Cambridge IGCSE Combined and Co-ordinated Sciences
Answers to questions
Biology
Chapter B1 Cells
B1.01 about 1500 times
B1.02 10 mm (1 cm)
B1.03 all cells
B1.04 cellulose
B1.05 It will allow all substances to pass through.
B1.06 It will allow some substances to pass through, but
not others.
B1.07 water
B1.08 It is a space inside a cell, surrounded by a
membrane, containing a liquid.
B1.09 It is a liquid containing sugars and other
substances dissolved in water, found inside a
vacuole in a plant cell.
B1.10 It absorbs energy from sunlight.
1
B1.11 DNA, in the form of chromosomes; this is the
genetic information of the cell.
B1.12 They are usually too long and thin, but become
shorter and fatter just before the cell divides.
Chapter B2 Movement in and out of cells
B2.01 It is the net movement of molecules from a
region of their higher concentration down a
concentration gradient to a region of their
lower concentration, as a result of their random
movement.
B2.02 For example: oxygen diffusing into an organism
across a gas exchange surface, or into a cell
across its cell surface membrane; carbon dioxide
diffusing out of an organism across a gas exchange
surface, or out of a cell across its cell surface
membrane; diffusion of carbon dioxide into the air
spaces of a leaf.
B2.03 a It increases kinetic energy.
b It will increase the rate of diffusion, because
the molecules move faster.
B2.04 a sugar molecule
B2.05 a membrane that allows some particles to pass
through, but not others
B2.06 Visking tubing, a cell membrane
B2.07 It is a dilute solution (or it has a high water
potential).
B2.08 It absorbs water by osmosis, swelling until
it bursts.
B2.09 The plant cell absorbs water by osmosis just like
an animal cell, but the strong cellulose cell wall
prevents it bursting.
B2.10 a the cell wall
b the cell membrane
B2.11 a cell that has taken up water so that the cell
contents are pressing outwards onto the cell wall
B2.12 the condition of a plant cell when it has lost so
much water that the cytoplasm and vacuole have
shrunk, pulling the cell membrane away from the
cell wall
B2.13 by putting a plant cell into a solution that is more
concentrated than the cytoplasm and cell sap
B2.14 The same solution as is outside the cell – the cell
wall is fully permeable, so both water and solute
molecules can diffuse freely through it.
B2.15 In Figure B2.04, the solution outside the cell has
a higher water potential than the cytoplasm or
cell sap. Water therefore diffuses down the water
potential gradient, into the cell, through the
partially permeable cell membrane.
In Figure B2.05, the solution outside the cell has
a lower water potential than the cytoplasm or
cell sap. Water therefore diffuses down the water
potential gradient, out of the cell, through the
partially permeable cell membrane.
Chapter B3 Biological molecules
B3.01 the chemical reactions that take place inside
the body
B3.02 Cells will lose water. Reactions take place in
solution in the cytoplasm. If there is not enough
water, this cannot happen. Water is also required
for transport (e.g. substances dissolve in the water
in blood plasma), and cooling (sweating and
transpiration).
B3.03 carbon, hydrogen, oxygen
B3.04 There are 6 carbon atoms, 12 hydrogen atoms and
6 oxygen atoms in one glucose molecule.
Answers to questions
B3.05 a simple sugar (monosaccharide)
b polysaccharide
c polysaccharide
B3.06 a
b
c
d
e
glucose
glucose
glycogen
sucrose
starch
B4.06 small holes, mostly on the lower surface of a leaf,
through which gases can diffuse
B4.07 sausage-shaped cells surrounding a stoma,
which can change their shape and open or close
the stoma
B3.07 carbon, hydrogen, oxygen
B4.08 Palisade mesophyll cells, spongy mesophyll cells
and guard cells contain chloroplasts. Epidermal
cells (and xylem vessels and phloem sieve tubes)
do not.
B3.08 heat insulation, energy store
B4.09 carbon dioxide and water
B3.09 The oils are an energy store for the embryo plant
to use when germination begins, before it can
photosynthesise.
B4.10 about 0.04%
B3.10 nitrogen, sometimes sulfur
B3.11 about 20
B3.12 They are made of long chains of smaller molecules
linked together.
B3.13 haemoglobin, any enzyme, antibodies, other
suitable example
B3.14 for example: transporting oxygen (haemoglobin);
the formation of new cells (for growth or repair);
forming hair (keratin); catalysing reactions
(enzymes)
B3.15 a substance that speeds up a chemical reaction
without itself being changed
B3.16 enzymes
B3.17 all of them
B3.18 For amylase, the substrate is starch and the
product is maltose.
B3.19 the temperature at which an enzyme works at its
fastest
B3.20 40 °C
B3.21 The enzyme molecule loses its shape at high
temperature, so the substrate will no longer fit into
the active site.
Chapter B4 Plant nutrition
B4.01 any suitable organic substance – for example,
sugar
B4.02 carbon dioxide and water
B4.03 the green pigment, found in chloroplasts, that
absorbs energy from sunlight, used to drive
photosynthesis
B4.04 epidermal cells
B4.05 to prevent water loss from leaf cells
B4.11 by diffusion, through the stomata
B4.12 Water is brought to the leaf in xylem vessels.
B4.13 More sunlight can be absorbed; more carbon
dioxide can diffuse into the leaf at the same time.
B4.14 Sunlight can reach all the cells in the leaf.
Carbon dioxide can diffuse quickly to all the cells
in the leaf.
B4.15 Glucose is soluble and fairly reactive.
B4.16 nitrogen (in a reactive form, such as nitrates)
B4.17 Nitrate ions are needed for making amino acids.
These in turn are used to make proteins, and
proteins are needed for growth.
B4.18 Sucrose, produced by photosynthesis in the
leaves, is supplied to them through phloem
sieve tubes.
Chapter B5 Animal nutrition
B5.01 a Carbohydrates, fats, proteins and vitamins are
organic. Minerals and water are inorganic.
b carbohydrates, fats and proteins
cto stimulate peristalsis and prevent
constipation
B5.02 heart disease, diabetes, stroke
B5.03 a disease of the coronary arteries of the heart,
which become partially blocked by deposits of
cholesterol, preventing sufficient oxygen reaching
the heart muscle
B5.04 Starvation means not getting enough food.
Malnutrition means having an unbalanced
diet, perhaps a diet lacking in one nutrient or
containing too much fat.
B5.05 a disease caused by a lack of a particular nutrient
in the diet
B5.06 scurvy (lack of vitamin C); rickets (lack of vitamin D);
brittle bones (lack of calcium); anaemia (lack of iron)
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Cambridge IGCSE Combined and Co-ordinated Sciences
B5.07 the breakdown of large, insoluble food molecules
into small molecules using mechanical and
chemical processes
B5.08 vitamins and minerals (and water)
B5.09 a simple sugars (glucose)
b amino acids
c fatty acids and glycerol
B5.10 breaking down large molecules of food into small
ones, using enzymes
B5.11 the teeth at the front of the mouth, used for biting
off pieces of food
B5.12 a mix of food remnants and bacteria coating
the teeth
B5.13 Bacteria in plaque can breed and penetrate
between the tooth and the gums, causing
inflammation and eventually even loss of the
tooth. Bacteria in plaque produce acids when
they metabolise foods. The acid dissolves enamel,
producing a hole through which bacteria can
reach the living part of the tooth.
B5.14 The mouth (in saliva); the small intestine (in
pancreatic juice). It breaks down starch to maltose.
3
B5.15 The acid provides the optimum pH for pepsin to
work, and destroys bacteria in the food.
B5.16 pancreatic juice and bile
B5.17 Bile salts emulsify fats, making it easier for
lipase to come into contact with them and
digest them.
Chapter B6 Transport in plants
B6.01 water and inorganic ions such as nitrate
B6.02 sucrose and amino acids
B6.03 a collection of xylem vessels and phloem tubes
B6.08 a An increase in temperature increases the rate
of transpiration. (This happens because, at
higher temperatures, water molecules have
more kinetic energy. They are more likely to
turn from liquid to gas, and will diffuse more
rapidly out of the leaf.)
b An increase in humidity decreases the rate
of transpiration. (This happens because the
greater quantity of water vapour in the air
outside the leaf means that the diffusion
gradient for water vapour is less.)
Chapter B7 Transport in animals
B7.01 a system of blood vessels with a pump and valves
to ensure one-way flow of blood
B7.02 blood containing a lot of oxygen
B7.03 the lungs
B7.04 the left side
B7.05 In a double circulatory system, blood flows from
the heart to the lungs, and then back to the heart
again before travelling to the rest of the body. In
a single circulatory system, blood flows directly
from the lungs or gills to the rest of the body.
B7.06 In a double circulatory system, oxygenated blood
is transported to body cells faster, at higher
pressure.
B7.07 a left atrium
b right atrium
B7.08 between the atria and the ventricles
B7.09 a right ventricle
b left ventricle
B7.10 They contain more cardiac muscle, which can
therefore provide a greater force when they
contract. This is needed to pump the blood
around the body.
B6.04 Water moves into root hairs by osmosis, down
its water potential gradient (or from a less
concentrated solution to a more concentrated
one), through the partially permeable cell
membrane of the root hair cells.
B7.11 It contains more cardiac muscle, needed to
produce more force to pump blood all around the
body rather than just to the lungs.
B6.05 evaporation of water from the surfaces of
mesophyll cells followed by loss of water vapour
from plant leaves, through the stomata
B7.12 The pulse is the regular expansion of arteries,
caused by blood surging through at high pressure
each time the ventricles contract.
B6.06 small holes, mostly on the lower surface of a leaf,
each surrounded by a pair of guard cells, through
which gases can diffuse into and out of the leaf
B7.13 to move oxygenated blood to the muscles more
quickly, to supply the oxygen they need to release
energy from glucose, by respiration
B6.07 measuring the rate at which a shoot takes up
water (and therefore the rate at which it loses
water by transpiration)
B7.14 a patch of muscle in the right atrium which
sets the pace for the beating of the rest of the
heart muscle
Answers to questions
B7.15 Extra CO2 (from respiring muscles) dissolves in
blood plasma, reducing its pH. This is sensed
by receptors in the brain, which increases the
frequency of nerve impulses sent to the pacemaker.
B7.16 The valves are pushed closed by the high pressure
of the blood in the ventricles. This prevents blood
flowing back into the atria.
B8.07 the voice box
B8.08 They sweep mucus, which contains trapped bacteria
and dust particles, up to the top of the trachea and
into the throat, where it can be swallowed.
B8.09 across the walls of the alveoli
B8.10 two
B7.17 a arteries
b veins
Chapter B9 Coordination and homeostasis
B7.18 The pressure of the blood in arteries is high
and pulsing, so the strong walls are needed to
withstand this pressure.
B9.02 nerves and hormones (the nervous system and
the endocrine system)
B7.19 The elastic walls allow the arteries to expand with
each pulse of pressure (produced by the heart)
and then recoil in between pulses; if they could
not do this, they might burst.
B9.01 any muscles or glands
B9.03 They have a nucleus, cell membrane and
cytoplasm.
B7.21 A large lumen provides less resistance to blood
flow, needed because blood pressure in the veins
is low.
B9.04 They have a long axon (or dendron) to transmit
impulses rapidly from one part of the body to
another. They have nerve endings to pass the
impulses onto another nerve cell or an effector.
They (may) have a myelin sheath around the
axon (or dendron) to speed up the impulses.
They have dendrites to receive nerve impulses
from other cells.
B7.22 Skeletal muscles in the legs squeeze inwards on
the veins when the muscles contract, pushing
blood along inside them.
B9.05 The CNS receives inputs from different receptors,
which it integrates, and produces nerve impulses
to send to appropriate effectors.
B7.23 five from: water, glucose, vitamins,
minerals (inorganic ions), hormones,
antibodies (and others)
B9.06 a in a small swelling just outside the spinal cord
b in the central nervous system – either the
brain or the spinal cord
c in the central nervous system – either the
brain or the spinal cord
B7.20 Capillaries deliver blood, containing oxygen and
nutrients, very close to every cell in the body.
B7.24 They transport oxygen.
B7.25 They have no nucleus, and contain haemoglobin.
They have a biconcave shape.
B7.26 a red pigment that absorbs and releases oxygen;
a protein found inside red blood cells
B9.07 They produce very quick, automatic responses
with no time wasted in making decisions. This can
enable escape from danger.
B7.27 tiny fragments of cells that help with blood clotting
B9.08 There are many possibilities. Answers should state
the stimulus and the response.
Chapter B8 Respiration and gas exchange
B9.09 a change in the environment that is detected
by a receptor
B8.01 to release energy from glucose for cells to use
B8.02 active transport; driving chemical reactions such
as protein synthesis; movement; producing heat;
transmitting nerve impulses; cell division
B9.10 retina
B9.11 conjunctiva, cornea, aqueous humour, pupil, lens,
vitreous humour, retina
B9.12 cornea and lens
B8.03 the release of a relatively small amount of energy
by the breakdown of food substances in the
absence of oxygen
B9.13 changing the shape of the lens to focus light rays
from different distances onto the retina
B8.04 yeast, humans (for short periods of time)
B9.14 a contract
B8.05 It produces lactic acid. It does not produce CO2.
It releases less energy.
b iThis reduces tension on the suspensory
ligaments
B8.06 It produces lactic acid, not ethanol. It does not
produce CO2.
iiwhich allows the lens to become its
natural, rounded shape.
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Cambridge IGCSE Combined and Co-ordinated Sciences
B9.15 dissolved in blood plasma
B9.16 any situation in which you are nervous, frightened
or angry
B9.17 It increases glucose concentration in the blood,
so muscles can use more for respiration; it
increases heart rate, increasing the supply of
glucose and oxygen to muscles; it increases
breathing rate – similar effect.
B9.18 the tip
B9.19 just behind the tip
B9.20 Auxin made in the tip diffuses down into the part
just below the tip. Auxin is like an animal hormone,
a chemical that is made in one part of the body
and moves to another where it has an effect.
However, auxin is not made in an endocrine gland
like animal hormones, and it is not transported in
the blood.
B9.21 It moves the leaves towards a light source,
maximising the amount of light available for
photosynthesis.
B9.22 It grows towards it.
5
B9.23 It stores fat as an energy reserve, which can be
used in respiration to release energy for cells to
use. It acts as a heat insulator, preventing loss of
heat from the body to the external environment.
B9.24 The water in sweat evaporates. This requires
energy, which is taken from the skin, thus cooling it.
B9.25 hypothalamus
B9.26 Vasodilation is the widening of the arterioles
supplying the blood capillaries near the surface
of the skin. It allows more blood to flow through
these capillaries, losing heat by radiation through
the skin surface.
B9.27 When a parameter changes in a particular
direction, this is sensed and measures are put into
place to change it back towards the norm.
Chapter B10 Reproduction in plants
B10.01 In asexual reproduction, there is only one
parent. Cells divide by a type of cell division
that produces genetically identical cells, so the
offspring are genetically identical to their parent
and to each other.
B10.02 a haploid cell that fuses with another haploid
gamete to produce a zygote – for example, an
egg or a sperm
B10.03 a diploid cell formed by the fusion of the nuclei of
two gametes
B10.04 so that when their nuclei fuse at fertilisation, the
new cell formed will have the normal two sets of
chromosomes
B10.05 a cell with two complete sets of chromosomes
B10.06 any part of the body
B10.07 a cell with one set of chromosomes
B10.08 egg or sperm
B10.09 sexual reproduction
B10.10 anthers
B10.11 ovules
B10.12 the transfer of pollen grains from the male part of
the flower (anther of stamen) to the female part
of the flower (stigma)
B10.13 Much of the pollen of wind-pollinated flowers will
not land on the stigma of a flower of the same
species and will be wasted. The pollen of insectpollinated flowers is more likely to be delivered
to an appropriate flower.
B10.14 down a tube that grows out of the pollen grain,
through the style and into the ovule
Chapter B11 Reproduction in humans
B11.01 cervix
B11.02 where the two sperm ducts join the urethra; it
produces fluid for sperm to swim in
B11.03 An egg bursts out of an ovary, and is caught in
the funnel of the oviduct.
B11.04 in the testes
B11.05 Cilia in the wall of the oviduct waft it along.
B11.06 in the oviducts
B11.07 Sperm are much smaller than eggs. Sperm can
swim but eggs cannot. Sperm have a head, a
long tail, and enzymes in a vesicle in the head.
Eggs have none of these, but they have a layer of
jelly surrounding them.
B11.08 when the embryo sinks into the lining of the uterus
B11.09 a developing baby in the uterus from about the
11th week after fertilisation
B11.10 by the umbilical cord, which contains two
arteries and a vein
B11.11 oxygen; glucose; any other soluble nutrients;
water
B11.12 so that it is prepared for the arrival of an embryo
if an egg is fertilised
B11.13 It is lost through the vagina.
Answers to questions
Chapter B12 Inheritance
B12.09 She could breed the black-spotted dog with a
liver-spotted dog. If the dog is heterozygous:
B12.01 DNA
B12.02 a pair of chromosomes that carry the same genes
in the same positions
B12.03 different forms of a gene
black spots
Bb
B
b
B12.04 a B and b (or any other upper and lower case
versions of the same letter)
b brown eyes
B
B12.05 23
B12.06 a Nn
b N or n
b
B12.07 normal wings
NN
N
N
N
normal wings
Nn
n
N
n
NN
normal
wings
Nn
normal
wings
All the offspring would have normal wings.
B12.08 a brown hair
Bb
B
b
B
b
brown hair
Bb
B
b
B
b
BB
brown
hair
Bb
brown
hair
Bb
brown
hair
bb
red
hair
If both parents were heterozygous,
then both can produce gametes containing
the b alleles. If two such gametes fuse to
form a zygote, the resulting child will have the
genotype bb and have red hair. The chance of
this happening is one in four each time they
have a child. By chance, this has happened
three times out of five.
b Person 1 must be heterozygous, Bb, because
at least two of his children have red hair and
so must have inherited a b allele from both
parents.
Person 3 has red hair, and so must have the
genotype bb.
Person 2 must also be heterozygous, Bb,
for the same reason. He has brown hair.
liver spots
bb
b
Bb
black
spots
bb
liver
spots
If the black-spotted dog is homozygous, all of its
gametes will have the allele B, so all the offspring
will have the genotype Bb and will have black
spots. Therefore, if any of the offspring have liver
spots, the breeder knows that the genotype of
the black-spotted dog is Bb.
Chapter B13 Variation and natural selection
B13.01 a
b
c
d
discontinuous
continuous
continuous
discontinuous
B13.02 a and d genes only
b and c genes and environment
B13.03 The more that populations of bacteria are
exposed to an antibiotic, the more likely that
bacteria resistant to this antibiotic will gain an
advantage over non-resistant bacteria. These will
breed and pass on their resistance genes to the
next generation.
B13.04 Choose sperm from a bull whose female offspring
and other female relatives have high milk yields.
Choose a cow that has a high milk yield, and
fertilise her eggs with sperm from the chosen
bull. Continue for several generations.
B13.05 a Grow wheat in conditions where it gets
infected by rust. Collect seed from any plants
that are not infected, or that are not harmed.
Grow this seed and repeat for several
generations, each time picking out seed from
plants that are least affected by rust.
b Some of the rust organisms may have a
variation that allows them to infect the
resistant wheat plants. These will have a
selective advantage, and be more likely to
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Cambridge IGCSE Combined and Co-ordinated Sciences
survive and reproduce, passing on the genes
for this characteristic to the next generation
of rust fungi. Over time, most of the rust fungi
may have this gene and be able to infect the
previously resistant wheat plants.
Chapter B14 Organisms and their
environment
B14.01 Almost all the energy in living organisms on
Earth originates from sunlight. (There are deepsea ecosystems that are based on energy from
geothermal vents on the ocean floor, but the vast
majority of life on Earth is ultimately driven by
solar energy.)
B14.02 a One example might be: Sun → maize (grown
for fodder) → cattle → human.
b One example might be: Sun → phytoplankton
→ zooplankton → fish → seal → shark.
c One example might be: Sun → grass →
grasshopper → rat → snake → hawk.
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B14.03 because, in photosynthesis, they use energy from
sunlight to produce the food that then powers
the rest of the food chain
B14.04 The further up the food chain you go, the less
energy is available from the original energy
provided by the Sun. This is because, at each
trophic level, the organisms use up a lot of energy
as they live and grow, so there is less available to
pass on to animals that eat them. Beyond about
five links in a chain, the energy has effectively
run out.
B14.05 photosynthesis
B14.06 protein or any named proteins, carbohydrates
or a named carbohydrate (glucose,
glycogen), fats
B14.07 It will increase, because the combustion of fossil
fuels produces carbon dioxide that is released
into the air.
B14.08 Growing trees take carbon dioxide from the air
for photosynthesis. If trees are removed, then
less carbon dioxide is removed. If the trees are
burnt, this produces carbon dioxide that goes
into the air.
B14.09 Tree roots help to hold soil in place, especially on
sloping land. Without trees, rain can easily wash
the soil down the slope. Trees intercept raindrops
as they fall, reducing the force with which they
hit the soil. Without trees, rain hits the ground
harder, so that soil is loosened and washed away.
Trees absorb water from the soil. Without trees,
less water is absorbed and more runs off the
surface of the land, increasing soil erosion
and flooding.
B14.10 untreated sewage, fertilisers
B14.11 oxygen
B14.12 Plastic bags are not able to be decomposed
by organisms. Instead, they remain in the
environment, where they can cause problems
such as being eaten by animals and staying,
undigested, in their alimentary canals. Paper
bags are easily broken down by decomposers.
Chemistry
Chapter C1 Planet Earth
C1.01 sulfur dioxide and nitrogen dioxide
C1.02 the burning of fossil fuels (mainly coal for sulfur
dioxide)
C1.03 damage to limestone buildings, death of trees,
acidification of lakes leading to death of fish
C1.04 a combination of nitrogen oxides and low-level
ozone that causes breathing problems, especially
for people with asthma
C1.05 It combines with the haemoglobin in red blood
cells, stopping them from carrying oxygen.
C1.06 because it does not react with the filament, which
would burn in air when it became hot
C1.07 Heat which would normally escape into space is
reflected back to the Earth’s surface by gases such
as carbon dioxide and methane in the atmosphere.
C1.08 It changes nitrogen oxides and carbon monoxide
to nitrogen and carbon dioxide.
C1.09 because solid matter is easiest to remove and
would interfere with subsequent processes
C1.10 to kill bacteria present in the water
C1.11 because the energy needed to boil the water
is costly
C1.12 It contains a high concentration of a particular
metal compound.
C1.13 Lime is calcium oxide, which is reacted with water
to make calcium hydroxide (slaked lime).
C1.14 It reflects heat back to Earth when present in
the atmosphere. Heat is kept in the atmospheric
layer.
Answers to questions
Chapter C2 The nature of matter
C2.01 a
b
c
d
liquid: particles close together but less regularly
arranged; particles able to move about
gas: particles far apart and irregularly arranged;
particles moving independently
freezing (solidification)
boiling
condensation
sublimation
C2.02 The impurity lowers the freezing point of the
liquid.
C2.03
Temperature / °C
80
liquid
C2.14 Ammonia, because it has a lower molecular mass.
Place cotton wool plugs soaked in ammonia
solution and hydrochloric acid at opposite ends of
a tube. Seal the tube at both ends. Allow the gases
to diffuse towards each other. A white smoke disc
of ammonium chloride will form where the two
gases meet. This disc is closer to the hydrochloric
acid end of the tube, as ammonia diffuses faster.
C2.15 hydrogen
0
C2.16 15 protons, 16 neutrons, 15 electrons
freezing
solid
C2.17 proton = 1, neutron = 1, electron = 0 (or X)
C2.18 Chlorine-37 has two more neutrons in
the nucleus.
–20
Time
C2.19 first shell, maximum 2; second shell, maximum 8
C2.04 A volatile liquid is one that evaporates easily; it has
a low boiling point.
C2.20 2,8,8,2
C2.05 ethanol > water > ethanoic acid. Ethanol is the
most volatile, ethanoic acid the least.
C2.22 6 in both cases
C2.06 a distillation
b fractional distillation
c crystallisation (evaporation to concentrate the
solution, cooling, crystallisation, filtration and
drying)
Chapter C3 Elements and compounds
C2.07 Sublimation is when a solid changes to a gas
without passing through the liquid phase (and the
reverse).
C2.08 coloured substances (e.g. dyes)
C2.09 by the use of locating agents that react with
colourless ‘spots’ to produce a colour that can
be seen
C2.10 Rf gives a standard measure of how far a sample
moves in a chromatography system, as it relates
the movement of the sample compound to how
far the solvent front has moved. It is equal to the
distance moved by the sample divided by the
distance moved by the solvent front.
C2.11 An element is a substance that cannot be broken
down into anything simpler by chemical means.
C2.21 8 in both cases
C3.01 fluorine
C3.02 2
C3.03 the bottom of Group I
C3.04 Metal: can be beaten into sheets, gives a ringing
sound when hit, conducts heat, conducts
electricity
Non-metal: is an insulator, has a dull surface
C3.05 Helium has a full first shell. The others all have
8 electrons in the outer energy level (shell/orbit).
C3.06 potassium hydroxide
C3.07 lithium + water → lithium hydroxide + hydrogen
C3.08 It is used in the treatment of drinking water; it will
bleach moist litmus paper.
C3.09 chlorine and fluorine
C3.10 metal to non-metal
C3.11 aluminium
C3.12 sodium
C2.12 A compound is a substance formed from two or
more elements chemically bonded together.
C3.13 Cl2
C2.13 solid: particles packed close together in a regular
arrangement; each particle only vibrating about a
fixed point
C3.15 because copper is a transition metal
C3.14 silicon
C3.16 a covalent b covalent
c ionic d metallic
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Cambridge IGCSE Combined and Co-ordinated Sciences
C3.17 because in hydrogen gas two atoms are covalently
bonded together
C3.18 an electrostatic force (attraction between two
oppositely charged ions)
C3.24 a
C3.19 a
H
c
H
b
H
O
H
c
N
H
H
H
d
H
C
H
9
H
H
C3.20 a
–
[Na]+
Cl
b
–
+
[Li]
F
C3.21 The calcium ion is ionically bonded to the
carbonate ion but the carbonate ion is held
together by covalent bonds.
C3.22 a
2–
[Mg]2+
–
Cl
2+
[Ca]
calcium hydroxide
nitrogen monoxide
nitrogen dioxide
sulfur trioxide
SiCl4
b
CS2
PCl3 (or PCl5)
d
SiO2
C3.25 a i
Na = 1, O = 1, H = 1
ii C = 2, H = 6
iii H = 2, S = 1, O = 4
iv Cu = 1, N = 2, O = 6
v C = 12, H = 22, O = 11
b i
potassium bromide
ii aluminium hydroxide
iii copper carbonate
iv magnesium nitride
v phosphorus trichloride
vi nitric acid
vii silicon tetrachloride
viii iron(ii) sulfate
ix methane
x sulfuric acid
c i
K 2SO4
ii AlF3
iii Fe2O3
iv Ca(NO3)2
v ZnCl2
vi NH3
vii HCl
viii CuSO4
ix SO3
C3.26 a
b
c
d
e
f
carbon, hydrogen and oxygen
8
carbon and oxygen
4
A liquid: it is a small covalent molecule.
No, it is covalently bonded.
C3.27 The ions are free to move and they carry
the charge.
O
b
–
Cl
C3.23 a
b
c
d
e
f
g
h
sodium iodide
magnesium sulfide
potassium oxide
lithium nitride
C3.28 because the ions are fixed in position and
cannot move
C3.29 a There are electrons between the flat planes of
atoms which are free to move.
b There are only weak forces between the
layers in graphite and therefore they can slide
over each other.
C3.30 because, in diamond, each carbon atom is
attached to four other carbon atoms, making a
strong lattice
Answers to questions
C3.31 because there are no charged particles to
move around
b magnesium + steam
→ magnesium oxide + hydrogen
Mg + H2O → MgO + H2
C3.32 because there are electrons which are free to
move in solid metals
c
C3.33 Both substances have a three-dimensional
structure in which the atoms are arranged
tetrahedrally and all the atoms are joined by
covalent bonds.
2Ca + O2 → 2CaO
d bromine + potassium iodide
→ potassium bromide + iodine
Br2 + 2KI → 2KBr + I2
e zinc + copper sulfate → zinc sulfate + copper
Chapter C4 Chemical reactions
C4.01 a physical
physical
d physical
C4.02 a exothermic
b exothermic
c
exothermic
d endothermic
C4.03 A new substance(s) has been formed.
C4.04 a iron + oxygen → iron(iii) oxide
b sodium hydroxide + sulfuric acid → sodium
sulfate + water
c
sodium + water
→ sodium hydroxide + hydrogen
C4.05 a 2Cu + O2 → 2CuO
b N2 + 3H2
c
2NH3
4Na + O2 → 2Na2O
d 2NaOH + H2SO4 → Na2SO4 + 2H2O
e 2Al + 3Cl → 2AlCl3
f
3Fe + 4H2O → Fe3O4 + 4H2
C4.06 a chlorine + potassium bromide
→ potassium chloride + bromine
b Iodine is less reactive than chlorine so it will
not displace chlorine from its salts.
C4.07 a combustion
b decomposition
c
Zn + CuSO4 → ZnSO4 + Cu
C4.09 a Solid sodium carbonate reacts with
hydrochloric acid solution to give sodium
chloride solution and carbon dioxide gas.
Water, a liquid, is also produced.
b chemical
c
calcium + oxygen → calcium oxide
redox
d neutralisation
C4.08 a sodium + water → sodium hydroxide + hydrogen
2Na + 2H2O → 2NaOH + H2
b i
ii
iii
iv
Ag+ (aq) + Cl–(aq) → AgCl(s)
Ba2+(aq) + SO42–(aq) → BaSO4(s)
H+(aq) + OH–(aq) → H2O(l)
2H+(aq) + CO32–(s) → H2O(l) + CO2(g)
C4.10 Reduction is the gain of electrons; oxidation
is the loss of electrons. During a redox reaction
the oxidising agent gains electrons; the oxidising
agent is itself reduced during the reaction.
C4.11 a The compound is split into its elements.
b The ions are not free to move in the solid, so
they cannot move to the electrodes to be
discharged.
c The vapour is brown.
d because bromine vapour is toxic
e the cathode
C4.12 a the cathode
b copper sulfate solution
C4.13 a 2Br – → Br2 + 2e–
b because electrons are gained by the lead ions
C4.14
Solution
Gas
(electrolyte) given
off at
the
anode
Gas given Substance
off or
left in
metal
solution at
deposited the end of
at the
electrolysis
cathode
silver sulfate
oxygen silver
sulfuric acid
sodium
nitrate
oxygen hydrogen
sodium
nitrate
C4.15 a i electrode Y
ii a cathode
b The solution would become acidic.
c To make the electrode conduct electricity.
10
Cambridge IGCSE Combined and Co-ordinated Sciences
Chapter C5 Acids, bases and salts
C5.01 A corrosive substance ‘eats’ things away.
C5.02 citric acid
C5.03 a alkaline
b neutral
c alkaline
d acidic
C5.04 It changes its colour depending on whether it is in
an acidic or alkaline solution.
C5.05 pH 1 is more acidic.
C5.06 green
C5.07 ethanoic acid
C5.08 hydrogen
C5.09 hydroxide ion, OH–
C5.10 a calcium ions and hydroxide ions
b ammonium ions and hydroxide ions
C5.11 a H2SO4
b HCl
C5.12 They are equal.
C5.13 blue
11
C5.14 white
b potassium hydroxide + sulfuric acid
→ potassium sulfate + water
2KOH + H2SO4 → K 2SO4 + 2H2O
C5.25 sodium hydroxide, potassium hydroxide, calcium
hydroxide (limewater), ammonia solution
C5.26 ammonia
C5.27 sulfuric acid (H2SO4), hydrochloric acid (HCl)
C5.28 a potassium hydroxide + hydrochloric acid
→ potassium chloride + water
b copper oxide + hydrochloric acid
→ copper chloride + water
c zinc + hydrochloric acid
→ zinc chloride + hydrogen
d sodium carbonate + hydrochloric acid
→ sodium chloride + water + carbon dioxide
C5.29 a
b
c
d
KOH + HCl → KCl + H2O
CuO + 2HCl → CuCl2 + H2O
Zn + 2HCl → ZnCl2 + H2
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
C5.30 a carbonate + hydrochloric acid
→ salt + water + carbon dioxide
C5.31 blue precipitate, copper(ii) hydroxide
C5.17 magnesium + oxygen → magnesium oxide
C5.32 Ammonia solution; you get a white precipitate in
both cases but the zinc hydroxide precipitate
re-dissolves in excess ammonia and the
aluminium hydroxide precipitate does not.
C5.18 carbon monoxide
C5.33 pink (purple)
C5.19 zinc hydroxide or aluminium hydroxide
C5.34 to make sure all the acid is used up/reacted
C5.15 sulfur + oxygen → sulfur dioxide
C5.16 S + O2 → SO2
zinc hydroxide + sodium hydroxide
→ sodium zincate + water
Zn(OH)2 + 2NaOH → Na2ZnO2 +2H2O
or
aluminium hydroxide + sodium hydroxide
→ sodium aluminate + water
Al(OH)3 + NaOH → NaAlO2 + 2H2O
C5.20 baking soda
C5.21 hydrochloric acid, to help digest our food
C5.22 calcium carbonate, magnesium hydroxide
C5.23 insoluble bases: copper oxide, zinc oxide; alkalis:
sodium hydroxide, potassium hydroxide
C5.24 a sodium hydroxide + hydrochloric acid
→ sodium chloride + water
NaOH + HCl → NaCl + H2O
C5.35 filtration
C5.36 pipette, burette
C5.37 If heated too strongly, the salt could dehydrate
(lose water of crystallisation) or even decompose.
method B
C5.38 a i
ii sulfuric acid
iiizinc oxide + sulfuric acid
→ zinc sulfate + water
b i
method A
ii hydrochloric acid
iii KOH + HCl → KCl + H2O
Chapter C6 Quantitative chemistry
C6.01 a covalent
b ionic
c
CH4, NaI, C3H6, ICl3, BrF5, HBr
Answers to questions
C6.02 a 32
C7.04
d 114
64
e 98
f
g 188
h 133.5
Energy
c
b 17
119
C6.03 a 0.20 g; 0.18 g; 0.08 g; 0.12 g
ZnSO4 (aq) + Cu(s)
Progress of reaction
b
C7.05 a rate increases
b rate increases
c rate increases
0.2
Mass of oxygen/g
EA
Zn(s) + CuSO4(aq)
C7.06 The reactions which would spoil the food are
slowed down at the lower temperature.
0.1
C7.07 at the beginning
C7.08 because the reactants are being used up
0
0
0.1
0.2
0.3
Mass of magnesium /g
c
The graph is a straight line, showing a fixed
ratio of oxygen to magnesium; this indicates a
fixed formula.
C6.04 a i
near the neck of the test tube
ii to flush out all of the air from the tube
iiito make sure the reaction was
complete
b i
C = 1.60 g, E = 1.28 g, F = 0.32 g
ii 0.02 moles
iii 0.02 moles
iv 1 mole
v CuO
vicopper(ii) oxide + hydrogen
→ copper + water
CuO + H2 → Cu + H2O
C6.05 a 0.02 moles
c 0.07 moles
b 2 moles
C6.06 a 36 000 cm3
c 12 000 cm3
b 1440 cm3
C6.07 a 2 mol/dm3
b 0.2 mol/dm3
c 1 mol/dm3
d 0.8 g of NaOH = 0.2 moles; 0.2 mol/dm3
Chapter C7 How far? How fast?
C7.09 A catalyst is a substance that speeds up a
chemical reaction but is not itself used up in the
course of the reaction.
C7.10 a biological catalyst
C7.11 manganese(iv) oxide
C7.12 a iron
b vanadium(v) oxide
C7.13 changes in temperature and pH
C7.14 The presence of a catalyst decreases the
activation energy of reaction.
C7.15 a An increased temperature means that the
particles are moving faster and will therefore
collide more frequently; when they collide,
more particles will 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 to the reactant and therefore more
frequent collisions.
c Greater concentration means there are more
reactant molecules present and so there will
be a greater frequency of collision.
C7.16 white to blue
C7.17 the presence of water
Chapter C8 Patterns and properties of metals
C7.01 endothermic
C8.01 They are soft and have a low density.
C7.02 endothermic
C8.02 Sodium gives a yellow flame, potassium a lilac
flame.
C7.03 Polystyrene is a good insulator (and absorbs very
little heat itself).
C8.03 hydrogen
C8.04 potassium hydroxide
C8.05 sodium + water → sodium hydroxide + hydrogen
12
Cambridge IGCSE Combined and Co-ordinated Sciences
C8.06 2K + 2H2O → 2KOH + H2
C8.07 lithium
C8.08 It is strong but light and it does not corrode.
C9.12 by reacting methane gas with steam
C8.09 It is more reactive than carbon (so its oxide cannot
be reduced by carbon).
C9.13 an iron catalyst, a moderately high temperature
(450 °C) and a high pressure (200 atmospheres)
C8.10 A thin layer of aluminium oxide forms on the
surface of the metal and sticks to it, giving it a
protective coating; with iron, the oxide forms but
flakes off and so does not protect the metal.
C9.14 so that they react the second time around
(saves producing more raw materials)
C8.11 They are strong and dense, have high melting
points, their compounds are often coloured, they
can show more than one valency, they or their
compounds often act as catalysts (any three).
C9.16 They are washed off fields by rain and end up in
streams and rivers.
C8.12 2 and 3
C8.13 blue
C8.14 (hydrated) iron(iii) oxide, Fe2O3
C8.15 the Haber process
C8.16 zinc + hydrochloric acid
→ zinc chloride + hydrogen
C8.17 copper
13
C9.11 because it forms an oxide layer which prevents
any further reaction with oxygen (corrosion)
C8.18 magnesium + copper(ii) sulfate
→ magnesium sulfate + copper
C8.19 A brown deposit is formed and the blue colour of
the solution fades to colourless.
C8.20 Mg + CuSO4 → MgSO4 + Cu
Mg(s) + Cu2+(aq) → Mg2+(aq) + Cu(s)
Chapter C9 Industrial inorganic chemistry
C9.01 to combine with the silicon dioxide (sand) and
remove it as slag
C9.02 Fe2O3 + 3CO → 2Fe + 3CO2
C9.03 oxygen
C9.04 to make an alloy which doesn’t corrode
(stainless steel)
C9.05 water and oxygen (air)
C9.06 It can be used to coat iron (galvanisation) or
can be attached to iron as blocks (cathodic
protection).
C9.15 because these are the three elements needed by
plants which can become used up in soil
C9.17 S + O2 → SO2
C9.18 a catalyst (vanadium(v) oxide) and a temperature
of around 450 °C
C9.19 because the reaction is too violent: a mist of
sulfuric acid is formed which is very dangerous
C9.20 a concentrated solution of sodium chloride
in water
C9.21 It converts a cheap raw material (common
salt) into three important chemicals: chlorine,
hydrogen and sodium hydroxide. There are no
waste products.
C9.22 to neutralise acidity in the water
C9.23 to remove silicon dioxide (sand) from the iron ore
C9.24 CaCO3 → CaO + CO2
C9.25 Ca(OH)2
C9.26 treating soil to remove excess acidity; removing
impurities from iron during the basic oxygen steel
making process
C9.27 because it is quick to recycle, and ‘new’ aluminium
is very expensive to produce
C9.28 conserving non-renewable resources
such as metal ores; avoiding dumping waste
in landfill
Chapter C10 Organic chemistry
C10.01 covalent
C10.02 4
C9.07 because of the high cost of electricity, which is
needed in large quantities
C10.03 diamond and graphite
C9.08 because this makes the temperature needed to
melt the aluminium oxide much lower
C10.05 methane, ethane, propane, butane, pentane,
hexane
CH4, C2H6, C3H8, C4H10, C5H12, C6H14
C9.09 because the oxygen produced at the anode
causes them to burn away
C9.10 Al3+ + 3e– → Al
C10.04 proteins, carbohydrates, nucleic acids (any two)
Answers to questions
C10.06
H
H C
C10.17 C2H4Br2
H H H H
H
H C
C
C
C
H
H H H H
methane
butane
H
Br Br
H
Boiling point / °C
C10.07
C
C
H
H
H
100
C10.18 ethene + hydrogen → ethane
C2H4 + H2 → C2H6
50
C10.19 finely divided nickel
C10.20 a propene + hydrogen → propane
0
b C4H8 + H2O → C4H9OH
–50
C10.21 methanol, ethanol, propanol
–100
C10.22 ethene + steam → ethanol
C2H4 + H2O → C2H5OH
–150
C10.23 yeast, carbohydrate source, water
1
2
4
3
5
6
Number of carbon atoms
The graph shows a smooth curve with a steady,
but decreasing, change in boiling point as the
hydrocarbon chain gets longer.
C10.08 ethane + oxygen → carbon dioxide + water
C10.09 natural gas
C10.10
C10.24 a carbon dioxide
b It is an air-lock – allowing the carbon dioxide
to escape but not allowing air/bacteria in.
c
yeast
d at around 37 °C
e This is the temperature favoured by the
yeast, which are living organisms.
C10.25 a
H
H
H
C
O
H
H
H
H
C
H
methanol
C10.11 ethene, propene, butene
C2H4, C3H6, C4H8
H
H
C
C
H
H
H
H
H
C
C
H
ethene
H
H
H
O
H
ethanol
H
C11.01 refinery gas, petrol (gasoline), naphtha, kerosene
(paraffin), diesel, bitumen
C10.14 bromine + ethene → 1,2-dibromoethane
H
C
C
Chapter C11 Petrochemicals and polymers
propene
H
C
14
H
C
C10.13 The bromine water is decolorised from brown to
colourless.
C10.15
H
b A homologous series of compounds is a
family of organic compounds that have the
same general formula, similar chemical
properties and a gradual trend in their
physical properties.
H
C10.12
H
C
H
C10.16 a propane + oxygen → carbon dioxide + water
b C3H8 + 5O2 → 3CO2 + 4H2O
C11.02 coal, natural gas, petroleum (crude oil)
C11.03 Cracking is the thermal decomposition of a longchain alkane to a shorter-chain alkane and an
alkene (or hydrogen).
decane → octane + ethene
C10H22 → C8H18 + C2H4
C11.04 road surfacing, ships’ engines, car engines,
aircraft fuel (domestic heating)
C11.05 C2H4 H
H
C
C
H
H
H
ethene
H
H
C
C
H
propene
H
C
H
Cambridge IGCSE Combined and Co-ordinated Sciences
C11.06 Addition polymerisation takes place when many
molecules of an unsaturated monomer join
together to form a long-chain polymer.
H
H
n
C
b
heat, catalyst
H
H
C11.07 a
high pressure
C
H
H
C
C
H
CH3
H
H
C
C
H
Cl
H
H
C
C
H
H
P1.02 1968 cm3
P1.03 a 0.71 mm
b 158 mm3
n
P1.04 18 cm3
P1.05 13.2 g/cm3
P1.06 7.6 g/cm3
P1.07 80 cm3; 7.75 g/cm3
P1.08 0.04 s
P1.09 0.87 s; 0.864 s
C11.09 a crates/plastic rope
Chapter P2 Describing motion
b insulation/pipes
P2.01 inches per minute
non-stick pans/gear wheels
P2.02 s/m, ms
C11.10 The monomers join together by a reaction
in which a small molecule (usually water) is
eliminated each time a link is made.
P2.03 a fastest: C
b slowest: B
P2.04 250 m/s
C11.11 a the amide link (or peptide link)
b
...
O
O
C
C
N
N
H
H
O
O
C
C
P2.05 75 km/h
N
N
H
H
...
Chapter C12 Chemical analysis and
investigation
P2.06 1728 000 km
P2.07 3.33 h (3 h 20 min)
P2.08
Distance
C12.01 because their hydroxides are insoluble and form
as precipitates
C12.02 aluminium and zinc hydroxides
C12.03 because iron has two different oxidation states
(iron(ii) and iron(iii))
C12.04 carbon dioxide
Time
P2.09
C12.05 silver nitrate
C12.06 nitric acid
C12.07 oxygen
Speed
15
Chapter P1 Making measurements
P1.01 3.23 mm
C11.08 tetrafluoroethene
c
Physics
C12.08 the ammonium ion
C12.09 a D
c
A
b
E
d C
C12.10 Add bromine water: it turns from brown to
colourless.
C12.11 the amount of water, the amount of fuel used, or
the time it was used for
C12.12 substance, appearance before heating, appearance
during heating, appearance after cooling
Time
P2.10 a A, C, G
c E
b
d
F
B, D
Answers to questions
10
P3.04 a 900 N
8
P3.05 1500 N
Speed / m/s
P2.11 a, b
6
P2.12
P3.07 25 m/s2
2
P3.08 800 kg
0
1
2
3
4 5 6
Time / s
7
8
9
Chapter P4 Turning effects of forces
45 m
P4.01 force F3 at end; it is at 90° to trapdoor and furthest
from the pivot
50
P4.02 The force of the wind has a greater turning effect
on a tall tree.
Distance / km
40
30
P4.03 X = 1000 N; Y = 1400 N
20
P4.04 Z = 90 N; 1.50 m
10
0
10
P4.05 a This is to lower their centre of mass.
10
0
20
30 40 50
Time / min
60
b The block on the arm is there to balance the
load. The blocks at the base are to lower its
centre of gravity, broaden its base and make it
more stable.
70
32 km/h
P2.13 km/s
P4.06 a The forces are equal and along the same
straight line, so there is no moment.
P2.14 1.5 m/s2
P2.15 0.20 m/s2
b No, because there is an unbalanced force to
the right.
P2.16 a
c
Speed / m/s
20
15
10
0
The cyclist is unstable, because the forces are
not balanced.
Chapter P5 Forces and matter
5
P5.01 22.0 cm
0
5
10
Time / s
15
20
b 2.5 m/s2
c 280 m
Chapter P3 Forces and motion
P3.01 a accelerate to right
b slow down / accelerate to left
c change direction
P3.02 a i unbalanced
ii 20 N to right
iii accelerate to right
b i balanced
ii no resultant force
iii no acceleration
c i unbalanced
ii 50 N downwards
iii accelerate downwards
P3.03 a mass = 1 kg; weight is less than 10 N
b mass = 1 kg; weight is greater than 10 N
P5.02
Load / N
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Length / mm
50
54
58
62
66
70
73
75
76
Extension / mm
0
4
8
12
16
20
23
25
26
3 4 5
Load / N
8
30
Extension / mm
c
333 N
P3.06 2.0 N
4
0
b
25
20
15
10
5
0
0
1
2
6
7
16
Cambridge IGCSE Combined and Co-ordinated Sciences
P5.03 7.5 N
P6.12 60%
P5.04 24 N
P6.13 25%
120
100
80
60
40
20
0
P6.14 200 J
limit of proportionality
P6.15 a decreasing
b constant
c increasing
Extension / mm
P5.05
P6.16 1000 J
0 1 2 3 4 5 6 7 8 9 10 11 12
Load / N
load at the limit of proportionality = 8.0 N
F
P5.06 p =
A
P5.07 pascal, Pa
P5.08 100 N on 1 cm
2
P5.10 600 000 N
27 600 N c
9200 Pa
Chapter P6 Energy transformations and
energy transfers
P6.01 kinetic energy
17
P6.02 thermal (heat) energy, light energy
P6.03 elastic potential energy
P6.04 gravitational potential energy; raise it upwards
P6.05 loudspeaker, buzzer, and so on
P6.06 light, sound, heat
P6.07
P6.18 speed
P6.19 0.5 J
P6.20 2560 J
P6.21 wasp
Chapter P7 Energy resources
P5.09 20 000 Pa
P5.11 a 3.0 m3 b
P6.17 100 m
P7.01 Both are variable (more wind and waves some
days than others).
P7.02 light energy → electrical energy (+ heat)
P7.03 k.e. and g.p.e.
P7.04 a coal, oil, gas
b wood, charcoal, peat (also straw and others)
P7.05 chemical energy → heat (+ light)
P7.06 Nuclear energy is converted to heat energy and
electrical energy.
P7.07 a non-renewable – because uranium is used up
b renewable – because new waves appear
every day
P7.08 uranium (nuclear fuel), geothermal energy,
tidal energy
Energy stores
Example
kinetic energy
moving car
gravitational
potential energy
water in cloud
chemical energy
petrol
nuclear energy
uranium
P8.02 gravity
strain energy
wound-up clockwork
toy
P8.03 joule (J)
P8.04 0.50 MJ
internal energy
hot water bottle
P8.05 a 1.0 J
Chapter P8 Work and power
P8.01 15 kg of feathers
b
P6.08 a chemical energy of fuel → internal energy of
room and water
b electrical energy → light and heat
c electrical energy → heat, k.e. and sound
P8.06 500 N through 10 m
P6.09 a 100 J
b 90 J
P6.10 a heat
b
P8.09 a 1000
sound
P6.11 harms the environment; wastes limited resources;
costs money
10 J
P8.07 none – it is not moving
P8.08 lift more bricks at a time (greater force); lift them
faster
P8.10 40 J/s
P8.11 100 W
P8.12 increased
b
1 000 000
Answers to questions
Chapter P9 The kinetic model of matter
Chapter P10 Thermal properties of matter
P9.01 A liquid takes up the shape of a container without
its volume changing.
P10.01
P9.02 boiling point (or condensing point)
P9.03 a solidification or freezing
b freezing point or melting point
P9.04 a Water is becoming hotter.
b Water and steam are present.
P9.05 Air is a mixture, so it does not have fixed melting
and boiling points.
P9.06 a because the particles are moving (they have
kinetic energy)
b gas
P9.07 a solid
b gas
P9.08 Air is a gas and water is a liquid. In these states,
the particles can move past each other, so we can
push past them. In a solid, such as a wall, particles
are in fixed positions, so that we cannot push
them apart.
P9.09 a Water molecules are too small to see.
b It was constantly jostled by molecules of the
water.
P9.10 Forces between tungsten atoms are stronger than
forces between iron atoms.
P9.11 a It is melting.
b Energy is required to break bonds between
particles (it increases their potential energy).
P9.12 The pressure will increase because the force of
the molecules on the walls of the container will be
greater (and collisions will be more frequent).
P9.13 a halved
b halved
c remains the same
P9.14
a The cold water gets hotter and expands. As its
volume increases, it pushes further up the tube.
b Set up two identical flasks, one with water,
the other with paraffin. Add a thermometer
to each. Place both in a hot water bath.
Record the level of the liquid in the tube as
the temperature increases.
P10.02 a The 2 kg of water at 30 °C has twice as much
internal energy as 1 kg. The internal energy
of the water is made up of the energies of
all the molecules. There are twice as many
molecules in 2 kg.
b The temperature is the same (because the
average energy of a molecule is the same in
each bucket).
c The average energy per molecule is the
same, as they are at the same temperature.
P10.03 0 °C = melting point of pure ice
100 °C = boiling point of pure water
P10.04 Place thermometer in pure melting ice and
mark 0 °C. Place in pure boiling water and mark
100 °C. Divide the scale between these two into
100 equal units.
P10.05 As the temperature rises, the air in the flask
expands and pushes downwards, so that the
water level drops.
P10.06 a approximately 40 to 50 °C
b At 20 °C, the resistance changes only a little
for each degree change in temperature.
It changes more rapidly around 50 °C.
P10.07 The temperature-sensitive junction of the
thermocouple is very small and can heat up
or cool down more rapidly than the bulb of a
mercury thermometer.
Chapter P11 Thermal (heat) energy transfers
P11.01 a copper, steel, other metals
b air, wood, plastic, glass
P11.02 a temperature difference
P11.03 marble (it has a greater thermal conductivity)
volume doubled
The volume is doubled but the number of particles
remains the same, so their collisions with the walls
are half as frequent.
P9.15 Decrease the temperature so that the particles
move more slowly. Then they will collide with the
walls with less force, and less frequently.
P11.04 convection
P11.05 a Particles of hot gas move faster.
b Particles of hot gas are further apart.
P11.06 When a fluid is heated, its expansion causes its
density to decrease. It rises because it is less
dense than the surrounding air. Cooler, denser air
sinks as a result of the pull of gravity.
18
Cambridge IGCSE Combined and Co-ordinated Sciences
P11.07 Warm air rises above the heater, and moves
around the room. Cold air flows in to replace it
and so is heated.
P12.09
period T
P11.08 No convection current would be established
because the air heated by the heater cannot rise.
P11.09 radiation
P11.10 infrared, ultraviolet
P11.11 The rate of infrared emission increases.
P12.10 a A has the greater frequency.
P11.12 a Matt black is a better absorber.
b Matt black is a better emitter.
c Shiny black is a better reflector.
b A will sound more high-pitched.
P11.13 Lids reduce heat loss by convection. Wooden or
plastic surfaces reduce heat loss by conduction.
P11.14
19
Feature
Reduces
Reduces
Reduces
conduction? convection? radiation?
double
glazing
yes
yes
yes
(if coated)
cavity wall
insulation
yes
yes
yes
carpet,
underfloor
insulation
yes
no
no
draught
excluders
no
yes
no
curtains
yes
yes
no
loft
insulation
(with shiny
foil)
yes
yes
yes
P12.11 Sound waves travel by the vibration of the
particles of a material. There are no particles
in a vacuum.
P12.12 (for example) shout from outside a closed
window
P12.13 In a compression, the particles are closer
together than before the wave is formed. In a
rarefaction, the particles are further apart. See
Figure P12.05 in the main text.
Chapter P13 Light
P13.01 a
b This is so that it looks the right way round in a
motorist’s rear-view mirror.
P13.02 a
normal
mirror
angle of
incidence i
P11.15 Heat is lost from head by convection, and a hat
greatly reduces this.
Chapter P12 Sound
P12.01 all three
P12.02 the air in the hollow tube
P12.03 a 600 ms = 0.6 s
b three-fifths
P12.04 They must be in a straight line so that the
distance travelled in the time interval measured
is equal to the separation of the microphones.
P12.05 Light travels faster than sound. For example,
lightning is seen before thunder is heard.
P12.08 a 20 Hz to 20 kHz
b upper limit in particular decreases
reflected ray
incident ray
b angle of incidence = angle of reflection
P13.03 60°
P13.04 No light reaches the place at which the image
appears to be formed.
P13.05
refracted ray
angle of
refraction
glass
air
angle of
incidence
P12.06 pitch gets higher
P12.07 loudness decreases
angle of
reflection r
incident
ray
normal
Answers to questions
P13.06 towards the normal
P13.21
P13.07 a
TIR
TIR
TIR
TIR
P13.22 Light travelling along the glass will be absorbed
by any impurities present.
P13.23
b It is parallel to its initial direction.
P13.08 a angle of incidence = 0°
b angle of refraction = 0°
P13.09 The angle of refraction is less than the angle of
incidence.
converging
P13.24 parallel rays
diverging
focus
P13.10 Rays of light are refracted as they pass through
the raindrops.
P13.11 2.4
P13.12 a Light travels more slowly in material B,
because the ray bends more on entering B.
b material B
P13.13 a glass
b away from the normal
P13.26 It is the point at which rays travelling parallel to
the axis of the lens are made to converge.
P13.14 1.58
P13.15 2.17 × 108 m/s
P13.16 25.4°
P13.17 total: 100% of the light is reflected internal:
reflection happens inside the transparent
material
P13.18 No, it will not be totally internally reflected
because 45° is less than the critical angle.
P13.19 a c = 48.8°
b See Figure P13.05c in the main text.
F
P13.27 Light rays pass through the point at which a
real image is formed, and it can be formed on a
screen. For a virtual image, the rays only appear
to emerge from that point, and the image cannot
be formed on a screen.
P13.28 The image arrow is below the axis.
P13.29 The rays from the image are dashed. They only
appear to be diverging from that point.
P13.30 a See ray diagram below.
b 7.5 cm
P13.20 n = 1.56
I
P13.25 Reverse the arrow on the rays so that they spread
out from the focus.
O
F
20
Cambridge IGCSE Combined and Co-ordinated Sciences
Chapter P14 Properties of waves
P14.17
P14.01 The first has distance on its horizontal axis, and
the second has time on its horizontal axis.
Displacement
P14.02
amplitude
Distance
or Time
Chapter P15 Spectra
P15.01 yellow, blue
The diagram should show that amplitude is
the height of a wave crest above the central
(undisturbed) level.
P15.02
spectrum
P14.03 Measure across, say, 10 ripples and find the
average separation by dividing by 10.
P14.04 1.5 cm (or 15 mm)
P14.05 a 100 Hz
b
0.01 s
P14.06 The molecules vibrate up and down.
P14.07 longitudinal
21
red
white light
prism
violet
orange
yellow
green
blue
indigo
P15.03 Some colours of light are more strongly refracted
because their speed decreases more.
P15.04 a red light
b
violet light
P15.05 a infrared
b
red light
P14.08 v = f l (speed v in m/s, frequency f in Hz,
wavelength l in m)
P15.06 a gamma rays
P14.09 300 m/s
P15.07 a Both violet light and red light travel equally
fast in empty space.
P14.10 wavelength 1 m has higher frequency
P14.11 frequency 90 MHz has longer wavelength
P14.12 a speed decreases
b wavelength decreases
c
frequency is unchanged
P14.13
reflected
waves
b radio waves
b Red light travels faster in glass.
P15.08 infrared radiation, microwaves
P15.09 Microwaves may transfer signals to and
from satellite; radio waves are broadcast,
and received by an aerial; remote control
uses infrared.
Chapter P16 Magnetism
P16.01 a
incident
waves
barrier
P14.14 Change the depth of the water – shallower water
gives slower ripple speed.
P14.15 Diffraction – ripples spread out into the space
beyond the gap.
P14.16 For greatest diffraction effect, the width of the gap
should be equal to the wavelength of the waves.
N
S
S
N
Adjacent N and S poles attract one another
with equal forces.
b
N
N
S
S
The adjacent N poles and the adjacent S
poles repel one another with equal forces.
Answers to questions
P16.02 a Soft magnetic materials are easier to
magnetise and demagnetise. Hard magnetic
materials are more difficult to magnetise and
also more difficult to demagnetise.
b A permanent magnet made of steel will retain
its magnetism for a longer time.
P17.04
rod
positive charges
attracted to rod
paper
P16.03
negative charges
repelled by rod
N
S
S
P17.05 a negative
b repel
N
P16.04 Copper and iron are mixed together.
Pass the electromagnet over the mixture of
metal. Because copper is not magnetic, the
electromagnet will attract only the iron, pulling
it out of the mixture.
P16.05 a
P17.06 The electric force causes the negative charges
(electrons) to repel each other. As a result,
some of them move through the wire to the
other sphere, so that it gains a negative charge.
(The charge on the first sphere decreases.)
Chapter P18 Electrical quantities
P18.01 a ammeter
b connected in series
c
A
P18.02 a, b
N
S
current in
22
A
A
current out
c
Ammeter readings are the same.
P18.03 a (for example) copper, gold, silver
b (for example) glass, Perspex, polythene
b When the current is reversed, the field is
reversed, so the arrows on the field lines are
reversed.
Chapter P17 Electric charge
P17.01 repel
P17.02
a positive (and equal in size to the negative
charge on the rod)
b attract
P17.03 Individual hairs all have the same charge, so they
repel. Hair and comb have opposite charges, so
they attract.
P18.04 a ampere, amp (A)
b coulomb (C)
P18.05 a 1000
b 1 000 000
P18.06 1 A = 1 C/s
P18.07 20 A
P18.08 40 C
P18.09 a potential difference
b volt (V)
c voltmeter
d
V
Cambridge IGCSE Combined and Co-ordinated Sciences
P18.10 a e.m.f. (electro-motive force)
b volt (V)
P18.11 a 6.0 Ω
P19.08 4
b
increase
b
30 V
P18.12 20 V
P18.13 a 10 Ω
P19.07 90 Ω
P18.14 14.5 mA (0.0145 A)
P18.15 a longer wire has greater resistance
b
P19.09 A long wire is like two or more short wires
connected in series. Their resistances add up to
give the combined resistance.
P19.10 A thick wire is like two or more thin wires
connected in parallel. Their effective resistance is
less than that of an individual wire.
P19.11 a 0.50 A
A
wire
b The 20 Ω resistor has the greater p.d.
across it.
P19.12 20 Ω
P19.13 20 Ω
V
P18.16 a 80 Ω
b
160 Ω
P18.17 The graph is a straight line through the origin.
P18.18 The graph is curved; twice the p.d. gives less than
twice the current.
P18.19 watts = volts × amps
23
P18.20 50 W
P18.21 2.5 A
P19.14 5 A; slightly above normal current
P19.15 a To protect the wiring of the circuits; if an
excessive current flows, the fuse blows and
breaks the circuit.
b An electromagnetic trip switch could be
used instead.
P19.16 Heating of wires, leading to melting of insulation
(poisonous fumes, possibility of fire) and possible
short-circuit between wires.
P18.22 2640 J
Chapter P20 Electromagnetic circuits
Chapter P19 Electric circuits
P20.02 The field lines are further apart.
P19.01 a
P20.01 clockwise
P20.03 It would rotate in the opposite direction
because its poles would be attracted the
opposite way round.
b
P19.02 1.4 V
P19.03 a light-dependent resistor
P20.04 a If the current was not reversed, the coil
would turn until its poles were facing their
opposites and then stop turning.
b The commutator reverses the current.
b
P20.05 A greater current gives a greater turning effect.
c
Its resistance decreases when light shines on
it.
P20.06 reverse the current; reverse the magnetic field
P20.07 force (motion) – thumb
magnetic field – first finger
P19.04 a
current – second finger
b used in temperature sensing circuit
c
Its resistance changes rapidly when
temperature changes a little.
P19.05 40 Ω
P19.06 The same current (1.4 A) flows through resistors B
and C.
P20.08 increase the current; increase the magnetic
field strength
P20.09 zero force
Answers to questions
Chapter P21 Electromagnetic induction
P21.01 a
heat
electrical
energy
b
k.e.
P22.07 a The number of protons is the same (and the
number of electrons in a neutral atom).
b number of neutrons
P22.08 a
heat
k.e.
electrical
energy
P21.02 The wire or magnet must move.
P21.03 move the N pole out of the coil; move the S pole
towards the coil
P21.04 Move the magnet faster; use a stronger magnet.
P21.05 bigger coil; more turns; stronger magnetic field;
faster movement
P21.06 so that less energy is lost during transmission
P21.07 primary coil; secondary coil; core
P21.08 step-up
P21.09 step-down
P21.10 2.5
P21.11 100
P21.12 a The core transfers the varying magnetic field
from the primary coil to the secondary.
b Its magnetism must change rapidly.
P21.13 The magnetic field in the core does not change,
so no e.m.f. will be induced in the secondary coil.
P21.14 current is less
P21.15 a 400 kV
b 250 A
c
1.5 MW
P21.16 a 157
b 1.53 A
c
No power is lost in the transformer.
Chapter P22 Atomic physics
P22.01 a protons, neutrons
b electrons
P22.02 There is electrostatic attraction between
opposite charges.
P22.03 a nucleon number = 17
b proton number = 8
P22.04
210
82
Pb
P22.05 47 protons, 60 neutrons, 47 electrons
P22.06 1840 approximately
Nuclide Proton
number,
Z
Nu-1
6
Nu-2
7
Nu-3
7
Nu-4
6
Nu-5
5
Nu-6
6
Neutron
number,
N
6
6
7
8
6
7
Nucleon
number,
A
12
13
14
14
11
13
b Nu-1, Nu-4, Nu-6
c
Nu-2, Nu-3
d boron (B), carbon (C), nitrogen (N)
P22.09 radon and thoron gases in atmosphere
P22.10 There is less atmosphere above them to absorb
cosmic rays from space.
P22.11 15% approximately
P22.12 (for example) medical, weapons fallout, air travel,
TV sets, working with radioactive materials,
nuclear discharges
P22.13 Geiger counter, photographic film
P22.14 a a
b b
P22.15 electron
P22.16 g
P22.17 a g
a
b
P22.18 a, b, g, X-rays
P22.19 g-rays are uncharged.
P22.20 a a
b It is most easily absorbed.
P22.21 a
210
206
4
Po → 82Pb + 2He + energy
84
b 84 = 82 + 2
c
210 = 206 + 4
P22.22 average (… the average time taken …)
P22.23 25
P22.24 55
P22.25 6000 years
P22.26 b-radiation is less easily absorbed than
a-radiation.
P22.27 The radiation must penetrate thick metal. a- and
b-radiation would be completely absorbed.
P22.28 The plastic is too thin to absorb the g-radiation used.
P22.29 The radiation must penetrate the ground to
reach the surface if it is to be detected.
24