 38 days
Man-made: any one from: medical
P8.18 2 days technology, the nuclear industry,
weapons testing, air travel[1]
Activity P8.01
4 alpha, beta, gamma[2]
1 The two graphs will have the same shape
because the activity/count rate and the number 5 15 g[1]
of atoms remaining undecayed decrease in the
same way. 6 a 4[1]

2 The half-life is approximately the same for b 9[1]

each graph (around four throws). c 5[1]

Questions d 9
4 Be[1]

P8.19 a i T
 he top third of the film would e 4 protons; 7 neutrons[2]
be darkened by exposure. The
f 11
Be[1]
bottom two-thirds would not as 4

the aluminium and lead would 7 a the time taken for half of the unstable
absorb the beta particles. nuclei to decay[1]
ii The top two-thirds of the film b 5 mg[1]
would be darkened but not the
bottom third as the lead would c Ionisation causes cells/DNA to mutate.[1]
absorb most of the gamma rays.
d Any two from: store it in a lead-lined
b The lightproof jacket is likely to be box; store it in a labelled cupboard;
paper which would stop alpha. Also, only qualified people handle it; handle
the range of alpha in air is only a few with tweezers; do not point source
centimetres so it is unlikely that alpha at anyone; record exposure times[2]
particles would reach the badge.

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

8 a 2 protons and 2 neutrons OR identical gas known as protostars. A protostar

to the nucleus of a helium atom[1] becomes a star once nuclear
fusion begins.
b Place paper between the rock and the
detector. If the count rate drops it b As the molecular cloud collapses,
is alpha.[2] its gravitational potential energy is
transferred to kinetic energy. Collisions
c 238
92 U → 23490Th + 42 α[3] between particles cause kinetic energy
to be transferred to thermal energy.
Chapter P9
P9.08 a 
Protostar: a very young star that is
Before you start still gathering mass from its parent
• Stars are more massive. Stars shine (emit molecular cloud.
light), planets reflect light. b Red giant: a star with a starting mass
• (thermo)nuclear fusion of fewer than eight solar masses that is
burning helium in its core. Its shell of
• This depends on the temperature of the star. hydrogen has expanded and cooled.
• A galaxy is a group of stars held together by c White dwarf: the final stage of a star
gravity. Our galaxy is the Milky Way. that started with fewer than eight
solar masses and has run out of fuel.
• Learner’s own answers.
d Supernova: an exploding star that
Science in context P9.01 began life with more than eight solar
1 Lack of a common definition would be masses and has run out of fuel.
very confusing. One example of this type of e Neutron star: a collapsed star
collaboration is the Système Internationale – composed almost entirely of
SI units. neutrons, formed when a star with
2 If Pluto remained a planet, then we would more than eight solar masses reaches
potentially have hundreds of planets. It would the end of its life.
be very hard to learn all their names. f Black hole: the final stage in the
life cycle of a star that started with
Questions more than eight solar masses. It has
P9.01 hydrogen (75%); helium (24%) enough mass left over after exploding
as a supernova to collapse to a point
P9.02 Eyes would have evolved to see radiation where gravity is so strong that not
in the ultraviolet region. even light can escape.
P9.03 (thermo)nuclear fusion P9.09 The flow chart should be like Figure
P9.05.
P9.04 a 144 million km
P9.10 a 
Nuclear fusion is where light
b 137 years
nuclei fuse (join) together to create
P9.05 a 
1.33 × 108 s heavier nuclei, but some mass turns
into energy.
b 3.99 × 1013 km
b The nuclei all have the same
c 18 000 years positive charge so they need to be
d 107 million years moving fast enough to overcome
the electrostatic repulsion between
P9.06 4.7 km/s; yes them. This is only possible at very
P9.07 a 
Within interstellar clouds of gas and high temperatures.
dust, the force of gravity pulls gas P9.11 It must be above or below the
molecules closer together to form galactic disc.
clumps. These clumps contract to
form spinning spheres of super-hot P9.12 4 × 1041 kg

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 CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS

Practice questions 6 Gravity caused a molecular cloud to collapse

into a protostar, which continued to pull in
1 D[1] more matter from the cloud. As the cloud
2 B[1] collapsed, its gravitational potential energy
was transferred into the kinetic energy of the
3 a distance[1] gas molecules, which was transferred into
b the distance travelled by light in thermal energy. Once it became hot enough,
one year[1] the gas turned into a plasma. Once the plasma
became hot enough, the protons (hydrogen
c because the distances are so huge[1] ions) moved fast enough to overcome
electrostatic repulsion and fused into helium,
4 a In this model, the Earth is central but we
releasing energy. The radiation pressure
now know the Sun is central OR in this
pushing outwards was equal to weight, acting
model, there are six planets but we now
inwards and the star became stable, which
know there are eight planets.[1]
is what the Sun is like now. Eventually, it
b The order of the planets other than will use up its hydrogen fuel so the radiation
Earth is correct OR the Moon orbits pressure will fall and the Sun will collapse.
the Earth.[1] Gravitational potential energy will transfer to
thermal energy. The core will get hot enough
c 760 seconds or 12.7 minutes[2] to fuse helium and the outer shell of the Sun
5 a galaxy[1] will expand and cool so that the Sun becomes
a red giant. When the helium runs out,
b gravity[1] the Sun will collapse into a white dwarf.[5]
c Milky Way[1] Award one/two marks: the description names
the main stages of the process, including at
least two of the italicised terms.
Award three/four marks: the description gives
a detailed description of the main stages and
uses at least four of the italicised terms.
Award five marks: a full, detailed description
of the process.

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72 with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023