ANSWERS
Cambridge
IGCSE® Biology
Practice Book
Answers
1 Characteristics of living
things
1
Characteristic
3
Exam focus
Definition
the breakdown of food in
cells to release energy
1
2
respiration
an increase in size, mass and
complexity of an organism
3
excretion
producing offspring, which
prevents extinction of the
species
sensitivity
this involves feeding
– obtaining nutrients
for growth, energy and
maintaining health
reproduction
in response to changes, e.g.
presence of a predator, to
find food or a mate
growth
the ability to detect
changes in the surroundings
movement
getting rid of the waste
products made by chemical
reactions in cells
nutrition
2
Any suitable sentence with seven words linked
to the characteristics of life, e.g. Most Rats Start
Gathering Rice Every Night.
Across 5 excretion 6 nutrition 7 respiration Down
1 sensitivity 2 reproduction 3 movement 4 growth
4
Organism
plant
animal
5
6
Product
1 carbon dioxide/
water
2 oxygen
1 carbon dioxide/
water
2 urea
(Breathing) is the process of getting oxygen into the
lungs and the removal of carbon dioxide.
Ref. to faeces being undigested food, which has not
been formed through metabolic processes.
Process
respiration
photosynthesis
respiration
deamination
(Respiration) is the release of energy from food
substances in cells.
4
B
Any three from: movement, excretion, nutrition
(feeding), sensitivity (irritability).
(a) Any two from: movement, excretion, sensitivity.
(b) Any two from: growth, reproduction, respiration.
Any three from: sensitivity, nutrition, growth,
excretion.
2 Classification of living
organisms
1
2
protoctists, fungi, plants, bacteria
A (a)(dragonfly) insect
(b)Key features – any two from: three pairs
of legs, two pairs of wings, one pair of
antennae, body divided into three parts, one
pair of compound eyes.
B (a) (earthworm) annelid
(b) Key features – any two from: elongated,
cylindrical body, segmented body, clitellum
present.
C (a) (snail) mollusc
(b)Key features – any two from: has a shell,
muscular foot, eyes on tentacles.
D (a) (spider) arachnid
(b)Key features – any two from: four pairs
of legs, body divided into abdomen and
cephalothorax, several pairs of simple eyes,
chelicerae for biting prey.
3 Any two from: no backbone, have exoskeleton,
segmented bodies, jointed limbs.
4 (fish and amphibians)
Common features – any two from: cold blooded,
have eyes, produce jelly-covered eggs (in water).
Differences: ref. to gills/lungs, fins/legs, scales/moist
skin.
(amphibians and reptiles)
Common features – any two from: four legs, eyes
and ears, cold blooded, lungs.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
1
ANSWERS
Differences: ref. to moist skin/scales, eggs jelly
covered/waterproof shell
(birds and mammals)
Common features – any two from: eyes and ears,
warm blooded, lungs.
Differences: ref. to feathers/fur, two legs/four legs,
eggs with hard shell/live young, beak/no beak (or
ref. to teeth), ears/ears with pinna, no mammary
glands/mammary glands.
5 (a) (i)Any three features from: multicellular, have
roots, stems, leaves, ref. to seed production.
(ii)Any three features from: (cellulose) cell wall,
sap vacuole, nucleus, cytoplasm, membrane.
(b) (leaf shape) broad
(leaf veins) parallel
(cotyledons) two
(grouping of flower parts) in threes
6 (a)(fungi) Any two from: presence of hyphae, ref.
to mycelium, chitin in cell walls, no chlorophyll
present, ref. to spores, enzymes secreted for food
digestion.
(bacteria) Any two from: small, cell wall – not
cellulose or chitin, membrane/cytoplasm present,
glycogen granules present, DNA in form of one
coiled chromosome, no nucleus.
(viruses) Any two from: very small, no special cell
structure, have a strand of DNA/RNA, surrounded
by protein coat/ref. to capsid, only show
reproduction.
(b) virus, bacteria, fungi
(c) only show reproduction as a characteristic of life
4 Cell structure and
organisation
1
2
3
cell wall
chloroplast
cytoplasm
Exam focus
B
(a) (i)Any two from: exoskeleton, segmented body,
segmented limbs.
(ii)Any two from: five pairs of legs, two pairs
of antennae, exoskeleton in the form of a
carapace, compound eyes.
(b)Ref. to maintaining constant body temperature/
warm blooded, moves around more to find food
or to find a mate.
1
2
3 Using simple keys
1
4
A insect, B arachnid, C myriapod, D crustacean,
E mollusc, F annelid, G nematode
2
Plant
A
B
1a 1b
– 
 –
2a
–
–
C
–

–
D

–

2b 3a 3b Name of plant
– –  Primula vulgaris
 –
– Narcissus
pseudonarcissus
–  – Ranunculus
ficaria
– –
– Hyacinthoides
non-scripta
Exam focus
1
2
A
B
C
D
E
Nucellus lapillus
Calliostoma ziziphinum
Patella vulgata
Littorina obtusata
Cerastoderma edule
(a)F
(b)F
(c)T
(d) T
(e) F
(f) T
(g) T
(h) F
(i) T
(j) T
(a)A membrane, B cytoplasm, C cell wall,
D chloroplast, E (sap) vacuole, F nucleus
(b) chloroplast, cell wall, (sap) vacuole
Cell part
Description
a fluid-filled space surrounded
by a membrane
a round or oval structure
containing DNA in the form
of chromosomes
a tough, non-living layer made
of cellulose, which surrounds
the membrane
membrane
jelly-like, with particles and
organelles in it
nucleus
an organelle containing
chlorophyll
sap vacuole
a partially permeable layer
that forms a boundary around
the cytoplasm
(a) contains cell organelles, site of chemical reactions
(b)prevents cell contents from escaping, controls the
passage of substances into and out of cell
(c)controls cell activities, controls cell division/
development
Exam focus
1
(a) cell membrane, cytoplasm, nucleus
(b) (i)chloroplast
(ii)chlorophyll, traps light energy for
photosynthesis
2 (a) Any two from: cell wall, chloroplast, sap vacuole.
(b) Function
Cell part
controls cell activities and development
contains cell organelles and is the
site of chemical reactions
waft mucus and bacteria away
from the lungs
controls what substances enter and
leave the cell
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
B
D
A
C
(a) Any five parts compared from:
Cell part
cell wall
membrane
cytoplasm
nucleus
chloroplast
sap vacuole
6
Liver cell Palisade mesophyll cell












(b) Functions of six parts, such as:
cell wall – prevents the cell from bursting
membrane – controls what substances enter
and leave the cell
cytoplasm – contains cell organelles
nucleus – controls cell activities
sap vacuole – contains sugars and salts
chloroplast – traps light energy for
photosynthesis.
5 Levels of organisation
1
2
7
chromosome, nucleus, cell, tissue, organ,
organ system, organism
Example
Term
leaf
heart
Any five named leaf cells (max. 3 marks for each),
with features described and functions stated, such as:
Epidermal cell: thin, transparent, no chloroplasts
present, allows light through/acts as a barrier to
disease organisms.
Palisade mesophyll cell: columnar, packed with
chloroplasts, for photosynthesis/to trap light energy.
Spongy mesophyll cell: mostly spherical shaped,
chloroplasts present, for photosynthesis/allows
gaseous exchange within the leaf due to air spaces
between cells.
Guard cell: found in pairs, mainly in lower epidermis,
contains chloroplasts, controls opening of stomata.
Xylem cell: long and thin, with lignified cell wall,
lacks end wall/cell contents, transports water and
mineral salts.
Phloem cell: sieve plate present in end wall,
transports sugars and amino acids/ref. to
translocation.
Name
Location
Function
plant
cell
root hair
cell
on surface of
young roots
animal
cell 1
sperm
cell
produced in
testes
animal
cell 2
ciliated
cell
bronchus/
oviduct
animal
cell 3
villus cell
small
intestine
absorption
of water/
absorption of
mineral salts/
anchorage of
plant into the
soil
fertilisation
of egg/
reproduction
waft bacteria
or mucus
away from
the lungs/
move egg
from ovary to
uterus
absorbs
digested food
molecules/
water
cell
organ
skeleton
tissue
root hair
spongy mesophyll
worm
3
4
organ system
organism
(a) magnification = observed size
actual size
12
(b)
= × 4.3
2.8
15
15
100 =
= 0.15 mm
; actual size =
100
actual size
(a)a group of cells with similar structure,
performing a special function
(b)Any two animal tissues and any two plant tissues
and their functions:
e.g. ciliated cells – waft mucus with dust or
bacteria away from the lungs
muscle cells – can contract to cause movement
red blood cells – transport oxygen around the
body
root hair cells – absorb water and mineral salts/
anchor the plant into the soil
xylem cells – transport water and mineral ions
from roots to leaves/provide strength for the
stem.
ANSWERS
3
Exam focus
1
5
Organ – several tissues grouped together to make a
structure with a special function, e.g. heart, leaf.
Organ system – a group of organs with closely
related functions, e.g. circulatory system, flower.
Tissue – a group of cells of similar structure that
work together to perform a special function, e.g.
muscle, xylem.
2
Cell
Organelle(s)
muscle
cell
mitochondria
red blood
cell
nucleus
More/
less/
none
more
none
Explanation
need a lot of
energy from
respiration for
contracting
provides more
space for
haemoglobin
(Continues overleaf)
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
3
ANSWERS
2
(Continued)
Cell
Organelle(s)
upper
epidermal
cell
chloroplasts
liver cell
mitochondria
more
xylem
nucleus
none
3
More/
less/
none
none
Explanation
makes the cell
transparent so
light can pass
through
carry out many
chemical reactions, requiring
energy from
respiration
allows water
to flow freely
through the vessel
(a)The leaf contains a number of different tissues,
which work together to carry out photosynthesis/
transpiration.
(b)
Leaf
part
A
B
C
D
E
F
Name
Function
(waxy) cuticle
waterproofs the leaf
upper epidermis allows light to pass
through/acts a barrier to
microbes
palisade
main site of photosynthesis
(mesophyll)
xylem
transports water and
mineral salts
phloem
transports products of
photosynthesis/carries out
translocation
guard cell
controls exit of water
vapour from the leaf
6 Diffusion and active
transport
1
movement of a substance from a region of high
concentration to a region of lower concentration
down a concentration gradient
2 (a) (i)oxygen
(ii)Any three points from: short distance, big
concentration gradient, small molecules, large
surface area, higher temperature.
(b) (i)Rate of diffusion would drop, because the
molecules have a lower kinetic (movement)
energy/molecules move more slowly.
(ii)Rate of diffusion would increase, because the
concentration gradient would increase or be
maintained.
3 (a) (i)labels to parts as shown in the following
diagram
(ii)arrows as those shown in the following
diagram (through a stoma, through air space
in spongy mesophyll, into palisade mesophyll
cell)
4
upper
epidermis
palisade
mesophyll
cell
air space
stoma
(b) (i)Upper epidermis has an impermeable layer of
waxy cuticle.
(ii)The guard cells close the stomata to reduce
transpiration, preventing gas exchange.
4 (a)F
(b)T
(c)F
(d) F
(e) T
(f) T
5 the movement of a substance across a membrane
from a region of lower concentration to a region
of higher concentration, against a concentration
gradient, using energy
6 (a)
Process(es)
plant A
Reason
roots have absorbed nitrate
until there is no concentration
diffusion only
gradient
the roots have absorbed
plant B
nitrate against a concentration
diffusion and active gradient, building up a higher
transport
concentration than that present
in the soil
(b)Plants need energy from respiration to carry out
active transport. Cyanide prevents respiration.
Exam focus
1
2
D
Type of
cell
Substance Process(es)
absorbed used
root
water
osmosis
hair cell phosphate 1. diffusion
2. active
transport
glucose
villus
cell in
small intestine
1. diffusion
2. active
transport
Gradient:
high to low/
low to high?
high to low
1. high to
low
2. low to
high
1. high to
low
2. low to
high
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
Energy
used?
no
1. no
2. yes
1. no
2. yes
7 Osmosis
1
2
roots, osmosis, higher, lower, membrane, turgid,
flaccid, wilting, small, partially
(a)Level in the hollow goes down, level in the dish
goes up.
(b)There is a higher concentration of salt in the
dish, so water moves from the hollow to the dish,
through the potato cells by osmosis.
(c)Water moves out of the root hair cells by
osmosis, so the cells become flaccid and die. The
plant then dies because it has lost its ability to
absorb water.
3
Substance
Diffusion
Osmosis
oxygen
water
phosphates
carbon
dioxide

 (accept )






4
5
concentrated the sugar solution, the more mass is
lost. Between 0.6 mol dm-3 and 1.0 mol dm-3, there
is no additional mass lost as the potato cells have
become fully flaccid in each case.
Zone C – at this point there is no net gain or loss
of mass by the potato core as the water potential
inside the cells is the same as the water potential of
the surrounding sugar solution.
6 (a)Ref. to transport medium/moves mineral salts or
sucrose or amino acids around the plant
maintains the turgidity of cells/to keep cells firm/
to prevent wilting.
Ref. to raw material for photosynthesis.
(b) (i)Ref. to root hair cells, absorb water by
osmosis, from a high concentration in the soil,
to a lower concentration in the cell.
(ii)Ref. to cortex cells, have a lower
concentration of water than epidermal
cells, so water moves by osmosis, until water
reaches xylem, ref. to transpiration pull.
(iii)Water in leaf cells evaporates, into air spaces,
higher concentration of water vapour in air
space than in atmosphere, so molecules move
out of leaf by diffusion, through stomata.
Exam focus
1
(a) (i)The concentration of water is higher
outside the cell, so water enters the cell, by
osmosis, the cell becomes turgid.
(ii)The concentration of water is higher inside the
cell, so water leaves the cell, by osmosis, the
cell becomes plasmolysed, then flaccid.
(b) (i)The concentration of water is lower inside the
cells than in the plasma, so water enters the
cells, by osmosis, the cells become turgid, then
burst because they have no cell wall.
(ii)Red blood cells are no longer able to
transport oxygen, so cells are unable to
respire, resulting in an energy shortage.
2 (a) (b)
Start
length/
cm
Length
after
1 hour/
cm
Change
in
length/
cm
0.0
5.0
5.3
0.3
0.2
5.0
5.1
0.1
2.0
0.4
5.0
4.7
–0.3
–6.0
0.6
5.0
4.4
–0.6
–12.0
0.8
5.0
4.3
–0.7
–14.0
1.0
5.0
4.3
–0.7
–14.0
Active
transport




There is a higher water potential in the soil than in
the root hair cells, so water passes into the root hair
by osmosis. The sap in the root hair cell develops
a higher water potential than the cell next to it
(cortex cell), so water moves across from cell to cell
until it reaches the xylem. Water moves up the xylem
vessels, so a water potential gradient is maintained.
Zone A – as the sugar solution becomes less
concentrated, more water enters the potato cells by
osmosis, so the tissue gains mass. The more dilute
the sugar solution, the more mass is gained.
Zone B – as the sugar solution becomes more
concentrated, more water leaves the potato cells
by osmosis, so the core loses mass. The more
%
change
in
length
Sugar
concentration
/mol dm-3
(c)
6.0
10.0
5.0
% change in length
(a) A alveolus/air sac B capillary C red blood cell
(b) (i)arrow from inside the alveolus to a red blood
cell
(ii)arrow from blood plasma to inside the
alveolus
(iii)arrow along capillary from pulmonary artery
to pulmonary vein
(c) (i)diffusion
(ii)Ref. to breathing to keep oxygen levels in the
alveoli high; ref. to blood constantly moving
through capillaries, bringing blood low in
oxygen.
4 (a) Acapillary – absorbs digested food molecules,
e.g. glucose, amino acids
B lacteal – absorbs fatty acids, glycerol
Cepithelial lining – one cell thick for efficient
absorption/has microvilli to increase surface
area for absorption
(b)to increase surface area for efficient absorption/
to increase rate of diffusion
(c) (i)diffusion
(ii)Any two from: walls are one cell thick, form a
network to provide a large surface area, close
to the surface of the villus.
(d)(i)When the concentration of glucose in the
intestine is the same as/lower than the
concentration in the capillary.
(ii)Energy is required.
ANSWERS
3
0.0
0.0
–5.0
0.2
0.4
0.6
0.8
1.0
sugar concentration/mol dm–3
1.2
–10.0
–15.0
–20.0
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
5
ANSWERS
(d)(i)0.26 mol dm-3
(ii)The concentration of sugar in the potato
cells is the same as the concentration in
the surrounding solution, so there is no net
movement of water molecules.
(e)Any two from: leave all the cores in the solutions
for the same amount of time, use the same
volume of solution in each test tube, cut all the
cores to the same diameter.
(f)Any one from: set up two or more cores for
each concentration, measure the length of the
cores in millimetres, weigh the cores instead of
measuring length.
8 Enzymes
1
2
(a)a chemical that speeds up the rate of a reaction
without being changed itself
(b)a biological catalyst, protein in nature, which
speeds up the rate of a reaction
(a)
enzyme
amylase
starch
maltose
substrate
end product
(b) Any two from: starch is a larger molecule, starch
is insoluble while glucose is soluble, starch is
a polysaccharide/polymer while glucose is a
monosaccharide/monomer.
(c)Protease only digests proteins, amylase only
digests starch.
The active site in protease will have a different
shape to the active site in amylase, so the
substrate (starch) will not fit.
3 (a)
rate / arbitrary units
optimum reaction
rate
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
the reaction is
speeding up
fastest here
Exam focus
1 (a) (i)lipase
(ii)protease/pepsin
(b)Enzymes digest molecules causing the stains, the
small molecules produced are soluble.
(c)The enzymes in the powder would be denatured,
so they would not digest the stains.
(d)Amino acids are small, soluble molecules while
proteins in blood are large, insoluble molecules.
2 (a) (i)amylase
(ii)maltose
(iii)Any two from: energy source, to convert to
cellulose, convert to materials for growth.
(iv)Starch is a large, insoluble molecule; maltose
is smaller, soluble.
(b) (i)Ref. to water passes through the micropyle.
(ii)Enzymes are only active in water; cells
become turgid – leading to expansion.
9 Nutrition and nutrients
1 (a) (i) starch
(iii)
denaturing is
taking place
here
(ii) obtaining energy
chemical bond
glucose unit
(b) (i) fat/lipid
the reaction is
slow here
(ii) energy/insulation/formation
of cell membranes/hormone
formation
(iii)
0
20
40
temperature/ ° C
60
(b) (i)The reaction would speed up because the
substrate and enzyme molecules would move
faster/gain more kinetic energy, so there
would be more collisions.
(ii)There would still be no reaction because all
the enzyme molecules have been denatured
by the high temperature.
4 temperature, pH, concentration of substrate
5 Any two from:
Baking, e.g. bread. Enzymes in yeast convert sugar
to ethanol and carbon dioxide. The carbon dioxide
6
makes the bread dough rise. The ethanol evaporates
as the bread is baked.
Brewing, e.g. beer or wine. Enzymes in yeast convert
sugar to ethanol and carbon dioxide. The ethanol
makes the drink alcoholic; carbon dioxide gives the
drink its ‘fizz’.
Cheese-making. The enzyme rennin, extracted from
cows’ stomachs, is used to clot milk.
Making baby foods. Trypsin (a protease) is used to
pre-digest baby foods.
6 (a) (i)Stir the mixture of feedstock and
microorganisms/distribute the heat through
the liquid.
(ii)Extracts the microorganisms from the filtrate.
(iii)Provides nutrients for the microorganisms to
grow, respire and produce enzymes.
(b)fungi, bacteria
(c)Microorganisms are filtered from the feedstock,
then crushed and washed with water.
glycerol
(c) (i) protein
chemical
bond
fatty acid
(ii) g
rowth/tissue repair/enzymes/
cell membranes/hormone
formation
(iii)
amino acid
chemical bond
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
Food tested
Chemical reagent used
Colour for a
positive result
reducing
sugar
iodine
solution
blue-black
fat
Benedict’s
solution
violet (halo)
ethanol
brick red
Biuret solution
(sodium
hydroxide + copper
sulfate solution)
white
emulsion
protein
starch
3
4
5
(a) iron
(b)water
(c)calcium
(d)fibre
(e)vitamin C
(a)Yeast is mixed with flour, some sugar and water
to make dough. The dough is kept warm to
allow the yeast to respire the sugar, producing
pockets of carbon dioxide. These make the
dough rise. Baking kills the yeast.
(b)Bacteria (e.g. Streptococcus thermophilus and
Lactobacillus bulgaricus) are used to ferment
milk at 46 oC. As a result, lactic acid is produced
(as fermentation progresses the pH drops).
The lactic acid makes the milk coagulate. The
temperature is then reduced to 5 oC to prevent
further bacterial action.
Any three from:
Name of
group
antioxidants
Function
of additive
stop food
reacting
with
oxygen
Advantage
Disadvantage
stop the
taste of the
food being
spoiled/
stop colour
changing
food
­becomes
more
­attractive
may have side
effects for
some consumers, e.g. stomach problems,
kidney stones
may be
hazardous to
health/trigger
allergic reactions/cause
hyperactivity
in children
e.g. sugar
increases
calorific
value, risking
obesity, artificial sweeteners can have
side effects
some
­additives, e.g.
sodium nitrite, may be
carcinogens
colourings
improve
the
appearance
of the food
flavourings
enhance
the taste
of the
food
improve
the flavour
preservatives
increase
the shelf
life of the
food
food can
be kept for
longer
1
2
3
A vitamin C
B amino acids
(a)Any two from: less saturated fat, more fibre,
more calcium.
(b) (i) Any one from: other red meat, liver, kidney,
eggs, green vegetables, chocolate, etc.
(ii) n
eeded for the formation of haemoglobin in
red blood cells
(iii)Ref. to anaemia, constant tiredness, lack of
energy.
(c) (i)filamentous fungus
(ii)better flavour, cheaper to produce
(d)Any two from: the food is cheaper to produce,
farmers have no vets’ bills, less energy lost/more
energy available.
ANSWERS
Exam focus
2
10 Plant nutrition
1 (a)
light
carbon dioxide + water
chlorophyll
glucose + oxygen
(b)(i) Sucrose
(ii) Starch
(c)Chlorophyll traps light energy.
(d)Any three from: shortage of oxygen, shortage
of food, shortage of nesting sites, shortage of
hiding places.
2 (a) palisade (mesophyll) cells
(b)guard cells
(c) (upper) epidermis cells
(d)xylem cells
(e)phloem cells
3 (a)Nitrate ions are needed to form amino acids, to
build proteins. Proteins are needed for growth.
(b)Magnesium ions are needed to make chlorophyll.
Chlorophyll is needed to trap light energy for
photosynthesis.
4
leaching
rapid
algal
growth
death
of
algae
decay
by
bacteria
death of
aquatic
animals
5
Boil the leaf in water: to kill the leaf – this makes it
permeable.
Boil the leaf in ethanol: to decolorise the leaf, since
chlorophyll dissolves in ethanol.
Rinse the leaf in water: boiling the leaf in ethanol
makes it brittle, so the water softens it.
Spread the leaf out on a white tile: so the results will
be easy to see.
Add iodine solution to the leaf: to test for the
presence of starch.
6 (a) (i)violet and orange/red
(ii)green
(b)Use a bright light to shine on the Elodea in a
beaker of water. Measure the light intensity using
a light meter, or measure the distance between
the lamp and the plant. Allow the plant to adjust
to the light intensity. Count the number of bubbles
produced by the plant over a fixed time period
(e.g. 1 minute). Move the lamp further away from
the plant. Measure the new light intensity or the
new distance between the lamp and the plant.
Allow the plant to adjust to the light intensity.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
7
ANSWERS
Count the number of bubbles produced by the
plant over the same time period. Repeat the
process for at least five different light intensities
or distances. Keep the temperature of the water
the same, use the same plant, use the same beaker,
the same time period for counting bubbles.
Alternatively, the oxygen could be trapped in
a graduated container such as an inverted gas
cylinder, so the volume of gas could be measured.
Exam focus
1
2
B palisade mesophyII
(a) (i)(Description): Any two from: plants would
show poor growth, stems weak, lower leaves
yellow/dead, upper leaves turn pale yellow.
(Explanation): nitrates needed to produce
proteins, which are needed for growth.
(ii)Any two from: apply animal manure, crop
rotation involving leguminous plants, apply
artificial fertilisers.
(b)Leaves turn yellow/ref. to chlorosis, from the
bottom of the stem upwards, poor plant growth,
ref. to inability to form chlorophyll.
3 (a)an external factor, which restricts the effects of
others
(b)Any two from:
Carbon dioxide – needed as a raw material for
photosynthesis, converted into carbohydrate.
Temperature – increased temperature speeds up
photosynthesis, as enzymes work faster at higher
temperatures.
Light intensity – light energy needed for
photosynthesis, more light speeds up the process,
so more carbohydrate produced.
4 Destarch two similar potted plants. Place them in
sealed bell jars/large transparent containers. To one
container add a CO2 absorber. Expose both plants
to same, optimum conditions, e.g. light, warmth.
Leave for 2 days. Test a leaf from each plant for
the presence of starch. Only the control plant
leaf (without CO2 absorber) will turn blue-black,
indicating the presence of starch.
5 (a) (i) A guard cells
B upper epidermal cell
C spongy mesophyll cell
D palisade mesophyll cell
(ii)B
D
C
A
(b)Xylem – transports water, mineral salts from
roots around the plant.
Phloem – transports sucrose, amino acids from
leaves to storage or growth regions of the plant.
11 Human diet
1 (a)Any two advantages from:
high carbohydrate level – for energy
good source of calcium – for strong bones and
teeth/to prevent rickets
protein present – for growth/repair.
Any two disadvantages from:
high in animal fat – can cause heart disease/
atherosclerosis/obesity
lack of fresh fruit/vegetables/fibre – to prevent
constipation
low in vitamin C – to prevent scurvy
low in iron – to prevent anaemia.
8
(b)Any two from: constipation, risk of obesity/
scurvy/anaemia, risk of heart disease/
atherosclerosis.
(c)(i)a diet that contains all the main nutrients in
the correct amounts and proportions
(ii)fibre
2 Any three from: too much food/too little food, too
much carbohydrate/fat/protein, too little fibre, too
few vitamins or minerals, the wrong balance of food.
3 (a) Any two from: addiction (alcoholism), cirrhosis
of the liver, stomach ulcers, cancer of the digestive
system, heart disease.
(b)Increases risk of miscarriage, results in a decrease
in average birth weight.
4 (a) Any three points and descriptions from:
climate change and natural disasters, e.g.
flooding or drought
pollution – can lead to breaks in the food chain,
poisoning of food sources, chronic diseases
could adversely affect workforce responsible for
producing food
shortage of water, due to diversion of rivers,
building dams for hydroelectricity
eating future seed stock due to food shortage
poor soil, or lack of fertiliser or inorganic ions, so
crops are poor
desertification due to soil erosion, as a result of
deforestation
destruction of forests, reducing numbers of
animals to hunt or food to collect
shortage of money for agriculture
war, making it too dangerous to farm the land
use of land for building houses or roads
pest damage or disease
increase in population.
(b)Any two from: transport in chilled containers,
picking fruit before it is ripe, preserving the
food, e.g. canning, storage in salt or vinegar,
freezing food.
Exam focus
1
Component
Function
1
carbohydrate source of
­energy
2
fat/oil
source of
­energy
3
protein
4
fibre/
roughage
5
water
growth,
­tissue repair,
­formation of
enzymes, etc.
adds bulk
to the diet
to maintain
­peristalsis
formation of
blood, ­medium
in which
­enzymes work,
transport of
nutrients, etc.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
Good food
source
e.g. rice, potato,
yam, cassava,
bread, cakes, etc.
butter, milk,
cheese, egg
yolk, fatty meat,
nuts, etc.
meat, fish, eggs,
soya, nuts, milk,
Quorn, etc.
vegetables,
fruit, wholemeal
bread, etc.
drinks, fruit,
vegetables
(b)
Deficiency
disease
scurvy
rickets
Constituent
Symptoms
Food
vitamin C
bleeding
under
the skin,
bleeding
gums
soft bones,
which
become
deformed,
bow-­
leggedness
citrus fruits,
black­currants,
cabbage, etc.
vitamin D/
calcium
2
A
B
C
D
E
F
G
H
(a)
oesophagus
stomach
duodenum
lleum
anus
rectum
colon
canine
slightly
more
pointed
than
incisors
premolar
two
points/
cusps
molar
four/five
cusps
one/two
roots
tearing
and
grinding
food
two/three
roots
chewing
and
grinding
food
3
(for vitamin D)
milk, cheese,
egg yolk, fish
liver oil
(for ­calcium)
milk, cheese,
fish
12 Digestion and
absorption
1
mouth
ANSWERS
2
mouth
gullet/oesophagus
stomach
large intestine/colon
rectum
anus
small intestine/ileum
duodenum
anus
food is ingested here.
colon
a tube, carrying boluses of food
between mouth and stomach
duodenum
has an acid pH and proteins
are digested here
ileum
first part of the small intestine
mouth
absorption of the products of
digestion takes place here
oesophagus
(gullet)
muscular, to control the
egestion of faeces
rectum
absorption of water
stomach
stores faeces
Name
incisor
Description chiselshaped
Function
biting
off
pieces
of food
biting
off
pieces
of food
4
(a)Physical digestion involves breaking large pieces
of food into smaller pieces. This increases the
surface area of the food, achieved by chewing
food in the mouth and churning food in the
stomach and intestine.
Chemical digestion involves the use of enzymes
to break down large insoluble molecules into
small, soluble ones.
(b)Starch is digested in the mouth and duodenum
by amylase in slightly alkaline conditions. It is
broken down to maltose. Maltase then breaks
down the maltose to form glucose.
Protein is digested in the stomach and
duodenum by protease. Conditions required
are acid in the stomach and alkaline in the
duodenum. The end products are amino acids.
5 Arguments for:
Tooth decay among children using the water supply
decreases.
There is no need to buy fluoridated toothpaste.
Arguments against – any two from:
It is a form of mass medication, so people have no
choice about whether or not they want the treatment.
Fluoride can cause mottling of the teeth/white
patches/fluorosis.
Fluoride is only a benefit to growing children –
adults do not benefit.
If people take proper care of their teeth,
fluoridation is unnecessary.
Exam focus
1
2
C
(a) (i)molar (accept premolar), 2 cusps visible/
2 roots visible
(ii) A root
B crown
C enamel
D dentine
E pulp cavity
F gum
G cement
H jaw bone
I nerve
(b) (i)enamel
(ii)(vitamin) D, (mineral) calcium
(iii)fluoride (reject fluorine)
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
9
ANSWERS
(c)Any six from: ref. to bacteria present on the
surface of teeth, food collects on teeth, combines
with bacteria to form plaque, bacteria feed on
sugars, producing acids, acid reacts with enamel,
forming hole, dentine is softer so dissolves faster,
cavity forms.
3 (a)Ref. to too large and insoluble to be absorbed
through the gut wall.
(b)diffusion, active transport
(c)Any two from: ref. to large surface area,
presence of microvilli, one cell thick (explanation)
speeds up diffusion.
(d) 1 (blood capillaries) absorb glucose, amino acids,
transport them away to maintain diffusion
gradient
2 (lacteal) absorbs fatty acids, glycerol
4 (a)
Part
Name
Function
A
oesophagus/
gullet
moves food
from mouth to
­stomach
B
ileum/
small
intestine
digestion
of ­maltose,
­peptides/
absorption of
products of
digestion (accept
absorption of
water)
Structural
feature
presence of
­circular and
longitudinal
muscles for
­peristalsis
presence of
villi to increase
surface area for
absorption
(b) (i)protein
(ii)Ref. to secretion of protease, hydrochloric
acid, muscular churning to mix food with
enzyme.
(iii)Ref. to deamination, excess amino acids
broken down, urea formed, energy source
produced.
13 Transport in plants
1
2
3
4
10
Transpiration – the loss of water vapour from the
leaves through the stomata by diffusion.
Translocation – the movement of sucrose and amino
acids from regions of production/storage to regions
of use for respiration or growth.
(a)Any three from: anchoring the plant in the soil,
absorption of water, absorption of mineral salts,
food storage organ.
(b)Root hair cells have a cell extension, increasing
the cell’s surface area to make it more efficient
for absorbing water and minerals.
(c)root hair cell, cortex, endodermis, xylem
(a)Any three from: increase in temperature,
increase in air movement, decrease in humidity,
increase in light intensity.
(b)Wilting happens when the amount of water lost
from the leaves of a plant is greater than the
amount taken into the roots. This results in the
plant having a water shortage. Cells become
flaccid and no longer press against each other.
Stems and leaves then lose their rigidity and wilt.
(a) Xerophyte
(b)Named plant:
e.g. cactus. Leaves reduced to spines – this
reduces the surface area for transpiration.
Reduced number of stomata. Stomata are
closed during the day – when conditions for
transpiration are greatest. Fleshy stem – to store
water.
e.g. marram grass. Very long roots to search
for water deep down in sand dunes. Leaves
have the ability to roll up in dry weather to
increase humidity around stomata, reducing
transpiration. Sunken stomata create high
humidity and reduce transpiration. Fine hairs
surround stomata, reducing air movement, so
humidity builds up and transpiration is reduced.
e.g. pine tree. Leaves are needle-shaped to
reduce surface area for transpiration. Sunken
stomata to create high humidity and reduce
transpiration. Thick waxy cuticle on the
epidermis to prevent evaporation from the
surface of the leaf.
(c)Any three from: ref. to spraying onto the leaves
of the plants, absorbed into the leaf, transported
by translocation; pest feeds on plant sap and
takes in the pesticide; which kills the pest.
Exam focus
1
2
3
C
D
Process
diffusion
osmosis
active
transport
transpiration
4
Definition
the movement
of a substance
from a higher
concentration to
a lower concentration down a
concentration
gradient
the movement
of water from
a higher concentration to a
lower concentration through a
partially permeable membrane
the movement of
a substance from
a lower concentration to a higher
concentration
against a concentration gradient,
using energy
the loss of water
vapour from the
leaves through
the stomata, by
diffusion
Explanation
oxygen diffuses
from the air into a
leaf, carbon dioxide
­diffuses out of a leaf,
mineral salts diffuse
from soil into root
hairs
osmosis is used to
­absorb water by
roots, cells absorb
water by osmosis
to become turgid,
which keeps young
stems rigid
plants obtain mineral
salts by active transport when the concentration of salts in
the soil is lower than
in the root cells
transpiration results
in more water ­being
drawn through
the plant, carrying
­mineral salts from
the roots
(a)Water enters the leaf in the xylem vessels
(A), then passes into the surrounding spongy
mesophyll cells (B). A thin layer (C) forms on
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
(cause)
(preventative measure)
Smoking
stop smoking
Obesitygo on a controlled diet/take regular
exercise
Stressfind ways of relaxing/identify
causes of stress and reduce them
Inherited
make sure other factors are
factorsreduced/monitor health
outer layer, made of tough
5
fibrous tissue to hold contents
together
14 Transport in humans
1
2
3
4
(a) left atrium, left ventricle
(b)aorta, pulmonary vein, coronary artery
(a)a group of cells of similar structure, carrying out
the same function
(b) (cardiac) muscle
(c)Cardiac muscle can contract.
(d)It needs to build up enough pressure, to move
blood to all organs, while the right ventricle only
moves blood to the lungs.
Ref. to vena cava, with valves, to prevent backflow
of blood, into right atrium, which contracts, to
increase blood pressure, to move blood through
tricuspid valve, into right ventricle, which contracts,
to increase blood pressure, tricuspid valve closes,
to prevent backflow of blood, ref. to pulmonary
artery, semilunar valve closes, to prevent backflow
of blood.
(a)x-axis drawn and labelled ‘time/min’, y-axis drawn
and labelled ‘pulse rate/beats per min’, points
plotted accurately, line drawn between points
ANSWERS
the surface of the cells, which evaporates and
saturates the air in the air spaces (D), then the
water molecules diffuse into the atmosphere
through the stomata (E).
(b)Transpiration from the leaves loses more water
than is being taken in by the roots, cells in
young stems lack water, become flaccid and stop
pressing against each other, so stems and leaves
lose their rigidity and wilt.
lumen, much narrower
than in a vein. This helps to
maintain high blood pressure
thick wall, made of muscles,
elastic fibres and fibrous
tissue, which prevents
bursting and maintains
pressure wave
6
1 mark for correct shape, 1 mark each for labels of
up to two features, 2 marks for annotations
(a)lungs labelled in upper box, body labelled in
lower box
(b)arrows in blood vessels and heart correct (see
diagram below)
(c)right atrium, right ventricle, vena cava,
pulmonary artery shaded
lungs
pulse rate/beats per min
140
120
100
rest of body
80
7
60
Stretch and challenge
40
8
20
0
Across 3 plasma 4 lymphocyte 5 platelet
Down 1 haemoglobin 2 nucleus
0.0
2.0
4.0
6.0
time/min
8.0
10.0
(b) (i)60 beats per minute
(ii)at 1 minute
(iii)at 8 minutes
(iv)Heart must beat faster to circulate more
oxygen, exercising muscles need more
oxygen, more glucose, and produce carbon
dioxide (or lactic acid) which needs to be
removed.
(v)Rate starts higher than 60 bpm, reaches a
higher peak, takes longer to return to normal.
(vi)Keeps heart muscle in good tone, results in
the heart being more efficient in maintaining
blood pressure.
(c)Any three of the following answers (you must
give the cause and the preventive measure for
each mark):
Any three of the following:
Permeable wall – to allow diffusion of materials
between the capillary and surrounding tissues.
Wall is one cell thick – allows fast diffusion/allows
white blood cells to squeeze between cells of the wall.
Lumen is one blood cell wide – slows down blood
flow to allow diffusion of materials and transfer of
tissue fluid.
Valves are absent – blood pressure is high enough to
keep blood flowing.
9 (a)Produced by lymphocytes, formed in lymph
nodes, antibodies make bacteria clump together,
so that phagocytes can digest them. They also
neutralise toxins produced by bacteria, and
remain in blood to provide long-term
protection.
(b)Phagocytes can move out of capillaries, to the
site of an infection; they engulf pathogens, and
kill them by digestion.
10 Donor organ used is of similar tissue type to that of
the patient, ref. to use of immunosuppressive drugs,
keep patient in isolation during recovery.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
11
ANSWERS
11 Returns tissue fluid (in the form of lymph) to blood/
prevents build-up of fluid in the tissues, produces
lymphocytes, absorbs fatty acids and glycerol from
the small intestine.
Exam focus
1
2
3
C
B
(a) A
C
E
G
J
L
B
D
F
H
K
M
aorta
left atrium
bicuspid valve
left ventricle
tricuspid value
vena cava
pulmonary vein
semilunar valve
tendon
right ventricle
right atrium
pulmonary artery
(b) (i)right atrium
(ii)pulmonary vein
(iii)semilunar valve
(iv) left ventricle
(v) tendons
(vi) vena cava
(vii) aorta
(viii) tricuspid valve
4 (a)Blood passes through the heart twice, for each
complete circulation of the body.
(b)(artery) Any two from: thick and tough wall,
narrow lumen, valves absent.
(vein) Any two from: thin wall, large lumen,
valves present.
(capillary) Any two from: permeable wall, wall
one cell thick, lumen one red blood cell wide,
valves absent.
5 (a) (i)transport of dissolved substances to cells/
removal of wastes from cells
(ii)transport of oxygen
(iii)produces antibodies to fight disease
(iv) engulfs bacteria to fight disease
(v) forms blood clots
(b) (i)biconcave disc shape/no nucleus/contains
haemoglobin (pink colour)
(ii)large nucleus
(iii)lobed nucleus/cell can change shape
15 Respiration
1
(a)glucose + oxygen
water + carbon
dioxide + energy
(b)ATP (adenosine triphosphate)
(c) (i)lactate/lactic acid
(ii)Lactic acid causes muscle cramp (muscle
fatigue), which will stop the athlete running.
An oxygen debt builds up, which needs to be
repaid.
2
Product
1 carbon dioxide
2 ethanol/alcohol
3
(a)
mouth
12
Food manufacturing process
breadmaking/brewing
brewing
trachea
bronchus
bronchiole
red blood
cell
alveolus/
air sac
(b) (i)diffusion
(ii)thin, moist, large surface area, has a
concentration gradient
4 (a)the volume of air breathed in/out during normal,
relaxed breathing
(b)the maximum amount of air that can be inhaled/
exhaled in one breath
5 cancer, emphysema, lungs, carcinogen, carbon
monoxide, tar, bronchitis, nicotine, tobacco, filter
6 intercostal muscles contract
ribcage moves up and out
diaphragm muscle contracts
diaphragm moves down
volume in the lungs increases
air pressure in the lungs decreases
air moves in to fill the lungs
Exam focus
1
2
D
(a) A spinal cord B left lung C heart
(b)(i)lung
(ii)Any four from: contains many alveoli,
contains many blood capillaries, for gas
exchange, ref. to oxygen and carbon dioxide,
ref. to diffusion.
(c)Any six from: intercostal muscles contract, ribs
move upwards and outwards, diaphragm muscle
contracts, diaphragm moves down, volume of
thorax increases, air pressure in thoracic cavity
decreases, to become lower than atmospheric
pressure, so air moves into the lungs.
3 (a)Volume of air per breath increases, from
normal tidal volume, e.g. from 0.5 litres, rate of
breathing increases, from 12 to over 20 breaths
per minute.
(b)Any three named chemicals and their effects from:
Carbon monoxide – any two from: poisonous
gas, combines with haemoglobin to produce
carboxyhaemoglobin, preventing red blood
cells from carrying oxygen, smoker gets out of
breath easily, increases risk of atherosclerosis,
thrombosis, coronary heart disease.
Nicotine – any two points from: addictive,
resulting in prolonged exposure of lungs to other
harmful chemicals, raises blood pressure, risk of
stroke, stimulates brain, can reduce birth weight
of baby if mother smokes during pregnancy.
Smoke particles – any two points from: irritates
air passages in lungs, causes inflammation,
increased mucus production, causes chronic
bronchitis, emphysema.
Tar – any two points from: ref. to carcinogen,
increases risk of lung cancer, paralyses cilia in air
passages, can cause bronchitis.
4 (a) (i)respiration
(ii)carbon dioxide
(iii)turns from colourless to milky
(iv) ethanol/alcohol
(b)Any five from:
Respiration of yeast is very slow at low
temperatures, as molecules have little kinetic
energy so few collisions.
30 ºC is optimum temperature for yeast
respiration, as molecules have lots of kinetic
energy to collide.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
16 Excretion in humans
1
blood, water, glucose, reabsorbed, ADH, more,
concentrated, osmosis, diffusion, active transport
2 (a) The removal of toxic materials, the waste
products of metabolism and substances in excess
of requirements from organisms.
(b)
renal
aorta
artery
urethra
3
4
capillary
nephron
bladder
ureter
(a)Surplus amino acids are removed from the blood
by the liver and broken down into urea by the
process of deamination.
(b)Any three from: breakdown of poisons/alcohol,
breakdown/removal of drugs, breakdown of
hormones, storage of vitamins, storage of iron,
controlling levels of glucose in the blood, making bile.
Any two advantages from:
The patient can return to a normal lifestyle – dialysis
may require a lengthy session in hospital, three times a
week, leaving the patient very tired after each session.
A dialysis machine is available for other patients to use.
Dialysis machines are expensive to buy and maintain.
Any two disadvantages from:
Transplants require a suitable donor – with a good
tissue match.
The operation is very expensive.
There is a risk of rejection of the donated kidney/
immunosuppressive drugs have to be used.
Transplants are not accepted by some religions.
Exam focus
1
(a) (i)A renal vein B left kidney C ureter
D bladder E urethra
(ii)(in part A) amino acids present, glucose
present, more salts
(iii)Any three from: smaller volume, more
concentrated, urea more concentrated, salts
more concentrated.
(b)Vena cava (X) has a thinner wall, larger lumen,
contains valves.
2 (a) (i)a method of removing one or more components
from a solution using the process of diffusion
(ii)
(pump) keeps blood flowing through the
machine
(dialysis fluid) receives wastes/toxins from the
blood by diffusion
(bubble trap) removes any air bubbles before
the blood is returned to the patient’s vein
(partially permeable membrane) allows small
molecules in higher concentrations to pass
out of the blood, but prevents loss of blood
cells, large molecules from blood
(b) (i)Visking tubing/cellulose
(ii)provides a large surface area, for efficient
diffusion
(iii)Any two from: to maintain a concentration
gradient, concentrations of removed
substances build up, so diffusion slows down.
(c)Any two from: expensive to buy/maintain, very
tiring for the user, may require frequent hospital
visits.
17 Reactions to
stimuli by plants and
invertebrates
ANSWERS
Enzymes in yeast begin to denature at 45 ºC, so
respiration slows down.
All yeast enzymes denatured at 100 ºC, so no
respiration.
1
(a) a plant response to gravity
(b)(i)Root. Advantage: access to water/access to
minerals/better anchorage.
(ii) Shoot. Advantage: access to light.
2 (a) taxic responses/taxes
(b)(i) avoid predators/protection from UV light
(ii) prevents dehydration/source of food
(c)They move faster in unfavourable conditions, so
will tend to move out of them, but move slower
in favourable conditions, so tend to stay there.
3 (a) auxin
(b) (i)The shoot bends/grows towards the light.
(ii)When a shoot is exposed to one-sided light,
auxins produced by the tip move towards
the shaded side of the shoot/auxins are
destroyed on the light side, causing an
unequal distribution. Cells on the shaded side
are stimulated to absorb more water than
those on the light side, making them bigger.
The unequal growth causes the stem to bend
towards the light.
(c) (i)weedkiller/chemical which kills weeds
(ii)They are sprayed onto plants, causing rapid,
uncontrolled growth and respiration that
results in the death of the plant.
Exam focus
1 (a) (i)mean numbers: A 3.2 B 0.8 C 5.4 D 20.6
(ii)
A dark and dry
B light and dry
C light and damp
D dark and damp
(iii)1 dark and damp 2 dry and light
(iv) taxic response/taxis
(v)Any two from: less risk of dehydration, less
likely to be found by predators, could be
a good food source (due to presence of
decaying materials/bacteria).
(b) (i)increases reliability of results/helps to identify
anomalous results
(ii)to give them more time to acclimatise to the
conditions/more time to explore the options
available
(iii)to prevent contact with the drying agent/
drying agent could be toxic/prevent drowning
18 Coordination
and response
1
(a)Central nervous system: made up of brain and
spinal cord, which have the role of coordination.
Peripheral nervous system: made up of nerves,
which connect all parts of the body to the central
nervous system.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
13
ANSWERS
(b) (i)a group of receptor cells responding to a
specific stimulus, e.g. light, sound, touch,
temperature, chemicals
(ii)
Sense organ
1 ear
2 eye
3 nose
4 tongue
5 skin
Stimulus detected
sound/body movement
light
chemicals/smell
chemicals (taste)
temperature, pressure, touch, pain
2
(a)Any three from: sensory neurone has dendron
present/very long, sensory neurone has no axon /
very short axon, cell body is near the end of the
sensory neurone, dendrites are present at the
end of the sensory neurone.
(b)1acts as electrical insulation/stops impulse
leaking out/makes transmission of impulse
more efficient
2 makes connections with other neurones
3 transmits the impulse along the neurone
4 coordinates the cell/contains DNA
3 (a)A chemical secreted by an endocrine gland. It is
transported in the bloodstream and usually has a
long-term effect on a target organ.
(b)Any three from: causes heart rate to increase,
blood supplies muscles with oxygen and glucose
more quickly, blood supply to skin reduced,
blood supply to digestive organs is reduced,
blood is diverted to vital organs, liver is
stimulated to convert glycogen to glucose.
(c)
Feature
Nervous
form of
transmission
transmission
pathway
speed of
transmission
duration of effect
electrical
impulses
nerves
Hormonal
(endocrine)
chemical/
hormones
blood vessels
fast
slow
short term
long term
4
Exam focus
1
2
C
(a)Any three from: used to treat disease, reduce
sensation of pain, help to calm the patient down,
used as anaesthetic, to cause unconsciousness.
(b) (i)
Drug
Effects on the
body
alcohol
small amounts –
relaxes the body,
large amounts
– acts as a depressant, slows down
reactions, coordination impaired,
creates mood
swings, can trigger
violence
has narcotic
effect, increases
relaxation, reduces
pain
(a) (i), (ii), (iii)
relay neurone B
spinal cord
motor neurone C
ganglion
pain receptors
(b)it contracts
(c)(i)synapse
(ii)acetylcholine
heroin
A sensory neurone
D biceps muscle
14
5 (a) A ciliary muscles – contract
B suspensory ligaments – slacken
C lens – thickens
(b) (i),(ii) D circular muscles – contracted
E radial muscles – relaxed
F pupil – constricted
6 (a)the maintenance of a constant internal
environment
(b) (i) 37 ºC
(ii) Increase in sweating – sweat is secreted
onto the skin surface. Water from sweat
evaporates, taking heat from the skin surface.
Vasodilation – arterioles dilate to allow more
blood to flow near the skin surface, so more
heat is lost through radiation.
7 (a) (i)Automatic action, generally a reflex, which
cannot be overridden.
(ii)faster
(iii)Any two examples from: heart beat,
peristalsis, uterine contractions during birth.
(b)The drop in glucose is detected by the pancreas.
It secretes glucagon. This is transported to the
liver in the blood. In the liver, glucagon converts
glycogen to glucose.
nicotine
(in
tobacco)
raises blood pressure, heart rate
Dangers to the
person using the
drug
increases reaction
times, so driving and
handling machinery
is impaired, can lead
to criminal activity,
promiscuity, alcoholism, financial problems, liver disease,
etc.
addictive, tolerance to
drug increases, so risk
of overdosing, risk of
infection from using
unsterilised needles
can lead to criminal
activity, promiscuity,
alcoholism, financial
problems, etc.
addictive, other
chemicals in the
cigarette can lead
to cancer, risk of
­atherosclerosis,
thrombosis, coronary
heart disease, etc.
(ii)Any three from: ref. to criminal activity, sexual
promiscuity, financial problems for family, dangers
for unborn children.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
Any eight from:
Homeostasis means maintaining a constant internal
environment.
Pancreas acts as a sensor in negative feedback and
acts as an effector by secreting hormones.
If glucose levels rise above normal, change is sensed
by the pancreas.
Insulin is secreted by the pancreas and passed into
bloodstream.
Insulin instructs the liver to remove excess glucose
from the blood.
Glucose is converted to glycogen and stored.
Rate of respiration in the liver is increased to use up
glucose.
Glucose levels return to normal.
If glucose levels fall below normal the pancreas stops
secreting insulin and starts to secrete glucagon.
Glucagon instructs the liver to convert glycogen to
glucose.
Glucose is passed into the blood, returning glucose
levels to normal.
4 (a) (i)
A scapula
B humerus
C biceps
D radius
E ulna
F triceps
(ii)tendon
(b) (i)(effector) a muscle or gland which responds
when it receives an impulse from a motor
neurone.
(antagonistic muscle) pairs of muscles which
oppose each other when they contract.
(ii)Triceps muscle contracts, pulling on the ulna.
(iii)Biceps relaxes.
19 Reproduction, growth
and development in
plants
1
(a)the formation of a new organism, without the
involvement of gametes or fertilisation
(b) (i)Ref. to binary fission. Inside each bacterium
the DNA replicates, then the cell divides into
two, with each daughter cell containing
identical DNA. The daughter cells grow
before dividing again.
(ii)Ref. to spore production. Spores may be
produced in a sporangium, which bursts when
ripe, allowing spore dispersal. The spores
germinate and grow into new individuals.
(iii)Ref. to stem tubers. The parent plant
photosynthesises and the food produced is
stored in underground stems. These swell
with starch, forming tubers. Connections with
the parent plant die. The tuber has buds that
can produce new stems and roots, forming a
new plant.
2
anther
protects the flower while in bud
ovary
often large and coloured to
attract insects
petal
produces pollen grains
containing male sex cells
sepal
sticky, to receive pollen grains
during pollination
stigma
contains ovules, the female sex
cells
ANSWERS
3
3 (i)
A stigma
B style
C ovary
D ovule (accept seed)
E filament
F anther
(ii)1 carpel
2 stamen
(iii)1Ref. to feathery/with a larger surface area/
hanging outside the flower – to increase the
chance of trapping pollen grains.
2Ref. to larger numbers of pollen grains/
pollen grains lighter – to increase chances of
pollination/to be more easily carried by the
wind.
4 (a)Growth – an increase in dry mass of an organism,
as a result of cell growth and division.
Development – an increase in complexity
through the differentiation of cells.
(b) (i)Named seed – any one from the following or
any other suitable example:
e.g. dandelion – has a group of fine hairs
called a pappus, which catches the wind and
acts like a parachute.
e.g. sycamore – has a wing with a large
surface area. It spins and falls slowly.
(ii)Named seed – any one from the following or
any other suitable example:
Blackberry – is a succulent fruit that attracts
animals because it is brightly coloured/
juicy/nutritious. When eaten, the seeds pass
through the animal’s gut without being
digested and are deposited with the animal’s
faeces.
Bur – has hooked seeds, which catch onto
an animal’s fur as it brushes past the parent
plant. Eventually, the seeds drop off or are
removed as the animal grooms itself.
(c)(i)Oxygen is needed for respiration to provide
energy for the growing seedling.
(ii)Warm temperatures activate/speed up
enzymes to release soluble nutrients for the
germinating seed.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
15
ANSWERS
(iii)Water activates enzymes and allows stored
foods to be broken down/digested/dissolved
for transport.
(d)(i)Stored food in the cotyledon is used for
respiration.
(ii)Photosynthesis starts, producing food
that can be stored or built up into new
tissues.
5 (a) Any two advantages from:
Variation in offspring is produced.
New varieties of plant can be created.
Seeds are formed, which allow dispersal away
from the parent plant.
Two disadvantages:
Two parents are usually needed.
Growth of a new plant tends to be slow.
(b)
Definition
self-­
The
pollination transfer
of pollen
from the
anther
to the
stigma of
the same
flower, or
to another
flower of
the same
plant.
crossThe
pollination transfer
of pollen
from the
anther of
a flower to
the stigma
of a flower
on a
­different
plant of
the same
species.
Advantage Disadvantage
Reduces the
Smaller
numbers of variation
in the
pollen
offspring/
grains
need to be less likely to
produced/ cope with
adapting
there is a
to environgreater
mental
chance of
change.
successful
pollination.
Reduces the
Increases
variation/ chance of
the ability fertilisation.
to adapt
to environ­
mental
change.
Exam focus
1
(a) (i)arrows from pollen grain down through the
stigma (A), style (B) around either side of the
ovary wall (C), into micropyle (D) to the ovule
(ii)Any six from: pollen grain germinates, pollen
tube grows, pollen tube contains the male
nucleus, grows down through the stigma (A),
through the style (B), through the ovary wall
(C), into micropyle (D) to the ovule, male
nucleus fuses with nucleus of ovule.
(b) (i)Any one from: pollen grain would be lighter/
have a larger surface area/no spikes on
surface/smooth surface.
(ii)Stigma would be feathery, hangs outside the
flower.
16
2 (a) (type of pollination) wind
(explanation) any six from:
A = stigma, which is feathery, hangs outside the
flower, has large surface area.
B = filament, which is long to expose the anther
to the wind.
C = anther, which hangs outside the flower,
exposed to the wind, contains large amounts of
light, smooth pollen grains.
(b)Any six from: mature anthers burst, releasing
pollen grains into air, wind carries pollen grains,
some are trapped by feathery stigmas, hanging
outside flowers, or other flowers of the same
species.
20 Reproduction, growth
and development in
animals
1
Across 2 prostate gland 5 seminal vesicle 6 testis
7 sperm duct 8 penis
Down 1 urethra 3 epididymis 4 scrotum
2 (a)Sperm released from the testes pass through
the sperm duct, into the urethra through the
penis. They are ejaculated into the vagina, swim
through the cervix and uterus and into the
oviduct.
(b)An ovum passes down the oviduct. A single
sperm penetrates the membrane of the ovum
by secreting a protease enzyme. The sperm
nucleus fuses with the ovum nucleus to form a
zygote.
3 AThe lining of the uterus is starting to build up,
under the influence of oestrogen.
BOvulation occurs – the wall of an ovary ruptures,
releasing an egg. This is due to secretion of LH
(luteinizing hormone).
CThe lining of the uterus is maintained, due to
high levels of progesterone, produced by the
corpus luteum.
DMenstruation occurs – the lining of the
uterus breaks down, due to a drop in
progesterone.
4 (a) placenta
(b)1 cervix
2 vagina
(c)zygote
(d)Any two from: oxygen, glucose, amino acids.
(e)carbon dioxide, urea
(f)amniotic fluid
(g) menstruation
(h) ejaculation
(i)oviduct (Fallopian tube)
(j) mitosis
5 (a) 1 A rubber sheath placed over the penis to stop
sperm entering the vagina.
2 The sperm ducts are tied or cut, so no sperm
can leave the testes.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
21 Inheritance
ANSWERS
3 Contains progesterone and oestrogen, which
prevent ovulation, or progesterone only –
which prevents implantation of a blastula.
4 A plastic-coated copper coil surgically inserted
into the wall of the uterus – which prevents
implantation of a blastula.
(b)condom
(c)Any two from: abstinence from sexual
intercourse, screening of blood used for blood
transfusions, use of sterilised needles for drug
injections, feeding a baby with bottled milk
when the mother has HIV, use of sterilised
surgical instruments.
6 (a) progesterone, oestrogen
(b) (i)FSH and LH treatment causes multiple release
of ova (eggs). The ova are collected. Some
of them are fertilised in a Petri dish using
the male partner’s sperm. The early embryos
produced are then inserted into the uterus to
achieve pregnancy.
(ii)
(advantage) Any one from: increases the
chance of pregnancy, can result in pregnancy
of a woman with blocked oviducts, fertilised
eggs can be screened for genetic diseases,
(disadvantage) Any one from: expensive,
quite a low success rate.
1
allele
a section of DNA, coding for a
specific protein
chromosome
having a pair of identical
alleles
dominant
a thread of DNA, made up of
genes
gene
a gene that always shows in
the phenotype
genotype
the characteristics visible in an
organism
Exam focus
1
2
3
D
A
(a)Testis is the male gonad, producing sperm; testa
is the seed coat, which is waterproof/protects
seed from microbes.
(b)Urethra is the tube carrying urine from the
bladder, passes through the penis in males;
ureter is the tube carrying urine from the
kidneys, to the bladder.
(c)Ovary is the female gonad, producing ova in
animals, ovules in plants; ovule contains the
female sex cell.
(d)Fertilisation is the fusion of the male and female
sex cells, to form a diploid zygote; implantation
is the embedding of an embryo, into the uterus
lining.
4 (a) (AIDS) virus, (Gonorrhoea) bacterium
(b)AIDS
(c)Ref. to may not use condom during sex when
under the influence of the drug.
Drug may be injected using an infected needle/
ref. to sharing needles.
5 (a)A ovary B oviduct (Fallopian tube) C uterus
(wall) D cervix E vagina
(b)Ref. to oviducts closed/blocked, so eggs cannot
pass down/sperm cannot reach egg.
(c) (i)
in vitro fertilisation
(ii)X placed on lining of uterus
(iii)Ref. to being expensive, ref. to low success
rate.
(d)Any three from: ref. to maintaining healthy
diet, ref. to eating more protein/iron/calcium/
vitamin C/energy-containing foods than normal,
avoid alcohol, avoid drugs, avoid contact with
rubella.
homozygous
an alternative form
of a gene
the genetic make-up of an
organism
phenotype
2
Parent phenotype
male
Parent genotype
XY
X
Gametes (sex cells)
First filial
generation (F1)
Phenotype
The ratio is
female
XX
x
Y
X
x
X
XX
XX
XY
XY
female
female
male
male
1
female:
1
male.
3 (a) Any two differences from:
Mitosis produces cells with the same number
of chromosomes as the parent cell/the diploid
number of chromosomes is maintained.
Meiosis produces cells with half the number of
chromosomes/haploid cells produced.
Mitosis produces identical cells. Meiosis results in
variation.
Mitosis involves body cells/somatic cells. Meiosis
happens in the gonads/ovaries and testes.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
17
ANSWERS
Mitosis results in growth or replacement of old
or damaged cells. Meiosis makes sex cells.
(b) leg muscle cell 8
sperm cell
4
zygote
8
skin cell
8
(c) (i)
Parent phenotype
grey
Parent genotype
GG
G
Gametes (sex cells)
Phenotype
g
x
Gg
grey
gg
x
G
Gg
F1 generation
black
g
Gg
grey
2
rat C
X
X
Y
(ii)50%
(iii)sperm cell, the Y chromosome determines
male, absence of Y in the zygote results in
female
(b) (i)an alternative form of a gene, pairs of
alleles occupy the same relative positions on
chromosome pairs
(ii)1 C
2B
(c)Rat E has genotype Gg, where G = grey fur,
g = white fur.
Gg
grey
(a) (i) rat B
X
grey
(rat B)
(rat E)
Parent phenotype
grey
grey
Parent genotype
Gg
Gg
x
(ii) (a Punnett square is acceptable)
Parent phenotype
grey
Parent genotype
Gg
x
g
G
Gametes (sex cells)
grey
x
g
G
F2 generation
GG
Gg
Gg
gg
Phenotype
grey
grey
grey
black
3
(a)The term describes a pair of alleles, neither of
which is dominant over the other. Both can
have an effect on the phenotype when they are
present together in the genotype. The result is
that there can be three different phenotypes.
(b) (i)
Parent phenotype
red
Parent genotype
CRCR
F2 generation
Phenotype
white
CWCW
x
CR
CR
Gametes (sex cells)
CW
CW
x
CRCW
CRCW
CRCW
CRCW
pink
pink
pink
pink
(ii)1 red : 2 pink : 1 white
Exam focus
1
(a) (i)Blood clotting can occur, due to reaction
between antibodies and antigens, leading to
death of the patient.
(ii)Ref. to possible transmission of HIV.
(b)
Parent phenotype blood group A
Parent genotype
IAIo
Gametes (sex cells)
18
IA
blood group B
IBIo
x
Io
IB
x
g
g
G
x
Gg
Ratio 3 grey: 1 black
4
G
Gametes (sex cells)
Io
F2 generation
IAIB
IAIo
IBIo
IoIo
Phenotype
AB
A
B
O
First filial
generation (F1)
GG
Gg
Gg
gg
Phenotype
grey
grey
grey
white
(a)A gene is a section of DNA that codes for a
protein, an allele is an alternative form of a gene.
(b)A diploid nucleus contains pairs of chromosomes,
e.g. in body cells. A haploid nucleus contains a
single set of unpaired chromosomes, e.g. sex cells.
(c)Phenotype describes the characteristics visible
in an organism, genotype describes the genetic
make-up of an organism.
(d)Homozygous refers to chromosomes that
have a pair of matching alleles controlling the
same characteristic, heterozygous refers to
chromosomes that have a pair of dissimilar alleles
for a characteristic.
(e)A dominant gene is a one that always shows in
the phenotype, a recessive only has an effect on
the phenotype if the genotype is homozygous.
22 Variation
1
(a) (i)a spontaneous change in a gene or a
chromosome
(ii)Any two from: faulty copying of DNA, faulty
separation of chromosomes during cell
division, exposure to radiation, exposure to
some chemicals.
(b) (i)During ova formation in the ovaries in
the division process (meiosis), one of the
chromosomes (number 21) sticks to its
partner. This results in one ovum with 24
chromosomes and one with only 22. The
ovum with 24 chromosomes is still viable.
If it is fertilised, the fetus formed has 47
chromosomes instead of 46.
(ii)Any three from: lowered life expectancy,
mental retardation, early puberty, a
distinctive round face/short neck.
2 (a)Continuous variation shows a complete range
of a characteristic within a population. It is
caused by both genes (often a number of
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
number of students
Parent genotype
HNHn
6
genotype of
first filial
generation (F1)
4
Phenotype
8
2
120 – 130 – 140 – 150 – 160 – 170 –
129
139 149
159 169
179
height / cm
Discontinuous variation graph, e.g.
percentage frequency
man
HN
woman
HNHn
x
Hn
x
Hn
HN
10
0
45
40
35
30
25
20
15
10
5
0
A
3
Parents
Gametes (sex cells)
height in a class
12
More of the next generation carry the
advantageous genes, resulting in a stronger
population, better adapted to a changing
environment. Gradually, over a long period of
time, the whole species becomes stronger.
5 (a) Any three symptoms from: episodes of pain,
younger children may develop painful swelling
in their hands or feet, older children can be
affected in their ribs/long bones/spine, increase
in vulnerability to other diseases, jaundice,
increased risk of leg ulcers, delayed growth in
children, progressive organ damage.
(b) (i) (ii)
ANSWERS
different genes) and the environment. When the
frequency is plotted on a graph, a smooth curve
is produced, with the majority of the population
sample grouped together and only small
numbers at the extremes of the graph.
e.g. height, body mass, intelligence, hand span,
shoe size.
Discontinuous variation is where there are
obvious, distinct categories for a feature. There
are no intermediates between categories. It is
caused by a single gene or a small number of
genes, with no environmental influence. When
the frequencies are plotted on a graph, bars are
produced that cannot be linked with a smooth
curve, e.g. blood group, ability to tongue-roll,
ear lobe shape.
(b)Continuous variation graph, e.g.
B
AB
blood group
O
ne named example of an animal, e.g. cow:
O
Select one variety of cattle with a higher than
average milk yield.
Select another variety that has a very high meat
yield.
Cross-breed the two varieties to form a new breed
with the benefits of both parental varieties, e.g.
high milk production in females, high meat yield in
males.
4 (a)the passing on of genes by the best adapted
organisms
(b)Named example, e.g. lion:
Variation within a lion population gives some
individuals an advantage over others, e.g. bigger
muscles in the legs of some lions enable them to
run faster/get food more successfully.
If there is a food shortage, the lions with the
biggest leg muscles are most likely to survive to
being an adult and pass on the advantageous
genes to their offspring.
The weaker individuals die before having the
chance to breed.
HNHN
HNHn
normal
some
haemoglobin, abnormal
no anaemia
haemoglobin,
sickle cell trait
HNHn
some
abnormal
haemoglobin,
sickle cell trait
HnHn
abnormal
haemoglobin,
sickle cell
anaemia
Exam focus
1 (a) (i)discontinuous variation
(ii)(example) any example of continuous
variation, e.g. height, body weight, hand
span, intelligence
(explanation) ref. to influence of genes, and
environment
(b) (i)The malarial parasite is unable to invade and
reproduce in the sickle cells.
(ii)Any two from: they have sickle cell anaemia
so red blood cells deform and become sickleshaped, when blood oxygen levels get low, so
cells become stuck in capillaries, e.g. in lungs.
2 (a)Involves transfer of pollen from the anther of a
flower to the stigma of a flower on a different
plant of the same species, so there is mixing of
genetic material leading to variation.
(b)Tubers form at the tips of underground stems of
the parent plant, so the tuber cells will have the
same DNA as the parent.
3 (a) (i)bacterium
(ii)Any three from: presence of cell wall,
presence of slime capsule, presence of single
strand of DNA, presence of flagellae, ref. to
small size.
(b)binary fission (accept asexual reproduction)
(c)Any two from: ref. to mutation, during cell
division, variation has provided resistance to the
antibiotic.
(d)Any three from: some of the bacteria will
have survived but have been exposed to the
antibiotic so mutations are possible, which can
result in a resistant strain forming so future
use of antibiotic will be ineffective, bacteria
in the patient will breed again causing disease
symptoms to return.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
19
ANSWERS
23 Energy flow, food
chains and food webs
1
(a)A list of organisms that shows the feeding
relationship between them. Arrows link the
organisms to represent the direction of flow of
energy.
(b) (i) (ii)
snail
thrush
sparrow hawk
clover
➞ primary ➞ secondary ➞ tertiary
producer
consumer
consumer
consumer
(c)(i)The thrush population would decrease/thrushes
die because they have fewer snails to eat.
(ii)The sparrow hawk population would
decrease/sparrow hawks die because they
have fewer thrushes to eat.
(d)Snails use less energy because they move less/
more slowly/don’t hunt.
Snails are cold blooded, so less energy used
maintaining a constant body temperature.
2 (a) (i)photosynthesis
(ii)sunlight
(iii)Any three from: light is reflected off shiny
leaves, light is the wrong wavelength for
chlorophyll to trap, light passes through
the leaves without passing through any
chloroplasts, light does not fall on the leaves.
(b) (i)Energy is lost at each level in a food chain. So,
very little of the energy entering the chain
through the producer is available to the top
carnivores.
(ii)
Fewer levels to lose energy from.
90% of the energy is lost at each level/a
smaller percentage of the energy trapped by
the producers is lost in a short food chain.
3 (a)
leopard
tertiary
consumer
baboon
secondary
consumer
scorpion
primary
consumer/
herbivore
locust
impala
grass
primary
consumer/
herbivore
producer
(b)When feeding on impala it is a secondary
consumer, but when feeding on baboons it is a
quaternary/fourth consumer.
(c)Any three from: over-predation or hunting,
disease, pollution, use of pesticides, lack of food
(or other resources).
(d)They represent the direction of flow of energy/
point towards the consumer of the previous
organism.
20
4
(a) The producer may be a single large plant, e.g. a
tree.
The top consumers may be parasites, which are
small but many feed on the previous level.
(b)There is a reduced amount of energy at each
successive level.
(c)The organisms have to be killed and burned to
measure their energy content.
Exam focus
1
(a) (i)an organism’s position in a food chain, food
web or food pyramid
(ii)e.g. maize ➞ locust ➞ lizard ➞ snake
(iii)
e.g.
snake
lizard
locust
maize
(b) (i)35%
(ii)(waxy) cuticle
(iii)Any two from: ref. to presence of large
numbers of chloroplasts, ref. to closely packed
nature of palisade cells, ref. to position
near upper surface of leaf, ref. to ability of
chloroplasts to migrate to top of cells.
(c) (i)90%
(ii)Any two from: movement, e.g. to find
food or a mate, maintaining constant body
temperature, some heat lost in urine or
faeces, not all of the food organism is
eaten by the consumer/some parts are
indigestible.
2 (a) (i)
(grass) (cow) (humans)
producer primary secondary
consumer consumer
(ii)Ref. to leaves, capture light energy, and
convert it into carbohydrates/stored food.
(iii)Any three from: movement, e.g. to find
food or a mate, maintaining constant body
temperature, building up proteins/muscles,
some heat lost in urine or faeces.
(b) (i) 200
× 100 = 0.2%
100 000
(ii)Ref. to fewer trophic levels, so less energy
lost/more energy conserved for top
consumer.
(c) (i)Ref. to greater range of vitamins and minerals
available in a mixed diet, meat contains a
greater range of amino acids.
(ii)
humans
cows
grass
maize
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
25 Population size
1
1
Exam focus
1 (a) (i)(root) nodule
(ii)bacteria
(iii)Any four from: ref. to nitrogen fixing
bacteria, in the root nodules, take in gaseous
nitrogen from air spaces in the soil, convert
it to compounds of ammonia, which are
changed to nitrates, then used to make
protein, for plant growth.
(iv)Any two from: add manure/compost, add
artificial fertilisers, use crop rotation, with
leguminous plants in the cycle.
(b) Any two from:
Feature
leaf shape
leaf veins
cotyledons
groupings of
flower parts
2
Maize
long and narrow
parallel
one
in threes
Bean
broad
branching
two
in fives
Any eight from: ref. to osmosis, water passes
through xylem, into leaves, evaporates into air
spaces, in spongy mesophyll, present in higher
concentration than in atmosphere, so diffuses,
through stomata, ref. to transpiration, forms clouds,
ref. to precipitation/rain, returns to soil, drains into
river, runs down to sea
(a) (i) (ii)
stationary phase
number of organisms
photosynthesis, respiration, combustion,
decomposition
2 A evaporation
B condensation
C transpiration
D precipitation (rain)
E osmosis
3 (a) (i)Present in soil/(leguminous plant) root
nodules. Convert nitrogen into compounds of
ammonia.
(ii)Convert compounds of ammonia into nitrates.
(iii)Present in waterlogged soil. Break down
nitrites into nitrogen.
(iv)Energy from the lightning converts gaseous
nitrogen into nitrogen oxides, which dissolve
in rain to form nitrates.
(b)adding artificial fertilisers
adding manure/compost
growing leguminous plants, then ploughing the
roots (with their nodules) into the soil
4 (a)photosynthesis, respiration
(b)Any two from: cutting down forests/
deforestation, combustion of fossil fuels,
increasing numbers of animals/increasing the
human population.
(c) Any three from:
ref. to melting of polar ice caps, causing flooding
of low lying land
ref. to a change in weather conditions in some
countries, increasing flooding
ref. to reducing rainfall – changing arable (farm)
land to desert
ref. to causing the extinction of some species
that cannot survive in increased temperatures.
ANSWERS
24 Nutrient cycles
log phase
death phase
lag phase
time
(b)Any three factors from: food supply, predation/
hunting, disease, use of contraceptives (for
human growth).
(c) (i)Ref. to no stationary or death phase, the log
phase will continue upwards instead of the
line levelling off.
(ii)Any four from: greater pressures on the
environment, more land needed for housing,
more land needed for growing crops, more
land needed for road building, deforestation
due to increased demand for wood for fuel/
housing, more pollution due to increased
industry/vehicle use, greater demands on
education, greater demands on health care.
2 Lag phase – the new population takes time to settle
and mature, before breeding begins. When this
happens, a doubling of small numbers does not have
a big impact on the total population size, so the line
of the graph only rises slowly with time.
Log (exponential) phase – there are no limiting
factors. Rapid breeding in an increasing population
causes a significant increase in numbers. A steady
doubling in numbers per unit of time produces a
straight line.
Stationary phase –– limiting factors such as shortage
of food causes the rate of reproduction to slow
down and there are more deaths in the population.
When the birth rate and death rate are equal, the
line of the graph becomes horizontal.
Death phase – there are more deaths than births,
due to factors, e.g. famine/disease/war/mass use of
contraceptives.
Exam focus
1 (a) (i)
1 lag phase label at start of graph
2 log phase label as the line rises steeply
(ii)(lag phase) any one from: the yeast
population takes time to settle/acclimatise
to new conditions/takes time to mature,
doubling of small numbers does not have big
impact on total population size.
(log phase) any one from: there are no limiting
factors, e.g. food or predators or disease/ref.
to rapid breeding in an increasing population
causes significant increase in numbers.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
21
ANSWERS
(b) (i)line flattens off, then falls
(ii)flattened line labelled as stationary phase,
dropping line labelled as death phase
(iii)lack of food, presence of predators, presence
of disease
(c)alcohol/ethanol
26 Human influences on
the ecosystem
1
Any four points from the following (note: this list is
not exhaustive):
The development/use of chemical fertilisers on
farm land – boosting levels of nutrients in the soil,
increasing crop yields.
The development/use of pesticides – these kill pests
that feed on or damage crops, so crop yields are
increased.
The development/use of herbicides – these kill
weeds that compete with crops for nutrients/light/
water/space, so crop yields are increased.
The development of biological control methods for
pest control as an alternative to pesticides – some
pesticides are non-selective.
The use of tractors/combine harvesters to enable
land and crops to be managed more efficiently.
Artificial selection to produce plant varieties that are
suited to particular climates/soil types, or breeds of
animals for specific purposes, e.g. optimum meat/
milk/wool production.
2 (a) deforestation
(b)Any three from: provide land for farming,
provide land for roads, provide timber for
building/furniture, ref. to fuel source.
(c)Any four from:
Reduction of habitats/food sources for animals,
which can result in their extinction.
Animal and plant diversity is reduced, so food
chains are disrupted.
The loss of plant species and their genes –
may be important for medical use/genetic
engineering in the future.
The removal of trees, so no roots to hold soil,
resulting in soil erosion and leaching of minerals.
Desertification can eventually occur.
Lack of roots, leading to flooding/mudslides/lakes
can become silted up.
Leaching of nutrients into lakes and rivers –
leading to eutrophication.
Less carbon dioxide is absorbed from the
atmosphere, increasing the greenhouse effect.
Less oxygen produced, so atmospheric oxygen
levels can drop.
Less transpiration – can lead to reduced rainfall.
3
C
G
A
E
B
F
D
4 (a) Any four from:
Ref. to bioaccumulation.
Occurs if the chemicals enter a food chain.
Plankton absorb the chemical but cannot excrete it.
Animals, e.g. small fish, feed on large numbers of
plankton.
22
Ref. to a build-up of the chemical because they
cannot excrete it.
Animals at the top of the food chain eat many
fish – accumulating high concentrations of the
chemical, which is toxic at these levels.
(b) (i)combustion of coal/oil, volcanoes
(ii)Any three from: damage to plant leaves,
eventually killing the plants, acidification of
lakes, destroying fish stocks, increasing the
risk of asthma attacks/bronchitis in humans,
corrosion of stonework on buildings, release
of soluble aluminium ions in soil – toxic to
fish when washed into lakes.
5 Any five from:
Large objects, e.g. sticks, are screened out of the raw
sewage.
Suspended grit is allowed to settle out by gravity in
a grit settling tank.
Organic matter is allowed to settle out by gravity in
a sludge settling tank.
The sludge is digested in a sludge digester.
Digested sludge can be used as fertiliser on
farmland.
Methane gas can be generated, for use a fuel.
The remaining liquid is sprinkled onto the top of an
aeration tank containing stones.
Microorganisms on the surface of the stones digest
any remaining organic matter.
Ref. to chlorination of water to kill any bacteria, so
it is safe to drink.
Exam focus
1
(a)Any four from: named species, e.g. tiger,
extinction would result in genes being lost,
which may be important for genetic engineering,
to produce chemicals such as medicines, species
may be important in food chain, so its loss could
endanger other species.
(b) (i)description of habitat of organism named in
(a), e.g. forest, in mountains
(ii)Any three from: use laws to protect habitat,
use wardens to protect habitat, control public
access, maintain species features of habitat,
e.g. by controlling water drainage or number
of prey animals or top carnivores.
2 (a) (farming) any four from:
Pesticides applied to land may leach into river,
and kill aquatic animals.
Ref. to bioaccumulation of chemicals, e.g. DDT,
in food chain, killing top carnivores.
Herbicides applied to plant crops may leach into
river, and kill aquatic plants.
Fertilisers leach into river, cause rapid growth of
river plants, plants die, bacteria feed on dead
plants, use up oxygen in respiration, so fish die.
Water extracted from river for agriculture, so
organisms in river die.
(b)(power station) any four from:
Waste water from power station is at high
temperature, so river organisms die/population
species change.
Radiation from power station leaks into river,
causes mutations, ref. to bioaccumulation in
food chains, makes fish unsafe to eat, causes
cancer in top carnivores.
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
Past exam questions
1
[4]
Feature
2
Amphibia Rep- Birds
tiles
Mammals
mammary
glands





fur/hair





scales/
scaly skin



 (except
feet
and
legs)

Tube
external
ears





feathers





1 mark for each row (ticks and name)
A
B
C
D
E
F
3
Fish
1 1
(a) (b)






2 2 3 3 4 4 5 5
(a) (b) (a) (b) (a) (b) (a) (b)










[5]
Name of
arthropod
Pediculus
Anopheles
Ornithodorus
Pulex
Musca
Periplaneta
(a)Any three from: growth, movement,
reproduction, respiration.
(b) 1 mark for each horizontal line
Feature
or:
ref. to finding shade or darkness
to avoid predators/very bright light may
damage chlorophyll or enzymes or
cytoplasm.
[2]
4 (a) C
iliated tissue – moves dust and bacteria up from
bronchi.
Root hair tissue – absorbs water and minerals
from soil.
Xylem tissue – transports water and minerals
through the stem.
Muscle tissue – contracts to cause movement. [4]
(b)A leaf contains different types of cells or tissues/a
tissue contains one type.
At least two named examples of tissues or cells
in a leaf, e.g. xylem, phloem, palisade mesophyll,
spongy mesophyll, etc.
A leaf/organ carries out a number of functions. [3]
5 (a) (i)
[4]
[3]
[4]
Animal cell
Plant cell
Bacterial cell
chloroplast
û
ü
û cytoplasm
ü
ü
ü
membrane
ü
ü
ü
nucleus
ü
ü
û
(c)Any three from: ref. to gradient/gradient
described for water, so water will move in
(to the cell), by osmosis/diffusion, cell will
become turgid/swell up/increase in size,
resulting in bursting/contractile vacuole
prevents bursting.
[3]
(d)Any two from:
(i)ref. to movement towards light/away from
light
using flagellum/reference to eye spot detects
bright light or a change in light intensity/
eye spot contracts in response to light
ref. to taxis.
[2]
(ii) Depending on response to (d)(i):
either:
light (energy) needed for photosynthesis
to make food/glucose/sugar/starch/
carbohydrate
A
B
C
D
Colour of indicator
at start
pinky red
pinky red
pinky red
pinky red
ANSWERS
(c) (town) any four from:
Sewage enters the river, causes rapid growth of
river plants, plants die, bacteria feed on dead
plants, use up oxygen in respiration, so fish die,
chemicals from factories enter river, killing river
organisms, water becomes unfit to drink.
Colour of indicator
after 6 hours
yellow
yellow
yellow
purple
(ii) Tube A
1 respiration occurs
2 carbon dioxide produced/added to water
3 becomes acidic/more acidic/pH falls
Tube D
4 photosynthesis occurs
5 carbon dioxide removed from water
6 becomes alkaline/less acidic/pH rises [4]
(b) Tube E
1 colour stays pinky red/does not change
2 respiration and photosynthesis balance out
3 carbon dioxide amount in water/pH does not
change
OR
1 colour goes purple
2 photosynthesis more than respiration
3 carbon dioxide amount in water drops/pH rises
OR
1 colour goes yellow
2 respiration more than photosynthesis
3 carbon dioxide amount in water rises/pH falls
Any one prediction – 3 marks.
[3]
6 (a) (i)heat
[1]
(ii)condensation/cooling of water vapour
[1]
(b) (i)transpiration/evapo-transpiration
[1]
(ii)humidity
temperature
wind/air movement
light/sunlight
Any three – 1 mark each.
[3]
(c) (i)reduced transpiration (in forest area)
leading to less water vapour (moving
inland)/less clouds form
thus less/no rainfall/less humid (inland)
Any two – 1 mark each. [2]
(ii)more surface runoff of rain water/flooding
increased surface wind speed
can result in greater erosion of soil/silting
up of streams/rivers/landslides
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
23
ANSWERS
24
desertification
destruction of habitats/disrupt food chains
possible extinction of animal/plant species
more carbon dioxide/less oxygen in
atmosphere
Any two – 1 mark each.
[2]
7 (a) osmosis
water diffuses/moves down water potential
gradient
through partially permeable membrane/sugars/
solutes in root hair cell (to lower water
potential)
[3]
(b)20.0
[1]
(c) (rate of water) uptake increases
positive correlation/exponential/not linear
e.g. 0.4 mm min–1 at 0 m s–1/no wind, 20 mm min–1
at 8 m s–1
[2]
(d)Any two from: temperature, humidity, light
intensity.
[2]
(e)(raw material for) photosynthesis/forming
glucose or carbohydrate
turgidity/support
transport of: solutes/named solute/food
substances
forming vacuoles/growth/(cell) expansion
taking part in chemical reaction(s); e.g.
hydrolysis/breaking down food substance
medium for chemical reactions
Any two – 1 mark each.
[2]
(f)loss of water (vapour) through stomata (in leaves)
evaporation from surfaces of (mesophyll) cells/
into air spaces (in leaf)
loss of water from leaf (cells) lowers water
potential
water moves into leaf (from xylem)
(this) pulls on/creates tension (in water column in
xylem)
cohesion of water molecules
[4]
(g) (Note question says structural adaptations.)
leaves, small/reduced to spines/are needles
no leaves
curled/rolled leaves
hairs on the leaves/stems
thick (waxy) cuticle
sunken stomata
few stomata
fleshy/succulent leaves/stems
small surface area: volume ratio
deep roots
long/extensive shallow roots
ignore stomata close during the day
Any three – 1 mark each
[3]
8 (a) (i)Any two from: oxygen, glucose, accept other
valid substances such as water, amino acids,
etc.
[2]
(ii) carbon dioxide/lactic acid [1]
(b) (i) (cardiac) muscle [1]
(ii) Ref. to contraction/shortening. [1]
(iii) Any three from: pressure will increase, the
blood will be forced out from the heart, into
the aorta, the volume of blood decreases. [2]
(c) (i) Any two from: high fat diet/cholesterol,
smoking, stress, lack of exercise, obesity,
genetic influence.
[2]
(ii)all parts of the artery below point B
shaded
[1]
(d) (feature) presence of valves
(explanation)prevents backflow of blood/
blood flows in one direction
(feature)
ref. to wide lumen
(explanation)allows blood to flow with
minimum resistance/flows more
easily
(feature)ref. to tough wall/collagen
present
(explanation)to prevent bursting
(feature)
thin/elastic walls
(explanation)makes it easier for body muscle
contractions to cause blood to
move forward
[4]
9 (a) (i)oxygen/dust/particles
[1]
(ii)carbon dioxide; water (vapour)
[2]
(iii)lower
[1]
(b)mix air with/bubble through lime water; which
goes cloudy/white/milky
[2]
(c)(diffusion is) random movement of particles/
molecules/ions from their high concentration to
their lower concentration/down concentration
gradient
Any two – 1 mark each
[2]
10 (a) because they are toxic/poisonous
[1]
(b) (i)ureter
[1]
(ii)(urinary) bladder
[1]
(iii)renal vein
[1]
(c)filter (from the blood)/ultrafiltration
plasma /soluble/dissolved substances/named
examples
reabsorption
of useful substances/named example
remainder becomes/forms urine
Any three points – 1 mark each. [3]
(d)(i)liver
[1]
(ii)urea
[1]
11 (a) (i)184
[1]
(ii)liver [1]
(iii)line meets/cuts horizontal axis at 4 pm
[1]
(iv) 9 am (approx.)
[1]
(b) (i)slows down nerve impulses/crossing
synapses
responses/reactions take longer
interferes with judgements
Any two points – 1 mark each. [2]
(ii)liver – causes cirrhosis/cancer/kills/destroys
cells
brain – damages/kills/destroys cells
stomach – irritates/damages wall/lining of/
cause ulcers
kidney – can cause damage to cells
heart – increased risk of coronary disease
Any two points – 1 mark each.
[2]
(iii)aggressive behaviour/fighting
family break up/loss of friends
inability to concentrate/poor time keeping –
loss of job
financial problems/money spent on alcohol
lack of personal care/hygiene
problems with law/theft
drunk driving/higher risk of accidents/lose
licence
homelessness
Any two points – 1 mark each.
[2]
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
(c)conditions not favourable:
cannot compete with S. thermophilus (or reverse
argument)
cannot increase until pH falls/changes (or reverse
argument)
cannot increase until oxygen concentration
decreases (or reverse argument)
grows slower than S. thermophilus
takes longer to adapt/feed
fewer L. bulgaricus to start with
idea that substance/condition provided by
S. thermophilus [2]
15 (a) (i)Any one from: NOx/oxides of nitrogen,
vehicle/car, exhausts/fumes/emissions/gases,
burning fossil fuels in houses/burning forests,
volcanic eruptions/snow melt.
[1]
(ii)Any two from:
Leaves/trees/producers/vegetation/plants
harmed/damaged/killed.
Trees more likely to get diseased.
Bark is damaged.
Roots killed.
(Sensitive species of) lichens killed.
(Named) microorganisms killed e.g. bacteria/
fungi.
Soil pH decreases/soil becomes more acidic.
Aluminium ions become mobile.
Nutrients/named example(s) leached.
Food chains/food webs disrupted.
Loss of habitat/less biodiversity/extinction of
species.
[2]
(b)Any two from:
Use alternative/renewable/green energy sources
(e.g. nuclear power/wind power/wave power/
solar power/hydrogen power).
Use low-sulfur fuels.
Reduce use of coal.
Flue gas desulfurisation/‘use scrubbers’/chimney
electrostatic precipitators/neutralise waste gases
with lime.
Catalytic converters.
Provide/use more public transport.
Car sharing/car pools/reduce use of cars/hybrid
cars/electric cars/use biofuels.
Walking/cycling.
Reduce food miles.
[2]
(c)(look for positive features, not absent ones
apart from unsegmented)
unsegmented/not segmented/shell/(muscular)
foot [1]
(d)(i) frogs/black-fly larvae
[1]
(ii)clams/snails/molluscs
[1]
(iii)Any two from:
enzymes do not function (well)
acid damages shells/scales/skin
calcium ions not available for shells/difficult
to make shells
aluminium in solution is toxic to fish/fish die
acid/low pH kills fish
fish produce (lots of) mucus
blocks gills
[2]
Cambridge IGCSE Biology Practice Book © Hodder & Stoughton Ltd 2013
ANSWERS
12 (a) (i)label G clearly indicating testis
[1]
(ii)label S clearly indicating sperm duct
[1]
(iii)label T clearly indicating testis
[1]
(iv) label U clearly indicating urethra [1]
(b)(stimulate) production of sperm
growth/development of pubic/axillary hair
growth/development of facial/body hair
breaking of the voice
widening of shoulder (girdle)
development of more muscle/more muscular
increased aggressive behaviour
growth of penis/testes
Any two points – 1 mark each.
[2]
(c)meiosis; four; haploid; half
[4]
13 (a)blue – because no white flowers in offspring/in
presence of inherited blue allele
[1]
(b) (i)blue – BB; white – bb
[2]
(ii) offspring – Bb
[1]
(iii)parents Bb bb
gametes B b b b
offspring genotypes Bb Bb bb bb
phenotypes blue, blue, white, white
ratio 2 : 2 or 1 : 1
Any four – 1 mark each.
[4]
(c) (i)shows extremes and all intermediates
(of cob length)
[1]
(ii)(amount of) light
(amount of) minerals
(amount of) water
temperature
Any three – 1 mark each. [3]
(iii)flower colour only blue or white/no
intermediate colours (thus is discontinuous
variation) [1]
14 (a) (i)high temperatures denature enzymes
kill bacteria
to give optimum temperature (for, enzymes/
bacteria) [2]
(ii)respiration is anaerobic; lactic acid
produced [2]
(iii)named example of a food additive:
colouring; preservative/stabiliser/emulsifier/
antioxidant; flavouring/(artificial) sweetener;
thickening agent [1]
(b) (description)
sigmoid (growth curve) or lag phase +
exponential/log + stationary phase
little/no growth, rapid growth, no
growth/‘levelling off’
(explanation)
lag phase:
small number of bacteria
produce proteins/enzymes/DNA
exponential phase:
binary fission/asexual reproduction
no limiting factors/no competition/plenty of
food/plenty of resources
stationary phase:
death rate = ‘birth’ rate
resources/food used up
pH not favourable/optimum [5]
25