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
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Coursebook answers
Biology
A multicellular organism is made of many
cells – for example, a human or a plant.
Chapter B1
Before you start
1
excretion, sensitivity, growth, reproduction,
movement, nutrition, respiration
2
You could look for cell walls, which all plant
cells have, but no animal cell does. You could
also look for chloroplasts – if the cell has
these, it is a plant cell. However, if it does not
have chloroplasts it could still be a plant cell.
In a multicellular organism, different
cells can become specialised to carry out
particular functions.
Science in context B1.01
In a multicellular organism, different
cells can become specialised to carry out
particular functions.
Questions
B1.01 Although plants might appear to be still
and unable to respond to changes in their
environment, they demonstrate sensitivity
and can move, albeit much more slowly
than animals. They also show the other key
characteristics of living things: they respire,
reproduce, grow, excrete waste gases, and
gain nutrition through photosynthesis.
B1.02 The responses from learners will vary,
depending on the organisms they choose.
It is important that the responses clearly
identify the characteristics of living things
that are carried out all the time by their
chosen organisms (such as respiration
and excretion), and the characteristics
that only happen at certain times (such as
growth and reproduction).
B1.03 A unicellular organism is made of
a single cell – for example, bacteria.
1
B1.04 The animal cells do not have any coloured
parts, which makes them difficult to see
without a stain, but the plant cells contain
green chloroplasts. Also, the plant cell
walls stand out because they are much
thicker than the animal cell membranes.
B1.05 a
ribosome
b
nucleus
c
chloroplast
d
cell wall
e
vacuole
f
cell membrane
B1.06 ribosome, nucleus, cell membrane
B1.07 For example:
Bacterial cell
Animal cell
Plant cell
has cell
membrane
has cell
membrane
has cell
membrane
has cell wall,
but not made
of cellulose
no cell wall
cell wall
made of
cellulose
has cytoplasm has cytoplasm has cytoplasm
no nucleus
has a nucleus
has a nucleus
DNA is
circular
DNA is not
circular
and forms
chromosomes
DNA is not
circular
and forms
chromosomes
has
ribosomes
has
ribosomes
has
ribosomes
does
not have
mitochondria
has
mitochondria
has
mitochondria
does
not have
chloroplasts
does
not have
chloroplasts
may have
chloroplasts
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
B1.08 1000
•
ribosome – where proteins are made
B1.09 a
•
mitochondrion – site of aerobic
respiration / releases energy
from glucose[6]
actual length in Figure B1.10 is 83 mm
b
83 mm = 83 × 1000 = 83 000 μm
c
Real size = 83 000 ÷ 20 000 = 4.15 μm
d
1 mm = 1000 μm. So you could fit
1000 ÷ 4.15 = 240.96. Rounded up,
this is 241 mitochondria.
6
a
nucleus[1]
b
Any six from:
Practice questions
protein synthesis requires energy
•
B is a mitochondrion; mitochondria
provide energy (do not accept
produce energy)
1
C[1]
2
a
taking in substances from the
environment; and using them
for energy, growth and development[2]
•
by aerobic respiration; which releases
energy from glucose
b
•
C is a ribosome
•
ribosomes are the site of
protein synthesis[6]
By detecting chemicals on the gills
of a fish, the tongue-eating louse is
demonstrating sensitivity.
By crawling into the fish’s
mouth, the tongue-eating louse is
demonstrating movement.[2]
c
Possible reasons include: short life
cycle; spends very little time
outside the host organism;
rare in the wild.[1]
3
B[1]
4
B[1]
5
a
Magnification = image size ÷ actual size.
Width of jellyfish in the photo is 89 mm.
Actual width of jellyfish is 50 mm.
So magnification is 89 ÷ 50 = ×1.78.
Round up to 2 significant figures: ×1.8[3]
(one mark for stating correct equation;
one mark for correct substitution into
equation; one mark for correct statement of
magnification, with a × sign and no unit)
b
c
ithe processes that make new
organisms; of the same species[2]
ii
2
•
Any three of the following pairs, two
marks per pair:
•
cell membrane – partially permeable /
controls what enters and leaves the cell
•
cytoplasm – where many metabolic
reactions take place
•
nucleus – contains DNA /
chromosomes / information about
which proteins the cell makes
Any one from:
•
has a nucleus
•
has mitochondria
•
has vesicles[1]
Chapter B2
Before you start
•
The particles are far apart and rarely collide
with each other. – gas
•
The particles vibrate on the spot. – solid
•
The particles are close to one another but can
move around. – liquid
•
The particles move freely in all directions. – gas
•
The particles stay in contact and slide past one
another as they move. – liquid
•
The particles are in fixed positions, close to
one another. – solid
Science in context B2.01
1
Learners cannot be expected to know any
detail about transplants or availability of
organs and should be encouraged to put
forward any suggestions that they have.
The real reasons are: the body will reject an
organ that is from a person with a different
tissue type, so it is very difficult to find a
kidney that will be accepted by the recipient’s
body; there are never enough donated
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
kidneys to go around – they need to come
from a healthy person who has recently died,
or from a close relative who is willing to
donate one.
2
This question looks ahead to factors that
affect the rate of diffusion, and to the concept
of a diffusion gradient. Learners may be
able to work out for themselves that keeping
the fluid flowing through will make sure that
the harmful substances do not build up in the
dialysis fluid, and may also be able to see that
this would stop the substances from diffusing
out of the blood and into the fluid.
Experimental skills B2.02
1
The answers provided by the learner will
depend upon which of the three variables is
chosen for investigation.
2
The independent variable is the variable
that is changed by the learner. The answer
provided by the learner will depend upon
which of the three variables is chosen
for investigation.
3
The answer provided by the learner will
depend upon which of the three variables
is chosen for investigation. However, it will
be important for the learner to identify a
sufficient range of values to show a pattern or
trend in the results.
4
The dependent variable is the variable that is
measured by the learner. This is the time taken
for the cubes to completely change colour.
This can then be used to calculate the rate
of diffusion.
5
The answer provided by the learner will
depend upon which of the three variables is
chosen for investigation. However, it will be
important for the learner to identify a method
by which the dependent variable can be
measured in a straightforward way.
6
The answer provided by the learner will
depend upon the nature of their investigation.
However, it will be important for the
learner to provide a comprehensive list of
variables to keep constant (standardised),
and to describe how this will be achieved in
each case.
Activity B2.01
The ‘particles’/people have diffused to fill the space
available by moving around and bumping into
each other (or in this case, avoiding bumping into
each other).
Questions
B2.01 a
Diffusion requires particles to
spread out.
b
For diffusion to occur, particles
must spread out from a region of
high concentration to a region of
lower concentration.
c
Diffusion depends on the movement
of particles in all directions so that
they can spread out effectively.
B2.02 the cell membrane
Experimental skills B2.01
1
The cubes had an alkali in them. As the acid
diffused into the agar jelly cubes, it neutralised
the alkali, so the indicator changed colour.
2
The total volume was the same.
3
The surface area of the eight small cubes was
double/larger than the surface area of the
large cube.
4
The time taken for the eight small cubes to
completely change colour was shorter than the
time for the one single cube. This is because
the surface area of the small cubes was greater
than that of the single cube.
B2.04 The water molecules are small enough to
pass through the holes in the membrane,
but the sugar molecules are too big.
The conclusion will depend on the results but
is likely to be: the greater the surface area, the
faster diffusion takes place.
B2.06 The dilute solution has the higher water
potential, because it contains more
water molecules.
5
3
7–9 The answers provided by the learner will
depend upon which of the three variables is
chosen for investigation.
Questions
B2.03 Water is the solvent and sugar is
the solute.
B2.05 from the dilute solution to the
concentrated solution
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B2.07 When an animal cell is placed in pure
water, water enters the cell by osmosis
through the partially permeable
cell membrane.
b
to allow time for the dye solutions to
come to the same temperature as the
water-baths[1]
c
Any two from:
B2.08 Plant cells have a strong cell wall
surrounding the cell membrane,
which stops the cell bursting.
•
the concentration of the dye solution
•
the volume of the dye solution
B2.09 Water moves out of the cell through the
partially permeable cell membrane.
•
the volume of the jelly cubes
•
the surface area of the jelly cubes[2]
The cytoplasm and vacuole shrink.
d
The cell membrane is pulled away from
the cell wall.
B2.10 The same solution that the cell is
immersed in. The only thing between the
external solution and space X is the cell
wall, which is fully permeable.
B2.11 The cells will take up water by osmosis,
because the water potential of the water
outside the cell is greater than the water
potential of the solution inside the cell.
The vacuole and cytoplasm will increase
in volume, so the cell membrane will be
pushed back against the cell wall, into its
normal position.
4
As the temperature increases, the
time to change colour decreases.[1]
iii
At higher temperatures, kinetic
energy of particles increases; so,
particles move faster / diffusion
happens more quickly.[2]
Any six from:
•
both animal cell and plant cell take
up water by osmosis
Each cell in the piece of potato gained water
by osmosis, because the solution inside the cell
was more concentrated (had less water, or a
lower water potential) than the water outside.
As each cell swelled up, this increased the size
of the potato strip.
•
because there is a water potential
gradient from outside the cell to inside
•
the volumes of both cells increase
•
the animal cell bursts but the plant
cell does not
3
Learners should find that they got shorter.
•
4
Each cell in the piece of potato lost water by
osmosis, because the solution inside the cell
was less concentrated (had more water, or
a higher water potential) than the solution
outside. As each cell lost water and shrank,
this decreased the size of the potato strip.
because the plant cell has a cell wall
(but the animal cell does not)
•
the plant cell becomes turgid
•
as the contents of the cell push
outwards on the cell wall
•
which is called turgor pressure[6]
1
Learners should find that they got longer.
2
Practice questions
4
ii
a
the net movement of water molecules;
from a higher water potential to a
lower water potential / down a water
potential gradient; through a partially
permeable membrane[2]
b
Experimental skills B2.03
ithe value at 20 °C, time 4.5 minutes;
because the time is shorter than the
time at 30 °C[2]
5
1
D[1]
2
B[1]
3
a
diffusion; random/net movement of
particles; down a concentration gradient[3]
a
more potassium in the plant cells
than in the water; more sodium in the
water than in the plant cells; use of
comparative figures[3]
b
active transport; if diffusion then
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
•
from respiration
Answers will depend on the foods that
learners tested.
•
to move potassium ions into the cell /
move sodium ions out of the cell
2
•
against their concentration gradients
A sensible answer will refer to the degree of
cloudiness of the emulsion. The clearer the
solution (the less the emulsion), the less fat/oil
is present.
•
reference to transport / carrier
proteins[4]
Chapter B3
B3.04 nitrogen
Experimental skills B3.03
Before you start
1
Question
1
Answers will depend on the foods that
learners tested.
2
The method could ensure that the mass
of each food tested for protein is equal.
This would make the comparisons of the
food types more valid.
a
O2
b
a molecule
c
an element
a
carbon, hydrogen, oxygen
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
mix of chemicals in the atmosphere and the oceans.
This is a big and very wide topic, and some learners
might like to research further into modern theories
about the origin of life.
3
a
starch[1]
b
carbon, hydrogen and oxygen[1]
c
made up of many glucose molecules;
joined in a long chain[2]
d
Add Benedict’s solution to the liquid;
heat; colour change from blue to
green / yellow / orange / red
indicates glucose.[3]
a
i
The mixture should not be heated.[1]
ii
The colour change is from blue to
purple or violet.[1]
2
Experimental skills B3.01
1
Answers will depend on the foods that
learners tested.
2
Learners should find that all the foods
containing starch and reducing sugar are of
plant origin. If they are processed foods with
several ingredients, then at least some of these
ingredients will have come from plants.
4
b
Questions
B3.01 glucose
ii
B3.02 The fat layer acts as an insulator.
It reduces heat loss from the animal’s
body to its environment.
B3.03 Birds don’t want to carry any more weight
than necessary, or they would waste a lot
of energy when they fly long distances.
Storing energy in fat allows them to keep
their weight much lower than if they
stored it as carbohydrate.
5
iCut the food into very small pieces;
mix with ethanol; pour some of the
ethanol into distilled water.[3]
a milky emulsion[1]
Chapter B4
Before you start
The incorrect statements are:
•
In a chemical reaction, atoms of one element
are rearranged to make atoms of other
elements. This is incorrect, because atoms do
not change in a chemical reaction. Atoms can
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
be arranged to make new compounds, or new
substances, but not new atoms.
•
7
Products are changed to reactants. This is the
wrong way round – reactants are changed
to products.
Answers will depend on the learner’s
experience as they did the experiment.
They are likely to include:
•
variables other than pH affecting the time
for the paper to rise to the top: for example,
differences in how much celery extract was
absorbed onto the paper; differences in
the sizes of the pieces of paper; differences
in how the paper behaved (it might have
flipped round sideways or hit the side of
the tube on its way up); these are all very
difficult to standardise, and learners may
suggest a different method of measuring
how much oxygen is released, such as
collecting in a gas syringe and measuring
the volume collected
•
difficulty in measuring the time precisely:
it is difficult to improve this, as it is
almost impossible to standardise the
moment at which the paper is placed
at the bottom of the beaker, and also
exactly when it reaches the surface of
the liquid.
Science in context B4.01
The production of the enzyme lactase, which is a
protein, requires the use of amino acids and energy
by the cell. In many adults, especially a long time
ago in our history, milk was not a fluid that was
consumed after they had passed a young age. So,
the production of lactase in older children and
adults would have been a waste of cellular resources
and energy.
Questions
B4.01 biological because they are made by
organisms; catalysts because they increase
the rate of chemical reactions
B4.02 a
b
carbohydrase
lactose
B4.03 As temperature increases from 0 to 37 °C,
the rate of reaction increases. The increase
is exponential. As temperature increases
above 37 °C, the rate of reaction
decreases and reaches 0 at 58 °C.
This decrease is steeper than the increase
at lower temperatures.
B4.04 a
2
b
7
c
between pH 5.6 and 10.4
Experimental skills B4.01
1
hydrogen peroxide catalase

→ water + oxygen
2
There was catalase on the filter paper, because
it had been dipped into the celery extract.
When the paper was put into the hydrogen
peroxide solution, the catalase broke down
the hydrogen peroxide, releasing oxygen.
The oxygen collected as bubbles on the paper,
which made it rise upwards.
3–5 These answers depend on the
learner’s results.
6
6
The experiment could be done again, this time
using a range of pH values clustered around
the value that gave the fastest times in the
original experiment.
Experimental skills B4.02
1
The liquid was alkaline, and the indicator
(thymolphthalein) is blue in alkaline
conditions. (Learners may also explain
that the liquid is alkaline because sodium
carbonate solution has been added to it.)
2
Lipase digested the fat in the milk, breaking it
down to fatty acids. These are acidic, and so
they reduced the pH. This caused the indicator
to change from blue to colourless.
3–4 These answers will depend on the
learner’s results.
5
The colour change does not take place
instantaneously. It is impossible to judge
precisely when the colour change occurs. It is
tricky even to judge this to the nearest second,
and it certainly cannot be done to the nearest
0.1 or 0.01 s.
6
This will depend on what the learner
experienced as they did the experiment.
The most likely suggestions for sources of
error and improvements are:
•
difficulty in deciding on the time of colour
change: it would help to have a set of
tubes with different pH values and the
indicator, for reference
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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•
difficulty in measuring volumes
of liquids accurately: syringes and
measuring cylinders could be replaced by
graduated pipettes
•
the possibility of unrecognised anomalous
results: the chance of this could be
reduced by having replicates, perhaps
three at each temperature.
b
i
Amylase works most quickly at pH 7
/ its optimum is pH 7. Four minutes
is the shortest time. Amylase does
not work at all / is denatured at pH 4
or pH 11.[3]
ii
Questions
Any three from:
•
the concentration of
amylase solution
•
the concentration of
starch solution
•
the volume of amylase solution
•
the temperature.[3]
B4.05 Explanations should refer to:
•
•
•
•
the increase in kinetic energy of
enzyme and substrate molecules as
temperature increases
therefore, an increase in the frequency
of collisions
5
a
the loss of shape of the active site of
the enzyme as temperature increases
above optimum, so that the substrate
no longer fits into it
denaturation.
B4.06 Explanations should refer to:
•
•
•
the active site of the enzyme only
having its ‘correct’ shape within a
narrow range around pH 7
the loss of shape of the active site
of the enzyme as pH decreases or
increases from the optimum, so that
the substrate no longer fits into it
denaturation.
Practice questions
7
1
A[1]
2
a
proteins; metabolic; active[3]
b
They increase the reaction rate
(of metabolic reactions); so that these
work well enough to sustain life.[2]
3
P: substrate; Q: active site; R: enzyme–
substrate complex; S: products[4]
4
a
The iodine went blue–black at the start
because the solution contained starch;
it stayed brown at the end because the
solution no longer contained starch;
because the amylase broke down
the starch.[3]
b
Any five points from:
•
activity of both enzymes increases
with temperature at first
•
maximum activity of enzyme A is at
40 °C (the optimum temperature for A)
•
maximum activity of enzyme B is at
70 °C (the optimum temperature for B)
•
beyond the optimum temperature, the
activity of both enzymes decreases to 0
•
enzyme A is denatured at 58 °C
•
enzyme B is denatured at 92 °C
•
for both enzymes, activity decreases
more rapidly than it increased.[5]
iBetween 40 °C and 60 C, activity
increases rapidly; as temperature
increases, kinetic energy of enzyme
and substrate molecules also
increases; so molecules move more
quickly and collide with each other
more frequently.[3]
ii
Between 70 °C and 90 C, activity
decreases rapidly; as temperature
increases above the optimum (70 °C),
the kinetic energy of the enzyme
causes the active site to lose its shape;
so substrate molecules can no longer
fit into the active site / the active site
is no longer a complementary shape
to the substrate molecules; so the
reaction cannot take place / the
enzyme is denatured.[4]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
Chapter B5
Questions
Before you start
B5.04 Starch is a storage material, and if you
are storing something you need to be able
to get it back again when required. Plants
need to be able to break down starch to
glucose, so they can use it in respiration
to provide energy. Cellulose, however, is a
structural material, used to make cell walls.
It needs to stay there, not be broken down,
or the cell walls would easily break apart.
1
carbohydrates and fats (and
occasionally proteins)
2
sunlight
3
through photosynthesis in plants, which use
energy from sunlight to make carbohydrates
Science in context B5.01
Carbon dioxide is a significant greenhouse gas
contributing to global warming and climate
change. The process of photosynthesis uses carbon
dioxide, so large-scale artificial photosynthesis
could help to reduce the concentration of carbon
dioxide in the atmosphere, helping to slow down
climate change.
B5.01 Animals get all of their energy from
organic substances, which they are not
able to synthesise themselves. Plants
synthesise organic substances from
inorganic ones, using sunlight as an
energy source.
B5.02 Chlorophyll absorbs energy from sunlight.
(Do not accept ‘attracts sunlight’.)
The energy enables carbon dioxide and
water to react to produce carbohydrates.
B5.03 two
Activity B5.01
8
B5.06 Some parts of a plant are not exposed to
light (e.g. roots) and some parts do not
have chloroplasts (e.g. flowers). These
parts cannot photosynthesise and make
their own carbohydrates, so they must
have sucrose delivered to them.
B5.07
Questions
1
The model shows that six molecules of carbon
dioxide and six molecules of water produce
one molecule of glucose and six molecules
of oxygen.
2
Accept any sensible suggestions.
For example, some pieces of orange card
could be used to represent energy in sunlight,
and a learner could hand some to the learners
who are building the glucose molecule.
The cards can be placed in the carton with the
glucose molecule, showing that the energy is
incorporated into it.
3
B5.05 glycogen
The oxygen that is released in photosynthesis
comes from water molecules, not carbon
dioxide. All the carbon and oxygen in
the carbon dioxide becomes part of the
glucose molecule.
Element
nitrogen
Mineral
salt
nitrate ions magnesium
ions
Why
needed
to make
amino
acids,
and then
proteins
to make
chlorophyll
Deficiency
weak
growth,
yellow
leaves
yellowing
of leaves,
often
especially
between
the veins
magnesium
B5.08 (Learners may differ in the knowledge
they already have about plant
reproduction; this is covered in more
detail in Chapter B11.) Pollination is
essential for sexual reproduction in plants.
Nectar attracts insects to the flower, and
the insects transfer pollen to another
flower, allowing fertilisation to take place.
B5.09 A: upper epidermis
B: palisade mesophyll layer
C: spongy mesophyll layer
D: stomata (surrounded by guard cells)
B5.10 It has a large number of chloroplasts,
where photosynthesis takes place.
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
This means that there is a lot of
chlorophyll, which transfers energy from
sunlight to energy in carbohydrates.
The cells are tall and thin, so many can
be packed into a small area, with few cell
walls for sunlight to pass through to reach
all of the chloroplasts.
Experimental skills B5.05
1
The plant releases oxygen as bubbles,
which we can see and count.
2
As light intensity increases, the rate of
photosynthesis increases.
3
Without the heat shield, temperature would
be an uncontrolled variable, so it would not be
possible to say whether changes to the rate of
photosynthesis were due to light intensity or
temperature.
4
The bubbles released may be different sizes.
It is also not easy to count them reliably.
Measuring volume will give a more reliable
indication of the quantity of oxygen released
and, therefore, the rate of reaction.
B5.11 They receive less sunlight than other
tissues in the leaf.
Experimental skills B5.01
1
Learners should find that the leaf becomes
blue- black, indicating that it contains starch.
2
Boiling breaks down cell membranes.
The membranes around the chloroplasts
and around the cell need to be broken down
to allow the iodine to come into contact with
the starch, which is inside the chloroplasts
inside the leaf cells.
3
Experimental skills B5.06
1
To allow any change in colour to be seen
more clearly.
Experimental skills B5.02
1
Learners should find that only the green parts
contained starch.
2
Chlorophyll is needed for photosynthesis.
Experimental skills B5.03
1
•
independent variable (temperature or
mass of sodium hydrogencarbonate
added) on the x-axis
•
dependent variable (number of bubbles
per minute) on the y-axis
•
good scales on both axes, going up in
sensible and regular intervals, and using at
least half of the grid provided
•
points plotted accurately, as neat crosses
•
lines drawn with a ruler between points.
2
To give the plant time to photosynthesise and
make starch.
2–4 These answers will depend on the learner’s
results, and their experience in carrying out
their planned investigation.
3
Light is necessary for photosynthesis.
Practice questions
Experimental skills B5.04
1
D[1]
1
2
D[1]
3
a
2
3
9
If the plant was not destarched, we would not
know whether any starch we found had been
made during the experiment or before.
Graph will depend on the learner’s results but
should show:
Either leaf could be said to be the control.
One has carbon dioxide and one does not;
it is justifiable to say that either one is the
experiment, and the other is the control.
The essential point is that you need both,
in order to compare the results.
This was to control a variable. The only
difference between the two flasks is that one
has a liquid that absorbs carbon dioxide,
and the other has a liquid that does not.
Carbon dioxide is necessary for
photosynthesis.
i
palisade mesophyll[1]
ii
Any two from:
•
cells contain many chloroplasts
•
in which photosynthesis
takes place
•
(chloroplasts) contain a lot
of chlorophyll
•
which transfers energy from light
to energy in carbohydrates
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4
5
•
cells are tall and narrow
•
allowing sunlight to reach
chloroplasts without having to
pass through many cell walls[2]
•
independent variable (concentration
of sodium hydrogencarbonate
solution) on the x-axis
b
Any two from B, E, I, H (do not allow A, F
or G, as these are not cells or tissues).[2]
•
dependent variable (distance moved
by meniscus) on the y-axis
c
It can change shape; to open or close
the stoma.[2]
•
d
Water moves up through the xylem
vessels in structure E; then into a
palisade cell in layer C by osmosis
and into a chloroplast.[2]
good scales on both axes, going up
in sensible and regular intervals,
and using at least half of the grid
provided
•
points plotted accurately, as
neat crosses
•
lines drawn with a ruler
between points. [1]
a
for photosynthesis; idea that
photosynthesis takes place
inside chloroplasts[2]
b
A; it does not contain any chloroplasts[2]
c
B[1]
d
Any two from:
•
it absorbs energy from light (do not
allow ‘attracts’)
•
the energy is used to make carbon
dioxide and water react together
•
chlorophyll transfers energy from
sunlight to energy in carbohydrates/
glucose
[2]
d
distance moved by meniscus/
rate of photosynthesis increases
as concentration of sodium
hydrogencarbonate solution increases[2]
e
i
Accept any two sensible suggestions,
for example:
glucose; used to release energy
in respiration
leakage of air into or out of
the syringes
•
variation in the plants
(size, activity)
•
difficulty in reading the position
of the meniscus precisely against
the scale on the ruler
ii
•
starch; as an energy store
Accept any two sensible suggestions
relating to the answers in i, for example:
•
cellulose; to make cell walls
•
•
sucrose; for transport
use petroleum jelly to make the
syringe plungers airtight
•
nectar; to attract pollinators
to flowers[4]
•
use plant pieces of identical mass
•
use a glass tube with a scale
on it[2]
a
independent variable is concentration
of sodium hydrogencarbonate solution
(or carbon dioxide concentration);
dependent variable is distance
moved by meniscus after 30 minutes[2]
b
•
(do not accept anything that sounds
like a mistake made by the learners,
such as not ensuring their eye is
parallel with the meniscus)[2]
Any two of these pairs:
•
10
Graph should show:
a
carbon dioxide and water; react to produce
glucose and oxygen; using energy from
sunlight; absorbed by chlorophyll[4]
b
6
c
sunlight provides the energy for
photosynthesis; bright sunlight ensures
light intensity is not a limiting factor[2]
Chapter B6
Before you start
1
Starch is a carbohydrate.
2
It is made of many glucose molecules
linked together.
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3
Protein molecules are made of amino acids
linked together.
4
Lipase digest fats to fatty acids and glycerol.
5
It is an enzyme. All enzymes are
protein molecules.
Science in context B6.01
Carnivores such as lions and hyenas may eat meat
that is not fresh, and is therefore likely to contain
large numbers of potentially harmful bacteria.
The strong acid in their stomachs helps to kill
these bacteria, preventing infection. It is also
possible that the acid helps with the digestion of
proteins from the meat in the stomach, where the
enzyme pepsin requires acidic conditions to work.
B6.03 Any two from: liver, pancreas, gall
bladder, salivary gland
B6.04 mouth, oesophagus, stomach, (duodenum,
ileum, colon, rectum), anus. The
bracketed terms can also be summarised
as ‘small intestine, large intestine’.
B6.05 a
mouth and/or oesophagus
b
mouth, stomach, duodenum
c
ileum, colon
d
anus
B6.06 mouth and duodenum
Questions
B6.07 stomach and duodenum
B6.01 For example:
B6.08 a
Nutrient
Main dietary
sources
Uses in the
body
carbohydrate
grains and
foods made
from them
– e.g. rice,
pasta, bread;
potatoes;
sweet foods
for energy,
which is
released in
respiration
fat
cooking
oil, meat,
eggs, dairy
products,
oily fish
for energy,
released in
respiration;
to make cell
membranes;
as an
insulator,
preventing
heat loss; as
a protective
layer around
body organs
protein
meat, fish,
eggs, dairy
products,
pulses (peas,
beans,
lentils), nuts
and seeds
making
new cells,
for growth;
making
proteins
such as
haemoglobin
and
antibodies
B6.02 The alimentary canal is part of the
digestive system. It is the tube that food
moves through, from the mouth to the
11
anus. There are also other organs in the
digestive system, such as the gall bladder.
b
pancreas
duodenum
B6.09 To emulsify fat means to break up large
drops of fat into tiny droplets which
disperse through the water contents of
the duodenum. This increases the surface
area of fat that lipase can contact, and so
lipase can break the fats into fatty acids
and glycerol more quickly.
Practice questions
1
C[1]
2
D[1]
3
a
G: large intestine / colon; J: liver[2]
b
A and D[2]
c
E[1]
d
Any six from:
•
secretes protease enzymes
•
which digest protein
•
to amino acids
•
reference to chemical digestion
•
secretes hydrochloric acid
•
which provides a suitable pH
for enzymes
•
kills microorganisms
•
churns food
•
reference to physical digestion[6]
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Chapter B7
B7.04 to absorb water and mineral ions from
the soil
Before you start
In the case of the plant cell, learners may show:
•
carbon dioxide / water / glucose / oxygen /
other nutrients entering the cell
•
carbon dioxide / water leaving the cell.
They should remember from the previous chapter
that water is moved around the plant through
xylem vessels, while glucose is transported (as
sucrose) through phloem vessels. Carbon dioxide
and oxygen diffuse in from air spaces in the plant,
while waste water vapour diffuses out of cells.
In the case of the animal cell, learners may show:
•
oxygen / glucose / water / other nutrients
entering the cell
•
carbon dioxide / urea leaving the cell.
They may know that these substances are brought
to and from the cell in the blood. They may also
give other detail, such as that oxygen enters the
blood in the lungs, or that nutrients enter the
blood in the small intestine.
Science in context B7.01
Learners may suggest osmosis. They will later
find that this is also how water reaches individual
cells in plants that do have xylem, and how it first
enters the plant and moves across the root into the
xylem vessels.
Questions
B7.01 support; transport of water and
mineral ions
B7.02 transport of sugars and amino acids
B7.03 In roots, both types of vessels are found
in the vascular bundles. The xylem is
found in the centre, whereas the phloem is
arranged around it.
In stems, both types of vessels are found
in the vascular bundles that are studded
around the middle of the stem. The
xylem is found on the inner side of each
of these bundles, with the phloem on the
outer side.
In leaves, both types of vessels are found
in the vascular bundles that pass through
the midrib of the leaf.
12
B7.05 It is long and thin, and therefore has a
relatively large surface area. This increases
the rate at which it can absorb water and
mineral ions.
B7.06 The solution in the soil has a relatively
low concentration of solutes compared
with the solution inside the root hair
cell. These solutions are separated from
each other by the partially permeable
cell membrane. Water moves into the
cell through this membrane by osmosis,
from a dilute solution to a more
concentrated solution.
B7.07 Water moves from an area of high water
potential in the soil into the lower water
potential inside the root hair cell, down a
water potential gradient. It continues to
move from cell to cell towards the centre
of the root, by osmosis, down the water
potential gradient.
Experimental skills B7.01
1
xylem
2
the vascular bundles (veins)
3
Temperature is the variable to be changed.
A suitable range would be between 0 °C and
perhaps 80 °C, with intervals of 10 °C or 20 °C.
This could be done using water-baths. The
most important variables to be kept constant
include the size of the celery stalk and the
concentration of the dye.
If the dye can be seen in the stalk without
having to cut it, learners could measure the
distance travelled by the dye in a set time
period – for example, every two minutes. If it
cannot be seen, they will need to have several
stalks at each temperature, and cut one of
them across at a set distance (e.g. 10 cm)
after a set time – say every two minutes – to
determine how long it takes the dye to travel
this distance.
The main safety risk is the sharp blade used to
cut the stalks. Learners should describe how
they will avoid cutting themselves or someone
else with the blade.
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Questions
B7.08 root hair cells, root cortex cells, xylem,
mesophyll cells
B7.09 a
liquid
b
liquid
c
gas
B7.15 Learners may start with any chamber of
the heart but the order must be as follows:
left atrium, left ventricle, right atrium,
right ventricle
Experimental skills B7.02
B7.16 left atrium and left ventricle
1
Answers will depend on the learner’s
experience as they used the potometer.
B7.17 away from
2
Water vapour is lost from the leaves of a plant
by evaporation (transpiration). This water is
replaced by water that moves out of the xylem
vessels in the leaves. As water leaves the top
of the xylem vessels, more water is drawn into
the bottom of the xylem vessels (transpiration
pull). This draws water in at the cut end of the
shoot, causing the air/water meniscus to move
up the potometer.
3
The line graphs should have:
•
time / minutes on the x-axis, with a
suitable scale that uses at least half of the
graph paper provided
•
distance moved by meniscus / mm
(or cm) on the y-axis, with a suitable
scale that uses at least half of the graph
paper provided
•
points plotted as neat crosses or
encircled dots
•
lines drawn from point to point with a
ruler or best fit lines
•
lines clearly labelled, either directly on the
graph or using a key.
Questions
B7.10 Leaves are a source, and the trunk and
roots are sinks.
B7.11 Trunk and roots are sources, and the
growing buds and leaves are sinks.
B7.12 Transpiration happens at the top of the
xylem vessels, reducing the pressure at
this point. The pressure is always lower
at the top of the xylem vessels than at the
bottom, so water always flows upwards.
B7.13 The left side contains oxygenated
blood, and the right side contains
deoxygenated blood.
13
B7.14 As it passes through the body organs
other than the lungs; oxygen diffuses out
of the blood into the body cells, where it
is used in aerobic respiration.
B7.18 towards
B7.19 The muscles in the walls of the ventricles
contract, squeezing inwards and reducing
the volume inside the heart. This increases
the pressure inside the heart and pushes the
blood out.
B7.20 In the heart wall / on the outside of the
heart. They provide oxygen and nutrients
for the heart muscle.
B7.21 Any two of: Using an ECG, measuring
pulse rate (e.g. by placing your fingers
over an artery and counting, or by using a
phone app or smart watch) or listening to
the sounds of the valves closing.
B7.22 The septum separates oxygenated blood
from deoxygenated blood, ensuring that
all of the blood that enters the aorta
is fully oxygenated. The bicuspid valve
is between the left atrium and the left
ventricle. It prevents blood flowing back
into the left atrium as the left ventricle
contracts, so that all the blood is forced
out into the aorta. There is another valve
at the entrance to the aorta, to prevent
blood flowing back into the left ventricle
when the heart relaxes again. These valves
ensure that blood flows forwards in the
aorta at high pressure.
Experimental skills B7.03
1
The line graph will depend on the
learner’s results.
2
Answers will depend on the learner’s
results. They are likely to find that heart
rate fluctuated a little before exercise,
then increased rapidly during exercise and
decreased slowly after exercise ended.
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3
ii
Muscle contraction needs energy, which is
obtained from aerobic respiration. As muscles
work harder, they need more energy and
therefore aerobic respiration needs to happen
more quickly. The muscles therefore need more
oxygen, which is supplied to them by the blood.
A faster heart rate moves blood more quickly,
supplying oxygen to the muscles more quickly.
Questions
B7.23 a
c
B7.24 a
c
3
b
artery
capillary
vein
in the lungs
b
in the body organs
c
pulmonary artery
B7.25 The blood pulses as it is forced through
the arteries – it is at high and fluctuating
pressure. The elastic tissue in artery walls
allows them to expand as a high-pressure
pulse of blood flows through, rather
than bursting. They can then recoil to
their normal diameter in between pulses.
This helps to even out the blood pressure.
Veins, on the other hand, carry blood
that has already been through capillaries
and has lost most of its pressure, and is
not pulsing.
phloem transports sucrose and amino
acids but xylem does not; phloem
transports in both directions (by
translocation) but xylem transports only
upwards (by transpiration)[2]
a
Carbon dioxide reacts with water; during
photosynthesis / to make glucose / to
make carbohydrates.[2]
b
Any two from: it is produced during
photosynthesis; it evaporates from
mesophyll cells; into the air spaces
in leaves[2]
c
i
B7.26 A white blood cell has a nucleus.
B7.27 A phagocyte normally has a lobed
nucleus, whereas a lymphocyte has a large,
round nucleus that almost fills the cell.
ii
B7.28 Blood plasma is the liquid part of the
blood. It is mostly water but it also contains
dissolved substances, including dissolved
nutrients, hormones, dissolved gases, and
excretory substances such as urea.
Practice questions
1
C[1]
2
a
number of stomata in 0.06 mm2 is 20
(allow 18, 19 or 21); so, number in 1 mm2
is 333 (to nearest whole number; allow 300
(for 18 stomata in image), 317 (for 19 in
image), or 350 (for 21 in image))[2]
b
14
i
mesophyll cells have a large surface
area in contact with the air spaces;
from which water evaporates; filling
the air spaces with water vapour that
can diffuse out through stomata[3]
root hairs absorb water from the soil;
a large surface area increases the rate
at which this happens[2]
iii
Any five from:
•
percentage hydration decreases
(over time)
•
from 100% at day 1 to 30%
at day 5
•
percentage hydration fluctuates
each day
•
drops during the day and
increases at night
•
drops more quickly than
it increases
•
drops by a greater amount than
it increases[5]
Any four from:
•
percentage hydration of the
soil drops
•
(so) less water can be taken in by
osmosis through root hairs
•
water lost by transpiration cannot
be (completely) replaced
•
during daylight, it is hotter /
stomata are open, so water loss
exceeds water uptake
•
at night, it is cooler / stomata are
closed, so water uptake exceeds
water loss[4]
it has wilted; leaves have collapsed /
other suitable description; leaf cells
have lost their turgidity / become
flaccid[3]
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4
plasma[1]
5
S and R[1]
6
a
Any two from:
•
white blood cell is larger
•
white blood cell has a nucleus
•
white blood cell has a less
regular shape
•
b
9
c
60 ÷ 0.75 = 80 beats per minute;
(allow error carried forward from b)[2]
d
The plotted line should have the same
shape as the existing line, but would
at all times be lower. [2]
a
i
A: nucleus; B: mitochondrion[2]
ii
Any two from:
white blood cell does not contain
haemoglobin[2]
magnification = 20 ÷ 0.007 = ×2860
(to 3 s.f.)[3]
7
between the capillary and
surrounding cells
•
by diffusion
•
any two examples of substances:
oxygen / carbon dioxide / named
nutrients[2]
iii
Any three from:
red blood cell is transporting
oxygen; reduces distance for oxygen
to diffuse, out of the capillary / to
surrounding cells[2]
(take up oxygen) when oxygen
concentration is high
•
at the alveoli / in the lungs
•
oxygen combines with haemoglobin /
forms oxyhaemoglobin
•
suitable description of
shape difference
•
carried in blood (from lungs) to rest
of body
•
red blood cell has no nucleus /
structure A
•
release oxygen when oxygen
concentration is low[3]
•
red blood cell has no mitochondria /
structure B
d
Any one from: fight pathogens /
produce antibodies / phagocytosis /
clear up dead body cells[1]
•
red blood cell contains
haemoglobin[3]
a
Any two from:
b
c
Any three from:
plasma[1]
•
measuring pulse rate
Chapter B8
•
ECG
Before you start
•
listening to valves closing[2]
There is a very wide variety of sentences that
learners could write. For example:
(activity of heart) increases when
exercising; beats faster and harder;
decreases gradually when
exercise finishes[3]
a
A: just starting to contract; B: just
starting to relax[2]
b
15
•
•
b
8
to allow substances to move
quickly/easily
diameter of cell in diagram is 20 mm
(magnification = image size ÷ actual size)
actual size is 0.007 mm
c
•
(time between A and next corresponding
position on the graph is) 0.75 s
(accept 0.74–0.76)[1]
Bacteria and viruses are pathogens, which are
destroyed inside our body by antibodies produced
by white blood cells.
Science in context B8.01
1
Learners may be aware that some parents
think vaccinations are harmful to health.
There is a lot of misinformation on the
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
it is important to take care when chairing
this discussion.
2
There is no correct answer to this question.
Opinions may be divided between those who
think it is a parent’s right to decide whether
or not to have their child vaccinated, and
those who think that the health of the school
community should take precedence over that
of an individual. These are not easy decisions
to make, and learners should be encouraged to
look at both points of view.
Questions
B8.01 A disease that can be passed from one
person (or other organism) to another.
Transmissible diseases are caused
by pathogens.
B8.02 Unbroken skin is a physical barrier that
stops most pathogens moving through to
the underlying tissues. If skin is broken, a
blood clot seals the wound and prevents
pathogen entry.
B8.03 The acid kills bacteria in food, preventing
infection by pathogens that might cause
food poisoning or other infections.
B8.04 Water that is not clean contains
microorganisms, and some of these are
pathogens. If you drink water containing
pathogens or use it in ways that allow
the pathogens to get from the water
into your eyes, nose or mouth, or into
cuts or grazes on the skin, it can cause
serious illness.
B8.05 The water in a deep well comes from deep
underground, where it is less likely to have
been contaminated with urine or faeces. It
is therefore less likely to contain pathogens
from the body of an infected person.
B8.06 a
Covering food keeps animals such as
houseflies away from it. Houseflies
transfer pathogens on their feet or in
their saliva. If the food is in a warm
place, these pathogens can breed
quickly, so that by the time someone
eats the food there are large numbers
of pathogens, which could cause food
poisoning or other illnesses.
b
16
Even if there are harmful bacteria on
the food, when their numbers remain
small there is less chance of getting ill
if you eat them.
B8.07 An antigen is a molecule on a cell that is
not normally found in the body – such as
a pathogen – and that the body recognises
as ‘foreign’. An antibody is a protein
secreted by lymphocytes, which can bind
to its complementary antigen.
B8.08 The antigen and antibody have
complementary shapes, so that they fit
together precisely. They do not have the
same shape.
B8.09 a
It takes time for the lymphocytes that
can make the appropriate antibody
for this pathogen to make contact
with the antigen on the pathogen,
then to divide and produce a clone of
identical cells, which can then make
large quantities of the antibody.
b
The number rises rapidly between
day 0 and day 1, and then decreases
more slowly, reaching 0 at the end of
day 3. The number of bacteria is able
to increase rapidly at first, because
there are no antibodies to stop them
dividing. But as the quantity of
antibodies increases, the bacteria are
immobilised or killed, and the rate
at which they die becomes greater
than the rate at which they reproduce.
Their numbers therefore fall.
B8.10 The body now contains memory cells,
which are able to react immediately to the
presence of the bacteria and very rapidly
produce large quantities of the specific
antibody that binds with the antigen on
these bacteria. The number of bacteria
therefore has time to increase only very
slightly, and is reduced to 0 by the end
of day1.
B8.11 The response would look like the first
graph because the antigens on this
new bacterium would be different.
The memory cells produced from the
first infection give no protection against
any other type of pathogen.
Keeping the food cold reduces the
rate at which bacteria can multiply.
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B8.12 Through having a transmissible disease
and recovering from it; by receiving
a vaccination containing dead or
inactivated pathogens.
B8.13 The pathogen is unable to breed in a
person who has been vaccinated. If
enough people have been vaccinated, this
greatly reduces the number of people who
can be a host for the pathogen, making it
much less easy for the pathogen to spread
through the population.
Practice questions
a
genetic material / DNA / RNA[1]
b
Any five from:
•
proteins in virus coat are antigens
•
lymphocytes make antibodies
•
which have complementary shape
to antigens
•
produce memory cells
•
which can produce antibodies quickly
on next exposure to the same antigen
•
these antibodies cannot bind with
other antigens
•
so cannot protect against new strains
of the virus[5]
1
C[1]
2
D[1]
3
a
pathogens; host; mucus[3]
b
i
idea that skin is a barrier to entry of
pathogens through it; blood clots to
seal wounds[2]
Chapter B9
ii
The exact response provided will differ between
learners. Most will find that the breathing depth
and rate increase after this moderate exercise.
4
a
b
hydrochloric acid; is secreted by the
stomach; killing microorganisms
in food[3]
Before you start
Any five from:
Science in context B9.01
•
introduction of dead /
weakened pathogens
•
(antigens on pathogens are)
recognised by (specific) lymphocytes
•
antibodies produced
•
antibodies are specific to
pathogen / antigen
There is no ‘right’ answer for this – it is intended as
an intriguing issue to encourage learners to think
separately about their breathing rate and heart rate.
One possible answer is that we use breathing for
purposes other than ‘staying alive’ – such as talking.
We have therefore evolved to have some control
over this process, whereas there is no advantage in
being able to consciously control heart rate.
•
memory cells produced
Questions
•
which respond quickly on second
entry of same pathogen[5]
i
Any three from:
B9.01 mouth or nose; trachea; bronchi;
bronchioles; alveoli; wall of alveolus; wall
of capillary
ii
17
5
•
increased
•
from 15 000 to 76 000 (allow some
leeway with figures)
•
fluctuated
•
maximum number of cases was
76 000 in 1957 / 1958[3]
rapid decrease in number of cases;
to 0 by 1991; many children now
immune to measles; reference to
herd immunity / few hosts for
measles virus[4]
B9.02 The arrow for oxygen goes into a red
blood cell, because oxygen is transported
in combination with haemoglobin in red
blood cells. The arrow for carbon dioxide
comes from the blood plasma, because
most carbon dioxide is transported in
solution in the plasma.
B9.03 The arrows in the bronchiole represent
mass flow. The arrows showing carbon
dioxide and oxygen moving into and out
of the blood represent diffusion.
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B9.04 Emphysema leads to a reduction of the
surface area of the alveoli. As a result, less
oxygen is able to diffuse into the blood
in a given time. This reduces the oxygen
supply to cells, which therefore cannot
undergo aerobic respiration as rapidly,
and cannot release as much energy as
normal. The person may therefore find
it difficult to exercise. (In addition,
the removal of waste products from
respiration is less efficient, because the
diffusion of carbon dioxide from the
blood into the alveoli is less efficient.)
Experimental skills B9.01
1
When you breathe out, air moves into the
short tube in A and the long tube in B.
Expired air therefore only bubbles through the
limewater in B.
When you breathe in, air is drawn from the
end of the short tube in A, causing air to be
pulled into the limewater in A through the
long tube. This leads to bubbles in A only.
2
Learners should find that the limewater goes
cloudy more quickly in tube B. This shows
that there is more carbon dioxide in expired
air than in inspired air.
•
2
Answers will depend on the learner’s results.
3
Answers will depend on the learner’s results.
However, suggestions may include the fact
that the learner’s ability to do intense activity
will vary from day to day, in light of the
temperature, food they have eaten, and so on.
Questions
B9.07 The reactants in aerobic respiration
are the products of photosynthesis.
The reactants in photosynthesis are the
products of aerobic respiration.
B9.08 every cell
B9.09 During photosynthesis in plants,
chlorophyll captures energy from sunlight
and transfers it to glucose molecules.
Practice questions
1
C[1]
2
C[1]
3
a
glucose + oxygen → carbon dioxide +
water
(one mark for reactants; one mark
for products)[2]
Questions
B9.05 The inner surface of the alveoli is moist.
Water from this surface evaporates and is
breathed out with expired air.
b
B9.06 The percentage is 78%. As nitrogen gas
is not used in the body, the nitrogen
concentration in the blood remains the
same as in the air in the lungs, because
nitrogen molecules diffuse between the air
and blood until equilibrium is reached.
Experimental skills B9.02
1
Look for:
•
axes the right way round, and fully
labelled with units
•
suitable scales on both axes – they should
go up in regular intervals and use at least
half of the grid provided
•
18
clean, clear, ruled lines that join precisely
at the centres of the crosses.
points correctly plotted as small,
neat crosses
4
a
b
Any three from:
•
muscle contraction
•
making protein molecules /
protein synthesis
•
cell division
•
active transport
•
growth
•
passage of nerve impulses
•
maintenance of a constant
body temperature[3]
i
12[1]
ii
0.5 dm3[1]
i
21[1]
ii
1.1 dm3[1]
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c
Any four from:
•
brain senses the pH of blood
•
pH decreases during exercise
•
because more carbon dioxide / lactic
acid is dissolved in the blood plasma
•
brain responds by sending more
frequent nerve impulses to the
breathing muscles (diaphragm and
intercostal muscles)
•
d
Any five from:
•
muscles need more energy
for contraction
•
deeper / more rapid breathing brings
more fresh air into the lungs
•
more oxygen can diffuse into the
blood more quickly
•
5
so they contract harder and
more frequently[4]
more oxygen is supplied to
the muscles
•
so aerobic respiration can
happen faster
•
releasing more energy from glucose[5]
a
5 minutes[1]
b
•during exercise not enough oxygen
was supplied to muscles
•
so they respired anaerobically (as well
as aerobically)
•
producing lactic acid
•
which is broken down by combining
with oxygen (when exercise finished)
•
reference to paying back the
oxygen debt[5]
is that no one has ever responded in less than 0.1 s,
and most reaction times are well above this value.
(If learners research this issue, they will find that
measured reaction times have steadily reduced
since 2004, but this is thought to be a reflection of
changes in the sensors and measuring technology,
rather than in the athletes themselves.)
Questions
B10.01 They have a cell membrane, nucleus,
cytoplasm, mitochondria and ribosomes.
B10.02 They have long, thin fibres of cytoplasm
stretching out from the cell body / they
have a very long axon, along which
impulses can travel long distances quickly.
B10.03 It coordinates electrical impulses
travelling through the nervous system;
it receives impulses from different
receptors and sends impulses to
appropriate effectors.
B10.04 a
in a small swelling just outside the
spinal cord
eyes: light; ears: sound; skin: temperature,
pressure; tongue: chemicals (taste); nose:
chemicals (smell)
Science in context B10.01
in the spinal cord
c
in the spinal cord
B10.05 Sensory neurones have long cytoplasmic
extensions on either side of the cell
body, whereas motor neurones have only
one long extension and relay neurones
have none.
B10.06 There is a very wide variety of possible
answers. Look for genuine reflex actions
that happen automatically, not reactions
that are decided on.
Activity B10.01
1
Divide the time by the number of people, to
find the mean reaction time.
2
People generally respond faster as the
experiment is repeated. This is because
learning is taking place.
3
Usually, the squeeze travels more slowly
when it is sent in the opposite direction.
This is because the people in the circle have
to ‘unlearn’ what they have just learnt and
start again.
Chapter B10
Before you start
b
Reaction times in sprint races have been measured
in thousands of races over the years. The evidence
19
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4
glucose from the blood; some of
this glucose is used for respiration in
liver cells, and some is converted into
insoluble glycogen and stored. This
reduces the concentration of glucose
in the blood.
Answers will depend on the sites that the
learner finds. There is no ‘correct’ answer
to which method is best. We have no way
of knowing whether the time given on the
website is correct or not. However, it is likely
to be very reliable.
d
Questions
B10.07 pancreas: insulin (and glucagon); adrenal
glands: adrenaline; testes: testosterone;
ovaries: oestrogen
B10.08 They travel in the blood plasma, usually
in solution.
B10.09 Any situation in which a person is
frightened or angry – i.e. any fight or
flight situation. Adrenaline is also secreted
when we are nervous, such as before an
interview or examination.
B10.10 It increases breathing rate and heart rate,
which provides more oxygen to muscle
cells so they can release more energy for
contraction, by aerobic respiration. It
makes the pupils wider, to allow more
light into the eyes for better vision of the
perceived danger. It also causes the liver
to release glucose into the blood, allowing
muscles to respire more quickly and
release more energy.
B10.13 Proteins are made by joining amino acids
together on the ribosomes. The process
requires energy, which is provided by
aerobic respiration in mitochondria.
As the islet cells in the pancreas make
a lot of proteins, they need a lot of
these structures.
Practice questions
1
C[1]
2
D[1]
3
a
B10.11 They are made by an endocrine gland
(the pancreas), are transported in the
blood, and affect target organs (in this
case, the liver).
B10.12 a
Her blood glucose concentration
begins at 85 mg per 100 cm3 and
does not change until 20 minutes
after eating. It then rises until
1 hour 20 minutes after eating, to
a maximum of 105 mg per 100 cm3.
After this, it falls until 4 hours after
eating, reaching a minimum of 79 mg
per 100 cm3. Finally, it rises again to
85 mg per 100 cm3 at 5 hours.
b
c
20
It took time for the starch in the
food to be digested by amylase and
maltase, producing glucose. The
glucose then had to be absorbed.
The pancreas detected the increase
in blood glucose concentration and
secreted a hormone called insulin.
Insulin causes the liver to absorb
Blood glucose concentration is
regulated by negative feedback.
The pancreas will not stop secreting
insulin until it detects that blood
glucose concentration levels have
fallen below the ideal concentration.
Then it will release glucagon, which
causes blood glucose concentration to
rise again.
4
i
chemical substance made by a gland;
carried in the blood; which alters
activity of target organs[3]
ii
adrenal (glands)[1]
iii
pancreas[1]
b
the action is slower; the effect
lasts longer[2]
a
i
by amylase; in the mouth; and in
the small intestine / duodenum[3]
ii
b
small intestine / ileum[1]
Any two from:
•
the contents of the cells would
be more dilute than the solution
around them
•
so they would lose water by osmosis
•
metabolic reactions in the cells
cannot take place if they lose too
much water[2]
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c
5
i
pancreas[1]
ii
reduces blood glucose
concentration[1]
a
for respiration; which supplies energy;
for any named process (e.g. active
transport, movement)[3]
b
pancreas[1]
c
i
starch broken down to glucose; by
amylase (and maltase); absorbed into
the blood from the ileum[3]
ii
d
e
6
sensors in pancreas detect blood glucose
concentration; if it is too high, insulin
is secreted and brings the concentration
down; if it is too low, glucagon is secreted
and increases the concentration[3]
water around B’s body warms up
(as heat is lost from his body to
the water)
•
heat transfers from hot object to
colder object
•
more heat lost from A’s body
than B’s body[3]
Chapter B11
Before you start
In the image on the left, the strawberry plant
is producing runners – a method of asexual
reproduction. In the image on the right, the
strawberry plant is producing fruits – a method of
sexual reproduction.
Science in context B11.01
There is a range of answers to this question.
Accept sensible ideas, for example, that there were
no plausible alternative ideas at the time.
c urve rises at same time as original
curve; to a higher level; remains
high for longer[3]
Questions
a
A: 37.4 °C; B: 37.5 °C[2]
B11.02 a
14
b
Any four from:
b
28
c
d
21
used by cells for respiration; insulin
secreted; which causes the liver to
take up glucose; glucose stored in the
liver as glycogen[4]
•
•
homeostasis
•
humans are endothermic / maintain a
constant body temperature
•
body produces more heat to maintain
body temperature
•
reference to shivering
•
reference to vasoconstriction
•
reference to increased metabolism[4]
Any two from:
•
air is more insulating than water
•
heat lost more easily from the body in
water than in air by conduction[2]
Any three from:
•
person A was moving but person B
remained still
•
idea that ‘new’ cold water was
constantly coming into contact with
A’s skin
B11.01 14
B11.03 The flower has brightly coloured petals, to
attract insects. The petals have guide-lines,
to guide the insect to the centre of the
flower. The anthers and stigma are within
the petals. They are arranged so that the
insect has to brush past them to reach the
nectar in the base of the flower.
B11.04 a
The stamens dangle out of the flower,
so that the anthers can swing in the
wind and release their pollen. The
stigmas are feathery and stick out
of the flower, so that they can easily
catch pollen blowing on the wind.
There are no petals to obstruct
the wind or movement of pollen.
b
Wind-pollinated flowers produce
much more pollen than insectpollinated flowers. Their pollen is also
much lighter, so it is more likely to
be floating in the air, where it can be
breathed in by a person.
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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
relatively large
cell
small cell
eggs need to be large to provide space for stored
nutrients; sperm need to be small to reduce the
energy required for swimming
contains stored
nutrients
no stored nutrients
the nutrients in an egg provide for the zygote and
embryo before implantation; sperm use nutrients in
semen (secreted by the prostate gland)
has a jelly coat
no need for a jelly coat
prevents entry of more than one sperm
does not have a
flagellum
has a flagellum,
containing many
mitochondria
sperm cell requires energy for swimming, provided
by aerobic respiration in mitochondria; flagellum
provides propulsion
has an acrosome,
does not have an
containing digestive
acrosome
enzymes
enzymes make a pathway through the egg’s jelly
coat, allowing the sperm head to enter
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
22
1
A[1]
2
A[1]
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3
a
Tube
A
B
C
D
E [2]
Water
✗
✓
✓
✓
✓
Oxygen
✓
✓
✗
✓
✓
Warm
temperature
✓
✓
✓
✓
✗
Light
✓
✓
✓
✗
✓
(all correct for two marks; with one
mistake one mark; with two mistakes no
marks)
b
B and D[2]
c
i
a male nucleus from a pollen grain;
fuses with a female nucleus from
an ovule[2]
ii
4
haploid nucleus, to produce a diploid
zygote when it fuses with a sperm nucleus;
food stores to provide for zygote and
embryo until implantation; jelly coat to
prevent entry of more than one sperm[3]
a
increases from 1990 to 1999; falls from
1999 to 2017; change in figures quoted,
e.g. from 2 million in 1990 to 3.2 million
in 1999[3]
b
b
produces new banana plants that are
identical to the parent (so the bananas
will be exactly the same variety);
predictable yields / flavour / other
named attribute[2]
HIV infection does not produce
symptoms immediately; people can be
infected and not know[2]
c
HIV enters white blood cells /
lymphocytes; destroys them / reduces their
numbers; so immune system cannot attack
pathogens / cancerous cells successfully;
allowing other infections to develop;
increasing risk of cancer developing[5]
d
number of people living with HIV/AIDS
is increasing, but number of deaths from
HIV/AIDS is decreasing; comparative
figures quoted; use of antiretrovirals;
allows people to live normal lives even
when infected; prevents AIDS developing
after HIV infection[5]
all new plants will be genetically identical;
if the parent did not have resistance to the
disease then nor will the offspring[2]
a
pin-eyed has stigma above anthers;
thrum-eyed has anthers above stigma[2]
c
7
c
asexual[1]
b
6
ovule[1]
haploid nucleus, to produce a diploid
zygote when it fuses with an egg nucleus;
acrosome containing digestive enzymes,
to make a pathway into the egg for the
head of the sperm; long flagellum for
propulsion to the egg; many mitochondria
to release energy by aerobic respiration,
for swimming[4]
a
c
5
8
b
i
thorax or mid-section[1]
ii
abdomen or rear section[1]
i
abdomen or rear section[1]
ii
thorax or mid-section[1]
Chapter B12
a
urethra[1]
Science in context B12.01
b
prostate[1]
1
c
testosterone[1]
It is likely that coat colour in the chinchillas is
controlled by genes.
2
Other characteristics of chinchillas, such
as body mass, are likely controlled by
genes but also some environmental factors
– for example, how much food is eaten by
an individual.
a
acrosome
flagellum
nucleus
mitochondrion
cytoplasm
cell membrane
Questions
B12.01 nucleus
[3]
(one mark for any two correct)
23
B12.02 gene; DNA molecule; chromosome;
nucleus; cell
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B12.03 All humans have the same genes (genes
for the same characteristics), but every
individual has a different combination of
alleles of those genes.
B12.13 a
B12.04 32
B12.14 TT
B12.05 This is so that, when the cell divides
by mitosis, each daughter cell gets an
identical set of alleles – so that the new
cells are genetically identical. This is
required for growth, repair of damaged
tissues, replacement of cells and asexual
reproduction.
B12.15 Tt
B12.06 With 46 chromosomes in the cell, there
is a lot of potential for them to become
tangled up together. If the two identical
copies of each chromosome are held
together, it is easier for them to separate in
an orderly way as the cell divides.
B12.07 The new cells produced have a reduced
number of chromosomes (half as many
chromosomes), compared with the
parent cell.
B12.08 14
B12.09 During sexual reproduction, two gametes
fuse – one from each parent – to form
a zygote. If the gametes were formed
by mitosis, they would each have the
diploid number of chromosomes and the
zygote would have double this number of
chromosomes. For the zygote to have the
correct diploid number of chromosomes,
each gamete must have half the normal
number (the haploid number) – so
gametes must be formed by meiosis.
B12.10 a
any upper case and lower case letter
– e.g. B for brown eyes and b for
green eyes
b
T and t
c
t
B12.16 TT and Tt
Activity B12.02
Answers will depend on what was used for the
‘alleles’, and how the learner did their experiment.
For example, perhaps the learner did not pick out
the different beads randomly – maybe one bead
was larger than the other, and more likely to be
picked up.
Questions
B12.17 a
NN normal wings, Nn normal wings,
nn vestigial wings
b
Parents’ phenotypes
normal wings
normal wings
Parents’ genotypes
NN
Nn
Gametes
N
N
n
N
n
NN
Nn
normal
wings
normal
wings
All the offspring would have normal wings.
B12.18 Although the predicted ratio is 3 brown:
1 red, this is only a probability so these
two parents could have three red and two
brown offspring.
Parents’ phenotypes
brown hair
brown hair
Parents’ genotypes
Bb
Bb
B
b
BB brown, Bb brown and bb green
Gametes
c
BB and bb are homozygous, Bb
is heterozygous.
Offspring genotypes
and phenotypes
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,
it is easy to tell the upper and lower case
letters apart.
N
Offspring genotypes
and phenotypes
B
B12.11 The allele for round leaves is dominant,
because this is the phenotype shown by a
heterozygous plant.
24
T
b
b
B
b
B
b
BB
Bb
brown hair
brown hair
Bb
bb
brown hair
red hair
Practice questions
1
B[1]
2
B[1]
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3
4
environment. Genes could determine the
maximum length to which fingers can grow,
while environment could affect whether or not
they reach this potential length.
a
heterozygous[1]
b
phenotype[1]
c
recessive[1]
d
allele[1]
a
i
ee[1]
B13.01 a
ii
EE[1]
b
continuous
c
continuous
d
discontinuous
b
E
e
E
EE
indented
Ee
indented
e
Ee
indented
ee
smooth
Questions
B13.02 a
genes and environment
c
genes and environment
[3]
d
genes alone
(one mark if all offspring genotypes
correct; one mark if phenotypes correctly
matched to genotypes; one mark if
expected ratio of 3 : 1 indented to smooth
is roughly equivalent to the actual
numbers of 302 : 99)
B13.03 a
b
Before you start
A gene is a region of DNA that encodes a protein.
An allele is a particular type of a gene. They are
passed between parents and offspring during the
process of reproduction.
The stichius form of the butterfly imitates the
poisonous common rose swallowtail butterfly,
because predators avoid eating the poisonous
butterfly. This imitation only gives the
mormon butterfly an advantage in areas where
the common rose swallowtail butterfly is
found and predators have learned to avoid it.
In other areas, the bright colouring would be
a disadvantage because it makes the mormon
butterfly more visible.
Female butterflies may carry eggs, and male
butterflies might be more common than females.
Experimental skills B13.01
1, 2 These answers will depend on the
learner’s results.
3
25
Learners should recognise that finger length
could be affected by both genes and the
discontinuous
It is caused entirely by genes.
The recessive allele codes for green
seeds – call it g. The dominant allele
codes for yellow seeds – G. Seeds
with the genotype gg are green
and are therefore homozygous and
pure-breeding. Yellow seeds can be
heterozygous, Gg, and can therefore
produce some yellow and some green
seeds when they are crossed.
B13.04 adiscontinuous; the kernels are either
white or brown.
Science in context B13.01
2
genes alone
b
Chapter B13
1
discontinuous
(Note: learners may see that there are
some dark brown kernels and some
light brown ones, and not be sure
whether to count these as brown or
white. Accept either interpretation.)
b
The ratio of 302 : 99 is approximately
equal to 3 : 1.
c
If learners consider that all the
brown kernels are the same, then
they are likely to suggest that the
allele for white is dominant, and the
allele for brown is recessive. Accept
any symbols that use upper case for
white and lower case of the same
letter for brown – for example, B and
b. The parents could have had the
genotypes Bb and Bb, which would
give a 3 : 1 ratio of white : brown in the
offspring phenotypes.
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B13.05 1 Variation: in the peppered moth
population, most peppered moths
were pale but a few were dark.
2 Overproduction: peppered moths
produce many offspring, most of which
do not survive. Only a small proportion
survive long enough to reproduce.
3 Best-adapted individuals are more
likely to survive and reproduce: when the
environment is polluted, dark moths are
better camouflaged than pale ones on tree
trunks. The pale moths are more likely
to be eaten by birds, while the dark ones
have a better chance of evading capture,
surviving and reproducing.
4 Alleles that confer useful adaptations
are more likely to be passed on: the allele
for dark wings is therefore more likely to
be passed on to the next generation than
the allele for pale wings.
B13.08 a
Choose an individual wheat plant
from a variety that has some
resistance to rust, and another
that has high yield. Transfer pollen
from one to the stigma of the other.
Collect the seeds, sow them and grow
the plants to their full size. Expose
them all to rust, and select those that
are most resistant, and that have the
highest yield, to breed. Continue for
many generations. You could also
bring in new individuals at some
stage, for example a different highyielding parent could be used to breed
with the best rust-resistant offspring
in generation 2 or 3.
b
B13.06 With less air pollution, more lichen grows
on tree trunks. Now pale moths are better
camouflaged than dark moths, so they are
more likely to survive, reproduce and pass
on their alleles for pale wings. Over time,
the pale wing allele gradually becomes
more common in the population of
peppered moths, so most moths now have
pale wings and few have dark wings.
Activity B13.01
1
The reliability of an investigation is improved
by taking repeats. This was done here for the
different types of beak, and also the different
types of food.
2
Answers will depend on the instruments used,
but should focus on the size, the ability to pick
up small objects, and the ability to manipulate
the instruments.
3
B13.07 The breeder should measure the methane
output of all the sheep. Select a female
and a male with low methane output
and breed them together. Measure the
methane output of the lambs and select
a male and a female with the lowest
methane output to breed together.
Continue for many generations.
26
Practice questions
1
D[1]
2
C[1]
3
a
species[1]
b
discontinuous[1]
c
continuous[1]
a
ny two from: mean milk yield increased;
A
no change in the first two years; relatively
steady change from then on; total change
is 366 kg per cow[2]
b
Any two from: select cows that produce
most milk and bulls whose female
relatives produce most milk; breed them
together; select offspring that produce
most milk; repeat for many generations[2]
Answers will depend on the instruments used.
Accept sensible alternatives.
Questions
The rust undergoes natural selection.
There will be variation among the
rust individuals, and some may have
alleles that allow them to infect
the resistant wheat plants. These
individuals have a selective advantage
– they are more likely to survive and
reproduce, as they have access to
more food than the rust individuals
that can only grow on non-resistant
wheat plants. The alleles for the
ability to infect resistant wheat plants
are therefore more likely to be passed
on to the next generation of rust
fungus. Over time, more and more
rust fungi in a population are likely to
have these alleles and be able to infect
previously resistant wheat plants.
4
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with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
c
d
5
breeder can simply choose animals that
produce most milk; selection is done
on phenotype, not genotype[2]
breeder was not selecting for protein
content / perhaps cows that produce
more milk have always had less protein in
their milk[1]
a
Any two from: they rise and then fall;
maximum number is in 2006; overall
change is from about 40 cases in 1993
to about 260 cases in 2012[2]
b
1650 cases out of 2150 = 76.7%[1]
c
Any two of the following pairs
(allow other suitable and biologically
correct suggestions):
•
reducing use of antibiotics – reduces
selection pressure on the bacteria
•
better hygiene when treating patients
/ description of this (e.g. washing
hands more carefully after touching
one patient before touching another)
– avoiding transmission of bacteria
between individuals
•
6
finding new antibiotics that kill
MRSA – so people infected with it
are less likely to die[4]
a
change in base sequence in DNA;
random[1]
b
ionising radiation / named example of
ionising radiation; chemicals / named
mutagenic chemical[2]
Chapter B14
creosote bush
c
primary consumer: kangaroo rat;
secondary consumer: kit fox; tertiary
consumer: coyote
d
Kangaroo rats are herbivores. Kit
foxes and coyotes are carnivores.
e
grasshopper
creosote
bush
kangaroo
rat
tarantula
kit
fox
coyote
jackrabbit
B14.02 Look for a correct and plausible food
chain, with arrows in the correct
direction. Producer, primary consumer,
secondary consumer and so on should be
correctly labelled.
B14.03 Energy is lost to the environment at each
level in a food chain. By the fifth step in
a food chain, there is not enough energy
to support a population of consumers at
this level.
B14.04 People can eat soya beans. A great deal of
energy is lost as it is transferred from soya
beans to cattle, so humans get less energy
by eating the cattle than they would have
done by eating the soya directly. (Some
learners may also appreciate the high
energy costs of transporting the soya
beans to this area, and the difficulties
in supplying water to the cattle in a
desert region.)
B14.05 a
photosynthesis
Science in context B14.01
1
Accept sensible suggestions. These will include
observations of animal behaviour in the wild,
and inspecting the faeces or pellets of animals
to determine what they had eaten.
2
In order to suggest food chains that existed
in communities in the distant past, scientists
would need to judge the behaviour of animals
from their anatomy and body structures, from
the fossil record.
Questions
B14.01 a
creosote bush → kangaroo rat →
kit fox → coyote
27
b
b
respiration and combustion
B14.06 For example: The lion dies. Its body
is decomposed, and some of the
carbon atoms in it become part of the
decomposers. They respire, and some
of the carbon atoms return to the air as
carbon dioxide. This is taken into a grass
plant and used in photosynthesis to make
glucose in the plant cells.
Practice questions
1
B[1]
2
A[1]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
3
a
the transfer of energy[1]
Science in context B15.01
b
grass / ladysmock[1]
c
ladysmock → caterpillar →
robin → kestrel
There are many reasons why it is important to
maintain species diversity and prevent extinction.
Learners might suggest examples relating to
conservation, medicine and the importance of
maintaining existing ecosystems.
or
ladysmock → caterpillar → short-tailed
field vole → kestrel
or
ladysmock → caterpillar → short-tailed
field vole → fox[2]
(one mark for the organisms, one mark
for arrows in the correct direction)
d
4
less grass eaten by voles; so more
food for rabbits and their population
increases; fewer voles for foxes to eat;
so foxes eat more rabbits and the rabbit
population decreases[4]
a
approximately 0.04% (allow 0.03–0.05)[1]
b
stomata[1]
c
photosynthesis[1]
d
decomposition / decomposing[1]
e
respiration[1]
f
Any four from: if there is not enough
oxygen; dead plants and animals do not
decompose; over millions of years, heat
and pressure transform them to fossil
fuels; which contain the carbon from the
bodies of the organisms; when fossil fuels
are burnt, carbon is returned to the air; as
carbon dioxide[4]
Chapter B15
Before you start
There is only one species of plant growing in this
field. Other, wild plants have been either removed
or their growth has been prevented. This means
that animals that feed on other species of plant
will not be able to live there. There are also areas
of bare land between the rows of plants. Perhaps
the land has been treated with pesticides to prevent
other plants (weeds) or animals from growing and
competing with these crops. This has limited the
diversity of the species that can live on this land.
28
Questions
B15.01 Each species has adaptations that increase
its ability to survive and reproduce in its
habitat. If that habitat is destroyed, the
species may not be able to survive and
reproduce in another habitat.
B15.02 Coral reefs and rainforests provide a very
wide variety of different habitats, which
means that many different species can
live there. A monoculture provides a very
narrow range of habitats, so only a few
species can live there.
B15.03 Any five from: reduced biodiversity;
habitat loss; risk of extinction of plant
and animal species; increased soil erosion;
increased risk of flooding; increased
carbon dioxide concentration in the air;
decreased transpiration so less water
vapour in the air
B15.04 Any five from: climate change; habitat
destruction; hunting; pollution;
overharvesting; introduced species (some
learners may also have other suitable
suggestions)
B15.05 The new species may be a predator of
some of the native species, or it may
compete with them for scarce resources,
such as food or nesting sites.
B15.06 Captive breeding is breeding animals in
captivity, such as in zoos. If the captive
breeding programme is successful,
numbers of the endangered species can be
increased. Eventually, it may be possible
to return some of them to the wild.
B15.07 Genetic diversity increases the chances
that a population of organisms will
be able to adapt to changes in their
environment, such as climate change. It
also reduces the chances of two harmful
recessive alleles being brought together in
the offspring of a breeding pair.
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with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
Practice questions
1
A[1]
2
C[1]
3
a
the number of different species
that live in an area[1]
4
ii
Any three from:
carbon dioxide / CO2[1]
•
c
they become endangered (or words
to that effect; accept ‘they could
become extinct’)[1]
idea that you cannot tell she is
pregnant until the 5th / 6th week
of pregnancy
•
concentration of PGFM rises
at week 5
•
can predict birth as likely to
take place three weeks after the
rise begins
•
can predict birth as likely to take
place when the level reaches 1.4
arbitrary units[3]
it increases / is enhanced[1]
a
a species whose numbers have fallen so
low; that it is likely to become extinct[2]
b
5
iso that proper care can be provided;
example of suitable care, for example,
providing a suitable place to give
birth / isolating from other animals /
providing suitable food[1]
b
d
29
b
a
Any three from:
•
loss of habitat
•
people use sandy beaches for pleasure
•
pollution (of the sea or beach)
•
(pollution) could reduce food supply
/ poison the turtles / increase risk
of disease
•
climate change
•
causing sea level rise so beaches now
covered by water
•
turtles do not begin to breed until
they are 30 years old
•
so unable to increase the population
quickly if it starts to fall
•
alternative valid points[3]
Any two from:
•
deforestation
•
use of land for mining
•
use of land for building roads
•
use of land for building homes /
factories
•
pollution[2]
iii
6
Any three from:
•
to prevent closely related animals
breeding together
•
to maintain genetic diversity
•
which reduces chances of
harmful recessive alleles coming
together in offspring
•
increases ability of the
population to adapt to changes
in their environment[3]
store seeds (in controlled conditions) for long
periods of time; maintain a population of a
species that is threatened in the wild; some
(stored) seeds germinated to provide fresh
seeds; collect seeds from different places to
ensure genetic diversity; maintain / increase,
genetic diversity by breeding individuals with
different alleles together (to produce more
seeds for storage); if habitat is restored then
plants can be returned to the wild[6]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
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
Science in context C1.01
1
2
Jupiter and Saturn are the biggest of the
planets in our solar system and are made of
hydrogen and helium in the gaseous state.
There is a progression outwards from the Sun
in terms of the structure of the planets. Those
nearest the Sun are rocky and relatively small;
beyond Mars the planets are gaseous.
Hydrogen molecules are the smallest of all
the elements and therefore the forces between
them are very small. The gas needs to be
highly compressed (so that the molecules are
close together) and at a very low temperature
(so that the molecules are moving slowly) in
order for it to condense into a liquid.
C1.04 aIf iodine is heated strongly then
the temperature rises very quickly.
The melting and boiling points are
close together, so the liquid stage is
not seen as it boils quickly.
b
Experimental skills C1.01
1
Substance B is a pure substance as the curve is
flat while the substance melts. Substance A is
a mixture as there is no single melting point –
that region of the curve is sloped.
2
Take temperature readings at shorter time
intervals (e.g. every 30 s). Using a digital
thermometer would give more accurate
readings. Using a temperature sensor linked
to a computer would allow the readings to be
taken continuously and enable the graph to
be plotted as the readings were being taken.
The samples can be re-heated and cooled
again, allowing duplicate sets of data to
be collected.
Questions
C1.01 a
freezing
b
boiling
c
condensation
C1.02 a
methane
b
Ethanol and mercury; they
have melting points below room
temperature, but boiling points above
room temperature.
c
The impurity alters the freezing point
of the liquid, often meaning melting
occurs over a range of temperatures.
C1.03 aVolatility describes how easily a liquid
evaporates. A volatile liquid is one
that evaporates easily; it has a low
boiling point.
b
c
30
You would need to heat the solid
slowly so that the temperature does
not rise too quickly. You could use an
electric heater to control temperature
more carefully, or you could use an
oil bath to heat the solid and carefully
control the temperature so it is kept
between the melting point (114 °C)
and boiling point (184 °C) of iodine.
Questions
C1.05 A = solid; B = energy released;
C = energy absorbed
C1.06 A = solid; B = liquid; C = liquid and gas
(vapour); D = gas
e thanol > water > ethanoic acid;
ethanol is the most volatile, ethanoic
acid is the least volatile
Experimental skills C1.02
1
silver iodide
; Both the melting point and boiling
B
point are above room temperature;
therefore, it is a solid at room
temperature.
2
silver
potassium
silver
potassium
→
+
+
nitrate
iodide
iodide
nitrate
3
the rates of diffusion of silver and iodide ions
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
4
because the rates of diffusion of the ions are
not the same; silver ions are less heavy and so
diffuse slightly more quickly
5
a
evaporation of the liquid; and
diffusion of the gas particles[2]
b
Particles moved more slowly;
because the temperature was lower.[2]
a
A solid; is cooling down.[2]
b
They are moving more slowly;
and getting closer together.[2]
c
Heat comes from the formation of
bonds (interactive forces) between
the particles.[1]
a
mmonia, which is alkaline, reached
A
the indicator first to change its colour;
because it moved more quickly;
because it was lighter.[3]
b
Around 50 s; Rate of diffusion is inversely
related to the molecular mass; heavier
molecules, such as HCl here, diffuse
more slowly than lighter molecules. [2]
Questions
C1.07 Evaporation of bromine takes place as
molecules escape from the surface of the
liquid. The gaseous bromine molecules
then spread throughout the gas jar
to completely fill the container. This
occurs because the molecules are moving
randomly and there are collisions with air
molecules. Thus, bromine molecules move
from a region of high concentration to low
concentration until they are completely
mixed with the air and at the same
concentration throughout.
C1.08 a
Methylamine molecules have a greater
mass than ammonia molecules and
so diffuse more slowly. The white
smoke ring will be more central than
for ammonia/hydrochloric acid,
slightly to the right of centre as
methylamine diffuses slightly faster
than hydrochloric acid.
b
hydrobromic acid or hydroiodic acid
C1.09 In Figure C1.19a the liquid levels are
the same because there is air both inside
and outside the porous pot cylinder.
In b, hydrogen diffuses into the pot more
quickly than air molecules diffuse out
because hydrogen molecules have less mass
than the air molecules. This produces an
increase in pressure inside the pot and so
the liquid level is pushed down on the left
(and up on the right).
6
7
Chapter C2
Before you start
1
‘H’ and ‘O’ are the chemical symbols for
a hydrogen atom and an oxygen atom,
respectively. Water consists of two hydrogen
atoms chemically bonded to one oxygen atom.
When atoms join together like this, they form
a molecule. A molecule must have more than
one atom in it.
2
You may have heard of protons, neutrons and
electrons; these are subatomic particles, and
they come together to make the many different
types of atom.
Science in context C2.01
Practice questions
1
The rings are made up of carbon atoms
(not many elements can form rings like
this). Carbon is the basis of the molecules
of life because it can form so many
different structures.
2
There are 19 atoms in all (count all the
corners), arranged in five hexagonal rings.
1
D[1]
2
B[1]
3
A[1]
4
a
moving slowly; close to each other[2]
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
31
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
C2.03 An element is a substance that cannot
be broken down into anything simpler
by chemical means. Atoms are the
particles that make up all substances.
An atom is the smallest particle of an
element that shows the properties of that
element. Atoms can join together to make
molecules.
C2.10 6 electrons (the number of electrons
does not change between isotopes of the
same atom)
C2.11 All the atoms of an element contain the
same number of protons (and the same
number of electrons).
C2.12 D
Each element has its own type of atom
and the atoms of an element all have the
same number of protons and electrons.
C2.13 C
C2.04 Protons are positively charged and
would therefore repel each other/the
presence of the neutrons counteracts
this repulsion and means that the nucleus
can hold together.
C2.15 C
C2.14 C
C2.16 a
–
+
F–
Li+
Experimental skills C2.01
1
LiF
b
The metal present is responsible for
determining the colour seen in the flame.
NaBr
–
+
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
which salts you tested.
sodium ion, Na+
c
Questions
KCl
+
C2.05 afirst 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
(positively charged) and 7 electrons
(negatively charged).
C2.07 aA, C: they have 4 electrons in their
outer shells
bromide ion, Br–
potassium ion, K+
–
chloride ion, Cl–
C2.17 A
C2.18 A
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
e
14: the number of electrons must
equal the number of protons in
an atom.
t he number of protons in the nucleus
of an atom[1]
b
mass number is protons + neutrons;
argon has two more neutrons[2]
C2.08 B
C2.09 Cl-35 has 18 neutrons whereas Cl-37 has
20 neutrons.
32
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
because delocalised electrons between
the layers of atoms are free to move.[2]
c
Particle
Charge
Mass
Position
in atom
proton
+
1
in the
nucleus
neutron
0
1
in the
nucleus
Chapter C3
electron
−
1
1840
orbiting
the nucleus
Before you start
b
d
hydrogen[1]
e
They both have full/complete
outer shells.[1]
a
C-14 has more neutrons in the nucleus; it
has 8 neutrons compared with 6 in C-12[2]
There are no right/wrong answers here as the
questions are written by individual learners.
Examples of questions could include: What
compound is represented by H2O? (water) Is CO2
an element or a compound? (compound) What
elements are present in sulfuric acid? (hydrogen,
sulfur, oxygen) Common formulae that they may
come up with that should be checked are O2, CO2,
H2O, NH3, HCl, H2SO4 and HNO3.
b
2,6[1]
Science in context C3.01
c
i
4[1]
1
ii
4[1]
Other costs: energy costs / safety costs in terms
of the physical plant / level of manpower
needed / cost of unwanted by-products.
2
Marketing should consider uses for the byproducts and then convincingly ‘sell’ their
usefulness.
[5]
3
4
It is the outer electrons of an atom that give
rise to its chemical properties. The isotopes
have the same number of electrons in the
outer shell.[2]
5
a
C[1]
Questions
b
The structure shown is of an ionic
compound; potassium bromide is the
only ionic compound in the list.[2]
C3.01 airon + oxygen → iron(III) oxide
6
7
b
sodium
sulfuric sodium
→
+
+ water
hydroxide
acid
sulfate
a
otassium has lost an electron;
P
chlorine has gained an electron.[2]
c
sodium + water →
b
diagram showing 1 shared pair of
electrons between atoms/3 pairs nonbonding electrons on each atom[2]
C3.02 a
2Cu + O2 → 2CuO
b
N2 + 3H2 → 2NH3
c
4Na + O2 → 2Na2O
d
2NaOH + H2SO4 → Na2SO4 + 2H2O
Cl
33
Graphite has layers which can slide
over each other; diamond has a
three-dimensional lattice in which
all the atoms are bonded.[2]
Cl
sodium
+ hydrogen
hydroxide
c
covalent[1]
e
2Al + 3Cl2 → 2AlCl3
d
KCl high melting point/Cl2 low melting
point (or b.p.); OR KCl is a solid at room
temperature and Cl2 is a gas; OR KCl
conducts electricity when dissolved or
molten/Cl2 does not conduct electricity[1]
f
3Fe + 4H2O → Fe3O4 + 4H2
a
raphite has a high melting point because
G
it has strong covalent bonds between the
atoms in the layers/conducts electricity
C3.03 a
H2 + Cl2 → 2HCl
b
2Cu + O2 → 2CuO
c
Mg + ZnCl2 → MgCl2 + Zn
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
C3.04 Solid sodium carbonate reacts with
hydrochloric acid solution to give sodium
chloride solution and carbon dioxide gas.
Water, a liquid, is also produced.
C3.05 a
b
d
e
Ag+(aq) + Cl−(aq) → AgCl(s)
Ba2+(aq) + SO42−(aq) → BaSO4(s)
C3.06 aHCl(aq) + KOH(aq) → KCl(aq) +
H2O(l)
4
C3.07 a
b
covalent
ionic
c
CH4, NaI, C3H6, ICl3, BrF5, HBr
C3.08 a
32
b
17
c
98
d
119
e
188
5
50 cm3 of methane forms 50 cm3 of
carbon dioxide; water condenses at
room temperature and pressure so not
counted; excess of oxygen is 50 cm3
so total is 100 cm3[3]
a
C2H4O[1]
b
88[1]
c
Mg(s) + 2C3H7COOH(aq) →
Mg(C3H7COO)2(aq) + H2(g)[4]
(1 mark for state symbols; 1 mark for
formula of magnesium butanoate;
1 mark for balancing; 1 mark for
correct substances)
0.02 moles
b
2 moles
c
0.07 moles
C3.11 a
36 000 cm3
b
1440 cm3
c
12 000 cm
d
The sum of the relative atomic masses
of the elements in a compound[2]
(1 mark if only the simpler terms,
masses or atomic masses are used)
3
e
Practice questions
magnesium butanoate (or any
ionic compound) is not made up
of molecules and so cannot have a
molecular mass[1]
1
A[1]
2
D[1]
3
a
H3PO4 (order of elements not critical)[1]
b
magnesium carbonate (s) + phosphoric
acid (aq) → magnesium phosphate (aq) +
carbon dioxide (g) + water (l)
Before you start
1
Wiring is most often made of copper (due to
its high conductivity and flexibility).
(1 mark for substances; 1 mark for
state symbols)[2]
2
Wiring is usually covered in plastic coating to
insulate the wires to ensure that the electricity
is conducted to where it is intended to go.
c
24 + 12 + (3 × 16) = 84
(partially correct calculation = 1 mark)[2]
34
volume ratio of propane to carbon
dioxide is 1 : 3; 100 × 3 = 300 cm3[2]
c
C3.09 100
C3.10 a
C3H8 + 5O2 → 3CO2 + 4H2O[2]
(Wrong answer to part a can be carried
through to gain marks here.)
CO2(g)
b
a
(1 mark for correct formulae; 1 mark
for balancing)
2HCl(aq) + CuCO3(s) → CuCl2(aq) +
H2O(l) + CO2(g)
2H+(aq) + CO32−(s) → H2O(l) +
 1.2 
  × 21 = 4.2 g[2]
6
(partial calculation = 1 mark)
H+(aq) + OH−(aq) → H2O(l)
b
the sum of the relative atomic masses of
the atoms present in a ‘formula unit’ of
a substance[1]
Chapter C4
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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3
Liquid metals do conduct electricity. Other
liquids that conduct include molten and
aqueous solutions of ionic substances.
Questions
C4.04 a
ydrogen at cathode and chlorine
h
at anode
b
potassium at cathode and chlorine
at anode
Science in context C4.01
1
Ions within the substances need to be free to
move. In a solid they are fixed in a lattice but
when in solution or molten, the ions are free
to move.
2
Ions are Na+, Cl–, H+, OH–; products are
chlorine, hydrogen and sodium hydroxide, all
of which have industrial uses.
3
(1) makes Al – used in a variety of processes
e.g. in aircraft manufacture
C4.05 Metal is formed at the cathode and a nonmetal at the anode.
C4.06 a
b
C4.07 2H2(g) → 4H+(aq) + 4e−
(3) products of electrolysis all have
applications in fuels (H2) or the
chemical industry.
Practice questions
C4.01 a
i, iii, iv and v conduct electricity.
b
iii and v are electrolytes (aqueous
solutions of ionic compounds).
C4.02 a
b
he ionic solid does not conduct
T
as the ions present cannot move
about (they can only vibrate at
fixed positions).
C4.08 fuel cells: a, d, e; petrol cars: b, c, f
1
C[1]
2
A[1]
3
a
E[1]
b
F[1]
c
D[1]
d
C[1]
a
i
4
5
b
arrows pointing (clockwise) away
from negative and towards positive
terminals of power supply[1]
c
dilute sulfuric acid[1]
d
carbon/graphite or platinum[1]
a
i
Experimental skills C4.01
35
Depends on the equipment available but a
reliable power pack to adjust the voltage
applied is useful / use of an ammeter rather
than a light bulb to detect flow of current.
The electrodes would need to be thoroughly
cleaned with sandpaper / washed in propanone
and then dried / weigh the electrodes on as
accurate a balance as is available.
cathode[1]
ii electrolyte[1]
Melt it or dissolve it in water.
C4.03 W
hen a metal conducts electricity it is
the delocalised electrons present in the
structure that move through the metal to
carry the charge. In aqueous solutions of
ionic compounds it is the ions present that
move to carry the charge.
2
A dark red-brown gas would
be produced at one electrode
(the anode). A ball of molten lead
would be formed in the container/at
the other electrode/at the cathode.
(2) electroplating is used in a wide range
of applications – means products are more
attractive/last longer
Questions
1
2Br−(l) → Br2(g) + 2e−
mass of cathode increases[1]
ii mass of anode does not change[1]
b
the blue colour would fade
to colourless[1]
c
4OH− → O2 + 2H2O + 4e−[2]
(1 mark for correct substances; 1 mark
for balancing)
d
i the anode would lose mass /
copper anode dissolves to form
ions; cathode increases in mass /
copper deposited on cathode[4]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
C5.03 The energy of the reactants is lower than
the energy of the products / upwards
arrow.
e
movement of copper ions; from anode
to cathode[2]
C5.04 Bond breaking is endothermic.
a
produce water as the only product of
reaction rather than NO2 and CO2
which are harmful to the environment[1]
b
any two from hydrogen – large fuel
tank, infrequent filling stations, can be
renewable, expensive; petrol – smaller
fuel tank, frequent filling stations,
not renewable, cheaper; or other
relevant points[2]
Chapter C5
Science in context C5.01
1
2
CFCs were very stable compounds and
were not degraded (broken down) until they
reached the upper atmosphere where they
released chlorine free radicals. These radicals
reacted with the ozone layer protecting
the Earth from harmful UV radiation.
‘Holes’ appeared in the upper atmosphere,
particularly over the Earth’s poles. CFCs were
banned by the Montreal Protocol. CFCs are
also greenhouse gases.
Use of refrigerants greatly improved food
storage and preservation and allowed for
the long-distance transportation of foods.
Air-conditioning made the workplace much
more comfortable in regions of intense or
extreme climate.
Questions
C5.01 an endothermic reaction
Energy / kJ
C5.02 a
Zn(s) + CuSO4(aq)
36
2H2O2
2H2O + O2
Progress of reaction
C5.06 For a reaction to take place, some bonds
in the reacting substances must first be
broken. Bond breaking is an endothermic
process and therefore there is always a
need for some energy to be supplied by the
surroundings to start off a reaction.
Practice questions
1
B[1]
2
Process
Temperature
change
Chemical
or physical
water vapour
changing to
water
increase
physical
salt solution to
salt and water
increase
physical
magnesium plus increase
hydrochloric
acid
chemical
burning
hydrogen to
form water
increase
chemical
iron rusting
increase
chemical
[5]
ZnSO4(aq) + Cu(s)
3
Progress of reaction
b
C5.05
Enthalpy / kJ/mol
6
ii the solution colour would not change /
concentration of copper ions in
solution remains the same[2]
Enthalpy change is shown by
the dotted green arrow. This will
be negative.
a
effervescence/fizzing/bubbles[1]
b
bubbling stops[1]
c
endothermic; because the
temperature goes down[2]
d
exothermic; products have less energy
than the reactants[2]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
C6.06 The rate of reaction slows over time as the
concentration of the reagents decreases.
Enthalpy / kJ
4
N2 + 3H2
Ea
ΔH
C6.07 A catalyst is a substance that speeds up a
chemical reaction but is not itself used up
in the course of the reaction.
2NH3
Progress of reaction
C6.08 The presence of a catalyst decreases the
activation energy of a reaction.
[2]
Chapter C6
Science in context C6.01
1
carbon dioxide + water → glucose + oxygen
The photosynthesis reaction maintains
the level of oxygen in the atmosphere and
removes carbon dioxide. The two biochemical
processes of photosynthesis and respiration
maintain the balance between these two gases
that are important for life. Other important
reactions include those involved in the making
of proteins and the copying of DNA.
2
The key factors in industry are achieving
sufficient product as economically as possible.
The reaction processes used must give a yield
at a reasonable rate as time is an economic
cost. The product must also be achieved in
a system that is safe and environmentally
sustainable.
C6.09 aAn increase in temperature means
that the particles are moving more
quickly and therefore collide more
frequently. When they collide,
more particles have energy greater
than the activation energy so there
will be more collisions that result in
a reaction.
b
There will be more surface area of
the solid exposed so there will be
more frequent collisions between the
reactant particles.
c
Greater concentration means
there are more reactant molecules
present and so there will be more
frequent collisions.
C6.10 a
A, B and D
b
A and B
c
reduction
Practice questions
Questions
1
B[1]
2
a
C6.01 a
physical
b
chemical
c
physical
b
d
physical
20
= 0.67; unit cm3/s[2]
30
c
gas syringe[1]
C6.02 a
exothermic
d
any two from:
b
exothermic
•
increase temperature;
c
exothermic
•
d
endothermic
use smaller pieces of
calcium carbonate;
•
use more concentrated acid[2]
C6.03 A new substance(s) has been formed.
C6.04 a
rate increases
b
rate increases
c
rate increases
3
a
because the reaction is complete
(has stopped)[1]
As the temperature increases the cross is
obscured (becomes hidden) in a shorter
time / the reaction rate increases with
temperature.[2]
C6.05 The reactions that would spoil the food
are slowed down at the lower temperature.
37
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b
4
5
6
As temperature increases, the particles
move more quickly and so collide more
frequently / the particles have more kinetic
energy and so more collisions involve
energy greater than the activation energy /
more collisions produce a reaction.[3]
C7.02 aAn indicator changes its colour
depending on whether it is in an
acidic or alkaline solution.
a
Smaller particles have a larger surface
area; so there are more collisions between
reactant particles[1]
C7.03 pH 1 is more acidic (1000 times more
acidic than pH 4).
b
At higher temperatures, collisions are
more frequent; and a higher proportion
have sufficient energy to produce a
reaction.[2]
a
C[1]
b
B[1]
a
D[1]
b
A[1]
c
C[1]
d
D[1]
Chapter C7
2
Many of these terms come from what
was an impressive age of Islamic science
and mathematics centred around the
Mediterranean (including southern Spain).
Modern terms such as algebra have an Arabic
origin. The period was linked to the practice
of alchemy, which included some truly
experimental science together with the more
mystical aspects and practices.
Strong alkali needs to be removed from
soap because it causes skin burns and can be
particularly dangerous for the eyes. Modern
soaps do have an interestingly wide range of
pH. Most are not actually neutral (pH = 7.0).
It is worth investigating; some are slightly
acidic, while others are mildly alkaline.
Questions
C7.01 aA corrosive substance dissolves or
‘eats away’ other substances.
38
b
citric acid
c
ethanoic acid
i
alkaline
ii
neutral
iii
alkaline
iv
acidic
Experimental skills C7.01
1
You need to consider the effectiveness of the
whole tablet and then the mass of powder
used. You need to work out a value for how
much acid has been neutralised per unit mass
of the tablet.
2
For example:
magnesium hydrochloric magnesium
→
+
+ water
hydroxide
acid
chloride
calcium hydrochloric calcium carbon
→
+
+
+ water
carbonate
acid
chloride dioxide
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
3
Science in context C7.01
1
b
To make the solid more accessible to the acid /
to increase the surface area of the solid and to
speed up the reaction.
Questions
C7.04 a
H2SO4
C7.05 a
iCuO(s) + 2HNO3(aq) →
Cu(NO3)2(aq) + H2O(l)
ii
b
C7.06 a
b
HCl
Zn(s) + 2HCl(aq) → ZnCl2(aq) +
H2(g)
Zn has lost electrons and H+ ions
have gained electrons; Zn atoms have
been oxidised.
blue
b
S(s) + O2(g) → SO2(g)
c
magnesium + oxygen →
magnesium
oxide
C7.07 An amphoteric oxide is one that will
neutralise either an acid or an alkali to
give a salt and water only.
Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) +
3H2O(l)
Al2O3(s) + 2NaOH(aq) → 2NaAlO2(aq) +
H2O(l)
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C7.08 zinc hydroxide or aluminium hydroxide
e
zinc
sodium
sodium
→
+
+ water
hydroxide hydroxide
zincate
Zn(OH)2(s) + 2NaOH(aq) →
Na2ZnO2(aq) + 2H2O(l)
C7.14 a
or
aluminium
sodium
sodium
→
+
+ water
hydroxide hydroxide aluminate
Al(OH)3(s) + NaOH(aq) → NaAlO2(aq) +
2H2O(l)
C7.09 a
nitric acid
c
carbonic acid
C7.10 asodium hydroxide and hydrochloric
acid
b
calcium hydroxide and nitric acid
c
ammonia (ammonium hydroxide) and
sulfuric acid
C7.11 a
b
nitric acid
potassium sulfate and ammonium
nitrate
Experimental skills C7.02
1
copper(II) sulfuric copper(II)
→
+
+ water
oxide
acid
sulfate
CuO + H2SO4 → CuSO4 + H2O
2
c
zinc sulfate
C7.13 ato make sure all the acid is reacted /
used up
39
b
filtration
c
pipette, burette
d
yellow
c
zinc
sulfuric
zinc
→
+
+ water
oxide
acid
sulfate
b
A method in which an acid solution
and an alkali are reacted precisely
to produce a salt solution; the salt
can be crystallised from the solution
produced.
c
An ionic equation includes only those
ions and molecules that actually take
part in the reaction.
b
sodium sulfate
white
Practice questions
1
D[1]
2
a
red[1]
b
calcium carbonate (s) + hydrochloric
acid (aq) → calcium chloride (aq) +
water (l) + carbon dioxide (g)[2]
(1 mark for compounds; 1 mark for
state symbols)
magnesium chloride
calcium nitrate
sulfuric acid
C7.17 a
Questions
b
b
C7.16 A and C / silver iodide and lead(II)
chloride
That the copper oxide was present in
excess / this makes sure that all the acid is
reacted / this is important as the solution is
concentrated by heating after filtration, and
hot, concentrated acid is dangerous.
C7.12 a
method B
C7.15 aPrecipitation is the sudden formation
of a solid when either two solutions
are mixed, or a gas is passed into a
solution.
sulfuric acid
b
If heated too strongly, the salt
could dehydrate (lose water of
crystallisation) or even decompose.
c
carbon dioxide is an acidic oxide
(or simply acidic)[1]
d
test with universal indicator; note
colour change; compare with colour
chart to find pH value[3]
3
B[1]
4
a
sodium chloride; sodium too reactive
and so unsafe[1]
b
sodium chloride[1]
c
barium sulfate[1]
d
potassium carbonate[1]
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5
a
bubbles / effervescence / fizzing[1]
b
to ensure all the sulfuric acid was
reacted / used up[1]
c
fizzing would stop, or excess solid
remains[1]
d
filter; heat to crystallisation point;
separate/dry crystals[3]
6
copper carbonate[1]
7
a
lead nitrate; sodium, potassium or
other soluble chloride[2]
b
mix solutions of the substances;
filter and keep the residue; wash the
residue; dry the residue[4]
white solids, transition metal compounds
are coloured / alkali metals have relatively
low melting and boiling points, transition
metals have high melting and boiling
points; alkali metals are highly reactive,
transition metals are less reactive.
C8.07 D
Practice questions
1
D[1]
2
B[1]
3
a
iodine[1]
b
lithium[1]
c
bromine[1]
d
potassium; chlorine[2]
a
high densities[1]
b
metals[1]
c
Group VIII / noble gases[1]
Chapter C8
Science in context C8.01
1
2
Discuss the historic social and religious
attitudes to the role of women in society in
different parts of the world – their role and
access to education; and opportunity to
pursue an independent career.
Consider the modern situation in different
cultures and the development of attitudes,
opportunities and perceptions.
4
Chapter C9
Science in context C9.01
1
The metallic nodules are rich in the metals
in demand and it would be relatively easy to
extract the required metals. There are various
different sites in different regions of the ocean
floor. The damage to the ocean floor itself
through what is effectively open-cast mining
would be significant, as would the damage to
the habitat of marine species about which we
know relatively little.
2
The dependence on a single land-based source
is open to political and economic dangers.
It could lead to exploitation of the local
population and create socio-economic tensions.
Questions
C8.01 potassium hydroxide
C8.02 lithium + water →
lithium
+ hydrogen
hydroxide
C8.03 aapproximately 40 °C (note that the
difference between one element and
the next is getting smaller as we go
down the group)
b
Rubidium will react more strongly
with water than potassium.
C8.04 chlorine (of the options available in a
school lab); also fluorine
C8.05 They all have 8 electrons in their outer
shell, except for helium in the first period,
which has the maximum possible of 2.
They all have a full outer electron shell.
C8.06 Any four from: alkali metals are soft,
transition metals are hard / alkali metals
have low density, transition metals have
high density / alkali metal compounds are
40
Questions
C9.01 acan be beaten into sheets / conducts
heat well / conducts electricity well /
can be drawn into wires
b
C9.02 a
b
is an insulator / poor thermal
conductor
graphite
any two group I metals, e.g. lithium,
sodium, potassium, etc.
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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
that observed when zinc reacts with copper(II)
sulfate solution.
2
Carry out the experiments in polystyrene
cups or wrap the boiling tube in cotton wool
to prevent heat loss / take more frequent
temperature readings to find the maximum
temperature reached more accurately.
C9.03 All metals conduct electricity, while nonmetals do not (except graphite); metals are
malleable and ductile while non-metals are
not; metals are good conductors of heat
while non-metals are not (except diamond.
Metals are formed from layers of positive
ions, surrounded by a ‘sea’ of delocalised
electrons. These mobile electrons can move
through the structure, allowing metals
to conduct electricity. The attraction
between the positive metal ions and the
free electrons (metallic bonding) acts in
all directions, so the layers of positive ions
can slide over each other without breaking
the overall structure. This is why metals
are malleable and ductile.
C9.04 B
metal
+ hydrogen
hydroxide
metal
+ hydrogen
oxide
b
metal + steam →
c
i
Mg + H2O → MgO + H2
ii
3Fe + 4H2O → Fe3O4 + 4H2
C9.07 a
b
D
brass (or steel)
C9.08 aany two from iron, chromium and
nickel
b
C9.12
magnesium+
copper(II) magnesium
→
+ copper
sulfate
sulfate
C9.13 Magnesium becomes coated with a
layer of copper / the colour of the blue
solution fades.
C9.14 Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s)
C9.05 copper and silver
C9.06 a
metal + water →
Questions
hardness and corrosion resistance
C9.09 D
Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)
C9.15 This question is speculative – look at the
first letters of the metals in order and see
if you can think of a phrase or sentence!
C9.16 water and air (oxygen) / salt water or
acid rain
C9.17 painting / oiling / greasing / coating with
plastic
C9.18 Zinc is more effective because if the
surface layer is broken the zinc will still
protect the steel beneath as it is more
reactive than iron (sacrificial protection)
/ chromium will not protect if the layer is
broken as it is less reactive than iron.
hydrogen
Experimental skills C9.02
b
potassium hydroxide
1
The formation of red–brown copper metal.
c
sodium+ water →
2
2CuO + C → 2Cu + CO2
d
2K + 2H2O → 2KOH + H2
C9.11 a
strong and has a low density
C9.10 a
b
c
sodium
+hydrogen
hydroxide
Aluminium is coated with a very
thin oxide layer that protects it from
corrosion.
copper
Questions
C9.19 To combine with the silicon(IV) oxide
(sand/silica) and remove it as slag:
CaCO3(s) → CaO(s) + CO2(g)
C9.20 carbon monoxide
iron(III)
carbon
carbon
→ iron +
+
oxide
monoxide
dioxide
Fe2O3 + 3CO → 2Fe + 3CO2
41
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C9.21 silicon(IV) + calcium → calcium
oxide
oxide
silicate
SiO2 + CaO → CaSiO3
7
1
D[1]
2
C[1]
Property
Applies Applies to
to most most nonmetals metals
they conduct
electricity
✓
they react with
oxygen in the air
✓
they are brittle
✓
they have high
melting points
✓
5
6
a
aqueous copper sulfate or copper sulfate
solution[1]
b
iron[1]
c
Cu(s) + 2AgNO3(aq) →
Cu(NO3)2(aq)+ 2Ag(s)[3]
d
Copper becomes coated with silver
coating; solution changes from
colourless to blue.[2]
e
Zinc is more reactive than copper.[1]
8
a
hematite[1]
b
carbon monoxide[1]
c
because of the high temperature in
the furnace[1]
d
calcium oxide/calcium carbonate; reacts
with impurities/silica/silicon(IV) oxide in
the ore[2]
a
the air[1]
a
its low density[1]
b
its resistance to corrosion[1]
c
alloy; conductor; metal; mixture[4]
d
any two from: it does not rust/corrode;
it is an alloy containing chromium and
nickel; it is harder than pure iron[2]
b
It produces the heat needed in the furnace;
the carbon dioxide is then reduced in the
furnace to give carbon monoxide.[2]
a
Layers of atoms / ions can slide over
each other.[1]
c
b
The larger atoms prevent layers
sliding over each other.[1]
It reacts with the silica (silicon dioxide)
impurity in the ore; forming calcium
silicate slag[2]
10 a
c
Yes; electrons are still free to move
around/between the metal ions.[2]
stops air/water reaching the metal;
so rusting cannot occur[2]
b
galvanisation[1]
a
bubbles / fizzing / effervescence;
zinc dissolves as it reacts[2]
c
still protects even if the zinc layer is
scratched or broken[1]
b
no reaction[1]
d
c
iron, zinc, unknown metal, calcium[2]
the zinc or magnesium is more reactive
than iron; these metals lose electrons/
form positive ions more readily than iron;
so they are corroded rather than the iron /
sacrificial protection[3]
(one out of order = 1 mark)
42
burning splint; pops[2]
✓
[6]
4
e
(1 mark for substances; 1 mark for
balancing; 1 mark for state symbols)
✓
they can easily be
bent and shaped
aluminium[1]
(glowing splint pops = 1 mark)
Practice questions
3
d
9
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Chapter C10
Science in context C10.01
1
Possible reasons include population density
(the greater the number of people, the higher
the levels of pollution will tend to be),
presence of particular types of industry (living
closer to large factories will generally mean
poorer air quality), impact of events such as
forest/bush fires, government initiatives to
reduce levels of airborne pollution, etc.
2
Factors that might encourage more
environmentally friendly options include
education (an understanding of the problems
caused to the environment), tax incentives
(reducing the cost of more environmentally
friendly solutions), cost savings (switching
off electrical equipment when not in use is
both good for the environment and saves
money), etc. Factors that might prevent more
environmentally friendly options include cost
(too expensive), habit (used to always using
the car / not walking), inconvenience (easier
to drive on a wet day than walk), lack of
education, etc.
Questions
C10.01 nitrogen 78%, argon 0.9% and oxygen
21%
C10.02 Harmful to life both on land and in the
water / increased acidity levels in lakes
can kill fish and other aquatic life / can
kill forests (many plants are extremely
sensitive to pH) / some building
materials will be damaged/corroded.
methane+ oxygen →
C10.03 a
carbon
+ water
monoxide
b 2C6H14 + 13O2 → 12CO + 14H2O
C10.04 Oxides of nitrogen are formed when
nitrogen and oxygen from the air react at
a high temperature (e.g. in a car engine).
They are linked to the formation of acid
rain and photochemical smog.
C10.05 2CO + 2NO → 2CO2 + N2
C10.06 Carbon dioxide: product of the
combustion of fossil fuels. Methane:
waste product from livestock (cattle) and
landfill sites.
C10.07 Increased use of fossil fuels.
43
C10.08 Rising sea levels so increased flooding
and faster rates of coastal erosion /
changes to the life cycles and migratory
patterns of animals and birds / more
severe droughts and crop failure / drying
out of grasslands increases the frequency
and severity of wildfires / more frequent
and severe weather patterns, with
associated problems such as flooding
and landslides / bleaching of coral reefs
and loss of marine life.
Strategies include reducing use of fossil
fuels for transportation and electricity
generation (e.g. by using renewable
sources of energy such as wind and
solar) / phasing out of diesel and petrol
cars and replacing with electric or
hydrogen-powered cars / removing CO2
from the atmosphere / reducing meat
consumption / improving separation of
household waste / planting more trees.
C10.09 Greenhouse gases absorb and re-emit
the longer wavelength radiation reflected
from the Earth’s surface.
C10.10 Cobalt chloride paper: colour change
from blue to pink. Alternatively,
anhydrous copper(II) sulfate: colour
change from white to blue.
C10.11 Measure melting or boiling point. For
pure water, the melting point is 0 °C and
the boiling point 100 °C.
C10.12 Microplastics removed by filtration
using a fine sand filter. Dissolved organic
compounds removed by an activated
carbon filter. Microbes removed by
disinfection using chlorine.
Practice questions
1
C[1]
2
B[1]
3
a
78%[1]
b
any two from argon, carbon dioxide, other
noble gases (neon, krypton and helium)[2]
c
i
B[1]
ii
A[1]
iii
C and D[2]
iv
C[1]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
4
a
b
c
5
oxides of nitrogen and sulfur cause
acid rain; this increases acidity of
lakes / rivers[2]
C11.02
inot enough oxygen / air for
complete combustion[1]
H
ii
methane
Carbon monoxide is toxic to humans
because it binds very strongly with
haemoglobin in red blood cells,
preventing them from carrying
oxygen around the body.[1]
desulfurisation / scrubbing; using
calcium oxide[2]
d
the air[1]
a
CO2 is produced from burning of fossil
fuels; needs to be reduced to reduce global
warming / reduce any sensible effect of
global warming[2]
b
methane; livestock or decomposition in
landfill sites[2]
c
They are greenhouse gases; allow short
wavelength energy from the Sun to reach
the Earth’s surface; but trap and re-emit
longer wavelength radiation reflected from
the Earth.[3]
Chapter C11
Science in context C11.01
1
2
The advantages of a space elevator are seen
in terms of the ease of transfer of astronauts
and goods to the space station without the
need for rocket launches from the Earth.
Subsequent exploration from the space
station would also be easier since there would
be no need for the technology to escape the
Earth’s gravity.
These different forms of carbon all conduct
electricity because of the mobile, delocalised
electrons associated with their layered
structure (see Chapter C2).
Questions
C11.01 methane, ethane, propane, butane / CH4,
C2H6, C3H8, C4H10
44
H
C
H
H
H
H
H
H
H
C
C
C
C
H
H
H
H
H
butane
C11.03 a
propane + oxygen →
carbon
+ water
dioxide
b C3H8 + 5O2 → 3CO2 + 4H2O
C11.04
H
H
C
C
H
H
C11.05 The bromine water is decolourised
from orange–brown to colourless.
There would be no change if ethane was
bubbled through bromine water. The test
is for unsaturation (a carbon–carbon
double bond): ethene is unsaturated,
but ethane is saturated.
C11.06 C2H 4Br 2
H
Br
Br
C
C
H
H
H
C11.07 ethane → ethene + hydrogen
C2H6 → C2H4 + H2
C11.08 a propene + hydrogen → propane
b C4H8 + H2O → C4H9OH
C11.09 a CH3CH(OH)CH3
b CH3CH=CHCH3
C11.10 Structural isomerism is a property
of compounds that have the same
molecular formula but different
structural formulae; the individual
compounds are known as structural
isomers.
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
C11.11 There is a steady increase in the boiling
point of the alcohols with increasing
number of carbon atoms.
C11.18 a
C11.19 a
150
Boiling point / °C
C11.20 a
100
50
C11.21
0 1 2 3 4 5 6
Number of carbon atoms
C11.12 a a carbon–carbon double bond, C=C
b –OH (a hydroxyl group)
C11.13 a C2H4
b as in Figure C11.06
C
CH3 n
H
Cl
H
H
H
H
H
H
C
C
C
C
C
C
H
C
H
high pressure
heat, catalyst
H
H
C
C
H
H
poly(ethene)
n
C6H5 H
C6H5 H
The monomers join together by a
reaction in which a small molecule
(usually water) is eliminated each
time a link is made.
nylon; the amide link
(or peptide link)
O
O
C
C
N
N
H
H
O
O
C
C
N
N
H
H
C[1]
3
a
a compound that contains carbon
and hydrogen only[1]
b
no colour change / orange–brown colour
remains[1]
c
Ethene and steam are compressed
to 6000 kPa and passed over a
phosphoric acid catalyst at 300 °C.[3]
d
as a fuel; as a solvent[2]
e
(addition) polymerisation[1]
a
C[1]
b
A and E[2]
c
a carbon–carbon double bond, C=C[1]
d
molecule must contain at least one
carbon–carbon double or triple bond[1]
e
C3H6[1]
C11.16 refinery gas, petrol, naphtha, diesel,
bitumen
C11.17 Addition polymerisation takes place
when many molecules of an unsaturated
monomer (e.g. ethene) join together to
form a long-chain polymer.
n
2
C11.15 bitumen: road surfacing; diesel: fuel
in diesel engines; naphtha: chemical
feedstock; gasoline: fuel in cars
45
C
B[1]
c propanol
ethene
C
1
b propene
H
H
H
Practice questions
C11.14 a butane
C
C
b
H
C6H5 H
b
n
H
a carbon–carbon double bond
b
H
H
4
5
–40 °C[1]
6
a
bitumen[1]
b
bitumen[1]
c
petrol (gasoline)[1]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
7
a
hydrocarbons[1]
b
different boiling points[1]
c
jet fuel (or heating systems)[1]
d
i
heat / catalyst[2]
ii
hydrogen[1]
e
The larger error is in the mass. Random
errors could be reduced by repeating
the experiment several times, checking
for and removing anomalies and then
calculating a mean average.
C10H22 → C4H8 + 2C3H6 + H2[2]
Chapter C12
Experimental skills C12.01
Science in context C12.01
1
residue
2
It will enable the material to dissolve
more quickly.
3
Salt is ionic and dissolves well in water. If the
solution is concentrated by heat, then the
excess solid can be crystallised out. This would
not be a good method for producing iodine
crystals for several reasons. Iodine is toxic
and, unlike sodium chloride, it has covalent
rather than ionic bonding so it is only partially
soluble in water.
1
2
Portable distillation units. Strengths: provide
access to distilled water in remote areas
without need for large/expensive equipment
/ may be powered by renewable sources.
Weaknesses: if using solar power, the unit
will only operate under certain conditions /
produce limited amounts of clean water / may
be limited access to replacement parts if there
is a failure / would need to be very robust if
used in the field / may require training in safe
use / could be expensive.
Desalination units. Strengths: provide access
to drinking water in areas with access to
seawater but limited freshwater / can be run
continuously / proven technology. Weaknesses:
may be limited access to parts if there is
a failure / the waste product can be toxic
to marine and coastal ecosystems / energy
intensive as require high temperature and
pressure / require training / could be expensive.
The filter straw needs to remove particles of
sand/silt/mud and harmful microbes such as
bacteria that can cause disease.
Experimental skills C12.02
1
boiling points
2
100 °C
3
Distillation involves heating the liquid so
that components start to evaporate. As they
evaporate, they travel up through the
apparatus and into the condenser. In the
condenser the temperature is lower and so
the gas will condense. Different fractions
separate at different temperatures due to
differences in their boiling points.
Questions
Questions
C12.01 The temperature should be recorded
either with a thermometer or a digital
temperature probe and meter. The
volumes could be measured with a
measuring cylinder or, for greater
accuracy, a fixed volume could be
measured using a volumetric pipette and
a variable volume by use of a burette.
C12.02 The teacher was not correct. The data
have a narrow spread of results and
so are precise; however, they are not
accurate as the average of these results is
not very close to the true value.
46
0.1
× 100% = 7.7%
1.3
0.5
Error in volume is
×100% = 5.0%
10.0
C12.03 Error in the mass is
C12.04 The ink in this pen is a mixture of at
least two different dyes.
C12.05 A substance that remains on the baseline
is insoluble in the solvent used. To
improve the experiment the learner
needs to use an alternative solvent, e.g.
ethanol instead of water.
2.3
= 0.82 (to 2 d.p.)
2.8
distance moved by sample
Rf =
distance moved by solvent front
C12.06 Rf =
Distance moved by sample = Rf ×
distance moved by solvent front
Distance moved by sample = 0.82 × 9.7
= 8.0 cm
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with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
Experimental skills C12.03
Questions
1
C12.11 Iron(II) chloride would initially produce
a green precipitate. Iron(III) chloride
would produce a brown precipitate.
Step a: The baseline needs to be drawn in
pencil, not pen, as the ink in the pen could be
soluble. If the ink used to mark the baseline is
soluble, it will also rise up the paper and affect
the results of the chromatogram.
Step c: The solvent level should fall between
the bottom of the paper and the baseline; if it
covers the baseline, the samples will dissolve
into the solvent and not travel up the paper.
Step d: The solvent should not travel all the
way up but must be stopped just before it gets
to the top of the paper. If this is not done, then
samples will continue to travel up the paper.
2
To reduce the amount of solvent lost through
evaporation.
Questions
C12.07 The nichrome wire probe is cleaned by
placing it alternately in a roaring flame
and in concentrated acid. Once clean,
it is dipped in the acid and then into
the sample containing the sodium ions.
Finally, the wire is held in a roaring
Bunsen flame. A yellow flame indicates
the presence of sodium ions.
C12.08 The lilac flame indicates the presence
of potassium ions. Potassium sulfate
is K2SO4.
The red flame indicates the presence of
lithium ions. Lithium sulfate is Li2SO4.
The blue-green flame indicates the
presence of copper ions. Copper sulfate
is CuSO4.
C12.09 C and E
C12.10 The use of state symbols in C shows
that this is a precipitation reaction,
producing solid copper(II) hydroxide.
Experimental skills C12.04
47
1
A precipitate is an insoluble compound/salt
produced during a precipitation reaction (a
reaction that produces an insoluble salt when
solutions of two soluble salts are mixed).
2
Iron(II) precipitates are green in colour;
iron(III) precipitates are brown in colour.
3
Ammonia is a base/an alkali.
C12.12 When sodium hydroxide solution is
added to copper(II) sulfate solution, a
light blue precipitate is formed. When
dilute ammonia solution is added to
copper(II) sulfate solution, a light blue
precipitate is formed at first, but as more
ammonia solution is added this dissolves
to produce a dark blue solution.
C12.13 All acids release H+ ions in solution,
and these ions react with carbonate ions
to produce carbon dioxide and water.
In general, therefore, the reaction of
a carbonate with any acid produces
carbon dioxide. Sodium carbonate
solution reacts with acids as follows:
Na2CO3(aq) + H2SO4(aq) → Na2SO4(aq)
+ CO2(g) + H2O(l)
Na2CO3(aq) + 2HCl(aq) → 2NaCl +
CO2(g) + H2O(l)
Na2CO3(aq) + 2HNO3(aq) →
2NaNO3(aq) + CO2(g) + H2O(l)
C12.14 Acidified silver nitrate would produce a
cream precipitate with the magnesium
bromide and a white precipitate with the
magnesium chloride.
MgBr2(aq) + 2AgNO3(aq) →
Mg(NO3)2(aq) + 2AgBr(s)
MgCl2(aq) + 2AgNO3(aq) →
Mg(NO3)2(aq) + 2AgCl(s)
C12.15 This would negate the results as the
sulfuric acid introduces sulfate ions and
so a white precipitate of barium sulfate
is immediately produced.
C12.16 Al → Al3+ + 3e−
C12.17 a Carbon dioxide was present.
b Ca(OH)2(aq) + CO2(g) → CaCO3(s)
+ H2O(l)
C12.18 The gas is not carbon dioxide and it is
not oxygen.
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
C12.19 The pieces of glassware are a volumetric
pipette that adds an accurate, fixed
volume of liquid and a burette, which
adds an accurate but variable volume
of liquid.
Other valid methods should also
be accepted.[6]
4
C12.20 Methyl orange and thymolphthalein
both produce clear colour changes at the
end-point, universal indicator does not.
C12.21 Swirling ensures everything is mixed
and also ensures liquid that might have
splashed onto the sides of the flask is
returned to the reaction, so the reaction
is complete.
C12.22 The mean titre would only use the
results within 0.10 cm3: i.e. mean titre =
(12.15 cm 3 + 12.10 cm 3 + 12.10 cm 3 )
=
3
12.12 cm3
Practice questions
1
C[1]
2
a
tripod; and evaporating dish/basin; (the
arrow also suggests a Bunsen burner)[2]
b
blue[1]
c
because copper oxide reacts with acid[1]
3
5
to be able to measure the volume
of the gas[1]
b
fully open the air hole at the base of
the chimney[1]
c
when crystals form around the edge
of the solution / when crystals form on the
stirring rod[1]
D[1]
6
Salt
Slowly adding
excess aqueous
sodium
hydroxide
Adding
acidified
silver
nitrate
potassium lilac
sulfate
colour
no reaction
no
reaction
copper
bromide
blue–
green
colour
light blue
precipitate
formed
cream
precipitate
lithium
iodide
red
colour
no reaction
yellow
precipitate
7
a
add aqueous sodium hydroxide or
aqueous ammonia slowly until in
excess; green precipitate which does
not redissolve[2]
b
add acidified barium nitrate;
white precipitate[2]
A maximum of 6 points from: Common
starting process:
•
crush lump of malachite
•
with a pestle and mortar
Flame
test
[5]
Processes in method 1:
48
a
(These two tests can be given in either order.)
•
dissolve in acid
•
named acid
•
filter
•
electrolyse filtrate
•
recover copper from cathode
8
A maximum of 6 points from:
•
a dd named volume of first vinegar
to a flask
•
add a named indicator (methyl orange
or thymolphthalein)
•
slowly add from a burette
Processes in method 2:
•
named alkali
•
heat crushed powder
•
note volume needed for neutralisation
•
to form copper oxide
•
•
heat with charcoal
repeat with same volume of second
vinegar
•
wash with dilute acid
•
•
filter and dry
larger volume used (titre) = more
concentrated acid[6]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
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
•
Use a ruler to make the measurements and
multiply to find the volume.
•
Divide the thickness by the number of sheets.
•
Use a piece of thread to follow the journey on
the map, then measure the length of the string
using a ruler.
•
Fill the cup with liquid and then pour the
liquid into a measuring cylinder.
•
Suspend the bag from a newtonmeter.
•
Pull a block across each surface using
a newtonmeter.
P1.02 a•Fill a measuring cylinder with
enough water that it will cover
the steel block and the block of
wood but not overspill.
•
Gently immerse the steel block
and record the reading on the
measuring cylinder. Raise the
steel block and allow any drips of
water to fall into the measuring
cylinder. Gently place the
wooden block into the measuring
cylinder. Lower the steel block
to immerse both the wooden and
metal blocks.
•
Record the new reading on the
measuring cylinder.
•
Subtract the smaller reading from
the bigger reading to find the
volume of the wooden block.
Science in context P1.01
1
Time
Time / s
Spanish
ship
3 years
94 608 000 0.42
Jules Verne
story
80 days
6 912 000
5.79
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
Atlantic
GlobalFlyer
3 days
259 200
154.32
2
Hypersonic
jet
6.5 hours
23 400
1709
13.5 g/cm3. This is much higher than the
density of most liquids. Mercury is unusual
because it is a metal which is liquid at
room temperature.
2
Speed
/ m/s
If it travelled a longer route than the winner.
In this race, the boats need to find wind, so do
not necessarily follow the shortest route.
b
P1.03 a
0.1 mm
b
3118.5 cm3 (or 3100 cm3 to 2 s.f.)
Questions
P1.04 a
4 g/cm3
b
1.43 × 10−3 m3
P1.01 a
2 cm, 4.5 cm and 1 cm
c
1958 kg/m3
9 cm3
b
40 000 kg
P1.05 a
0.215 m, 0.1025 m, 0.065 m
Questions
b
P1.06 a
9.71 × 10−2 g
b
49
18 cm3
0.22 cm3
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
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
(1.0 g/cm3) so a match will float.
P1.12 a
C
P1.07 50.4 mm3
P1.14 a
114.3 km/h
Runner
b
Time on
digital
clock
Time on
analogue
clock
A
9.87 s
10
B
10.34 s
10
P1.16 8 minutes
C
10.01 s
10
P1.17 a400
b
P1.09 a
Any random error with starting or
stopping the stopwatch would be
divided by 20.
Length
of string
/m
Time for 20 Time for 1
oscillations oscillation
/s
/s
0.00
0.0
0.20
0
20
40 60 80 100
Time / s
100 seconds
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
0.80
39.4
1.970
b
5.0 km/h
1.00
40.5
2.025
c
2
1.20
44.4
2.220
d
1.40
47.9
2.395
between C and D (between 5 p.m.
and 5.30 p.m.)
e
between E and F (between 6 p.m. and
7 p.m.)
f
6.15 km/h
g
10 km/h between B and C
How period of oscillation varies
with length of oscillator
P1.19 a
1 m, or correct reading from
student’s graph
Distance / km
0.
80
0
1.
00
0
1.
20
0
1.
40
0
1.
60
0
60
0
40
0
0.
0.
00
60
0.
2
0.
0
c
00
0
Period of
oscillation / s
100
0.000
Length of string / m
50
40
30
20
10
P1.10 a
10.44 m/s
50
200
400 m
2.50
2.00
1.50
1.00
0.50
0.00
b
300
b
c
d
31.7 m/s
P1.15 5.36 × 1011 m = 5.36 × 108 km =
536 million km
All three runners record the same
time on the analogue clock, so the
winner cannot be determined.
b
B
P1.13 300 m/s
Distance travelled / m
P1.08 a
b
0
He started from rest and had to
accelerate, so he ran slower than his
average speed which means he must
also have run faster.
b
0
10 20 30 40 50 60 70 80
Time / min
Average speed = 72 km/h
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
P1.20 20 km/s
c
16 + 48 = 64 m
P1.21 2.1 m/s2
d
s = (u + v)t = (12 + 20) × 4 = 64 m
P1.22 0.2 m/s2
b
A, C, G
c
F
d
E
driver applies brakes
20
Speed / m/s
driver sees hazard
25
Speed / m/s
A = bh = 0.7 × 20 = 14 m
25
P1.24
20
15
10
5
0
15
constant deceleration
10
car stops
5
0
1
2
P1.27 a
P1.23 a
B, D, H
0
1
2
1
0
1
gradient =
2 3 4
Time / s
=
2 3 4
Time / s
A = 12 bh
= 12 × 3.3 × 20 = 33 m
vertical height
horizontal width
–20 m/s
3.3 s
= –6.1 m/s2
P1.25 a, b
A = 12 bh = 12 × 5 × 6 = 15 m
b
6.1 m/s2 (see calculation above)
c
thinking distance = 14 m;
braking distance = 33 m;
stopping distance = 47 m
(see calculation above)
Speed / m/s
12
10
A = bh = 5 × 12 = 60 m
8
Mass
Weight
6
scalar
vector
4
unit = kilogram
unit = newton
measure of the
amount of matter
in a body; does
not change
with position
value depends
on local value of
acceleration due
to gravity
measured with a
(top-pan) balance
measured with a
newton meter
A = bh = 5 × 6 = 30 m
2
0
0
2
4 6 8
Time / s
10
c
Total distance = 105 m
P1.26 a, c
P1.29 a
mass = 1 kg; weight is less than 9.8 N
Speed / m/s
25
b
20
A = 12 bh = 12 × 4 × 8 = 16 m
15
A = bh = 4 × 12 = 48 m
5
51
mass = 1 kg; weight is greater than
9.8 N
P1.30 ai
10
0
P1.28
0
1
2 3 4
Time / s
b
a=
v − u 20 −12
=
= 2 m/s2
t
4
686 N
ii
70 kg
iii
10.12 N
iv
5000 kg
v
7.69 × 10−3 N/kg
b
always the same
c
The force of gravity is much
(15 033 times) greater on Jupiter.
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P1.31 a
unbalanced; 20 N to left;
accelerate to left
18
balanced; no acceleration
16
c
unbalanced; 50 N downwards;
accelerate downwards
14
P1.32 a
500 N
b
1.6 m/s
c
22 000 kg
d
0.15 N
P1.33 a
23.52 N
b
23.52 N
c
Load / N
b
2
12
10
8
6
4
same; weight is a force
2
P1.34 66.7 m/s2
0
Experimental skills P1.03
0
0.05
Getting started
1
a
to stop the apparatus toppling
b
to ensure the ruler is vertical
2
100 g = 1 N
3
independent: load applied, dependent: extension
1
The line should pass through the origin.
P1.41 a
bigger
2
Where the force is proportional to the
extension, the graph line is straight. Beyond
the limit of proportionality, load and
extension are not proportional and the line is
no longer straight.
4
No, once the spring was stretched beyond
the limit of proportionality it remained
longer than its original length once the load
was removed.
Questions
P1.35 22 cm
52
P1.39 moment of a force (Nm) = force (N) ×
perpendicular distance from pivot to
force (m)
P1.40 a
50 cm
Values will depend on the learner’s results.
b
further from
c
90°
P1.37 35 N
P1.45 3.3 m
P1.38
Load / N Length / m Extension / m
Activity P1.02
0.0
1
2.6
1.422
0.026
5.3
1.448
0.052
7.9
1.475
0.079
10.6
1.501
0.105
13.2
1.536
0.140
15.9
1.579
0.183
15 Nm
P1.43 A longer spanner will allow them to apply
a force at a greater distance from the
pivot, so they can apply a smaller force to
achieve the same turning force.
P1.44 231.4 N
0
b
P1.42 F3 will have the biggest turning effect,
because it acts at the equal largest
distance and at 90° to the object. (F2 acts
at the same distance but will have a
smaller turning effect because it does not
act at 90° to the object.)
P1.36 18 N
1.396
0.2
The load is between 10 and 12 N at the
limit of proportionality.
Questions
3
0.1
0.15
Extension / m
aThe worker needs to be able to do both
tasks and so the force which can be used
depends on the worker’s strength. If it was
much more difficult to push the bucket
down than to pull it up (or vice versa),
a worker might not be able to complete
both tasks.
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b
2
Without the shadoof, it would be harder
to lift the bucket than to push it down.
With the shadoof, the bucket is lifted
using the longer arm of the beam, so the
moment of the force is increased.
The figures given below are examples –
students may have estimated the arm lengths
differently. The important point is that the
counterweight arm is shorter than the water
arm, and so the weight of water lifted is less
than the counterweight.
arm distance
arm distance
approx 3 m
approx 0.5 m
fulcrum
water
weight
counter
weight
150 N
25 N
Experimental skills P1.04
Getting started
•
P1.46 a
lines drawn connecting opposite
vertices, cross in centre
b cross in centre of circle
c lines drawn connecting each vertex
with the centre of the opposite side,
cross in centre
d cross in centre of inner circle
P1.47 a
Both buses would topple if tilted any
further because their centres of mass
would be to the right of the ‘pivot’
(the right-hand wheel) which would
exert a clockwise moment.
b Stability reduces as the centre of mass
moves upwards. This means that the
bus can be tilted through a smaller
angle before it topples over.
c This is to reproduce the worst-case
scenario (most extreme situation).
P1.48 a
Wide tyres increase the surface area
and so decrease the pressure on the
ground. This means tractors can drive
on soft ground without sinking in.
b A sharp knife edge has a smaller
area, which increases the pressure and
makes cutting easier.
F
A
Learners should draw the diagonals of the
rectangle. The centre of gravity is where
they cross.
P1.49 p =
•
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
P1.50 pascal, Pa
Questions
P1.53 1.88 × 106 N
1
Practice questions
Lines should intersect, or approximately
intersect, depending on the accuracy of the
learner’s work.
2
Repeat the experiment.
3
Answer will depend on the learner’s response
to Q2.
4
Try to balance the shape with this point on
your fingertip.
5
53
Questions
Because the centre of gravity is the point
from which the weight acts, and weight is a
downward force.
1
C[1]
2
C[1]
3
0.8 cm[1]
4
300 N to the left[2]
5
0.0043 m/s[1]
6
a
Object Mass
/g
Volume Density
/ cm3
/ g/cm3
1
160
200
0.8
2
240
20
12
3
6400
800
8
4
540
45
12
[4]
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7
b
3[1]
c
3[1]
d
2 and 4[1]
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
[3]
W = mg; woman 588 N, elephant 49 000 N
F
[1]
A
b
p=
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:
54
a
torch switched on
chemical (store) in
battery
light radiation (transfer)
from light bulb
thermal (transfer)
from light bulb
b
wound up toy
elastic/strain (energy
store)
kinetic (store)
thermal (transfer)
/ sound radiation
(transfer)
c
radio-controlled car
chemical (store) in
battery
kinetic (store); maybe
sound radiation
(transfer)
thermal (pathway)
d
Bunsen burner
chemical (store)
internal (store); thermal
(transfer)
light radiation
(transfer)
e
loudspeaker in use
electrical (pathway)
from mains along wire
to vibration (store) of
the diaphragm
sound radiation
(transfer)
thermal (transfer)
f
ringing bicycle bell
vibration (store)
sound radiation
(transfer)
thermal (transfer)
g
solar-powered battery
light radiation
(pathway)
chemical (store)
thermal (transfer)
h
hairdryer in use
electrical (pathway)
kinetic (transfer);
thermal (transfer)
sound radiation
(transfer)
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
Science in context P2.01
1
2
The Moon has no fossil fuels. There is no life
on the Moon, so biofuels are not an option.
The Moon does not have an atmosphere, so
wind power is impossible. There is no liquid
water, so there cannot be any wave or tidal
energy – or coolant for nuclear power stations.
There is solar energy but a lunar day lasts
four weeks and we do not have the (battery)
technology to store enough solar energy to
power a lunar colony through two weeks of
lunar night.
Learner’s own answers, but they are likely
to be in favour. There are huge reserves of
thorium fuel available. Lifters produce tiny
amounts of radioactive waste, an accidental
meltdown would be impossible, and it would
be extremely difficult to make a nuclear bomb
using a lifter.
Questions
P2.01 kinetic energy
P2.02 an object can gain gravitational potential
energy by being raised
P2.03 strain energy or elastic potential energy
P2.04
Store
Examples
a
kinetic
energy
any moving object,
e.g. a train or a
runner
b
gravitational any high-up object,
potential
e.g. a bungee
energy
jumper or a plane
c
elastic
energy
d
internal
energy
any stretched,
squashed or wound
up object, e.g. a
compressed spring
or a stretched
bungee cord
any warm object,
e.g. a cup of tea or
an iron
P2.05
Physical clue
Which energy
store is changing?
material changing elastic
shape
object changes
speed
kinetic
chemical reaction
chemical
change of
temperature
internal / thermal
nuclear fission or
fusion
nuclear
P2.06 a
chemical (store) → thermal energy
(transfer) → internal energy of
surroundings (store)
b
electrical (transfer) → increases
internal energy (store) of light bulb
→ light radiation (transfer) + thermal
radiation (transfer)
c
electrical energy (transfer) → kinetic
energy (store) + thermal energy
(transfer) + sound (transfer)
Activity P2.01
Energy changes will depend on the devices
considered. They may be presented in a table as
in the ‘Before you start’ section, or as an energy
flow diagram.
Questions
P2.07 a
60 J
b
56 J
P2.08 a
thermal
b
sound
P2.09 Energy is expensive, supplies are often
limited, and our use of energy can
damage the environment.
P2.10 0.6 or 60%
P2.11 0.32 or 32%
P2.12 150 J
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.)
55
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P2.17 wasp
P2.18 any one from: wind, solar, waves, tidal,
geothermal, hydroelectric, biomass
P2.27 Advantages: a small amount of fuel
produces a large amount of energy; does
not produce greenhouse gases that lead to
global warming
P2.19 any one from: fossil fuels, nuclear
Disadvantages: not renewable; high costs
of decommissioning and dealing with
waste; accidents can be catastrophic
P2.20 because the resource is constantly being
replaced / is not used up
P2.21 chemical
Activity P2.02
P2.22 When we burn biomass, we are releasing
energy that came from the Sun in the
recent past. In the case of trees, the energy
might have been captured ten or a hundred
years ago. Manure might be from food
that captured energy a few days or months
before. When we burn coal, the energy
released is from sunlight trapped by plants
hundreds of millions of years ago.
1
any two from: burning biomass (wood from
trees); using thermal energy from hot springs;
generating heat from solar panels
2
burning biomass (wood from trees); solar
3
Any sensible suggestion, such as: solar; wind;
hydroelectricity. It would be difficult to justify
investing in the infrastructure for a small tidal
power station or a geothermal power station
for a five-year study.
4
Take rechargeable batteries to store energy
or build a small dam and install a pumped
storage HEP.
5
The woodland because, in the context of
a five-year mission, this a non-renewable
resource.
6
Learners’ own plans, with justification.
7
Learner’s own answers, with justification.
8
Learner’s own answers. This should prompt
interesting discussion.
Fossil fuels are the remains of organisms
(plants and animals) that lived in the
past. Many of the Earth’s coal reserves,
for example, formed from trees that lived
in the Carboniferous era, between 286
and 360 million years ago. Those trees
captured sunlight by photosynthesis,
they grew and eventually they died. Their
trunks fell into the swampy ground, but
they did not rot completely, because there
was insufficient oxygen.
P2.23 nuclear and geothermal
P2.24 The Sun heats some parts of the Earth’s
surface more than others. The surface
warms the air above it so that some parts
of the atmosphere are warmer than
others. Heated air expands and moves –
this is a convection current (see Chapter
P3). This is the origin of winds.
P2.25 Advantage: any one from: solar power is
becoming cheaper; it can be used in remote
locations (away from the electricity grid); it
is renewable; there are no fuel costs; it does
not contribute to global warming
Disadvantage: any one from: unreliable /
does not necessarily produce power when
you want it; diffuse (needs a large area
of land or roof space to generate power);
expensive initially
P2.26 Burning fossil fuels releases carbon
dioxide which contributes to global
warming, and sulfur dioxide which leads
to acid rain.
56
Questions
P2.28 Nuclear fusion is when the nuclei of
atoms fuse (join together) and fission is
when a heavy nucleus splits into two or
more smaller nuclei.
P2.29 c
P2.30 the weight of the box; the height of
the stairs
P2.31 12.5 kJ
P2.32 a
gravity; 1 N
c
b
6J
gravitational potential energy to
kinetic energy
P2.33 He could lift each brick more quickly
or he could lift more than one brick at a
time. In other words, he could do more
work or he could work more quickly.
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P2.34 a
1000 or 103
b
9
1 000 000 or 106
a
625 N[1]
b
work done = force × distance
(in the direction of the force)[1]
c
2 × 105 J[1]
d
power =
e
349 W[1]
P2.35 100 W
P2.36 a
10 450 000 J or 10.45 MJ
b
121 W
P2.37 144 kJ
Practice questions
Chapter P3
1
A[1]
Before you start
2
B[1]
3
Energy cannot be created or destroyed –
it can only be transferred from one energy
store to another.[1]
Learners may list elements or everyday
substances. Substances such as gels can be difficult
to categorise.
renewable: any one from solar, wind,
waves, tidal, biofuel; non-renewable:
any one from fossil fuels, nuclear[2]
5
a
work[1]
b
more[1]
c
energy[1]
d
less[1]
a
joule, J[1]
b
joule, J[1]
c
watt, W[1]
a
1
Ek = mv2[1]
2
b
3.61 J[1]
c
3.61 J[1]
d
gravitational potential energy = mgΔh[1]
e
7.69 × 10−2 m (7.69 cm)[2]
a
ny one from: wind power is renewable /
A
does not contribute to global warming /
has no fuel costs.[1]
7
8
b
Wind is an unreliable source of energy
because the wind is not always blowing
when there is demand for electricity.
There would need to be 1250 turbines
to generate the same power output as
one coal-fired power station. This would
lead to a large area being covered
with turbines[2]
We need liquid water to drink, irrigate crops, etc.
Without water vapour there could be no rain so
the water cycle would not happen. Without ice, all
the water currently in polar ice, glaciers, etc. would
be liquid, with a consequent rise in sea levels.
Learners may consider many other aspects.
Science in context P3.01
1
Sketch graph with axes labelled as shown.
Density is at a maximum at 4 °C.
1000.1
Density of freshwater / kg/m3
4
6
57
work done
[1]
time taken
1000.0
999.9
999.8
999.7
999.6
2
0
1
2
3 4 5 6 7 8
Temperature / ºC
9 10
If water froze from the bottom up, fish would
be forced upwards by the ice and they would
die. All life in areas where the temperature
falls below freezing would be affected by
this effect.
Questions
P3.01 solid, liquid, gas; volume; volume; space;
melts, liquid
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
P3.03 diagrams similar to those in Table P3.02
P3.04 a
solid
c
P3.05 a
b
c
b
gas
gas
rownian motion is the motion
B
of small particles suspended
in a liquid or gas, caused by
molecular bombardment.
Kinetic theory says that the molecules
in a liquid or gas are constantly
moving. If small smoke particles (or
similar particles) are suspended in a
liquid or gas, the moving liquid or
gas particles collide with the smoke
particles, causing them to change
direction repeatedly.
The particles would move more slowly
and change direction less frequently in
the colder experiment. This is because
the air molecules would be slower and
so would hit the smoke particles less
often and with less force.
P3.06 Molecules in liquids and gases are free to
move, so we can push them aside as we
pass through. In a solid, the particles are
held together and so do not move apart.
P3.07 gas; pressure; faster; increases; increases
P3.08 The air particles will move more slowly.
They will hit the walls of the balloon with
less force and less often. The pressure
inside the balloon will decrease and so it
will partially deflate.
P3.09 a
The speed increases.
b
They hit the walls more often.
c
They hit the walls with more force.
d
The pressure increases.
P3.10 expands; contracts; metals; bend
P3.11 When it is hot the bridge expands and the
rollers move to the right. In the cold it
contracts and the rollers move to the left.
P3.12 a
ethanol
b
58
Ethanol expands most so will make
the thermometer easiest to read. It is
also safe if the thermometer is broken.
P3.13
water vapour cools
Temperature / °C
P3.02 A liquid takes the shape of its container
without its volume changing.
water vapour condenses
water cools
100
water solidifies
0
Time
ice cools
P3.14 a
evaporation
b
fastest; cooler
P3.15 Unfolding the towel increases the surface
area, sun increases the temperature and
wind provides a draught. These three
factors all increase the rate of evaporation.
P3.16 solids; hotter; cooler; an insulator;
polystyrene
P3.17 A metal spoon would conduct thermal
energy from the soup to your hand. The
wooden spoon does not conduct thermal
energy, so it stays cool and easy to hold.
P3.18 Marble is a better conductor than wood
so more thermal energy would flow from
your feet to the marble, cooling your
feet down.
P3.19 Air is a very poor conductor. The layer
of air trapped between two thin layers of
clothing will reduce the loss of thermal
energy from the body.
P3.20 a
Copper is a metal and so contains
free electrons which carry thermal
energy through the metal.
b
Wood is solid, so the particles are close
and in fixed positions which allows
vibrations to be passed on. Air is a gas,
so its particles are far apart and do not
pass on thermal energy easily.
P3.21 Arrow drawn above the heat source,
pointing upwards, labelled ‘hot water’.
Arrow drawn on the opposite side of
the pan, pointing downwards, labelled
‘cold water’.
P3.22 Arrows showing cold water sinking below
the ice and warm water rising at the sides.
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P3.23 The water at the top will heat up and
become less dense so it will stay at the top
and the water at the bottom will stay cold.
P3.24 a
Diagram for hot gas shows fewer
particles than diagram for cold gas.
Particles in the hot gas have longer
arrows to indicate faster movement.
b
2
Dull dark surfaces are better absorbers of
infrared radiation than light shiny surfaces.
Questions
P3.30 a
The rollers are metal and are in
contact with the hot metal so are
heated by conduction.
As the gas is heated its particles
gain energy and move faster and
further apart, so the gas expands.
This decreases the density of the gas
so it rises.
b
The glowing metal is very hot so
emits a lot of heat radiation which
heats the worker’s face.
c
The hot metal heats the air around
it, causing convection currents which
heat the air in the building.
P3.25 C
P3.26 Space is a vacuum which means there
are no particles. Both conduction and
convection require particles for thermal
energy to be transferred.
P3.31 a
It is painted black to absorb the
maximum amount of infrared
radiation from the Sun.
P3.27 The engine and the wheels are glowing
yellow which means they are still hot.
P3.28 The shiny suit will reflect heat radiation
away, keeping the worker cool.
P3.29 A shiny teapot reflects the heat back into
the tea/emits less radiation so the tea stays
hot for longer. The dark teapot emits
a lot of heat radiation so the tea cools
more quickly.
Experimental skills P3.01
Getting started
The experiment is about heat loss by radiation,
so it is best to stop heat loss by other methods.
The lids will prevent lots of the heat loss by
convection, and the wooden or plastic surface will
reduce heat loss by conduction.
same size containers; same volume of water;
same starting temperature
2
Cooling curve graphs of learner’s results.
The black can will cool more quickly.
3
Dull dark surfaces are better emitters of
infrared radiation than light shiny surfaces.
59
Graph of learner’s results. Temperature
should rise for both cans, but black can heats
more quickly.
c
Cold water enters at the bottom so
that as it is heated, it will rise due
to convection. It leaves from the
top because this is where the water
is hottest.
1
A[1]
2
D[1]
3
liquid; gas[2]
4
When a fluid is heated it expands; this
causes its density to decrease; so it rises
above the colder denser fluid.[4]
5
Solid: particles are in fixed positions;
and only vibrate around these positions.
Liquids: particles are free to move; but
remain close together.
Gas: particles are very spread out; and
move completely freely.[6]
6
a
conduction [1]
b
Water at the bottom is heated and so
it expands. The hot water rises; and
is replaced by cold water which is
then heated.[3]
c
add insulation[1]
a
he particles move in a random
T
manner / frequently change direction.[1]
b
air molecules[1]
Experiment B
1
The back is insulated to reduce heat
loss by conduction.
Practice questions
Experiment A
1
b
7
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
c
8
9
The kinetic model says the air molecules
are moving. The movement of the smoke
particles can be explained by them
being bombarded by air molecules.[2]
a
o that there is only one independent
S
variable – the surface.[1]
b
Matte black: 71.2 °C; matt white:
64.5 °C; shiny silver: 60.4 °C[3]
c
Zain’s results will be less precise OR
He will not be able to tell which of
shiny black or matte white would
emit more as both would be
recorded as 65 °C.[1]
a
6 cm3[1]
b
The pressure increases; because the
particles are now hitting the walls of
the syringe more frequently.[2]
c
The air molecules have heated up
and so move faster; causing the gas
to expand.[2]
Chapter P4
Before you start
P4.02 a
the same
c
Waves transfer information or energy, without
transferring matter.
Science in context P4.01
dimmer
P4.04 340 m/s
P4.05 a
0.5 m
b
10 Hz
Experimental skills P4.01
Getting started
Changing the speed of the motor changes the
frequency of the waves produced.
A small piece of cork placed in the water will
move up and down.
Questions
1
Diagram should show the waves being
reflected at a 90° angle. The wavelength should
be unchanged.
2
a
iagram should show the waves
D
continuing in the same direction
but with a shorter wavelength in the
shallower water.
b
Diagram should show the waves bending
towards the normal, with a shorter
wavelength in the shallower water.
3
Line drawings similar to photos in
Figure P4.12.
4
Change the depth of the water.
Questions
P4.06 a
waves reflect upwards; reflection
Both methods use reflected waves to calculate
distance. Both methods make use of the
equation speed = distance/time.
b
waves get closer together; refraction
c
waves get closer together and bend
towards the normal; refraction
2
One method uses light waves and one uses
sound waves.
d
waves spread to make semicircles;
diffraction
3
Sound waves cannot travel through the
vacuum of space, and light waves would are
refracted when travelling from air to water and
back again.
1
Questions
b
P4.07 a
The waves diffract as they pass through
the doorway, creating semicircular
waves which reach person B.
b
longitudinal
P4.08 a
so that it can easily be read in the
rearview mirror of a car
P4.01 a
energy; matter
60
different
P4.03 Wavelength marked from a point on one
wave to the same point on an adjacent
wave (e.g. crest to crest or trough to
trough). Amplitude marked from rest
position to a crest or trough.
Examples of waves: water, light, sound,
microwaves and other electromagnetic waves,
earthquake waves, waving your hand, a crowd
doing a Mexican wave.
Learners may find the second part hard to
answer – it is the main point of this chapter.
They may suggest vibrations or repeated
movements, or wave behaviour such as reflection.
b
transverse; longitudinal
b
ECILOP
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P4.09 a
30° (the angle of reflection for 60°).
b
She may have measured the angle to
the surface rather than to the normal
or misread her protractor.
P4.10 Diagram similar to Figure 4.16 but with
the angles of incidence and reflection both
drawn and marked as 40°.
P4.11 a
The first mirror reflects the light
straight down to the second mirror
which reflects it towards the eye.
The light turns through 90° at
each mirror.
b
The light is reflected twice. The first
mirror inverts left to right and the
second inverts it back.
P4.12 a, b Diagram should be similar to
Figure 4.21d.
c
6 cm
Experimental skills P4.02
Getting started
1
2
Questions
P4.15 1.52
P4.16 a
i = 50°, r = 31°
b
P4.17 Glass has a lower refractive index than
diamond so the ray will bend away from
the normal as it passes from diamond
to glass.
P4.18 a
34.7°
b
P4.20 No, because TIR only happens when
the angle of incidence is greater than the
critical angle.
P4.21 a
x = angle of incidence, y = angle of
reflection, z = angle of refraction
c
Questions
towards; refraction; incidence; away from
2
The ray passes straight through and is
not refracted.
P4.13 a
Ray bends towards the normal.
b
Ray bends away from the normal.
sin x
= refractive index,
sin z
As x increases, y will increase too and
these will have the same value. z will
also increase. Eventually, when x is
equal to or greater than the critical
angle for the material, the ray will be
totally internally reflected.
P4.22 any two from: endoscopy,
communications, sensory play
P4.23 a
Questions
x = y,
x < critical angle
Draw a line (using a pencil and ruler) to join
up the lines on either side of the block.
1
197 000 000 m/s (to 3 s.f.)
P4.19 Total because all the light is reflected;
internal because the reflection happens
inside the material.
b
Mark dots along the ray and then remove the
apparatus and draw a line (using a pencil and
ruler) to join the dots.
1.5
b
he light is not refracted because it
T
enters the plastic along the normal.
45°
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
The value of
sin i
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
refractive index is constant.
61
d
The critical angle is less than 45°.
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Activity P4.04
infrared is also used in the TV remote
control; radio waves carry the TV signal.
object
F
F
image
The image is real, diminished and inverted.
This is a camera.
P4.35 The radiographer is working with X-rays
all day so the cumulative effect would be
much greater than for the patient.
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.
This is a projector.
Answers should include:
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
principal focus on the right of the lens.
c
X-rays help doctors diagnose problems
d
telescopes like this can be used to detect radio
waves from space
e
infrared radiation can be used to cook food.
b
c
Diagram shows rays converging at
the principal focus on the right of the
lens, but closer to the lens than for
part a.
Diagram shows ray carrying on in a
straight line through the lens.
P4.26 refraction; less; dispersion
P4.27 Diagram showing light refracting towards
the normal as it enters the prism and away
from the normal as it leaves. Emerging
light is dispersed and the colours red and
violet should be labelled.
P4.28 red, orange, yellow, green, blue,
indigo, violet
P4.29 Drawing of two waves, one with a longer
wavelength than the other. The wave with
the longer wave should be labelled red and
the other labelled violet.
P4.30 a
gamma rays, X-rays, UV, visible light,
IR, microwaves, radio waves
b
radio waves, microwaves, IR, visible
light, UV, X-rays, gamma rays
P4.31 5.6 × 1014 Hz
P4.32 infrared and microwaves
P4.33 X-rays and gamma rays
P4.34 Microwaves carry her mobile phone
signal; visible light lets her see the TV;
infrared from the fire warms her and
62
Students should produce a poster, which will
help reinforce their knowledge of the different
waves in the em spectrum, and their wavelengths,
frequencies, uses and dangers.
P4.38 The drummer hits the skin, causing it
to vibrate. This makes the surrounding
air vibrate. The vibrations pass through
the air, causing the listener’s eardrum
to vibrate.
P4.39 There are no particles to vibrate so sound
cannot travel.
P4.40 The bell is initially loud but as the air is
pumped out the sound becomes quieter
until it cannot be heard as there are no
particles to carry the sound wave.
Experimental skills P4.03
Getting started
The longer the distance from the wall, the greater
the time between hitting the blocks and hearing
the echo. This reduces the error due to the
reaction time of the person starting and stopping
the stopwatch. It is difficult to measure the time
accurately because the reaction time is quite long
compared with the time between hitting the blocks
and hearing the echo.
Questions
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
reaction time affects accuracy.
Questions
9
total internal reflection[1]
d
a plane mirror[1]
a
decreases[1]
P4.41 396 m
b
stays the same[1]
P4.42 The microphones record the sound
immediately, whereas a human with a
stopclock has a reaction time.
c
increases[1]
d
stays the same[1]
P4.43 a
the number of vibrations per second
10 a
300 000 000 m/s[1]
b
b
Hertz (Hz)
c
Sound B is louder and higher pitched
than sound A.
Practice questions
3 m[1]
Chapter P5
Before you start
Mind map will depend on what learners have
retained from prior experience and will give a
good idea of where they are starting from.
1
D[1]
2
B[1]
3
a
P is infrared; Q is X-rays[2]
Science in context P5.01
b
1
Learners should discuss the balance between
the need to keep experiments safe and the
benefits of learning about a potentially
hazardous phenomenon; the need to carry out
a risk assessment before proceeding; and the
possibility that some experiments are too risky
and should not be undertaken.
2
If a scientific experiment affects the situation
it is trying to explain, then the results will be
invalid as they cannot be said to describe or
explain the situation as it naturally occurs.
4
5
frequency[1]
a
the number of vibrations or waves
per second[1]
b
hertz / Hz[1]
c
ultrasound[1]
a
Light travels much faster than sound.[1]
b
i
transverse; at right angles to; can[3]
ii
c
6
7
990 m; one mark for answer,
one for unit[2]
b
1.2 s; one mark for answer,
one for unit[2]
c
5800 m/s[1]
Questions
P5.01 positive; negative; repel; attract
P5.02 a
b
a
focal length[1]
c
8
longitudinal; parallel to; cannot[3]
a
2250 m; one mark for answer,
one for unit[2]
b
Ray drawn from the top of the object
parallel to axis. This ray bends to
pass through the principal focus on
the right. Inverted arrow drawn at the
point where rays cross.[3]
P5.03 a
diminished; inverted[2]
P5.04 a
The ray is reflected, turning through
90° so it travels vertically down.[1]
riction between the child and the
F
trampoline leads to a build up of
static electricity. Electrons will be
transferred either to or from the child.
The hairs must all have the
same charge.
ammeter
b
in series (in line)
c
a circle containing a capital A, as
shown in Figure P5.06
a
It is travelling along the normal.[1]
b
63
c
b
ircuit similar to Figure P5.06, with a
C
second ammeter on the left-hand side
of the circuit.
They are the same.
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P5.05 a
b
ampere / amp / A
c
1000
1 000 000
40 Ω
b
16 Ω
C
P5.06 1 A = 1
s
P5.17 watts = volts × amps
P5.07 a
P5.18 a
110 s
b
5A
30 V
d
9.6 kW
b
1.5 kWh
5.33 mA
c
270 C
P5.19 72 W
d
77.1 s
P5.20 0.21 A
voltmeter
P5.21 8640 J
Diagram as P5.09 with a voltmeter
connected in parallel across the lamp.
P5.22 a
b
P5.09 a
c
480 W
b
P5.08 a
potential difference
c
5 kWh
0.5 kWh
P5.23 3 days
b
electromotive force or e.m.f.
c
volts, V
P5.24 13 dirhams
P5.25 a
433 W
b
21p
Experimental skills P5.01
c
1 hour
d
14p
Getting started
e
83 W
f
16p
g
5 hours
h
0.72p
i
0.1 unit
j
1.6p
To measure voltage, use a voltmeter wired in
parallel with the component you are measuring
the voltage through. To measure current, use an
ammeter wired in series with the component you
are measuring the current through.
P5.26 iron, cobalt, nickel
Question
P5.27 Unlike poles attract; like poles repel.
No, the resistance stays the same.
P5.28 See Table P5.07.
Questions
P5.29 Steel is a hard magnet but iron is a
soft magnet.
P5.10 a
48 Ω
b
increase
P5.11 a
120 Ω
b
4 mA
c
7.5 V
d
1.5 Ω
P5.12 a
60 V
b
120 V
P5.13 a
3 kΩ
b
120 V
P5.30 a
P5.14 3.75 mA
P5.15 a
b
long
wire
V
Diagram should be like Figure P5.22.
b
The arrows point away from the
magnetic north pole.
c
The field is strongest where the field
lines are closest together.
d
at the poles
P5.31 a
he strength of an electromagnet can
T
be changed and it can be switched on
and off.
b
a supply of electricity/electric current
5V
A
64
P5.16 a
P5.32 Friction with the carpet causes you
to become charged. The charge flows
through you and into the metal handle.
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 aelectrons; cloth; rod; negatively
charged; positively charged
b
c
iv
Diagram similar to Figure P5.27
but showing that the rod has
lost electrons and the cloth has
gained them.
Allow one mark for a basic answer
which will result in the drawing of
one correct field line. Allow two
marks for and an answer which will
result in correctly plotting the shape
of the field lines. Allow three marks
for an answer which will result in a
correct field diagram with arrows
on the field lines.[3]
When an acetate rod is rubbed with
a cloth, electrons move from the
rod to the cloth. This means the rod
becomes positively charged and the
cloth becomes negatively charged.
Practice questions
1
D[1]
2
D[1]
3
Any two of: iron, steel, cobalt, nickel[2]
4
a
electrons[1]
b
negative[1]
5
4.08 J[1]
6
20 Ω[1]
7
a
b
iagram should be like Figure P5.06.
D
Allow 1 mark for the correct shape of the
field lines and 1 mark for correct arrows
showing the direction of the field lines.[2]
8
A magnetically soft material loses its
magnetism easily, whereas a magnetically
hard material retains its magnetism.[1]
aNegatively charged particles are
transferred from the hair to the comb.
One mark for negatively charge
particles; one mark for transfer
from hair to comb.[2]
9
b
electrons[1]
c
All his hairs have the same charge
(positive); so they repel.[2]
a
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
and 2 on the paper to indicate the two
ends of the compass needle, as shown
in the figure.
dot 2
dot 1
65
c
You will need a bar magnet, plotting
compass, pencil and plain paper.
iii
Continue this process, until you have
moved round to the other pole of the
magnet or until you have gone off
the page.
Move the compass away from the
magnet and position it so that one
end of its needle is marked by dot 2.
Mark dot 3 at the other end.
V
[2]
One mark for ammeter in series;
one mark for voltmeter in parallel.
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,
one for unit[2]
b
0.6 kWh; one mark for answer,
one for unit[2]
c
5.2 A; one mark for answer,
one for unit[2]
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CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
Chapter P6
Before you start
1
To identify the type of circuit, trace the path
of the current from the power supply all the
way around the circuit until you return to the
power supply. If there is only one possible
route around the circuit, it is a series circuit.
If there is more than one possible route, it is a
parallel circuit.
2
When two lamps are connected in series,
the total resistance is the sum of the
individual resistances. If resistance increases,
current decreases.
3
Learners may compare the resistance of thin
wires versus thick wires or explain using an
analogy such as students walking along a
crowded corridor. Consider what would happen
if a parallel corridor was added – the result
would be that the overall flow of students
would be faster.
P6.05 Wire has resistance, like a resistor.
A longer wire is like having resistors in
series (i.e. a chain of resistors) whose total
resistance is the sum of the resistors, so a
longer wire has a higher resistance.
P6.06 A thicker wire is like having resistors in
parallel, whose combined resistance is less
than the smallest resistance value.
P6.07 a
b
P6.08 a
0.33 A
the 30.0 Ω resistor
2.4 Ω
b
1 A (through 6 Ω resistor);
1.5 A (through 4 Ω resistor)
c
2.5 A
Science in context P6.01
P6.09 multi-way bar extensions; block adapters
1
P6.10 fuse
2
3
Students will probably notice that they
can list ten electrical appliances easily but
find the non-electrical ones more difficult.
These may include things such as tin opener,
carpet sweeper, scissors, or corkscrew.
Descriptions may refer to lack of
entertainment appliances such as TV and
computers. They may also consider the
difficulty of life without washing machines,
etc. Some may consider the social benefits of
a simpler lifestyle.
This is an open question (there is no right
answer) and depends on whether humans can
control the behaviour of robots and other
artificial intelligences.
Questions
P6.01 a
b
P6.03 90 Ω
P6.11 It can lead to a fire.
P6.12 A fuse contains a thin section of wire that
melts and breaks the circuit if the current
passing through is too high.
P6.13 5 A; a fuse of 3 A would melt every time
the hairdryer was switched on. Fuses
rated higher than 5 A would allow too
big a current to flow before melting and
breaking the circuit.
P6.14 a
b
c ircuit symbol for a resistor:
see Table P6.01
circuit symbol for a variable resistor:
see Table P6.01
P6.02 They are the same (1.4 A).
66
P6.04 Each lamp can be controlled by its own
switch. If one lamp breaks and does not
allow current to flow, the other lamps will
still work. All the lamps will be brighter
for the same supply voltage.
his is to prevent too high a current
T
entering the house where it could melt
the insulation on wiring, giving off
poisonous fumes or causing a fire.
trip switch
P6.15 When the current gets too high, the
wires will overheat which can cause the
insulation to give off poisonous fumes,
melt or catch fire.
P6.16 The earth wire provides a low resistance
electrical path to ground and reduces the
chances of a fatal electric shock.
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for wire breaks, one mark for
stops current[2]
P6.17 If the fuse was connected to the earth
or neutral wire, a person could still
be electrocuted when they touch the
appliance.
P6.18 Double insulation is where the electric
circuit for an electrical appliance is inside
a case made from an electrical insulator
(e.g. plastic), which is inside the outer case.
This means it is impossible for a live wire
to touch the outer casing of the appliance.
Water is a conductor, so this could lead
to an electric shock.[1]
Chapter P7
Before you start
current (I): the rate at which electric charge passes
a point in a circuit; amps
potential difference (V): another name for the
voltage between two points; volts
Practice questions
1
B[1]
2
A and C[2]
3
a
1: ammeter; 2: voltmeter[2]
b
1: current; 2: voltage or p.d.[2]
c
1: amps; 2: volts[2]
4
0.2 A[1]
5
a
decreases[1]
b
increases[1]
c
increases[1]
a
1 mark for correct placement of ammeter;
1 mark for correct placement of voltmeter
6
d
resistance (R): a measure of the difficulty of
making an electric current flow through a device or
a component in a circuit; ohms
energy (E): the capacity for doing work; joules
power (P): the rate at which energy is transferred;
watts
charge (Q): a property of an object which causes
it to attract or repel other objects with charge;
coulombs
electromotive force (e.m.f.): the voltage across the
terminals of an electricity supply; volts
Equations
Q = It
E = IVt
V = IR
E = QV
P = IV
A
P=
E
t
Science in context P7.01
V
7
8
67
1
Answers will depend on learner response
but should help them to realise the effect
of motors on our lives, e.g. using a washing
machine instead of handwashing.
Again, dependent on learner response but
could include antibiotics, plastics, planes, etc.
[2]
b
The lamp will be less bright.[1]
c
13.3 Ω; one mark for answer,
one for unit[2]
2
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]
a
fuse is a safety device to stop
A
dangerously high current which
could cause a fire.[1]
P7.01 current; circular; right-hand grip;
bar magnet
b
C[1]
c
A fuse contains a thin section of wire
which melts and breaks if the current
becomes too high; award one mark
P7.02 an iron core
P7.03 clockwise
P7.04 Energy transferred by electricity is
transferred to the kinetic energy store
of the motor and to the thermal energy
store of the surroundings by heating and
by sound.
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
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P7.05 a
b
urn the magnet round to reverse
T
the field. Swap the power supply
connections to reverse the current.
The motor effect only happens
when current flows across the field
(when the current cuts the magnetic
field lines).
P7.06 direction of magnetic field
(first finger); direction of current
(second finger); direction of force or
motion of wire (thumb)
P7.07 a
right
P7.16 step-down
P7.17 50 turns
P7.18 a
b
P7.19 a
b
1000 A
ii
10 A
Higher voltage means lower current
so less energy is lost as thermal energy
in the wires.
32 000 W
12.8 W
b
up
P7.20 0.1 A. Assume the transformer is
100% efficient.
c
into the page
Practice questions
P7.08 field, conductor (in either order);
field strength, speed, number of turns
of wire (in any order); reversed
1
D[1]
2
D[1]
P7.09 C
3
a
Fleming’s left-hand rule[1]
b
out of the page[1]
a
primary[1]
b
decreases[1]
c
increases[1]
P7.10 Move the wire.
P7.11 The magnet could be turned round so the
opposite pole is moved in, or the original
pole could be moved out of the coil.
P7.12 With the cell, the current always flows
in one direction (d.c.). With the generator,
the current constantly changes
direction (a.c.).
P7.13 a
A: primary coil; B: iron core; C:
secondary coil
c
Step-up. It has more turns on the
secondary coil than on the primary coil.
b
P7.15
g rid; pylons; voltage; reduce;
transformers
b
P7.14 a
4
5
Any two from: use a stronger bar magnet;
move the magnet faster; use a coil with
more turns.[2]
6
a
leming’s left-hand rule. Extend the
F
thumb and first two fingers of the left
hand at right angles to each other, with
the first finger pointing in the direction of
the field and the second in the direction
of current, and the thumb will give the
direction of force or motion.[2]
b
The commutator; it reverses the
connections to the battery so the motor
spins continuously.[2]
c
Any two from: increase the current;
increase the strength of the field; increase
the number of turns on the coil.[2]
a
abels for: primary coil; secondary coil;
L
soft iron core. More turns on secondary
coil than on primary coil.[4]
b
A transformer will not work with
d.c. because the magnetic field in the
transformer is unchanging.[1]
step-down
6V
Np
Ns
Vp
Vs
Step-up
or stepdown?
10
20
6
12
step-up
10
100
1.2
12
step-up
2000
50
240
6
stepdown
10 000 20
68
i
115 000 230
stepdown
7
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
8
9
a
is a step-up transformer. It increases
A
voltage to decrease energy losses in the
cables. B is a step-down transformer. It
reduces the voltage to a safe level for use
in homes.[4]
b
500 000 V; one mark for answer,
one for unit[2]
a
he ammeter registers a current; because
T
the wire cuts through the field lines and
a current is induced.[2]
b
i
no current[1]
ii
The current is bigger and in the
same direction.[1]
iii The current is the same as in the
first experiment.[1]
iv The current is bigger and in the
opposite direction.[1]
10 a
b
due to the high current[1]
0.83 A
One mark for calculating V1 = 240 V;
one mark for calculating I1 = 0.83333;
one mark for rounding this to 2 s.f.
(I1 = 0.83333); one mark for getting
both units correct.[4]
Chapter P8
Before you start
1
False. Atoms contain protons, neutrons and
electrons and these are all made up of even
smaller particles.
2
False. There are 118 different atoms, though
many of the larger ones are unstable.
3
True.
4
False. Atoms have no overall charge, but the
protons and electrons have charge.
Science in context P8.01
1
2
69
The answer to this is commercial rather
than scientific. The owners would have
had to put in place safer working
procedures if they had admitted the
radium was dangerous and this would have
cost money.
makes employers accountable for the safety
of their workers. Also, the internet makes it
much easier for the workers to research safety
themselves. The women in the factories would
have found it much more difficult to research
the properties of radium.
Both these questions could lead on to discussion
of the need for people to be scientifically literate,
and the need for unbiased scientific research to be
available to all.
Questions
P8.01 nucleus; protons; neutrons; mass; protons;
neutrons
P8.02 a
5
b
12
c
5 protons, 7 neutrons and 5 electrons
P8.03 a
b
27
60
27
Co
P8.04 a
arbon-12 has 6 protons, 6 electrons
C
and 6 neutrons. Carbon-14 has 6
protons, 6 electrons and 8 neutrons.
b
isotopes; proton; nucleon; chemical
P8.05 a
Nucleus
Proton
number Z
Neutron
Nucleon
number N number A
Nu-1
6
6
12
Nu-2
7
6
13
Nu-3
7
7
14
Nu-4
6
8
14
Nu-5
5
6
11
Nu-6
6
7
13
b
Nu-1, Nu-4 and Nu-6
c
Nu-2 and Nu-3
d
Nu-5 is boron; Nu-1, Nu-4 and
Nu-6 are carbon; Nu-2 and Nu-3
are nitrogen.
P8.06 Nu-1 +6, Nu-2 +7, Nu-3 +7, Nu-4 +6,
Nu-5 +5, Nu-6 +6
P8.07 The radiation which we are exposed to all
the time from radioactive sources.
While it isn’t possible to say this could never
happen again, Health and Safety legislation
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
P8.08 Natural, any three from: materials in the
ground, building materials, cosmic rays,
food and drink, gases in the atmosphere.
P8.20 a
eta particles or gamma rays would
B
penetrate through the smoke easily.
b
Alpha particles are stopped by the
plastic casing or by a few centimetres
of air.
c
A short half-life would mean the
smoke detector would need to be
changed frequently.
Artificial, any three from: medical uses,
weapons testing, air travel, nuclear
power stations.
P8.09 cosmic rays
P8.10 unstable; two protons; two neutrons;
electron; electromagnetic
P8.11 It comes from inside the nucleus.
P8.12 gamma rays
P8.13 The number of protons changes and this
is what determines which element it is.
P8.14 a
P8.15
4
Po → 206
82 Pb + 2 α + energy
210
84
b
84 = 82 + 2
c
210 = 206 + 4
218
84
0
Po → 218
85 At + −1β
P8.16 a
b
800
200
P8.21 More radiation would pass through the
sheet, increasing the count rate on the
detector. This would lead to the rollers
being moved slightly further apart so the
thickness would increase.
P8.22 The radiation used is gamma which can
penetrate through plastic.
Practice questions
1
D[1]
2
C[1]
3
Natural: any one from: rocks and soil,
cosmic rays, food and drink, gases in
the atmosphere[1]
P8.17 38 days
Man-made: any one from: medical
technology, the nuclear industry,
weapons testing, air travel[1]
P8.18 2 days
Activity P8.01
1
2
The two graphs will have the same shape
because the activity/count rate and the number
of atoms remaining undecayed decrease in the
same way.
4
alpha, beta, gamma[2]
5
15 g[1]
6
a
4[1]
b
9[1]
c
5[1]
d
9
4
e
4 protons; 7 neutrons[2]
f
11
4
a
t he time taken for half of the unstable
nuclei to decay[1]
b
5 mg[1]
c
Ionisation causes cells/DNA to mutate.[1]
d
Any two from: store it in a lead-lined
box; store it in a labelled cupboard;
only qualified people handle it; handle
with tweezers; do not point source
at anyone; record exposure times[2]
The half-life is approximately the same for
each graph (around four throws).
Questions
P8.19 a
i
ii
b
70
he top third of the film would
T
be darkened by exposure. The
bottom two-thirds would not as
the aluminium and lead would
absorb the beta particles.
The top two-thirds of the film
would be darkened but not the
bottom third as the lead would
absorb most of the gamma rays.
The lightproof jacket is likely to be
paper which would stop alpha. Also,
the range of alpha in air is only a few
centimetres so it is unlikely that alpha
particles would reach the badge.
7
Be[1]
Be[1]
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
8
a
2 protons and 2 neutrons OR identical
to the nucleus of a helium atom[1]
b
Place paper between the rock and the
detector. If the count rate drops it
is alpha.[2]
c
238
92
Before you start
Stars are more massive. Stars shine (emit
light), planets reflect light.
•
(thermo)nuclear fusion
•
This depends on the temperature of the star.
•
A galaxy is a group of stars held together by
gravity. Our galaxy is the Milky Way.
•
Learner’s own answers.
Science in context P9.01
1
2
b
U → 23490Th + 42 α[3]
Chapter P9
•
gas known as protostars. A protostar
becomes a star once nuclear
fusion begins.
Lack of a common definition would be
very confusing. One example of this type of
collaboration is the Système Internationale –
SI units.
If Pluto remained a planet, then we would
potentially have hundreds of planets. It would
be very hard to learn all their names.
P9.08 a
Protostar: a very young star that is
still gathering mass from its parent
molecular cloud.
b
Red giant: a star with a starting mass
of fewer than eight solar masses that is
burning helium in its core. Its shell of
hydrogen has expanded and cooled.
c
White dwarf: the final stage of a star
that started with fewer than eight
solar masses and has run out of fuel.
d
Supernova: an exploding star that
began life with more than eight solar
masses and has run out of fuel.
e
Neutron star: a collapsed star
composed almost entirely of
neutrons, formed when a star with
more than eight solar masses reaches
the end of its life.
f
Black hole: the final stage in the
life cycle of a star that started with
more than eight solar masses. It has
enough mass left over after exploding
as a supernova to collapse to a point
where gravity is so strong that not
even light can escape.
Questions
P9.01 hydrogen (75%); helium (24%)
P9.02 Eyes would have evolved to see radiation
in the ultraviolet region.
P9.03 (thermo)nuclear fusion
P9.04 a
b
144 million km
P9.09 The flow chart should be like Figure
P9.05.
P9.10 a
Nuclear fusion is where light
nuclei fuse (join) together to create
heavier nuclei, but some mass turns
into energy.
137 years
P9.05 a
1.33 × 108 s
b
3.99 × 1013 km
c
18 000 years
d
107 million years
b
P9.06 4.7 km/s; yes
P9.07 a
Within interstellar clouds of gas and
dust, the force of gravity pulls gas
molecules closer together to form
clumps. These clumps contract to
form spinning spheres of super-hot
71
As the molecular cloud collapses,
its gravitational potential energy is
transferred to kinetic energy. Collisions
between particles cause kinetic energy
to be transferred to thermal energy.
The nuclei all have the same
positive charge so they need to be
moving fast enough to overcome
the electrostatic repulsion between
them. This is only possible at very
high temperatures.
P9.11 It must be above or below the
galactic disc.
P9.12 4 × 1041 kg
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023
CAMBRIDGE IGCSE™ COMBINED AND CO-ORDINATED SCIENCES: COURSEBOOK ANSWERS
Practice questions
6
1
D[1]
2
B[1]
3
a
distance[1]
b
the distance travelled by light in
one year[1]
c
because the distances are so huge[1]
a
I n this model, the Earth is central but we
now know the Sun is central OR in this
model, there are six planets but we now
know there are eight planets.[1]
b
The order of the planets other than
Earth is correct OR the Moon orbits
the Earth.[1]
c
760 seconds or 12.7 minutes[2]
a
galaxy[1]
b
gravity[1]
c
Milky Way[1]
4
5
Gravity caused a molecular cloud to collapse
into a protostar, which continued to pull in
more matter from the cloud. As the cloud
collapsed, its gravitational potential energy
was transferred into the kinetic energy of the
gas molecules, which was transferred into
thermal energy. Once it became hot enough,
the gas turned into a plasma. Once the plasma
became hot enough, the protons (hydrogen
ions) moved fast enough to overcome
electrostatic repulsion and fused into helium,
releasing energy. The radiation pressure
pushing outwards was equal to weight, acting
inwards and the star became stable, which
is what the Sun is like now. Eventually, it
will use up its hydrogen fuel so the radiation
pressure will fall and the Sun will collapse.
Gravitational potential energy will transfer to
thermal energy. The core will get hot enough
to fuse helium and the outer shell of the Sun
will expand and cool so that the Sun becomes
a red giant. When the helium runs out,
the Sun will collapse into a white dwarf.[5]
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.
72
Combined and Coordinated Sciences for Cambridge IGCSE™ – Martindill, Haywood & Tarpey
with M. Jones, G. Jones, Harwood, Lodge, Millington, Sang & Follows © Cambridge University Press & Assessment 2023