Cambridge International General Certificate of Secondary Education

0653 Combined Science March 2024

Principal Examiner Report for Teachers

COMBINED SCIENCE

Paper 0653/12
Multiple Choice (Core)

Question Question Question Question

Key Key Key Key
Number Number Number Number

1 B 11 C 21 A 31 D

2 D 12 A 22 B 32 B

3 C 13 B 23 C 33 D

4 D 14 C 24 A 34 D

5 A 15 B 25 D 35 A

6 B 16 C 26 D 36 C

7 C 17 D 27 C 37 D

8 B 18 A 28 C 38 B

9 A 19 B 29 B 39 D

10 D 20 A 30 C 40 C

General comments

Candidates performed very well on Question 7 and Question 12 in the biology section, Question 16 and
Question 24 in the chemistry section, and Question 32 and Question 39 in the physics section.
Question 5, Question 14, and Question 31 proved most difficult for candidates.

Comments on specific questions

Question 1

Most candidates chose the correct option, however, some opted for option A or C. Option D was dismissed
by almost all candidates.

Question 2

Most candidates chose the correct option. Some candidates chose the incorrect option B (cytoplasm), with a
few incorrectly opting for the nucleus (option C).

Question 5

Some candidates found this question challenging. The most common incorrect option selected was option B,
indicating that candidates knew that magnesium deficiency led to a decrease in chlorophyll, but did not make
the link from a decrease in chlorophyll to the effect that this would have on growth rate.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

Question 6

Most candidates chose the correct option. All candidates dismissed a fat deficiency link to a lack of red blood
cells. Some candidates incorrectly chose either calcium or glucose.

Question 9

Most candidates chose the correct option. Some candidates chose the incorrect option B (bronchus).

Question 11

Most candidates chose the correct option. The most common incorrect option selected was Option B (fusion
of a female zygote and a male gamete).

Question 13

Most candidates chose the correct option. Several candidates incorrectly opted for A (combustion and
fossilisation).

Question 14

Candidates chose the incorrect option B more often than the correct option C. They were expected to
understand that as the pressure of a gas increases, the particles move closer together without any change in
the speed of movement of the particles.

Question 15

Many candidates chose the correct option. The most common incorrect option selected was Option D.

Question 19

Most candidates understood that the addition of oxygen to a substance is an oxidation process (Option B).
Some candidates chose the incorrect option C (neutralisation).

Question 20

Some candidates chose the incorrect option D rather than the correct answer, A. Option B and C were also
selected by some candidates. They were expected to know that acids react with metals to produce hydrogen
gas, as well as the positive test for this gas.

Question 23

Some candidates chose the incorrect option B rather than the correct option C. They were expected to know
that molten ionic substances, such as sodium chloride, and metals or mixtures of metals, such as brass, are
electrical conductors. They should also know that naphtha is a hydrocarbon, and that as hydrocarbons
contain only covalent bonds, they are not electrical conductors.

Question 30

A few candidates chose either option A or B, both of which suggested that rotating the block changes the
force it exerts on the table. The force, of course, does not change and most candidates gave an answer
consistent with this understanding. The most frequently chosen answer was the correct option C, which
stated that the pressure decreases. However, there were candidates who gave option D. It is possible that
there was some confusion caused because the area of contact increases or perhaps the diagram was
misinterpreted.

Question 31

This question asked about the work done W and this depends only on the force exerted and the distance
moved. The time taken does not affect the work done. The correct answer D was the most commonly
chosen, but option C was selected almost as frequently. Some candidates chose A or B, but these were less
popular.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

Question 34

The most straightforward approach to this question was to deduce from the graph the fact that water at the
point indicated passes through a complete cycle in 0.20 s. It then follows that in 1.0 s, the water oscillates up
and down through five complete cycles and that this corresponds to five wavelengths passing through the
point. The correct answer was the most popular option selected. The other options were selected by a similar
number of candidates as each other, with A just slightly more commonly selected than B or C.

Question 38

The correct answer, option B, was the most commonly chosen and the other option that suggested a
decrease in the current (option A) was also selected by several candidates. Only a small number of
candidates gave an answer that suggested that an increase in the resistance would produce an increase in
the current. Those candidates who realised that the ammeter reading would decrease but thought the
voltmeter reading would increase may have not fully understood which voltage was being read by the
voltmeter or may have been attracted by the pattern of a decrease paired with an increase.

Question 40

Most candidates selected the correct option C. A small number of candidates selected either A or B. Some
candidates chose option D, which suggested that the fuse supplies a current in the circuit.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

COMBINED SCIENCE

Paper 0653/22
Multiple Choice (Extended)

Question Question Question Question

Key Key Key Key
Number Number Number Number

1 D 11 A 21 C 31 D

2 D 12 B 22 A 32 C

3 A 13 C 23 B 33 C

4 B 14 C 24 B 34 C

5 C 15 B 25 A 35 A

6 C 16 C 26 D 36 A

7 A 17 C 27 D 37 C

8 D 18 D 28 D 38 B

9 C 19 A 29 B 39 B

10 B 20 D 30 C 40 A

General comments

This paper is designed to test the entire subject content of the syllabus and not just the extension material.

Candidates performed very well on Question 1, Question 3 and Question 9 in the biology section,
Question 14, Question 25 and Question 26 in the chemistry section, and Question 28 and Question 30 in
the physics section.
Question 7, Question 16, and Question 34 proved most difficult for candidates.

Comments on specific questions

Question 4

Candidates usually picked the correct option B. However, some candidates incorrectly thought that A was
the temperature at which the enzyme worked best. A very small number of candidates chose C, and D was
the least selected.

Question 6

Most candidates chose the correct option C (pancreas). Some candidates incorrectly chose option B or
option D. Very few candidates selected option A.

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0653 Combined Science March 2024
Principal Examiner Report for Teachers

Question 7

Most candidates chose the correct option A. Option C was chosen by some candidates. Candidates should
be reminded that the pulmonary artery takes deoxygenated blood from the heart to the lungs.

Question 10

Most candidates chose the correct option B. Some candidates incorrectly opted for C, thinking that male
flowers lacked petals.

Question 11

Most candidates chose the correct option A. Some candidates incorrectly thought that an egg cell has a
flagellum.

Question 13

Most candidates chose the correct option C. Some candidates incorrectly thought that combustion removes
carbon dioxide from the atmosphere.

Question 21

Candidates were able to use a reaction equation to determine which substance is reduced during the
reaction. They also understood the meaning of oxidising agent and reducing agent.

Question 22

Candidates knew very well where metals and non-metals are positioned within a period of the Periodic
Table.

Question 23

Candidates were expected to know that alloys are mixtures of a metal with another element, and that the
presence of the metal makes alloys electrical conductors. They are also expected to know that solid salts
contain ions that are not free to move, and that these salts only conduct electricity in the molten or the
aqueous state.

Question 27

Many candidates were able to complete the equation for the cracking of octacosane, C28H58, by choosing
from the list of suggested other products.

Question 31

More candidates selected the incorrect option B than selected the correct option D. The two options were the
two energy stores that relate to the situation, namely the gravitational potential energy store and the thermal
energy store. The parachutist is falling and so the energy in the gravitational potential energy store is
decreasing rather than increasing. It is probable that candidates who selected the gravitational potential
energy store realised that it is involved in some way but did not relate the constant speed of the parachutist
to the presence of air resistance. The work done against air resistance is the mechanism that transfers
energy from the gravitational potential energy store to the thermal energy store.

Question 32
1
This question required knowledge of and the application of the equation KE = mv 2. Many candidates were
2
able to do this and then to select the correct option. The only incorrect option chosen by a significant number
of candidates was option A. To obtain this answer, it was necessary to subtract the initial speed from the
final speed and then to square the answer. This is not mathematically identical to squaring the speeds before
performing the subtraction and so it generated an incorrect answer.

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0653 Combined Science March 2024
Principal Examiner Report for Teachers

Question 34

The way in which this question was answered illustrated a common and widespread misunderstanding of the
role of electrons in thermal conduction in metals. Most candidates realised that options A and B both
suggested the translation of atoms within the structure in some way and were incorrect. Of the two options
that involved electrons in the conduction process, a majority opted for the incorrect option D. This option
suggested that thermal energy is conducted in a metal by vibrating electrons transferring energy to their
neighbours. This is essentially a description of a mechanism similar to that of the mechanism by which atoms
transfer energy in both metals and non-metals but with electrons substituted for atoms. The transfer of
thermal energy by electrons is more accurately described by the correct option C.

Question 35

The most commonly selected option was the correct option A. A noticeable number of candidates choose
option D which, in terms of the arrangement of options, is the exact opposite answer. These candidates
probably knew that black and dull surfaces are good absorbers of thermal radiation and then incorrectly
suspected that good emitters of thermal radiation will have the opposite properties since emission is the
opposite of absorption. Good emitters of thermal radiation are also, of course, good absorbers. Few
candidates chose either of the other two options.

Question 36

When light passes through a thin converging lens, it is possible to draw a diagram with three rays that can be
drawn exactly without any other rays being drawn first. Of these, the ray that first passes through the nearer
focal point, then changes direction as it passes through the lens and which then emerges parallel to the
principal axis, is the one needed to answer this question. This was the lower of the two rays shown and it
passes through the principal axis at the focal point. Hence option A was correct. This was the most popularly
selected answer, although some candidates choose either option B or option C. Option D was only very
rarely selected.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

COMBINED SCIENCE

Paper 0653/32
Theory (Core)

Key messages

Candidates who did well on this paper:

 read the questions carefully
 were familiar with the contents of the syllabus
 were able to express their responses in a clear way
 showed their working in numerical answers
 were able to apply their knowledge to unfamiliar situations.

General comments

Many candidates had prepared well for the examination and produced very good answers. There was
evidence that other candidates were not fully familiar with the contents of the syllabus.

The use of space on the paper was good. Very few candidates repeated the question, and most responses
were written within the allocated answer lines in the paper.

Comments on specific questions

Question 1

(a) This question was generally well answered. The most common error seen was vacuole matched
with site of photosynthesis. Candidates should be reminded that photosynthesis occurs in the
chloroplasts which are in the cytoplasm. The large vacuole in plant cells pushes the cytoplasm
outwards so that it forms a thin lining inside the cell wall. This pressure of the vacuole against the
cytoplasm and the cell wall keeps plant cells firm and provides them with support.

(b) (i) Most candidates stated testes, the correct response. There was no pattern to the incorrect
answers. Most incorrect responses referred to other parts of the male reproductive system, for
example sperm duct and prostate gland.

(ii) Many candidates were familiar with this type of calculation and scored full credit. Others multiplied
the magnification by the length to give the answer 18 000 mm.

(c) (i) Most candidates stated oviduct to gain credit. Ovary was the most common wrong answer.

(ii) Most candidates completed the sentences correctly. Errors included stating gamete for the first
response and zygote for the second response. Candidates should be aware that the fertilised ovum
is called the zygote which then divides into the ball of cells called the embryo.

Question 2

(a) This question was generally answered well.

(b) Most candidates found this question challenging. The answer required a description of the loss of
an electron by a lithium atom. There were many incorrect answers, including changes in electrons,
the gain of an electron, both loss and gain of electrons, ionic bonding and that it shares electrons.

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(c) (i) Many candidates completed the equation correctly. The most common error in balancing was
stating 2Li instead of 4Li on the left-hand side of the equation. Candidates are reminded that there
are two atoms of lithium in Li2O, and to balance the oxygen atoms in the equation, 2Li2O must be
formed, therefore needing 4 atoms of lithium to react.

(ii) This question was generally answered well.

(iii) Most candidates answered this question correctly. Some candidates were not familiar with the term
exothermic, and many of their responses were descriptions of the chemical reaction described in
the stem of the question.

(d) Most candidates answered this correctly.

(e) Most candidates gained credit by using their knowledge of Group l metals and information given in
the question. Uncreditworthy answers included references to the lithium exploding, and that lithium
is a poor conductor of heat.

(f) Generally, candidates found this question challenging. A few responses referred to the finite supply
of metals and gained credit. Responses that were not awarded credit included vague references to
recycling being better for the environment, descriptions of the practical advantages of recycling and
the fact that it is cheaper. The question indicated that cost should be excluded from the answer, so
careful reading of the question would have avoided these incorrect answers.

Question 3

(a) Some candidates stated nuclear fission correctly. Others stated nuclear fusion, nuclear power,
combustion, thermal energy, or exothermic reaction. It was important for candidates to have the
correct spelling and clear handwriting in this response. A response such as nuclear fuission did not
gain credit as it was not clear whether (nuclear) fusion or fission was intended.

(b) (i) Most candidates drew the correct symbol for a fuse. Incorrect responses included symbols for
switches, heaters and variable resistors. Candidates should be aware that the syllabus contains a
list of electrical symbols required for the examination.

(ii) Some candidates found this question challenging. The main misconception was stating that the
role of a fuse was to control the current instead of preventing the current from getting too high,
therefore protecting the circuit.

(iii) The main point here was for candidates to state that the insulation was damaged, leaving the bare
wire exposed. Many candidates stated short circuit but there was not sufficient evidence to show
how that could arise.

(c) (i) Most candidates did the calculation correctly. Some candidates did not state the correct unit, Ω,
instead writing R or W.

(ii) Candidates found this question challenging. Many responses stated that a parallel circuit allows
one branch to continue operating if the other branch fails. This information was provided in the
introduction to the question, so was discounted from responses. Candidates are reminded that the
current in a series circuit is the same throughout the circuit. A series connection would not allow the
currents to be different.

Question 4

(a) (i) Many candidates stated white blood cells and gained credit. Others stated red blood cells and
haemoglobin.

(ii) Many candidates gained credit for this question. Incorrect responses included pulmonary vein,
vena cava, and just artery and vein. The blood vessel that transports blood from the heart must be
an artery, since the blood vessels leaving the heart must be arteries, and since the artery is going
towards the lungs, it is the pulmonary artery.

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0653 Combined Science March 2024
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(iii) Candidates who were familiar with the syllabus completed this question well. Others responded
with a range of answers. Examples for the first response included (A hormone is a chemical
substance produced by a …): heart, brain, DNA, organ. For the second response (Hormones alter
the activity of a specific …….. organ) the range of incorrect answers included: body, reproduction,
human and tissue.

(b) (i) Most candidates answered this correctly.

(ii) Most candidates labelled the diaphragm correctly. There was no consistent pattern to the incorrect
responses. Some candidates mislabelled other parts of the respiratory system. Others did not
attempt this question.

(c) (i) Candidates found this question challenging. Many candidates stated that the water vapour is lost
from the leaves by transpiration without demonstrating any knowledge of the process of
transpiration, the diffusion of water vapour through stomata in the leaf. A common error was stating
osmosis instead of diffusion. Osmosis occurs in a liquid medium and during transpiration the
diffusion of water vapour is a gas.

(ii) The inverse relationship between transpiration rate and humidity was stated correctly by most
candidates.

Question 5

(a) Most candidates identified nitrogen and oxygen correctly. Fewer candidates gained credit for the
white area in the pie chart, with carbon dioxide and water vapour being the least chosen
responses.

(b) Many candidates gained credit for stating an adverse effect of carbon monoxide. Fewer knew an
adverse effect of oxides of nitrogen. There were many vague responses that did not gain credit, for
example, affects plants, breathing problems, bad for health, or dangerous to humans.

(c) (i) Most candidates could interpret the information in the question to complete the word equation with
the correct reactant and products. Some candidates tried to write the equation using symbols.
Candidates are reminded to read the question carefully before answering.

(ii) Most candidates chose a pH value in the acceptable range. Incorrect responses included pH
values of 7 or above.

(d) Many candidates gained full credit for this question. Partial credit was awarded to those candidates
who showed one pair of electrons being shared. Incorrect responses included two pairs of
electrons in the bond and incorrect or missing electrons in the rest of the molecule.

Question 6

(a) (i) Many candidates stated Q to gain credit for this question. The most common error was S. Force S
represents the frictional forces that oppose the movement, whereas force Q is the driving force
which makes the boat move to the right.

(ii) Many candidates successfully stated weight to gain credit. Gravity, stated by some candidates, was
not accepted. Candidates are reminded that the force labelled R is the weight, which is the product
of the mass and the gravitational field strength.

(iii) This question was challenging for most candidates. Forces S and Q must be equal and opposite so
that the boat will not accelerate or decelerate. If there was a difference between the value of the
forces the speed would change. Incorrect responses included that the boat won’t move if the forces
are the same, and that the boat might overturn if the forces aren’t balanced.

(b) Many candidates calculated the resultant force correctly, but they did not describe the direction of
the force accurately. The direction of movement of the force was towards the boat so that the fish
can be retrieved when caught.

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Principal Examiner Report for Teachers

(c) (i) Most candidates correctly interpreted the positive gradient of the graph as increasing speed.

(ii) Candidates found this question more challenging. Many stated that the speed of the fish was
decreasing. These responses did not gain credit. A decreasing speed would produce a line on the
graph with a negative slope. The graph shows that at 2 sec the speed goes directly to zero.
Therefore, the fish must have stopped.

(d) (i) Most candidates knew that there would be a decrease in temperature of the fish as thermal energy
is transferred from the fish to the ice. The ice, in turn, will gain thermal energy and start to melt.
Some candidates stated that the temperature of the ice increases. This response did not gain credit
because thermal energy from the fish would be used to change the state of the ice before raising
the temperature. There would not be enough thermal energy given out by the fish to melt the ice in
the bucket and then raise the temperature.

(ii) Many candidates did well in this question. The equation  = m/V was known by most candidates
and credit was awarded for this. Before the equation could be applied to the data, the mass of the
bucket had to be subtracted from the total mass of the bucket and ice. Some candidates did not do
this.

Question 7

(a) (i) Many candidates found this question challenging. The key to obtaining a correct answer involved
interpreting the diagram. Incorrect responses included respiration, decomposition and fossilisation.
Some of these terms are often found at the bottom of other diagrams of the carbon cycle, but they
do not represent process B.

(ii) The equation for photosynthesis was well known by many candidates. A common error was
sunlight as the second reactant, rather than water. Candidates are reminded that sunlight is a
necessary condition for photosynthesis to take place, not a reactant.

(iii) This was generally answered well.

(b) (i) Some candidates found this question challenging, stating food chain instead of food web. A food
chain does not have any branches, but a food web does contain branches, showing that more than
one organism can feed on the same food.

(ii) Most candidates answered this correctly.

(iii) Only a few candidates drew the arrow the wrong way round. Candidates should be aware that the
arrow shows the direction of energy flow, in this case from the gazelle to the lion.

(c) Most candidates stated a suitable environmental condition for germination. A few candidates stated
warmth as a condition. Careful reading of the question excluded this as a response, as it had
already been mentioned.

Question 8

(a) The first part of the question needed an explanation stating that the hydrocarbon contains a double
bond. Common errors included that the hydrocarbon contains only single bonds, or a statement
that the molecules are unreactive. Some candidates described unsaturated in terms of a solution
which can dissolve more solvent. This was the wrong context for the term unsaturated, which in
this case is the topic alkenes. More candidates gave a correct definition of the term hydrocarbon.
Candidates are reminded that the hydrocarbon molecule consists of only hydrogen and carbon
atoms. There are many molecules that contain hydrogen, carbon, and other elements. These are
not hydrocarbons.

(b) Most candidates gained at least partial credit for this question. They expressed their answers in a
variety of ways. The important points to make were the random arrangement of particles in a gas
and that they move quickly. Candidates who referred to the word ‘packed’ were not given credit
because this implies that the particles are close together.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

(c) Candidates found this question challenging. This was because they had to visualise the state of
ethene at a temperature below its melting point. A common error was to say that –190°C was a
higher temperature than –169°C, disregarding the negative sign in front of the numbers.

(d) Many candidates gained credit in this question by stating combustion. Incorrect responses included
reduction, and various attempts to write either word or symbol equations.

(e) Many candidates gained credit for this question. Ethene is an unsaturated hydrocarbon, so addition
polymerisation is possible.

Question 9

(a) (i) The first part of the question was generally well answered. Candidates stated the electromagnetic
spectrum for the regions of visible light and infrared radiation. The second part of the question was
more challenging. Successful candidates recalled that the frequency of visible light is higher than
infrared. Incorrect responses included lower, longer and shorter.

(ii) Many candidates gained credit for this question. Some candidates stated that radiation is the only
way in which energy is transferred through space, without stating why conduction and convection
cannot be transferred through space.

(b) (i) Most candidates used the average speed = total distance/time equation successfully. Some
candidates were not successful in converting the days to hours, so only partial credit could be
awarded in these cases.

(ii) This question was generally answered well.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

COMBINED SCIENCE

Paper 0653/42
Theory (Extended)

Key messages

Candidates who did well on this paper:

 had learned the syllabus material thoroughly, including definitions of important terms
 read the questions carefully and avoided irrelevant material in their answers
 used the allocation of marks for each question to guide the level of detail they should include in their
answers
 in calculations, set out their working clearly and included the symbolic relationship between the relevant
variables.

General comments

Many candidates demonstrated strong knowledge with understanding in each of the science disciplines and
wrote clear, well-organised answers. Candidates usually showed their working in calculations, whether
instructed to do so or not, and this is good practice. Working was often set out very clearly which made it
easier to award partial credit for correct steps even if the final answer was incorrect.

Candidates generally had no difficulty in finishing the paper in the time allowed.

In Biology, candidates showed good knowledge of the human digestive system Question 1, were often able
to interpret data in the biological contexts in Question 4, and were familiar with human reproduction and the
dangers of smoking in Question 7.

In Chemistry, many candidates were able to draw a dot-and-cross covalent bonding diagram in Question 2,
and stronger candidates showed excellent understanding of the reasons for differences in boiling point in
terms of particle interaction. Candidates showed that they understood electrolysis at the particle level in
Question 5, and many were familiar with word and balanced chemical equations. Many candidates showed
good knowledge of organic chemistry in Question 8.

In Physics in Question 3, many candidates were familiar with the use of relationships involving speed,
distance and time and also wave speed, frequency and wavelength. In Question 6, many candidates
completed an electrical power calculation accurately and showed that they had learned that the currents in
the branches of a parallel circuit combine to give the overall current. Stronger candidates were familiar with
the process of nuclear fusion and fission. Most candidates were successful in most parts of Question 9,
which tested understanding of a force diagram, the calculation of the area under a speed/time graph and the
calculation of kinetic energy.

Comments on specific questions

Question 1

(a) (i) Most candidates correctly identified the liver. However, some candidates did not seem to realise
that they had to label the liver on the diagram.

(ii) Most candidates correctly identified the pancreas.

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(b) In answering this question, candidates needed to be careful in their choice of words. Any word
which meant ‘pieces’ was accepted for the first space. ‘Molecules’ was not accepted. There were
no alternatives for ‘molecules’ in the second space. Credit was not awarded for the word ‘particles’.

(c) The function of amylase was familiar to many candidates. Credit was not awarded for stating that
‘carbohydrates’ rather than ‘starch’ were broken down. Credit was awarded for the digestion
products glucose and maltose. Some candidates suggested sucrose or maltase.

(d) Stronger responses made the two key points that the environment in the stomach is acidic, and
that enzyme A works best in acidic conditions. Many candidates were awarded partial credit
because they stated only one of the key points, possibly because they thought that they had given
enough information to gain full credit. Stronger responses avoided vague answers such as “the
enzymes in the stomach are acidic” or “enzyme A has a low pH”.

Question 2

(a)(i)-(iv) Candidates generally had few difficulties gaining credit. Candidates knew (i) and (ii) very well with
(iii) and (iv) proving to be equally familiar for some candidates.

(b) Many candidates were familiar with the bonding diagram of a nitrogen molecule.

(c) This was a challenging question for many candidates. The best answers referred to the structural
differences between potassium nitrate and nitrogen, the difference in the attractive forces in these
substances and the difference in the energy required to separate particles. Candidates needed to
refer to both substances when making these comparisons and so full credit could not be awarded
for a description of only one of them even if the description included correct information. Common
misconceptions included the ideas that potassium nitrate must have a higher boiling point because
it contains a metal or that it was a compound, whereas nitrogen is only an element. Some
candidates did not appear to realise that their answers needed to explain the reasons for the
difference in boiling point. This was revealed in answers such as “potassium nitrate is a crystalline
solid but nitrogen is a gas and so they must have different boiling points”.

Question 3

(a) Many candidates were awarded full credit. Most used the relationship time = distance ÷ speed to
find the time in hours, 2250. The instruction in the question to ‘show that the time is 94 days’ meant
that candidates needed to state how 2250 hours converted to days. Some candidates missed this
final step and wrote “2250 hrs = 94 days”.

(b) Most candidates suggested ‘white’ and ‘shiny’. Alternative suggestions such as ‘a light colour’ and
‘smooth’ were accepted but answers such as ‘made of metal’ or ‘reflective’ were not.

(c) (i) Most candidates correctly stated visible and infrared.

(ii) Most candidates knew that they had to use the relationship wave speed = frequency  wavelength.
Many candidates omitted to convert the wavelength to metres but if their working was clear they
were awarded partial credit. Candidates who selected 470 nm rather than 800 nm could also gain
partial credit if clear working showed this was the only mistake.

Question 4

(a) This proved to be quite a challenging question. Some candidates stated that “the root was the stem
and the stem was the root” but this gained only partial credit. Credit could not be awarded for
vague answers such as “root and stem”. Some candidates missed the point that the root and stem
diagrams were interchanged and made suggestions such as “the stem should not have
projections”. Others described features that they assumed had been omitted from the diagrams.

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 Cambridge International General Certificate of Secondary Education
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Principal Examiner Report for Teachers

(b) Some candidates were very well-prepared for this question and some excellent answers were
seen. Most candidates were awarded partial credit for describing the pattern shown on the graph,
others went on to explain it.

(c) (i) Most candidates had learned the balanced equation for photosynthesis and were awarded full
credit.

(ii) The question asked candidates for a cell structure and not the type of cell where photosynthesis
occurs. The required answer, chloroplast, was given by many candidates but a similar number
suggested palisade mesophyll. The other most common incorrect answer was chlorophyll.

(d) Most candidates answered this question about feeding relationships very well. The most common
reasons for full credit not being awarded were that the musk ox was assigned to trophic level 1 and
the snowy owl was assigned to levels 2 and 3.

Question 5

(a) (i) In general, candidates were familiar with the importance of mobile ions in electrolysis. Some
candidates stated that atoms or molecules had to be mobile. Others made simple statements such
as “zinc chloride has to be a liquid for electrolysis to work” or “solid zinc chloride does not conduct”.
Some others suggested that zinc chloride had to be molten to avoid unwanted products from an
aqueous electrolyte.

(ii) Most candidates correctly expressed the idea that the electrodes must not react. Any wording that
suggested this idea was accepted. Answers such as “the electrodes must have a full outer shell”
were not accepted.

(iii) Candidates had to refer directly to the gain of electrons by positive ions. The wording in the
question was intended to prompt candidates to mention electrons but this was often missed. Some
candidates suggested that electrons were gained by chloride ions or the electrode. Credit was
awarded for a correct electrode equation showing electron gain by zinc ions.

(b) Some candidates were familiar with halogen displacement and gained full credit. However, some
candidates wrote ‘bromide’ rather than ‘bromine’ or omitted the products altogether. Some
candidates mistakenly included water in the equation. Partial credit was awarded for a fully correct
balanced equation, but candidates should be advised that if a word equation is requested, this
should be given.

(c) Many candidates knew the meaning of the term ‘diatomic’, but their answers needed to express the
idea that diatomic molecules contain only two atoms bonded together. Answers such as “for
example Cl 2” without explanation did not gain credit.

(d) Many candidates were familiar with this equation. The credit available for correct balancing
depended on correct chemical formulae.

Question 6

(a)(i)-(ii) The terms ‘fusion’ and ‘fission’ were familiar to many candidates, but they were often reversed.
Other common incorrect suggestions for both fusion and fission included thermal energy, solar
power, radiation, radioactivity and combustion.

(iii) Most candidates found it challenging to define fusion and fission and any wording that showed
candidates understood that fusion involved a joining process and fission involved splitting was
credited. Wording that suggested that chemical bonds were being formed or broken was not
accepted. One type of answer that was not credited was the suggestion that fusion was a natural
process but fission was man-made.

(b) Most candidates were very familiar with the relationship power = p.d.  current and could use it to
find the power supplied to the heater. Common errors included forgetting to convert 1920 W to kW
and incorrect forms of the formula for power.

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 Cambridge International General Certificate of Secondary Education
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(c) (i) Most candidates identified the circuit symbol for a motor. The most common mistake was to
suggest meter.

(ii) Many candidates understood that the currents in the parallel branches add to give the current in the
main circuit and were awarded full credit. Some candidates did not realise that this was a
straightforward question and attempted complicated calculations involving resistance in parallel
circuits even though no values of resistance were given.

(iii) Many candidates wrote answers that were statements of Ohm’s Law. Credit was awarded to
candidates who realised that ammeter A1 showed the total current in the main circuit and that
changing the resistance in one of the branches would change the overall resistance, therefore
changing the main current.

Question 7

(a) This was answered very well and many candidates gained full or partial credit. One mistake which
was frequently made was to suggest that sperm cells rather than egg cells contain an energy store.

(b) Many candidates had learned the functions of the placenta and were awarded credit for describing
the transfer of nutrients to the fetus and the removal of waste from the fetus. The term ‘food’ was
not accepted as an alternative for nutrients. Some candidates also referred to the placenta
preventing the transfer of toxins to the fetus. A common reason why some candidates did not gain
credit was that they described the functions of the uterus and amniotic fluid rather than answering
the question set.

(c) Generally, this question was very well answered. Many candidates identified either carbon
monoxide or tar as the toxic components affecting gaseous exchange. The reduced oxygen uptake
by red blood cells caused by carbon monoxide was familiar to many candidates as was the
damaging effect of tar on the lungs generally and the alveoli in particular. Candidates needed to
specify that tar is associated with lung cancer rather than simply stating “cancer”.

Question 8

(a) (i) Most candidates recognised fractional distillation. Of the few incorrect answers, cracking or simple
distillation were the most common suggestions.

(ii) This was answered very well by many candidates. Some candidates reversed the properties of the
two fractions.

(b) Many candidates had learned the definition of homologous series and so were awarded full credit.
It was important to avoid phrases such as “compounds that have the same properties” which was
not accepted as an alternative for “similar chemical properties”.

(c) (i) Most candidates were awarded credit for this question.

(ii) Most candidates were familiar with at least one condition needed for cracking and many gained full
credit. Unqualified answers such as temperature or heat were not accepted.

(iii) The strongest answers stated clearly that saturated hydrocarbon molecules contain only single
bonds or contain single bonds between the carbon atoms. Answers such as “compounds with
single bonds” were not accepted. Answers that attempted to describe the relative unreactive nature
of saturated hydrocarbons, without reference to bonding, were not accepted.

Question 9

(a) (i) Most candidates correctly stated force S. The most common incorrect answers were R and Q.

(ii) Almost all candidates answered this correctly.

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 Cambridge International General Certificate of Secondary Education
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(b) (i) There were many excellent answers to this calculation. Credit was awarded for evidence that
candidates knew that distance was related to the area under the graph. This could have been a
direct statement or evidence from arithmetic expressions. Clear working allowed some candidates
to be awarded partial credit for correct steps in the calculation.

(ii) Many candidates used the relationship energy = power  time and included all the steps required to
show that the total energy was 300 kJ. Answers that showed the energy in J were accepted if the
units were clearly stated.

1
(iii) The relationship, KE =  m  v 2 was familiar to most candidates, many of whom gained full
2
credit. A common mistake was to state the answer in J rather than kJ.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

COMBINED SCIENCE

Paper 0653/52
Practical Test

Key messages

 It is essential that confidential instructions are carefully followed. For Question 1, some candidates did
not start with water which was hot enough to collect data of sufficient quality to process.

 Candidates need to take careful note of instructions given in the questions. Where they are instructed to
record answers ‘to the nearest 0.5 °C’, for example in Question 3(a)(i) and (ii), it is essential that values
are given to one decimal place, which may be .0 or .5.

 To gain full credit in the planning question, it is important for candidates to read the question carefully
and investigate the variables stated in the question. It was common for candidates to choose to vary
incorrect variables. It is also essential that all bullet points in the question are addressed. Not
addressing some of the bullet points prevents full credit from being awarded.

General comments

It appeared that some candidates did not make use of the ‘Notes for use in Qualitative Analysis’, which are
provided at the back of the paper and are in the syllabus. It is essential that chemical observations are made
in line with these notes, and that observations are recorded to give both a colour and a state.

Guidance for the requirements for the practical component can be found at the back of the syllabus.
Teachers are referred to Section 4.

It should be further noted that guidance on the proper presentation of graphs is given in the ‘Mathematical
requirements’ and ‘Presentation of Data’ sections at the back of the syllabus.

Comments on specific questions

Question 1

In some cases, the water provided by centres was not at a high enough temperature. The starting
temperature for some experiments was below 50 °C. In addition, the starting temperature for the two tubes
was often very different, implying either that different sources of water were used or that the candidates took
too long setting up their experiments. It is essential that the confidential information is followed carefully to
ensure that candidates can record high quality data.

(a) (i) Almost all candidates correctly entered data to show a decrease in temperature in both tubes.
Some included units (°C) in the body of the table. This is not good practice but was ignored in this
question.

(ii) Most candidates correctly calculated the change in temperature for both test-tubes.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

(iii) In order to draw a conclusion for results, candidates needed to refer to the aim of the original
investigation. The information at the start of the question referred to the student investigating the
effect on heat loss of standing in a huddle. Therefore, to draw a full conclusion, candidates needed
to link the temperature changes to heat loss. The strongest answers identified that heat loss was
lower in the huddle. However, some candidates only referred to temperature change being greater.
This only described the results and did not make a conclusion so could not be awarded credit.
Another common error was to only describe the change, stating that “temperature decreases”.
Again, this was not a conclusion for this investigation.

(b) The strongest answers identified that the initial temperature of the two test-tubes was not the same.
It should be noted that candidates need to avoid giving generic phrases. Some candidates gave
vague answers such as “more reliable”, “more accurate” or “easier to see”.

(c) This question asked candidates to identify a variable. Stronger answers identified a variable that
would differ between either individual penguins or between different huddles or would differ over
time. Such answers referred to external temperature, the surface area of different huddles, wind
speed or the thickness of the feathers on the penguins. Some candidates incorrectly listed an
adaptation of penguins, which was likely to be the same for all penguins, rather than a variable.
These answers did not gain credit. Such answers included comments such as “penguins have
feathers” or “penguins are white”.

Question 2

Some candidates gave brief answers to the planning question and others left some or all of the question
unanswered. It was common for candidates to miss some of the bullet points and to only give a partial plan
to address some of the aspects of the investigation.

There were two common reasons why full credit could not be awarded for the planning question. Some
candidates did not refer carefully to the factor that they were asked to investigate (in this case intensity of
exercise). Many answers did not clearly vary the exercise intensity or develop a clear method of doing so. It
was also quite common for candidates to plan an investigation of other variables, such as age or fitness
level, or to vary more than one factor at a time. Best practice is to consider the bullet points carefully and to
use these to structure answers. For full credit it is essential that content is included against each of the bullet
points.

Apparatus: Most candidates suggested the use of a stop-clock or timer, but not all candidates clearly
described how it would be used to measure pulse rate. Fewer candidates suggested appropriate exercise
equipment such as a treadmill or fitness weights.

Method: The minimum viable method was to measure initial and final pulse rate before and after exercise of
variable intensity. Some candidates stated that they would do this. Answers which did not investigate
intensity of exercise as the main variable could not be awarded full credit.

A common error in the method included omitting measuring initial pulse rate, so basing the results only on
the pulse rate after exercise. In addition, many candidates did not clearly state that they would vary the
exercise intensity. As this was the main point of the investigation, such answers could not gain full credit.

Some candidates gave details of their method, and the strongest answers included a clear description of how
the intensity of the exercise could be varied. Common suggestions included walking, jogging and running or
the use of different speeds on a treadmill. Other answers suggested lifting weights for different numbers of
repetitions. Some candidates identified the need for pulse rate to return to normal between periods of
exercise and some gave clear safety precautions, such as the need to wear suitable shoes or to check the
fitness of the individual before the test began.

Measurements: Some candidates gave a detailed description of how they would measure the exercise
intensity. Examples included setting the speed on a treadmill or measuring the duration of the exercise.
However, some candidates made errors in the use of units. Candidates are expected to use SI units. ‘Min’ is
acceptable as an abbreviation for minutes, but ‘m’ is metres and so cannot be accepted as a unit of time.
Similarly seconds or s are both acceptable, but ‘secs’ is not an accepted abbreviation for seconds. Several
candidates did not make any clear point relating to the measurement of any of the variables.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

Constant Variables: Candidates needed to refer back and double check the factor that they were asked to
investigate and then identify other factors that needed to be controlled. A common error was to vary an
incorrect factor, such as the person doing the exercise or the type of exercise, rather than keeping these
constant so that only the intensity was changed. Stronger answers referred to varying the speed or number
of repetitions within a fixed controlled time and identified the need to either use the same person or use
people with the same characteristics such as age, sex, weight and fitness level.

Processing Results: This bullet point was often omitted, or vague references were made to drawing graphs
without a clear statement of the identity of the axes. Some candidates included a sketch of the axes of a
graph to process their results. This is good practice. Stating that it was necessary to take an average did not
automatically earn credit unless it was clear that candidates would average several readings conducted
under identical conditions.

Question 3

Throughout this question it appeared that some candidates did not make use of the qualitative analysis notes
which are provided at the back of the paper. Observations should routinely include both a colour and a state,
for example ‘blue precipitate’. Vague descriptions such as ‘cloudy blue’ were not accepted.

(a) (i) The instructions stated that the temperature readings needed to be recorded to the nearest 0.5 °C,
so the correct answer needed to show a ‘0’ or ‘5’ after the decimal point, for example 19.0 or 19.5.
Many candidates ignored this instruction and gave answers to the nearest degree. A further error
was to give values which did not show a ‘0’ or ‘5’ after the decimal point, such as 19.2, which
cannot be a reading from a standard thermometer.

(ii) Almost all candidates correctly recorded a higher temperature at Step 5.

(iii) Most candidates gave a correct colour for the residue, but many either left the appearance of the
filtrate blank or gave incorrect answers such as ‘clear’. It should be noted that ‘clear’ is not an
acceptable alternative for ‘colourless’ as coloured solutions are also clear.

(iv) Almost all candidates correctly subtracted the two values to calculate the temperature increase.

(v) Most candidates correctly substituted their temperature increase into the equation and calculated a
final value. However, the instruction to ‘give your answer to three significant figures’ was often
ignored. Some candidates quoted values to four or more significant figures.

(vi) The main reason for stirring in this experiment was to ensure that the temperature was even across
the mixture before the measurement of temperature was taken. Some candidates stated this.
Others made the reasonable points that stirring ensures complete reaction or speeds up the
reaction. These answers were awarded credit. However, many candidates stated that stirring is to
mix the reactants which did not explain why it is done sufficiently.

(vii) Most candidates suggested the use of insulation or a lid to prevent heat loss. A common error was
to suggest an external source of heat, for example keeping it hot with a Bunsen Burner or heated
water bath.

(b) Most candidates stated that a ‘blue’ colour was seen. This alone was not awarded credit. For
descriptions of qualitative tests, it is essential that a colour and state are given, as modelled in the
notes for qualitative analysis which are provided at the back of the paper. It is essential that
candidates refer to these during the examination. To earn credit, candidates needed to clearly state
‘blue precipitate’ and ‘dark blue solution’.

(c) (i) In common with (b), candidates should have recorded qualitative test observations by recording a
colour and a state. The correct answer here was ‘white precipitate’ (the colour of the solution was
ignored and did not contribute to the answer). Some candidates instead attempted to give a visual
description of the contents of the test-tube, describing cloudiness or layers. These answers were
not accepted.

(ii) Most candidates identified the positive ion in the salt as a copper ion, but fewer were able to
identify that the salt was a chloride. A number of candidates did not answer this question.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

Question 4

It should be noted that guidance for the construction of graphs is given in the ‘Mathematical Requirements’
and ‘Presentation of Data’ sections at the back of the syllabus.

(a) (i) This question was usually answered well. Almost all candidates recorded their values for current to
two decimal places and their values for voltage to one.

(ii) Most candidates recorded values showing the correct trend of voltage increasing with a decrease
in current.

(b) This question was answered well. Most candidates correctly calculated resistance values. It should
be noted that candidates were not instructed how many decimal places to use in their values, so
any number were accepted. However, wherever appropriate, values should be rounded
appropriately.

(c) (i) Most candidates chose suitable, linear scales which enabled the plotted points to cover at least half
the grid. Almost all candidates plotted points correctly. Errors were usually due to incorrect values
being entered on the axes and some candidates using non-linear scales.

(ii) The line of best fit was not well drawn by most candidates. Some attempted to join the points with a
wavy line that went through all of the points. Thick, feathered lines or lines that were not clearly
straight were not accepted.

(iii) This question was challenging for many candidates. Many omitted both the calculation and
annotation on the graph. Some attempted to draw a triangle on the graph but this was often very
small. Gradient triangles should occupy at least half the length of the line of best fit.

(iv) Some candidates gave the correct unit for resistance per unit length, but again, this question was
often left unanswered. Ohms alone was the most common incorrect answer.

(d) Candidates needed to think about the practical difficulties they had encountered in the procedure.
Expected answers included difficulty in placing the crocodile clip exactly on the metre rule.
However, most answers were generic and referred to “not doing the experiment correctly” or
“parallax error” or “human error” or “error when taking readings”. Generic answers of this type were
not accepted.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

COMBINED SCIENCE

Paper 0653/62
Alternative to Practical

Key messages

 Candidates need to take careful note of instructions given in the questions. Where they are instructed to
‘record your answer to the nearest 0.5 °C’, for example in Question 1(a)(i), it is essential that values are
given to one decimal place, which were .0 or .5 in this case.

 To gain full credit in the planning question, it is important for candidates to read the question carefully
and investigate the variables stated in the question. It was common for candidates to choose to vary
incorrect variables. It is also essential that all bullet points in the question are addressed. Not
addressing some of the bullet points prevents full credit from being awarded.

 When asked to record values in a table, it is essential that candidates use the other values in the table
as an indicator of the resolution to which they should record their readings. For example, in Question
4(a)(iii) the value of the potential difference needed to be recorded to two decimal places.

General comments

In general, the performance on this paper was good. This was particularly the case in the quality of
responses seen for the planning question. There were few omissions and almost all candidates attempted
the planning question at some length.

Although the alternative to practical is a paper-based assessment, it is still intended that candidates have a
substantial amount of practical work integrated into their course. The assessment is designed around written
questions, but it is not intended that candidates only practise using written questions. Some candidates
appeared to have had limited practical experience. Guidance for the requirements for this component can be
found at the back of the syllabus in Section 4.

Comments on specific questions

Question 1

(a) (i) Almost all candidates read the thermometer correctly and recorded their value to 0.5 °C. A few
candidates rounded their reading incorrectly to either 65 or 66.

(ii) Most candidates correctly calculated the change in temperature for both test-tubes. Resolution was
not tested in this question; values expressed as 22 and 12 were accepted, but it should be noted
that calculated differences in temperature should be recorded to the same resolution as the raw
data, leading to the difference being expressed as 22.0 and 12.0.

(iii) In order to draw a conclusion for results, candidates needed to refer to the aim of the original
investigation. The information at the start of the question referred to the student investigating the
effect on heat loss of standing in a huddle. Therefore, to draw a full conclusion, candidates needed
to link the temperature changes to heat loss. The strongest answers identified that heat loss was
lower in the huddle. However, some candidates only referred to temperature change being greater.
This only described the results and did not make a conclusion so could not be awarded credit.
Another common error was to only describe the change, stating that “temperature decreases”.
Again, this was not a conclusion for this investigation.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

(iv) The question asked candidates to predict the change in temperature. Some candidates did not
read the question fully and suggested a final temperature for the test-tube, such as 60 °C, rather
than suggesting a temperature change. For credit, candidates needed to justify their answer. Many
answers only referred to the temperature of the outside tube in comparison to the middle tube of
the huddle. Answers justifying a temperature change in the correct range were not always fully
correct. Reasons such as “it would lose heat faster than the middle test-tube” only explained why
the temperature change would be greater than 12.0 °C. A full reason needed to also justify why the
temperature change would be less than 22.0 °C, by stating that less heat would be lost than by the
single test-tube. Therefore, only answers that correctly referenced both test-tubes gained credit.

(b) The strongest answers identified that the initial temperature of the two test-tubes was not the same.
Many candidates gave vague answers such as “more reliable”, “more accurate” or “easier to see”.
Candidates needed to avoid giving generic phrases and should have referred to the data in the
question.

(c) This question asked candidates to identify a variable. Stronger answers identified a variable that
would differ between either individual penguins or between different huddles or would differ over
time. Such answers referred to external temperature, the surface area of different huddles, wind
speed or the thickness of the feathers on the penguins. Some candidates incorrectly listed an
adaptation of penguins, which was likely to be the same for all penguins, rather than a variable.
These answers did not gain credit. Such answers included comments such as “penguins have
feathers” or “penguins are white”.

(d) The relevant point was that both test-tubes would fall to room temperature or to the temperature of
the surroundings. Some candidates stated this clearly. Others gave answers which were not
awarded credit, such as that the test-tubes lose all their heat or cool down completely. These
answers were incorrect as all their heat was not lost. Heat was only lost until the temperature
became the same as the environment around the test-tubes.

Question 2

There were two common reasons why full credit could not be awarded for the planning question. Some
candidates did not refer carefully to the factor that they were asked to investigate (in this case intensity of
exercise). Many answers did not clearly vary the exercise intensity or develop a clear method of doing so. It
was also quite common for candidates to plan an investigation of other variables, such as age or fitness
level, or to vary more than one factor at a time. Best practice is to consider the bullet points carefully and to
use these to structure answers. For full credit it is essential that content is included against each of the bullet
points.

Apparatus: Most candidates suggested the use of a stop-clock or timer, but not all candidates clearly
described how it would be used to measure pulse rate. Fewer candidates suggested appropriate exercise
equipment such as a treadmill or fitness weights.

Method: The minimum viable method was to measure initial and final pulse rate before and after exercise of
variable intensity. Many candidates stated that they would do this. Answers which did not investigate
intensity of exercise as the main variable could not be awarded full credit.

A common error in the method included omitting measuring initial pulse rate, so basing the results only on
the pulse rate after exercise. In addition, many candidates did not clearly state that they would vary the
exercise intensity. As this was the main point of the investigation, such answers could not gain full credit.

Some candidates gave details of their method, and the strongest answers included a clear description of how
the intensity of the exercise could be varied. Common suggestions included walking, jogging and running or
the use of different speeds on a treadmill. Other answers suggested lifting weights for different numbers of
repetitions. Some candidates identified the need for pulse rate to return to normal between periods of
exercise and some gave clear safety precautions, such as the need to wear suitable shoes or to check the
fitness of the individual before the test began.

© 2024
 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

Measurements: Many candidates gave a detailed description of how they would measure the exercise
intensity. Examples included setting the speed on a treadmill or measuring the duration of the exercise.
However, some candidates made errors in the use of units. Candidates are expected to use SI units. ‘Min’ is
acceptable as an abbreviation for minutes, but ‘m’ is metres and so cannot be accepted as a unit of time.
Similarly seconds or s are both acceptable, but ‘secs’ is not an accepted abbreviation for seconds. Several
candidates did not make any clear point relating to the measurement of any of the variables.

Constant Variables: Candidates needed to refer back and double check the factor that they were asked to
investigate and then identify other factors that needed to be controlled. A common error was to vary an
incorrect factor, such as the person doing the exercise or the type of exercise, rather than keeping these
constant so that only the intensity was changed. Stronger answers referred to varying the speed or number
of repetitions within a fixed controlled time and identified the need to either use the same person or use
people with the same characteristics such as age, sex, weight and fitness level.

Processing Results: This bullet point was often omitted, or vague references were made to drawing graphs
without a clear statement of the identity of the axes. Some candidates included a sketch of the axes of a
graph to process their results. This is good practice. Stating that it was necessary to take an average did not
automatically earn credit unless it was clear that candidates would average several readings conducted
under identical conditions.

Question 3

(a) (i) Most candidates correctly read the thermometer in step 5 at 55.5 °C, but many stated 24 as the
reading for step 2. The instructions stated that the temperature readings needed to be recorded to
the nearest 0.5 °C, so the correct answer was 24.0. 24 alone was not credited.

(ii) Almost every candidate correctly subtracted the two values to calculate the temperature increase.

(iii) Most candidates were able to substitute correctly into the provided equation and compute a correct
value. Fewer candidates then correctly quoted this value to three significant figures, as the
question requested. Some gave values to more than three significant figures and some made
errors in rounding. These included adding unnecessary zeros, such as 1250.0 which was incorrect.
Some gave only three figure answers, such as 125 rather than the correct value, 1250.

(iv) The main reason for stirring in this experiment was to ensure that the temperature was even across
the mixture before the measurement of temperature was taken. Some candidates stated this.
Others made the reasonable points that stirring ensures complete reaction or speeds up the
reaction. These answers were awarded credit. However, many candidates stated that stirring is to
mix the reactants which did not explain why it is done sufficiently.

(v) Most candidates suggested the use of insulation or a lid to prevent heat loss. A common error was
to suggest an external source of heat, for example keeping it hot with a Bunsen Burner or heated
water bath.

(vi) Candidates were asked for a labelled diagram to include the filtrate and residue. Most knew the
basic set-up for a filter, with a funnel represented over a collecting vessel, but the fine detail of the
diagram was sometimes missing. A few candidates drew other separation apparatus such as a set-
up for simple distillation. There were some common errors in responses. Some candidates did not
label the filtrate and residue. Some showed a funnel either without a filter paper or with the filter
paper represented incorrectly. A correct diagram should have shown the filter paper as a distinct
continuous line, without gaps, in a V shape inside the funnel. Many represented the filter paper
incorrectly as curved or with a hole at the bottom. A fully labelled diagram should have had, at a
minimum, a label for the filter funnel, filter paper and a suitable collecting vessel such as a test-
tube, beaker or flask. Some candidates did not give all the necessary labels. It should be further
noted that diagrams should be represented scientifically as two-dimensional line drawings. It is not
correct to draw the top or bottom three dimensionally on the filter funnel.

(b) (i) Most candidates knew that initially a blue precipitate forms. However, many added that this was
insoluble. Fewer identified the formation of a deeper blue solution on the addition of excess
aqueous ammonia. It should be noted that it is incorrect to describe the precipitate as green-blue
as this could be confused with iron(II).

(ii) Most candidates identified the anion as a chloride ion.

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 Cambridge International General Certificate of Secondary Education
0653 Combined Science March 2024
Principal Examiner Report for Teachers

Question 4

(a) (i) Almost all candidates knew the correct symbol for a voltmeter, and many positioned it across the
resistance wire correctly. Common errors included positioning the voltmeter in series in the circuit,
in parallel to one of the components in the circuit or to represent it in parallel to the wire but with the
connectors either too close together or too far apart. To be correct, the wires from the parallel
circuit that included the voltmeter needed to meet the resistance wire at 0 cm and at the point of the
crocodile clip. Some candidates represented the voltmeter correctly in parallel directly across the
central part of the circuit.

(ii) Some candidates correctly identified that opening the switch prevents overheating of the wire.
Danger from electric shock was a common incorrect answer.

(iii) When recording results in a table it is essential that candidates follow the pattern of resolution of
the other values. In this case, all other values of the potential difference were recorded to two
decimal places, so it was essential that a voltage of 1.10 was recorded for 45.0 cm. Many
candidates did not follow the pattern, stating that this value was 1.1. Most candidates correctly
gave the current to two decimal places.

(b) Almost all candidates substituted into the equation and correctly calculated the value of the
resistance.

(c) (i) The graph question was answered well. Almost all candidates chose an appropriate scale so that
the points plotted occupied more than half the available grid and plotted points correctly. Errors
were usually due to incorrect values being entered on the axes. Some candidates gave non-linear
scales, and some reversed the values on the axes, despite the axes being labelled in the question.

(ii) Most candidates gave an acceptable line of best fit based on their plots. Where the relationship
was a straight line, it was expected that candidates use a ruler and that their pencil should be
sharp. Thick, feathered lines that were not clearly straight were not accepted. The line needed to
be single and continuous. Dot to dot lines between points were not accepted. Where there was a
spread of data, candidates needed to draw their line to show the best trend, with any points not
exactly on the line spread evenly on each side. Further guidance can be found in the syllabus.

(iii) Most candidates gained at least partial credit, either for a correct gradient calculation or by showing
a triangle on the graph that was correctly drawn and occupied at least half the length of the line of
best fit. A relatively common error was to misread the values from the graph to use in the
calculation of the gradient. Some candidates counted squares rather than using the values on the
axes. Many candidates drew very small triangles which did not occupy half the available line.

(iv) Most candidates gave the correct unit for resistance per unit length. Ohms alone was the most
common incorrect answer.

(d) Only a few candidates answered this correctly. “To calculate an average” or “to avoid anomalies”
were common incorrect answers. The strongest answers referred to using the repeated readings to
check for and to identify and exclude anomalous readings from the data set. Some candidates
correctly stated that repeated similar readings are an indicator of high-quality data.

(e) The strongest answers identified features of the practical procedure that were likely to result in a
variation of results. For example, difficulty in placing the crocodile clip exactly on the metre rule.
Some candidates identified differences between the equipment that different students might use for
the procedure, such as differences in the diameter of wire. Weak, generic answers such as
“parallax error”, “human error” or “error when taking readings” were not accepted.

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