CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Exam-style questions and sample answers have been written by the authors. In examinations, the way marks are awarded
may be different.
ractical Workbook
P
answers
Chapter 1
Practical investigation 1.1
Exam-style questions
1
1
2
3
4
5
6
Suitable drawing made of the organism
chosen by the student, with clear lines drawn
in pencil, drawing larger than the original,
correct shape and proportion, main features
observable, main features correctly labelled.
Main features of student’s drawing correctly
identified.
Correct group identified for the organism
chosen.
Student should use magnification = image
size / actual size to calculate a number greater
than 1 if the image is correctly larger than the
original.
Student’s own checklist matches that of their
drawing.
To ensure that the drawing is clear and
that the student can demonstrate their
understanding.
Reflection
a
b
c
d
e
Student draws a diagram that satisfies
each of the marking points: clear lines
drawn in pencil [1] ; drawing larger
than the original [1] ; correct shape and
proportion [1] ; main features observable
[1] ; main features correctly labelled [1] ;
17 mm or 1.7 cm (accept +/– 1 mm) [1] ;
magnification = image size / actual size
[1] ; correct calculation = magnification =
measured size / actual size; magnification
= student’s own measurement of their
wing diagram / 17 mm; answer should be
greater than 1 if diagram is larger, and
given to three significant figures [1] ;
Musca domestica (student answer should
[1]
be in italics, or underlined). ;
Any two from: two pairs of wings (but
not visible in flies); body divided into
head, thorax and abdomen; three pairs of
[Max. 2]
jointed legs. ;
Student correctly identifies the points not done
correctly in the diagram.
1
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 2
Practical investigation 2.1
Practical investigation 2.3
1
1
2
3
4
5
6
7
Suitable drawing made, with clear lines drawn
in pencil, drawing larger than the original,
correct shape and proportion, main features
observable, main features correctly labelled.
Any observable features labelled (such as cell
wall).
Cell wall provides strength and support,
cytoplasm is the site of cell reactions, the
nucleus controls the activity of the cell.
Accept any sensible answer, such as
mitochondria, cell membrane, chloroplast etc.
The resolution is not high enough to
distinguish between the smaller parts of the
cell.
To see the cells in a single layer; clearer to see
the cells.
You might see the same structures but they
might not be as clear or obvious without the
staining solution.
Practical investigation 2.2
1
2
3
4
5
Student’s drawings of cells, with clear lines
drawn in pencil, drawing larger than the
original, correct shape and proportion, main
features observable, main features correctly
labelled.
Limited to cell membrane, nucleus, cytoplasm.
Cell membrane controls what enters and leaves
the cell, cytoplasm is the site of cell reactions,
the nucleus controls the activity of the cell.
Site of cellular respiration.
Health and safety, to protect against airborne
pathogens being released.
2
3
4
Student’s drawings of cells, with clear lines
drawn in pencil, drawing larger than the
original, correct shape and proportion, main
features observable, main features correctly
labelled, magnification included.
Student’s answer should include the
calculation for objective lens × eyepiece lens.
Student’s answer should match the specimens
viewed.
To show understanding and so that the viewer
knows what they are looking at.
Reflection
Student’s own reflection.
Exam-style questions
1
a
b
c
d
Drawing larger than original [1] ; clear
lines [1] drawn in pencil [1] ; main
features labelled [1] ; correct shape and
proportion [1] ;
50 mm or 5.0 cm (accept +/– 2 mm) ; [1]
Student’s measurement matches that of
the drawing. ;
[1]
Magnification = image size / actual size
[1] ; correct numbers substituted [1] ;
correct answer given based on answers to
parts b and c [1]. ;
Reflection
Use a microscope with greater resolution or
magnification.
2
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 3
Practical investigation 3.1
Practical investigation 3.3
1
2
1
2
3
4
5
6
Time stated in seconds.
Student sketch shows diffusion of colours
towards the centre.
The colours / dyes dissolved into the water
and diffused towards an area of lower
concentration.
The diffusion would happen faster because the
warmer water would allow for faster diffusion
of the colours.
Method should include a range of water
temperatures for the independent variable,
suggestion that the time taken to reach the
centre can be measured, and some attempt to
control all other variables such as sweet size,
volume of water, room temperature, etc.
The reaction will happen faster.
Any sensible suggestion such as using a pipette or
a way of adding the water slowly.
Practical investigation 3.2
2
3
4
4
5
Reflection
Reflection
1
3
Colour change stated with time in seconds as
observed.
The colour diffused out of the gelatine into
the water as it moved down the concentration
gradient.
Use an acid of higher molarity / strength.
Repeat the readings and take an average.
Unlikely to be able to add at the same time so
therefore the results might be less valid as some of
the beetroot could have been in the solution for
longer than others.
Practical investigation 3.4
1
2
3
4
3
Data recorded by student.
Add the two lengths together before dividing
by two.
Student should divide the difference by the
original length, before multiplying by 100.
Student’s answer should refer to water moving
into the beetroot by osmosis where there has
been an increase of length. The water moves
into the beetroot when water concentration is
higher outside of the beetroot. If there is no
change in length, then the water concentration
inside and outside of the beetroot must have
been similar.
Method should refer to measuring the mass
of the beetroot, using a measuring balance to
either 2 or 3 decimal places.
Student’s drawing should show water moving
into the tubing and becoming bloated / larger.
The tube becomes more filled / larger/ more
bloated or similar wording.
As the water potential inside the tubing was
lower than outside, the water moved down the
concentration gradient by osmosis, into the
tubing.
Any sensible answer, such as increase the
concentration gradient, or by using warmer
water.
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 3 continued
Exam-style questions
1
a
Three correct answers for distilled water
[1] ; three correct answers for sucrose
solution [1] ;
Mass of potato / g
Solution
c
d
4
After
Change
1.30
1.79
+0.49
1.31
1.71
+0.40
1.21
1.66
+0.45
20%
sucrose
solution
1.51
1.45
–0.06
1.60
1.53
–0.07
1.69
1.43
–0.26
40%
sucrose
solution
1.40
Distilled
water
b
Before
1.40
1.40
For distilled water: (0.49 + 0.40 + 0.45) /
3 = 0.45 g; for 20% sucrose solution:
(−0.06 + −0.07 + −0.26) / 3 = −0.13 g
[1] ; for calculating total change in mass,
[1] ; for dividing by 3, and [1] for the
correct answers with units. ;
Water molecules move down their
concentration gradient from an area
where there are more to an area where
there are fewer [1]. ; Therefore, in the
potato placed in the distilled water, the
water moved from the high concentration
of water molecules outside of the potato
[1] ; into the lower concentration of water
molecules inside [1] ; by osmosis, which
caused an increase in the mass of potato
[1]. ; (Accept opposite argument for
potato placed in 20% sucrose solution.)
Any sensible answers between 1.40 g
and 0.80 g [1] ; with correct ‘change’
calculations completed [1]. ;
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 4
Practical investigation 4.1
Recording data
1
3
2
3
4
5
Student’s table should include types of
orange / fruit used in the first column. The
next columns should record the amount
of juice / ml required to turn the DCPIP
colourless.
Student’s answer should match their data.
Student data should be described with
reference to figures from their own table.
Student should also state any obvious pattern
or relationship.
Repeat the investigation.
Any sensible suggestion, such as different
prices of orange, different origins of orange,
organic vs non-organic, raw vs cooked orange.
Use equipment that can measure the colour of
the solutions, or any other sensible suggestion
along these lines.
Reflection
No, as different people might have different
opinions on when it turned colourless. This means
that we might get different results and the results
might not be as valid.
2
5
5
Reflection
Students are likely to say that it was difficult to
crush each food for testing with a solution or that it
was difficult to keep the mass the same when adding
water. Any sensible suggestion for improvement,
such as making a large sample of crushed food that
can then be used for multiple tests. This ensures that
the samples are the same for each test. Use the large
sample to remove the exact mass required.
Practical investigation 4.3
1
2
3
Practical investigation 4.2
1
4
Any two sensible safety suggestions: wear
safety spectacles, wash hands.
Student outlines the correct test for three
different foods, any from:
• Reducing sugar: heat with Benedict’s
solution and observe the colour change
(from blue to orange-red)
• Protein: add biuret’s solution and observe
the colour change (from blue to purple /
mauve)
• Starch: add iodine solution and observe
the colour change (from brown to
blue-black)
• Fats / lipids: add ethanol and water in
equal quantity and observe the change
(cloudy layer forms)
Student’s table completed and correct food
group identified.
Student’s answer should include the correct
colour change for the foods tested.
Repeating the investigation more than once,
or multiple times.
4
Student’s own drawing of the suspended DNA.
Student may answer either way here but if
they can see the twisted nature of the DNA
then they may be able to link this to the
double helix structure of DNA.
Breaks down the membrane to release the
DNA from the nucleus.
Some students may not have followed the
method correctly, or with enough care.
Exam-style questions
1
2
a
b
c
d
e
Biuret reagent ;
[1]
Protein ;
[1]
From blue to purple / mauve ;
[1]
A and C ;
[1]
Because there was a colour change [1] ;
from blue to purple [1] ;
Method should include:
• Grind the sample of food and add water [1] ;
• Add the food to a test-tube [1] ;
• Add a few drops of Benedict’s solution [1] ;
• Place the test-tube with Benedict’s and food
into a water-bath [1] ; with description or
drawing of the water-bath [1] ;
• Leave for a few minutes and observe the
colour change [1] ;
• The solution will turn from blue to green
or to an orange-red colour [1] ; in the
presence of a reducing sugar [1] ;
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 5
Practical investigation 5.1
Practical investigation 5.2
1
1
Student’s table should be similar to:
Test
-tube
Solutions
added
Testing agent
used
Colour
change
A
Starch
Iodine
From
brown to
blue-black
B
Starch +
amylase
Iodine
None
C
Starch
Benedict’s
None
D
Starch +
amylase
Benedict’s
From blue
to orangered
2
3
4
5
2
The starch has been broken down into
reducing sugars which turn orange-red when
tested with Benedict’s solution.
Reducing sugar / glucose / any named sugar
There is no colour change; the iodine solution
remains brown.
To break down the starch into smaller
molecules / sugars
3
4
5
6
6
Testtube
Solutions
added
Testing agent
used
Colour
change
A
Starch
Iodine
From
brown to
blue-black
B
Starch +
amylase
Iodine
From
brown to
blue-black
C
Starch
Benedict’s
None
D
Starch +
amylase
Benedict’s
None
6
7
Student’s own table should include the
temperature of the water-bath in the first
column, with space for readings taken for the
time that the solution became colourless in the
other columns, with units included in column
headings (°C for temperature and s or min for
time).
Student’s line graph should match the results
gathered and include:
• Axes drawn using a pencil and ruler
• Axes labelled with correct units
• Points plotted using a sharp pencil
• Points joined by straight lines that do not
extend past the final point
Student’s answer should match the graph.
Student’s answer should match the data, using
conditional sentences that include the IV and
the DV. Such as, ‘as the temperature increased,
the rate of reaction of the amylase increased’.
The enzyme denatured and so the physical
nature of the enzyme changed. This means
that substrates can no longer bind to the
enzyme and reactions cannot take place. In
this investigation, the amylase was not able to
break down the starch.
Any sensible range such as: 10, 20, 30, 40,
50 oC.
Repeat the experiment at least twice.
Reflection
Sensible ideas such as: work as a team, plan which
team member will be responsible for each stage
and annotate the method to that effect.
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 5 continued
Practical investigation 5.3
1
H2O2
concentration / %
Volume of oxygen collected every 30 seconds / cm3
0
30
60
90
120
150
180
210
240
270
60
40
20
0
Student data included in table.
2 Student’s own calculations from the data in Q1.
3 Student’s answer should refer to the data gathered: As the concentration of
hydrogen peroxide increases from (student data to student data), the rate of reaction
increases from (student data to student data). This is because the catalase acts as a
catalyst and allows the reaction to happen at a faster rate.
4 To compare the effect of hydrogen peroxide.
Reflection
Student’s own reflection but may include assigning specific roles to each team member.
Exam-style questions
1
a
Any three from:
• temperature ;
• pH ;
• enzyme concentration ;
• type / source of enzyme ;
• quantity / volume of solutions ;
• same equipment used. ;
[Max. 3]
b
i
Enzyme
activity
Temperature / °C
[1] ;
pH
[1] ;
Substrate concentration
[1] ;
ii
Enzyme
activity
iii
Enzyme
activity
7
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 5 continued
2
a
Temperature / oC
Time taken for starch to be broken down / s
Attempt 1
Attempt 2
Attempt 3
10
250
240
280
Average
257
20
240
240
271
250
30
65
55
63
61
40
72
70
69
70
50
110
120
131
120
60
247
278
271
265
70
300
301
312
304
[1]
b
350
300
250
Time taken 200
for starch
to break
150
down / s
100
50
0
c
8
0
10
20
30
40
50
Temperature / °C
60
70
Correct axis drawn [1] ; units added to labelled axis
[1] ; appropriate size and scale of graph (at least half of
the graph paper) [1] ; plotted correctly [1] ; lines joined
together [1] ;
Reference to: as the temperature increases from 10 to
20 oC, the time taken remains stable [1] ; but between 20
and 50 oC, the time taken falls to as low as 61 seconds
[1] ; before increasing again from 50 oC upwards [1] ;
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 6
Practical investigation 6.1
Exam-style questions
1
1
2
3
4
Student’s drawing of epidermal peel should
include labelled stomata, with clear lines
drawn in pencil, drawing larger than the
original, correct shape and proportion, main
features observable, main features correctly
labelled, magnification included.
Student’s own data.
Student’s explanation linked to conditions
from where leaf was obtained. For example,
if the leaf was gathered from a plant in warm,
dry conditions then it may be that more
stomata were closed to prevent loss of water.
Student’s answer should identify the
independent variable as named locations or
conditions (such as in shade, direct sunlight,
range of temperatures, etc.). The dependent
variable should be the number of open /
closed stomata. Controlled variables should
include species of plant, surface area of leaf,
any equipment named, same microscope, etc.
a
b
c
Reflection
Student’s own reflections.
Practical investigation 6.2
1
2
3
4
5
6
9
d
Student’s own data.
Student correctly calculates the average from
own data (combined with that of peers if
required).
More oxygen bubbles produced indicates
higher rate of photosynthesis.
Student’s own data but expected results will be
similar to: red / blue/ green / other.
Light intensity.
Student states method but includes an
independent variable that alters the light
intensity. This can be done by making the
light source brighter / dimmer, or by moving
the light source towards / away from the leaf.
Accept any sensible named suggestion.
Student’s method should include six from:
• Place leaf into boiled water for
30 seconds ;
• Remove leaf and place into ethanol
solution ;
• Place ethanol and leaf into
water-bath to keep warm ;
• Remove leaf after 15 minutes ;
• Wash leaf with water and place onto
white tile ;
• Add iodine solution ;
• Starch is present where iodine turns
blue / black ;
• Any safety point mentioned ; [Max. 6]
Positive result (blue/black) in the green
parts of the leaf [1] ; but no colour
change from yellow iodine in the white
parts of the leaf [1]. ;
Where there is no chlorophyll in the white
areas there will not be any photosynthesis
[1] ; and so there will be no stores of
starch in those areas [1]. ;
6CO2 + 6H2O ➞ C6H12O6 + 6O2
correct reactants [1] ; correct products
[1] ; balanced equation [1] ;
e
Leaves contain
many veins
Leaves are
wide and flat
Leaves are thin
Leaves have stomata
on the underside
Any three from:
• wide, flat leaf ;
• thin leaf ;
• presence of veins ;
• stomata. ;
[Max. 3]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 7
Practical investigation 7.1
Exam-style questions
1
2
1
3
4
Student’s own data.
a and b Student correctly uses Q = mc ∆T to
calculate the energy transferred in joules for
each food in their table.
a Student correctly identifies the food with
the highest energy value.
b This food heated the water to the highest
temperature and so transferred the most
energy to the water.
Using the same size / mass of food, holding
the food the same distance from the water,
using the same starting temperature for the
water, using the same equipment for each trial,
allowing the food to burn for same time, or to
completion of burning.
Reflection
Student identifies possible improvement and
makes sensible suggestions. For example, for the
food burning at the same distance from the water,
an improvement would be a second boss clamp
and stand to hold the food in place.
Practical investigation 7.2
1
2
3
4
5
10
Student’s diagram of the eggs drawn with
clear pencil lines.
Student’s own observations of the eggs. One
of these should be smooth and one should be
cracked and shrivelled.
Fizzy drinks contain sugars that combine with
bacteria to form acids. This acid attacks the
teeth and weakens the protective enamel that
surrounds them.
The amount of solution should be the same
for valid results. The eggs should be from the
same source and this can be verified by taking
from the same carton of eggs. The quality and
validity of results might be affected as you
cannot be sure any change is due to the type
of solution.
It might not be possible, or safe, to use real
teeth and so using the eggshells allows us to
model the effect of acids.
a
b
c
d
Q = mc ∆T [1] ;
Q = 30 × 4.2 × 27 [1] ;
Q = 3402 J or 3.4 kJ [1] ;
Any two sensible safety precautions from:
safety spectacles ; use Bunsen burner
safely with yellow flame ; dispose of food
safely after burning ; do not handle hot
equipment ;
[Max. 2]
Carbohydrates, fats, vitamins, minerals,
water, protein, fibre (all correct for one
mark) ;
[1]
Any correct food stated that is rich /
known for that nutrient. (One mark for
each food per food group.) Common
examples include:
• Carbohydrates: bread, pasta, rice,
potatoes ;
• Fats: oils, dairy products, fatty meats,
chocolate ;
• Vitamins: oranges, fruit, oily fish,
eggs ;
• Minerals: milk, broccoli, fruit,
vegetables ;
• Water: water ;
• Protein: eggs, milk, meat, fish ;
• Fibre: cereals, bread, nuts ; [Max. 7]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 8
Practical investigation 8.1
Practical investigation 8.3
1
2
Method
3
4
5
6
Student’s own results in the table.
The correct temperature chosen to match the
data in the table.
The difference correctly calculated between
the furthest and the shortest distances in the
student’s table.
Xylem.
Five would be ideal but accept any answer
between four and ten.
Students may have used different plants, or
differently sized stems. Students may also
suggest natural variation between different
plants and parts of plants.
4
Recording data
1
Reflection
Student’s own reflection.
2
Practical investigation 8.2
1
2
3
4
5
Water vapour / condensation / water collected
inside the bag.
Turns blue.
Water.
Condensation.
Investigation should outline a similar method
to Practical investigation 8.2 but by using two
different types of plant. Answer may identify
differences between the leaves as a factor,
control variables should be identified such as
plant size, surrounding conditions, and size
and type of polythene bag.
Student’s method should be similar to:
• Ensure that there are no air gaps between
the plant and the potometer tubing.
• Open the clip and fill the tubing with the
water, close the clip immediately.
• Record the position of the water
meniscus.
3
4
5
Student’s table should have the independent
variable in the left column (either surface
area of leaf or number of stomata) and the
distance travelled by the bubble should be
in the right-hand column. The table should
include the time taken for the recordings.
Student uses own data. Transpiration rate =
distance travelled by the meniscus / time taken.
Units should be correct (for example cm/min).
Student correctly identifies variable with
greatest transpiration rate.
Student makes reasonable suggestion. For
example, the greater the surface area of the
leaf, or the greater the number of stomata, will
both result in higher rates of transpiration.
This is because more water can be lost from
the leaf.
Type of plant, size of plant, temperature,
humidity, or any other named variable. To
make the experiment valid and to be sure
that any change in rate was as a result of the
independent variable.
Reflection
Any sensible suggestion such as using graph paper
with smaller squares, or technology to help count
the number of stomata.
11
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 8 continued
Exam-style questions
1
a
b
Any two from:
• time the plant was observed for ;
• time intervals ;
• temperature of the room ;
• leaves taken from the same plant ;
• same equipment used each time ;
[Max. 2]
i
all four averages correct ;
[1]
ii correctly dividing the average distance
by time [1] ; time converted into
minutes [1] ;
Leaf
Distance moved by air
bubble / mm
1
c
d
12
2
3
Average
Transpiration
rate / mm / minute
1
120 101
72
97.7
1.6
2
109 115 154
126
2.1
3
70
61
80
70.3
1.2
darkness
0
1
1
0.7
0.01
The temperature of the room could have
been varied [1] ; improve by keeping the
temperature the same and not adjusting
the heating throughout the day [1]. ;
Some of the water is used up by the
plant / stored by the plant. ;
[1]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 9
Practical investigation 9.1
Practical investigation 9.3
1
1
2
3
2
Student’s own drawing should be in pencil
and have structures labelled (this may include
aorta, pulmonary vein, atrial wall, valve
tendons, ventricle wall, valve flaps).
a To prevent bacteria from coming into
contact with skin or clothes.
b To destroy or remove any bacteria that
may be on the hands or skin.
c To destroy any bacteria that remain on the
surface and prevent coming into contact
with anyone who touches the work
surface.
d To prevent airborne pathogens from being
ingested.
4
5
Reflection
Student’s own reflections.
6
Practical investigation 9.2
1
2
3
4
5
6
7
8
Student completes the table using their own
data.
Beats per minute (or BPM) in columns 2, 3,
and 4.
Correct calculation from student’s own data.
Correct calculation from student’s own data.
It is most likely that there will be a small
decrease in the heart rate. Accept any answer
that matches the student data as results may
vary between different people.
Sportsperson or athlete may be able to use the
techniques to help them relax and perform
better in high-intensity or high-pressure
competitions.
Any sensible suggestion such as heart monitor,
wearable activity tracker, or other electronic
pulse measuring device.
Not all members will be of the same sex,
fitness, age, diets, etc. This means that results
might vary a lot within the group.
Reflection
Student’s own reflections.
13
Student completes the table using their own data.
Correct calculation from student’s own data.
Student’s graph should contain:
• graph covers at least half of the grid
• x-axis contains the treadmill speed
• y-axis contains the average heart rate
• correct units shown (km/h and beats per
minute)
• points plotted correctly
• points joined together using pencil and ruler.
As treadmill speed increases, the heart rate
increases.
The body requires more oxygen and glucose to
be pumped around the body for cells to carry
out respiration.
The differences in participants – they might have
been different ages, sexes, fitness levels, diets, etc.
Reflection
Student’s own reflections.
Exam-style questions
1
a
b
c
d
Any three from
• age, sex, fitness, weight / mass, height,
diet of the participants ;
• Accept any sensible named variable
not stated.
[Max. 3]
Improve the validity of his results / the
investigation. ;
[1]
Health of participant / ability to stop the
exercise if feeling ill or dizzy. ;
[1]
Method should include any six from:
• at least 3 male and 3 female
participants ;
• of similar age and fitness ;
• description of measuring heart rate
before and after exercise ;
• time stated for length of exercise ;
• attempt to control the variables of
temperature, equipment, type of
participant, etc. ;
• one valid safety point ;
• repeat each reading at least once and
find the mean ;
[Max. 6]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 10
Practical investigation 10.1
Exam-style questions
1
1
2
3
4
5
6
7
8
Student’s drawings should include bacterial
growth or spores on the dish.
Description of counting a smaller area and
multiplying to estimate the total number of
spores.
Student’s answer matches their Petri dish.
Incubation at 25 oC, use of nutrient broth,
sealed contained, away from agents that
destroy or inhibit bacterial growth, or any
other sensible suggestion.
Bacteria would not grow.
To provide a sterile environment for the
investigation.
The bacteria would multiply too quickly
which is dangerous / hazardous.
The airborne bacteria that would be released
would be very dangerous for those that ingest
or inhale them.
Reflection
a
b
Any eight from: Prepare two agar plates
[1] ; heat an inoculating loop in a hot
Bunsen burner flame [1] ; Using the loop,
collect bacteria from the door handle
and from the keyboard [1] ; add the
bacteria to the agar plates [1] ; and seal
the Petri dishes with tape [1]. ; Place the
Petri dishes in an incubator [1] ; between
20 oC and 30 oC [1]. Count the number
of bacterial spores in the dishes [1] ; after
a named time period [1]. ; Allow one
mark for safety [1]. ;
[Max. 8]
60 mm (accept 59 to 61 mm) ;
[1]
i
ii Convert mm to μm (60 × 1000
= 60 000 μm) [1] ;
Actual length = image length /
magnification [1] ;
= 60 000 μm / 12 000 [1] ;
answer = 5 μm [1] ;
Student’s own reflections.
Practical investigation 10.2
1
2
3
4
5
6
7
14
Student states correct names of solutions.
Suitable biological drawing of the dish, with
clear lines drawn in pencil, correct shape and
proportion, main features observable, main
features correctly labelled.
Student’s answers match their Petri dish, units
provided (mm).
Student’s answer matches the results of
the dish.
The antibacterial agent was the most effective
and was able to destroy more of the bacteria.
They destroy bacteria in the mouth that may
otherwise attack our teeth. This prevents
infection and tooth decay.
To observe if it was the antibacterial
mouthwash that had an effect on the bacterial
growth, as a control for the investigation.
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 11
Practical investigation 11.1
Practical investigation 11.3
1
1
2
3
4
5
6
7
Student’s own table contains acceptable
results.
Student’s answer should be the difference
between the two answers given in Question 1.
Heat energy released during respiration.
Collate results and calculate the mean /
average.
To reduce heat loss to the surroundings.
They act as a control so that the results can
be compared. This will allow any change
in temperature to be attributed to the
independent variable.
To observe the temperature change and link
this to the germination of the seed, so that any
temperature change was not due to growth/
respiration of bacteria/fungi.
2
3
Reflection
Student’s own reflections.
4
Practical investigation 11.2
1
2
3
4
5
15
Student’s diagram correctly labelled. Possible
structures include the trachea, the C-shaped
tracheal rings, the bronchi, the bronchioles,
the pleural membrane and possibly some of
the blood vessels that travel to and from the
heart.
The lung floated / did not sink.
The density of the lung is less than the density
of water, due to the amount of air and air
space in the lung, even when deflated.
Compare the surface area of the lung before /
after the inflation. The most suitable method
might be to compare the displacement of
water when the lung is submerged but accept
any sensible suggestion.
Clean / sterilise with disinfectant to remove
unwanted bacteria.
5
6
7
8
9
Student’s method should be similar in style
and structure to the method in the experiment
in 11.3 of the Coursebook. The student
should state how the breathing rate is achieved
and measured, the type and length of exercise,
and how the breathing rate will be measured
every minute after exercise until the rate
returns to the resting rate.
The table should include the following
headings for each student tested: Breathing
rate at rest / breaths per minute, breathing rate
for every minute after exercise (this may go up
to 5 to 10 minutes depending on activity and
student fitness).
Student’s graph should match data from
the table with Time / minutes on the x-axis,
and Breathing rate / breaths per minute on
the y-axis. The graph should be drawn to an
appropriate scale and the plots joined pointto-point with a ruler.
Students should describe the increase in
maximum breathing rate during exercise,
before describing the gradual decrease in
breathing rate after the exercise has finished.
To provide oxygen required to break down the
lactic acid produced during exercise
Lactic acid
The time taken for the body to break down the
lactic acid and return to the normal breathing
rate. This is the time taken to repay the oxygen
debt.
By selecting participants of similar age / sex /
fitness / diets / lifestyle
The results might have varied because of the
differences and cast doubt on whether the
independent variable made a difference.
Reflection
Student’s own reflections related to possible
issues in their own method, such as time available
to carry out the exercise, the different types of
participant, or other sensible answers.
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 11 continued
Practical investigation 11.4
1
2
3
a–d Student observations.
a Temperature of air increases as it passes
through the respiratory system.
b Water vapour will turn the white (anhydrous)
copper sulfate crystals from white to blue.
c Limewater turns cloudy/milky in the
presence of carbon dioxide.
d Oxygen relights a glowing splint.
Suggestion of use of technology or data
logger or probe.
Exam-style questions
1
2
3
16
a
Student’s graph shows breathing rate on
the y-axis [1] ; against time on the x-axis
[1] ; with appropriate units [1]. ; Curve
sketched showing breathing rate at rest
for 3 minutes, before rising to a peak at 10
minutes, falling back to the resting rate at
14 minutes [1]. ;
b Breathing rate increases gradually from 3
to 10 minutes [1] ; before decreasing back
to the resting rate at 14 minutes [1]. ;
c Muscles had produced lactic acid during
exercise [1] ; which requires oxygen to
break down into carbon dioxide and
water [1]. ; Breathing rate remains high
[1] ; until this oxygen debt [1] ; has been
paid off.
d Any two sensible variables such as height /
mass / weight / fitness / age / sex of the
person, same environmental conditions. ;
[Max. 2]
Breathing rate is ‘normal’ before running [1]. ;
Breathing rate increases gradually as she runs
[1]. ; Breathing rate reaches a maximum level
[1]. ; Breathing rate increases to take in more
oxygen for respiration [1]. ; Allow student
credit if their answer includes reference to
breathing deeper as part of the increase in
oxygen uptake.
C6H12O6 + 6O2 ➞ 6CO2 + 6H2O
correct reactants [1] ; correct products [1] ;
a balanced equation [1] ;
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 12
Practical investigation 12.1
Practical investigation 12.3
1
1
2
2
3
4
5
6
7
Student’s table includes readings from each
attempt and a column to calculate the mean.
Student’s answer matches the corresponding
value in Table 12.1.
Yes, a combination of anticipation, and the
body reacting faster to the stimulus.
Student’s prediction should be that the
reaction time was faster as they can feel the
ruler moving.
Outline of method similar to original method
but with the ruler touching the hand before
release
Accept suggestions such as use of data loggers
to remove human error or the use of video
footage to capture and check exact distances.
Suggestion of method involving blindfold and
reaction to a sound stimulus, such as a bell
attached to the ruler.
5
Student’s table completed with answers.
Student’s answer matches that in the table.
Student’s answer matches that in the table.
More receptors in those parts of the body so
the two pins could be detected separately.
Each person is different and might have
different numbers of receptors in one area
than other people might have.
Reflection
Any sensible ethics concern such as religious
preferences for exposed skin, being respectful of
each other and being aware that testing on ‘live’
subjects requires sensitivity.
17
Reflection
Student’s own reflections.
Exam-style questions
1
Practical investigation 12.2
1
2
3
4
3
Completed table.
The pupil becomes smaller to prevent
excessive light damaging the eyes; the reaction
of the heel and the knee are involuntary
actions useful for walking; and the eyelids
close and open quickly to prevent foreign
objects from entering the eye. The double
vision occurs because the pressure on the
eyelid distorts the signal sent to the brain.
Each person is different and reacts in different
ways; some students might not have the
stimuli carried out in the same way. For
example, some students might have tapped the
heel or the knee in the wrong place.
a
b
c
Axes labelled with units [1] ; even scale
and graph occupying half the grid [1] ; all
four bars plotted correctly [1] ; with gaps
between bars [1]. ;
does not allow for any anomalies [1] ; as
each student might have different results
with more attempts [1] ;
Drawing should include: sensory neurone
connected to some sort of stimulus
[1] ; relay neurone and CNS connecting
sensory neurone [1] ; to motor neurone
[1] ; motor neurone connected to effector
[1] ; response shown, such as muscle
contraction [1]. ;
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 13
Practical investigation 13.1
1
2
3
4
Student records correct data with units for
mass and length. Student’s diagram includes
all labelled parts, such as the medulla and the
cortex areas; with clear lines drawn in pencil,
drawing larger than the original, correct shape
and proportion, main features observable.
Correct formula shown (magnification =
image size/actual size), student’s answer
greater than 1 and given to three significant
figures.
Student correctly identifies one of the internal
structures and links this to the appropriate
function. These may include: medulla is where
filtration takes place, or the cortex where
water levels are regulated.
Any sensible suggestion such as using a
microscope or magnification instrument.
6
7
8
Reflection
Student refers to possible heat loss before taking
the starting temperature and suggests ways to
minimise this effect. Examples include practising
the technique to minimise the time, or having the
materials partly placed and using a funnel to add
the water through a small gap.
Practical investigation 13.3
1
2
Reflection
Student’s own reflections.
Practical investigation 13.2
1
2
3
4
5
18
Student’s table includes columns for starting
temperature, end temperature and temperature
change. Table headings include units and
the different materials are named in the first
column.
Student’s calculations match data from
the table.
Student describes, using data from the table,
how the temperature decreases for all of the
tests and identifies which materials caused the
most/least change.
The material prevents the heat energy from
escaping and keeps it trapped inside the
beaker or cup.
The hairs on the outside of the skin become
erect, causing an insulating layer of air to be
trapped. This, along with a layer of fat and
any clothes that the person may be wearing
minimises the heat energy escaping from
the body.
To make the investigation (more) valid.
The same volume of water at the same starting
temperature could be used.
This is a control to see that the materials did
have an effect on the rate of cooling of the
beakers/cups.
3
4
5
6
Student’s table includes suitable headings and
units.
Student’s answer describes the different
changes, using data from the table to support
that the cotton wool ball soaked in acetone
showed the greatest drop in temperature,
followed by the cotton wool ball soaked in
water. The dry cotton wool ball showed no (or
negligible) change in temperature.
The alcohol in the aftershave evaporates
quickly, having a pronounced cooling effect on
the skin.
As the water evaporates, the heat energy
leaves the skin and lowers the internal body
temperature. This results in feeling cooler.
Student’s table is similar to the table in the
investigation but shows an extra column for
repeat readings and the calculation of the
mean change in temperature. All headings and
units are included.
To compare what happens when no solution is
added to the cotton wool.
Reflection
The data logger will record the temperature change
more accurately and eliminate human error.
The data logger will also record the temperature
change at more regular intervals.
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 13 continued
Exam-style questions
1
a
b
c
d
19
Line graph [1] ; with sensible scale
covering at least half of the paper [1] ;
correctly plotted [1] ; axes labelled with
units [1] ; points joined together by a line
going through each of the points [1]. ;
As time passes [1] ; body temperature
decreases [1]. ;
Shivering (rapid contraction and
relaxation of the muscles) [1] ; hairs at
the skin become erect [1] ; and trap an
insulating layer of air [1] ; description of
vasoconstriction [1] ; to reduce blood flow
and heat loss from the blood [1]. ;
The maintenance of a constant internal
environment. ;
[1]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 14
Practical investigation 14.1
Practical investigation 14.3
1
1
2
3
Student’s drawings of flower, with clear lines
drawn in pencil, drawing larger than the
original, correct shape and proportion, main
features observable.
Student correctly identifies the main features
and functions of the flower: stigma (collects
pollen), anther (produces pollen), sepal
(protects flower), stamen (male part and
includes anther), petals (attract insects), ovary
(produces female sex cells).
Student shows formula (magnification =
image size/actual size), working and correct
answer with units. The answer should be
greater than 1.0 as the drawing should be
larger than the petal.
2
3
4
5
Reflection
Student’s own reflections.
Practical investigation 14.2
1
2
3
4
5
6
a–d Student’s predictions and observations.
Student describes the difference in growth –
boiling tube A shows normal growth, boiling
tube B shows little or no growth at all.
The removal of oxygen from the surroundings
prevents germination as oxygen is required to
do so.
As a control, to show that the removal of
oxygen was a factor in the different results.
Caustic substances are extremely harmful
to the body and must be handled by a fully
trained professional.
The seeds would begin to grow as the removal
of oxygen would not have killed the seeds
while in boiling tube B.
Reflection
Any valid comparison between student methods
(such as range of temperatures, or attempts to
control variables).
Exam-style questions
1
a
b
c
d
e
Reflection
Student’s own reflections.
Student’s method includes three different
temperatures and a way of measuring the
growth of the seeds. Method should also
include an attempt to control any variables
such as humidity, same species, etc.
Student’s table includes headings and units.
Student’s calculations match data from the
table.
Student uses data from their table to describe
the differences in growth. Student explains
that the cress seeds will grow best within the
range of room temperature as that is when the
enzymes involved in breaking down molecules
that supply the seeds with the nutrients used
for growth are most active.
Mustard seeds and cress seeds might have
different rates of germination as they are
different species.
2
a
b
c
d
20
Stamen ;
[1]
Contains the filament/anther [1] ; and is the
male reproductive organ of a flower [1]. ;
Petal ;
[1]
Student drawing larger than the carpel
in the practical workbook [1] ; labelled
as the carpel (or stigma, style and ovary)
[1] ; smooth outline drawn in pencil [1] ;
shape and size in proportion [1] ; drawn
with sharp pencil [1]. ;
The carpel stigma/style/ovary [1] ; is the
female reproductive organ of a flower [1]. ;
Any sensible range that includes at least
three different temperatures [1] ; around
the 30 oC mark [1] ; such as 10, 20, 30, 40,
50.
At least three times, accept any answer
between three and five. ;
[1]
wear safety spectacles, wash hands, any
other sensible precaution ;
[1]
% change = (change / original) × 100 [1] ;
= (7 / 4) × 100 [1] ; = 175% [1] ;
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 15
Practical investigation 15.1
1
2
3
4
5
Egg in water: no breakage; egg without water:
egg breaks.
Amniotic fluid
Fetus
The fluid protects against external forces and
knocks that the fetus may experience.
As a control/to compare what would happen
if the water was not there to protect the egg.
Reflection
Improve reliability by repeating more than once,
improve validity by making sure that the eggs
come from the same chicken and are the same age,
improve engagement by trying with different eggs
from different species or birds.
Exam-style questions
1
a
b
c
d
e
2
a
b
c
d
21
Pituitary gland. ;
[1]
The egg is released / Ovulation. ;
[1]
Oestrogen [1] ; and progesterone [1]. ;
The egg has not been fertilised and
progesterone ceases being secreted [1] ;
so the uterus wall breaks down [1] ; and
menstruation begins [1]. ;
The concentration of progesterone would
not decrease [1] ; as progesterone will
continue to be secreted until the fertilised
egg [1] ; is fully sunken into the wall of
the uterus [1]. ;
Amniotic fluid. ;
[1]
To support the embryo/fetus [1] ; and to
protect it from external forces [1]. ;
The fetus has developed limbs [1] ; and the
placenta is joined to the umbilical cord [1]. ;
Any three from:
• named nutrients/food materials ;
• oxygen ;
• carbon dioxide ;
• waste materials ;
[Max. 3]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 16
Practical investigation 16.1
1
2
3
2
Observations of cloned cauliflower:
a After one week: a few mm of growth.
b After two weeks: a full floret should be
visible.
a DNA would be identical.
b The cauliflower asexually reproduced
by mitosis to produce new cells that are
genetic copies of the original sample.
Contamination will lead to growth of bacteria
and fungi, link to potential safety and health
hazards if this happens. More importantly, the
experiment will fail due to death of the plant
if this was allowed to occur.
a
b
i
[1] ;
ii
[1] ;
iii
[1] ;
iv
[1] ;
i
Description
Number of
people
Male
9
Female
6
Student’s own reflections.
Male with Marfan
syndrome
2
Exam-style questions
Female with Marfan
syndrome
2
Homozygous dominant
0
Homozygous recessive
11
Reflection
1
a
b
c
d
e
22
(One mark for each correct answer.) ;
Observable feature [1] ; of an organism.
Has two identical alleles [1] ; of a
particular gene [1]. ;
i
A version of a gene. ;
[1]
ii An allele that is always expressed if
present in the genotype. ;
[1]
iii An allele that is present in the
genotype but is not expressed in the
presence of a dominant allele. ;
[1]
Genotypes stated as BB and bb
[1] ; genetic cross drawn [1] ; possible
genotypes shown [1] ; correct answer
stated as 0% [1]. ;
B
B
b
Bb
Bb
b
Bb
Bb
100% ;
Heterozygous
4
[6]
ii
If individual B was homozygous
dominant [1] ; then all of her
offspring would be sufferers of
Marfan syndrome [1]. ;
[1]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 17
Practical investigation 17.1
Practical investigation 17.2
1
1
2
3
4
5
6
7
8
Student’s table matches the data collected with
correct headings and units.
a Students correctly tally the number of
students in each category. Categories
should be evenly split across the range of
data for that characteristic. Tally should
use the correct tally method and have the
final number in bracket next to the tallies.
b Histogram drawn to show data from tally
chart (hand size and units on the x-axis,
number of students on the y-axis), bars
drawn touching each other in order of
increasing or decreasing magnitude.
Bar chart drawn to show the number of
students with each eye colour (eye colour on
the x-axis, number of students on the y-axis),
blocks should not be touching.
Student describes the pattern for the data of
their data/chart/histogram.
Continuous
Height, hand size, eye colour, hair colour, arm
span.
Increase the sample size and survey more
students, i.e. the idea that the more students
that are surveyed, the more reliable the data
will be.
No, because the sample size is very small and
does not account for older / younger people,
different race and origins, etc.
2
3
4
5
Student’s diagrams showing that the leaf in
sunlight will have more stomata open than the
leaf in darkness but this will vary on leaf type,
environmental conditions and magnification
used.
Student accurately counts the number of
stomata shown for each leaf – student should
have more open stomata on the leaf in
sunlight.
Student describes the difference in open
stomata and links this to the need for the
plant to prevent water loss and/or to take in
more carbon dioxide.
More reliable test, to compare the effect of the
amount of sunlight.
Use the same leaf, place in sunlight and take a
varnish sample. Then, place the same leaf into
darkness and repeat the observation. The leaf
must not be removed from the plant and it
must be fed and watered as normal.
Exam-style questions
1
a
b
c
Reflection
If no, it is because of human error. Students often
miscount, or miss people out.
23
d
Continuous ;
[1]
Histogram drawn [1] ; blocks touching
[1] ; blocks drawn in increasing or
decreasing magnitude [1] ; suitable axis
labels [1] ;
Similar pattern described for boys, girls or
both, of few students at the extreme [1] ;
and most students gathered around the
mean [1]. ;
Large sample of the population gathered. ;
[1]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 18
Practical investigation 18.1
Practical investigation 18.2
1
1
• Four-week date and observation: soil
drying out, food breaking down, some
evidence of mould, any growth of
bacteria or life noted.
• Eight-week date and observation: food
broken down, biodegradable waste
starting to break down, any growth of
bacteria or life noted.
• Twelve-week date and observation: all/
most of food/kitchen waste decomposed
completely and most biodegradable waste
broken down. Non-biodegradable waste
still evident.
2 Organic waste decomposes quickly; other
waste will not decompose in the time allowed.
3 The layer that contains the organic kitchen
waste as nitrates from the food would be
released back into the soil.
4 Decomposition.
5 The rate would increase as the worms help to
decompose some types of waste.
2
3
4
5
6
7
8
Student’s table should include ‘organism type’
and ‘number of organisms counted’ for each
sample of the quadrat.
Student’s bar chart, axes correctly labelled,
bars not touching, key to label bars if
necessary.
Student describes the pattern of data
gathered.
Student makes comparison between two
different areas that have different population
sizes for the same species.
Student refers to factors such as light, water
or available food. Student may also refer to
factors such as human footfall or the presence
of predators.
To improve the reliability of the data taken.
To reduce bias and improve validity of the
method.
This would take too long and there may be
change over the time taken anyway.
Reflection
Student’s own reflections but will likely involve
carrying out more repeats to increase reliability.
Exam-style questions
1
a
b
c
d
e
f
2
a
b
c
24
Lag phase ;
[1]
Log or exponential phase ;
[1]
Stationary phase ;
[1]
Death phase ;
[1]
The conditions for growth are ideal [1] ;
large number of cells reproducing quickly
at the same time [1]. ;
Lack of food or reduction in the ideal
conditions [1] ; so some cells begin to die
[1] ; the death rate exceeds the birth rate [1]. ;
total number of caterpillars added
together / number of gardens [1] ; 28 / 7
[1] ; answer = 4 caterpillars [1]. ;
average number of caterpillars (4) ×
total number of gardens (32) [1] ; = 128
caterpillars [1]. ;
Any sensible answer from:
• natural variation in populations of
different gardens ;
• some gardens have more / fewer
predators or prey ;
• some gardens have greater resources
and food available ;
• some caterpillars might not have been
counted / human error ;
[1]
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CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 19
Practical investigation 19.1
Reflection
1
Student’s answer should qualify that humans
might make errors / have subjective views of
colour changes / methods carried out differently /
any other sensible named example. Scientists can
remove the subjective views by measuring known
quantities.
2
3
4
5
6
Completed student table with accurate
observations for each Petri dish.
Student describes the pattern of data from
their investigation/table.
The pH will affect the activity of enzymes,
thus affecting growth. The pH may also affect
the availability of nutrients.
Student explains the effect of acid rain on soil
pH and that the optimum pH for most plant/
crop growth is around pH 7. The acid used
represents acid rain and the growth of the
cress seeds shows what might happen to crops/
plant life if acid rain falls and reduces the pH
of the soil. Acid rain has a significant impact
on the growth of crops if the rain becomes
too acidic.
The height/mass of the cress could be
measured to compare the growth under
different acidic conditions.
By taking more readings / repeats.
Practical investigation 19.2
1
2
3
4
5
25
Student’s diagram should show the cotton
wool turning brown / black and the universal
indicator turning orange / pink / red.
a Cotton wool turned brown/black.
b Universal indicator turned orange/
pink/red.
Shows that the gases produced are acidic.
These gases dissolve in water vapour and
condense in the air as clouds before falling as
acidic rain.
Limewater turns cloudy as the burning of coal
produces carbon dioxide. Limewater turning
cloudy is a positive test for carbon dioxide.
Student outlines an investigation that burns
different quantities of coal. The coal is heated
until completion and the pH of the gases
produced are measured using a pH probe or a
pH scale.
Exam-style questions
1
2
B ;
[1]
a garden area A ;
[1]
b soil closer to neutral pH (7) would be best
for growing most plants ;
[1]
c pH probe would have greater accuracy
[1] ; and removes the subjective nature of
judging a colour change [1] ;
d Different areas of the garden will have
different conditions [1] ; such as garden
area C might receive more rainwater [1] ;
than the other areas. Accept any other
valid point to explain why the soil might
be more acidic [1]. ;
e Any two from:
• same type of plant ;
• same species of plants ;
• same temperature ;
• humidity ;
• other named conditions ;
• same amount of water ;
[Max. 2]
Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021
CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 20
Practical investigation 20.1
1
2
3
4
5
6
Student’s results in table with correct headings
and units.
Student’s graph includes correct axis drawn,
units added to labelled axis, appropriate size
and scale of graph (at least half of the graph
paper), plotted correctly, both lines joined
together and labelled accordingly.
The pectinase caused more juice to be released
from the apple than from the apple that was in
water only.
Pectinase broke down the pectin in the cell
walls, releasing the juice more easily and
faster. This allows a greater yield to be
produced for commercial gain.
As a control, to compare the effect of
pectinase, to confirm that it was pectinase that
caused the release of the juice from the pulp.
Results might be different due to differences in
the type of apple. One apple is different from
another, certainly if from different species or
types of apple.
Reflection
5
6
7
8
Practical investigation 20.3
1
2
3
4
5
Student’s own reflections.
Practical investigation 20.2
1
2
3
4
26
Two safety precautions, such as wash hands
after touching the apple, consult safety
information, clean surfaces.
Student’s method – should contain the range
of variables used (at least three temperatures
around 45 oC, i.e. 30 oC, 40 oC, 50 oC), as well as
how to measure the dependent variable (how
to measure the volume of juice produced, i.e.
by mass, or with a measuring cylinder). Credit
should be given for any attempt to control the
variables and for a safety point.
Student’s temperatures should be sensible
and safe, such as any three between 10 oC and
60 oC.
Student’s table should include at least three
different temperatures and units, with correct
headings.
Student’s answer of the best temperature.
Produced the most juice.
This is close to the optimum temperature for
most enzymes. The enzyme will carry out
more reactions at this temperature and in the
case of pectinase; will break down more pectin
and release more juice from the fruit.
Repeat the investigation and take a mean for
the volume of juice produced; ensure that all
variables are constant.
Student’s drawings should be drawn in pencil
and include a label to show where the stains
had / had not been removed.
Student describes the difference between the
stains drawn in their notes.
The biological washing powder contains
enzymes that break down the stains faster so
that more stain was removed compared to the
non-biological washing powder.
Protease; accept other option used in washing
powders, such as lipase.
Student’s method suggests washing materials
with similar stains at different temperatures
for comparison. Some effort made to identify
and control the variables, safety points should
be noted.
Exam-style questions
1
a
b
C ;
[1]
Any six from:
• named use of pectinase, such as
commercial fruit juice, skin peeling ;
• protease, lipase used in washing
powders, detergents, baby food ;
• enzymes used to catalyse reactions
involved ;
• faster reactions ;
• lower temperatures required ;
• higher yield ;
• any other sensible point related to
common use of the enzymes ; [Max. 6]
Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021
CAMBRIDGE IGCSE™ BIOLOGY: PRACTICAL WORKBOOK
Chapter 20 continued
c
d
27
Any five from:
• suitable equipment identified ;
• fruit named ;
• fruit chopped into small pieces and
pectinase added ;
• repeated at different pH levels for the
enzyme ;
• enzyme and fruit pulp incubated at
optimum temperature ;
• fruit pulp filtered into measuring
cylinder ;
• comparison of volume of fruit juice
collected ;
• safety points mentioned ;
• repeat testing for reliability ; [Max. 5]
Any two from:
• same temperature ;
• same quantity of pectinase ;
• same equipment ;
• same source of pectinase ;
• same apples / species ;
• any other valid point ;
[Max. 2]
Cambridge IGCSE™ Biology – Broderick © Cambridge University Press 2021