CIE AS & A Level Biology Papers 4 prediction - 2025
CIE AS & A Level Biology Papers 4 prediction- 2025
To excel in A level Biology Exam, consistent practice with CIE AS & A Level Revision resources is key. CIE AS & A Level Biology Papers 4 prediction will guide you for exam pattern.
IITian Academy offers a vast collection of questions that can aid your understanding of specific topics and solidify your concepts. By practicing regularly and focusing on these key areas, you’ll be well-prepared for the A level Biology exam
Question 1
(a) A mitochondrion contains DNA and ribosomes and is the organelle in which aerobic respiration takes place.
Suggest the functions of the DNA and ribosomes in a mitochondrion.[3]
(b) Oxidative phosphorylation takes place in the mitochondrion.
Different stages of oxidative phosphorylation are listed below.
They are not listed in the correct order.
Complete Table 8.1 to show the correct order of the stages.
Two of the stages have been done for you.[4]
(c) ATP can be converted to ADP and inorganic phosphate by the enzyme ATPase.
State the type of reaction taking place.[1]
(d) Some parasitic worms, such as tapeworms, live in a mammalian gut where there is no oxygen.
Suggest how a tapeworm produces ATP in this environment.[5] [Total: 13]
Answer/Explanation
Ans:
8 (a) (DNA for) transcription/ codes for mRNA ;
(ribosomes for) translation ;
synthesis of, respiratory enzymes / named enzyme/ inner membrane proteins ;
(b) 
S U W all above R ;
S U W in correct order ;
Q X T all below R ;
Q X T in correct order ;
(c) hydrolysis / dephosphorylation/ exothermic / exergonic ;
(d) anaerobic respiration ;
substrate level phosphorylation (in glycolysis);
at triose phosphate → pyruvate step ;
(net) gain of 2ATP (per glucose) ; A 2 used and 4 produced
pyruvate, reduced/ gains hydrogens (from reduced NAD) ;
forming lactate ;
NAD regenerated/NADH2 re-oxidised ;
this allows glycolysis to continue ; I ethanol pathway
Question 2
(a) Neurones transmit impulses from one part of a mammal’s body to another.
The table contains statements that refer to motor and sensory neurones.
Complete the table, indicating with the letters M, S or B, whether each statement applies to:
- motor neurones only (M)
- sensory neurones only (S)
- both motor and sensory neurones (B).
The first one has been done for you.[3]
(b) A synapse is a junction between two or more neurones.
Describe how an action potential arriving at a presynaptic membrane of a neurone can result in the depolarisation of the membrane of a post-synaptic neurone.[5]
(c) Acetylcholinesterase is an enzyme found in the synaptic cleft.
Outline the role of acetylcholinesterase.[2] [Total: 10]
Answer/Explanation
Ans:
6 (a)
all correct = 3 marks
3/4 correct = 2 marks
1/2 correct = 1 mark
(b) 1 Ca(2+) channels open (in presynaptic membrane/presynaptic knob) ;
2 Ca2+ enter (pre)synaptic knob ;
3 vesicles contain, neurotransmitter/ACh ;
4 (vesicles) move towards/fuse with, presynaptic membrane ;
5 (ACh/neurotransmitter) released/exocytosis ;
6 (ACh/neurotransmitter) diffuses (across cleft) ;
7 binds to receptors on postsynaptic membrane ;
8 Na(+) channels open ;
9 Na+ enters post-synaptic neurone ;
penalise lack of mention of ions in mp2 and 9 once only
(c) hydrolyses/breaks down, ACh ;
stops continuous production of action potentials (in post-synaptic neurone) ;
Question 3
(a) Explain the significance of cereal crops in the human diet. [8]
(b) Describe and explain how gibberellins are involved in the germination of wheat or barley seeds. [7] [Total: 15]
Answer/Explanation
Ans:
9 (a) 1 high, carbohydrate/ starch, content ; A 70–80%
2 source of, energy /ATP ;
3 protein provides amino acids ;
4 for growth ;
5 low in fat ; A 2–4%
6 contains essential fatty acids ;
7 source of, vitamin B/ vitamin E ;
8 deficient in, vitamin A/ vitamin D/ vitamin C ;
9 ref. to Golden Rice and vitamin A ; A ref. to other valid examples
10 wide range/AW, of minerals ;
11 named mineral plus use in human body ; e.g. calcium for bone development
12 high in fibre ;
13 for peristalsis/prevents constipation ;
14 easily, dried/ stored ;
15 AVP ; e.g. staple diet for much of the world/named staple crop and location
16 AVP ; e.g. different parts of grain have different nutrients/ref. to processing grain
(b) 1 seed is, dormant/metabolically inactive ;
2 water enters seed ;
3 embryo, produces/releases, gibberellin ;
4 gibberellin stimulates aleurone layer ;
5 (by) affecting, gene coding/transcription of mRNA, for amylase ;
6 to produce amylase ;
7 amylase hydrolyses starch ;
8 in endosperm ;
9 to, maltose/glucose ;
10 embryo uses sugars for respiration ;
11 energy /ATP, used for growth ;
Question 4
Gold ions (Au3+) are toxic to most microorganisms. However, the bacterium Delftia acidovorans is frequently found in sticky layers, called biofilms, that form on the surface of gold deposits.
D. acidovorans produces a peptide synthase that catalyses the synthesis of a small peptide called delftibactin. When isolated, delftibactin can precipitate Au3+ ions as small particles of metallic gold. Delftibactin is a secondary metabolite.
(a) Name another example of a secondary metabolite and explain what is meant by the term.[3]
example
explanation
(b) A mutant strain of D. acidovorans has been identified in which the gene coding for peptide synthase is inactive.
The wild-type (normal) and mutant D. acidovorans were grown on agar plates and then flooded with gold chloride solution, which contains Au3+ ions. The appearance of such a plate after this treatment is shown in Fig. 2.1.
With reference to Fig. 2.1, suggest how delftibactin protects D. acidovorans from toxic Au3+ ions.[3]
(c) Wild-type and mutant D. acidovorans were grown in standardised conditions:
- wild-type and mutant bacteria were grown in the absence of Au3+ ions
- wild type and mutant bacteria were grown in the presence of Au3+ ions
- mutant bacteria were grown in the presence of Au3+ ions and of delftibactin.
The results are shown in Fig. 2.2.
Explain whether or not the results shown in Fig. 2.2 support the idea that delftibactin is protective.[4]
(d) The secondary metabolite, delftibactin, could be used to remove the toxic Au3+ ions that are present in the waste produced by gold mining.
Describe how delftibactin could be produced on a large scale.[5] [Total: 15]
Answer/Explanation
Ans:
2 (a) example:
penicillin/ other named antibiotic ;
explanation any two from:
substance made by a microorganism during stationary phase/AW ;
A growth of microorganism has almost stopped
produced, when there is a shortage of nutrients /when population is under stress ;
not needed for normal metabolism (of microorganism) ;
(b) 1 wild-type bacteria, secretes /releases, delftibactin ; I produces
2 delftibactin makes soluble gold ions into insoluble gold ; A precipitates gold
3 insoluble gold is not toxic ; ora
4 insoluble gold, stays outside the bacteria/ not in bacterial cytoplasm ;
5 (so) no/ fewer, soluble gold ions enter bacterium (from solution) ;
A D. acidovorans for wild-type
A Au / metallic gold/ solid/ gold particles / gold precipitate for insoluble gold
A Au3+ / gold ions / ions for soluble gold
(c) 1 without Au3+ numbers of wild-type and mutants similar/AW ;
support
2 with Au3+ fewer mutants than wild-type ; ora
3 with Au3+ fewer mutants than without Au3+ ; ora
4 with Au3+ and (added) delftibactin more mutants than with Au3+ alone ; ora
does not support
5 with Au3+ and (added) delftibactin fewer mutants than without Au3+ ; ora
6 only one set of data /no statistical analysis ; A no repeats
(d) 1 grow the wild-type, bacterium/D. acidovorans ;
2 in fermenter ;
3 ref. to (fed) batch culture ;
4 ref. to sterilised ;
5 nutrients at start (batch)/ nutrients at intervals (fed) ;
6 carbon/ nitrogen, sources ;
7 ref. to aeration/ provide oxygen ;
8 ref. to constant temperature/water jacket ; A environmental conditions kept constant
9 details of fermenter ; e.g. paddles / stirrers
10 harvest delftibactin/ downstream processing ;
Question 5
(a) The unicellular green alga, Chlorella, a photosynthetic protoctist, was originally studied for its potential as a food source. Although large-scale production proved to be uneconomic, the many health benefits provided by Chlorella mean that it is now mass
produced and harvested for use as a health food supplement.
Fig. 1.1 shows cells of Chlorella.
In one study into the productivity of Chlorella, carbon dioxide concentration was altered to investigate its effects on the light-independent stage of photosynthesis.
- A cell suspension of Chlorella was illuminated using a bench lamp.
- The suspension was supplied with carbon dioxide at a concentration of 1% for 200 seconds.
- The concentration of carbon dioxide was then reduced to 0.03% for a further 200 seconds.
- The concentrations of RuBP and GP (PGA) were measured at regular intervals.
- Throughout the investigation the temperature of the suspension was maintained at 25 °C.
The results are shown in Fig. 1.2.
(i) State precisely where in the chloroplast RuBP and GP are located.[1]
(ii) Explain why the concentration of RuBP changed between 200 and 275 seconds.[2]
(iii) Calculate the rate of decrease per second in the concentration of GP between 200 and 350 seconds.
Show your working and give your answer to two decimal places.
answer arbitrary units per second [2]
(b) Explain how the decrease in the concentration of GP leads to a decreased harvest for commercial suppliers of Chlorella.[2] [Total: 7]
Answer/Explanation
Ans:
1 (a) (i) stroma ; [1]
(ii) lower CO2 concentration ;
less, carbon fixation/CO2 combining with RuBP/RuBP converted to GP ; RuBP reformed from TP ; [max 2]
(iii) 0.01 ;;
A 0.012 or 1.8 ÷ 150 or \(\frac{2.0-0.2}{150}\) or \(\frac{2.0-0.2}{350-200}\) for 1 mark
(b) less TP ;
(so less) conversion to, (other) carbohydrates / lipids / amino acids / proteins ; A named examples, e.g. glucose/ hexose/ cellulose/ starch
AVP ; e.g. 1 – (amino acids) used to make proteins for, growth/ cell division
e.g. 2 – (carbohydrate/ lipid) for respiration for, growth/ cell division
Question 6
Deer mice, Peromyscus maniculatus, are small rodents that live in North America. Like all mammals, their blood contains haemoglobin which combines with oxygen in the lungs, and unloads its oxygen in respiring tissues.
Deer mice show variation in their genotypes for the genes that code for the α-polypeptide chain of haemoglobin. In most populations of deer mice, the majority of individuals have the genotype A1A1, while a smaller number have the genotype A0A0.
(a) In mice with the genotype A1A1, the amino acid at position 64 in the α-polypeptide chain is aspartic acid. In mice with the genotype A0A0, the amino acid at this position is glycine.
Suggest how the change from aspartic acid to glycine in the α-polypeptide chain could have been brought about.[2]
(b) The genotypes of deer mice from three different populations, each living at a different altitude, were analysed. Fig. 5.1 shows the relative proportions of deer mice with aspartic acid (white areas) and glycine (black areas) at position 64 in the α-polypeptide of
their haemoglobin.
(i) Describe the effect of altitude on the frequency of the haemoglobin alleles in these populations of deer mice.[2]
(ii) The partial pressure of oxygen is relatively low at high altitudes. Haemoglobin containing glycine at position 64 in the α-polypeptide chain has a higher affinity for oxygen than haemoglobin with aspartic acid at this position.
Suggest how natural selection could account for the difference in allele frequency in deer mice living at high altitudes and low altitudes.[4] [Total: 8]
Answer/Explanation
Ans:
5 (a) random/ spontaneous ;
mutation ;
base/nucleotide/triplet, change/ substitution ; R addition/ deletion
(b) (i) as altitude increases frequency of A0 increases ; ora for A1
A0 more frequent at high altitudes / A1 more frequent at low altitudes / intermediate frequency of either allele at intermediate altitude ;
(ii) idea of (pre-existing) genetic variation in deer mouse population ;
at high altitude mice with, glycine/A0, more likely to survive/ have selective advantage ; ora
mice (with A0 ) reproduce (at high altitude) ; ora
and pass on the A0 allele ; ora
partial pressure/ concentration, of O2 acts as a selection pressure ;
ref. to disadvantage of haemoglobin with very high affinity at low altitude ;
as less able to unload oxygen (in respiring tissues) ;
Question 7
Spraying insecticide on the walls inside houses is the main method of controlling a species of Anopheles mosquito in rural India. A number of different insecticides have been used.
Malathion was the main insecticide used for many years. In 2005 the newer insecticide, deltamethrin, was used instead and the use of malathion was discontinued.
A laboratory study was carried out using mosquitoes collected from two sites in India. The percentage of mosquitoes killed by malathion and deltamethrin was estimated.
The results of the study are shown in Table 4.1
(a) With reference to Table 4.1, describe the difference in effectiveness of the two insecticides.[3]
(b) The researchers concluded that at Jamnagar, the mosquitoes had evolved resistance to deltamethrin.
Explain how the mosquitoes evolved resistance.[4]
(c) Explain how the data in Table 4.1 show evidence that the use of malathion was discontinued after 2005.[2]
(d) The resistance of mosquitoes to malathion was found to be due to a difference in the shape of one enzyme.
Name the type of variation controlling malathion resistance in the mosquito population.[1]
(e) Some students suggested that resistance to malathion could be due to a gene with two alleles. They proposed that the allele for resistance to malathion would be dominant to the allele for non-resistance.
Using this assumption, the data in Table 4.1 can be used to calculate the frequency of resistant mosquitoes and the frequency of the allele for resistance in a mosquito population.
Use the Hardy-Weinberg principle to calculate the frequency, p, of the allele for resistance in Jamnagar in 2005.[3] [Total: 13]
Answer/Explanation
Ans:
4(a) three from
1 (overall) deltamethrin, more effective / better, (at killing mosquitoes) ;
2 figures for malathion and deltamethrin with named site and year R Jamnagar in 2007 or mean 78.5% for malathion and 97.5% for deltamethrin ;
3 malathion, kills higher percentage (of mosquitoes)/is more effective, than deltamethrin in Jamnagar in 2007 ;
4 percentage of mosquitoes killed by deltamethrin decreasing in Jamnagar ;
5 percentage of mosquitoes killed by malathion increasing (in both locations) ;
4(b) four from
1 (random) mutation /genetic variation ; A description of mutation
2 deltamethrin acts as a selection pressure ;
3 resistant mosquitoes have selective advantage ; ora
4 resistant mosquitoes, survive /reproduce ; ora
5 resistance alleles passed on ;
6 increase in frequency of resistance allele ; ora
7 natural /directional, selection ;
4(c) two from
1 percentage of mosquitoes killed (by malathion) increases ;
2 (malathion) selection pressure removed /resistance to malathion is no longer a selective advantage ;
3 idea of resistance not needed ;
4(d) discontinuous ;
4(e) p=0.13 ; ; ;
allow max 2 for working
q2 / frequency of non-resistant (mosquitoes) = 0.76
q = 0.87
Question 8
Table 8.1 shows the total number of plant species, the total number of insect species and the
number of habitats in three areas, A, B and C.
(a) Identify the area with the highest biodiversity.
Give reasons for your choice of area.
area ………………
reasons …………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………… [3]
(b) Identify the area that is likely to be affected the most if the environment changes.
Give a reason for your choice of area.
area ………………
reason ……………………………………………………………………………………………………………………..
…………………………………………………………………………………………………………………………………
[1]
(c) State one reason why it is important to conserve biodiversity in all three areas.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………… [1]
[Total: 5]
▶️Answer/Explanation
Answer:
8(a) 1 C ;
2 greater/ highest / most, number of (plant + insect) species / species richness ;
3 greater/ highest / most, number of habitats ;
8(b) area A because if one species, increases / decreases (in abundance), this may affect the whole, community / food web /
ecosystem ;
8(c) any one from:
1 species may have, medicinal / economic / aesthetic, benefits ;
2 (to maintain) genetic diversity / genetic variation / alleles ;
3 ref. to ethical / moral / stewardship ;
Question 9
The monkey flower, Mimulus guttatus, is cross-pollinated by bumblebees. It does not normally self-pollinate.
Since the number of bumblebees in many parts of the world is falling, an experiment was carried out in Kansas to investigate the effects on these plants of the loss of pollinators.
- 1600 Mimulus plants were grown in a field.
- 1600 Mimulus plants were grown in a glasshouse which bumblebees could not enter.
Seeds were repeatedly collected and sown for several generations at each site.
At first, the plants in the glasshouse produced few seeds, but after five generations the plants were able to self-pollinate and the number of seeds produced was almost the same as that of the plants in the field.
After five generations, the flowers of the plants in the glasshouse were significantly smaller than those of the plants in the field.
(a) Explain why offspring produced by cross-pollination and self-pollination differ in their genetic variation.[3]
(b) Suggest how smaller flowers could lead to an increase in self-pollination.[1]
(c) Explain how natural selection produced the smaller flower size of the plants grown for five generations in the glasshouse.[5] [Total: 9]
Answer/Explanation
Ans:
3 (a) self-pollination ora for cross-pollination
1 gametes / alleles / genes /DNA, come(s) from one parent ;
2 gives, less genetic variation/more genetic uniformity ;
3 results in inbreeding ;
4 increases homozygosity / decreases heterozygosity ;
(b) anthers and stigma/ stamens and carpels, closer together ;
(c) 1 range of flower size in original population ;
2 genetic variation (affecting flower size) in original population ; I mutation
3 change in environment/ selection pressure,
is absence of, bees / insect pollination (in greenhouse) ;
4 plants with small, flowers / petals, are,
selected for/reproduce/ at a selective advantage ; ora
5 alleles for small size passed to offspring ; ora I gene
6 frequency of, advantageous / smallness, allele increases ; ora
7 directional selection ;
8 temperature/ irrigation/ space/ competition, different in field and glasshouse ;
9 small size explanation linked to factor in mp8 ;
4 (a) (i) 1 habitat loss / urbanisation/roads /agriculture ; R deforestation
2 human damage (to plants) ; e.g. trampling / camping/ picking
3 climate change ; e.g. drought/ storms
4 soil erosion ;
5 loss of pollinators ;
6 use of herbicides ;
7 competition with/ eaten by, introduced species ;
8 pollution ;
(ii) 1 to maintain biodiversity ;
2 to maintain, food chains / food webs / stability of ecosystems ;
3 to maintain, genetic diversity / genetic variation/ gene pool ;
4 resources (for humans) ; e.g. biofuel/ food/medicines /wood
5 aesthetic reasons /(eco)tourism ;
6 to maintain, nutrient cycle/ soil structure/ climate stability ;
7 idea of ethical duty ;
(b) 1 gibberellin moves (from embryo) to aleurone layer ;
2 gene, switched on/ transcribed/used to make mRNA ;
3 amylase produced ; I released/ stimulated
4 (amylase), hydrolyses / digests, starch to maltose ; I breaks down/ converts / glucose
5 for, respiration/ATP/ energy ;
6 for, growth/development/ cell division/mitosis, in embryo ;
7 AVP ; e.g. role of, DELLA/PIF
(c) (i) survival:
1 less risk of extinction (for high seed survival compared with low survival) ;
germination percentage:
for low survival:
2 as % germination increases, risk of extinction decreases ;
for high survival:
3 as % germination increases risk of extinction decreases until,
30–36 % germination, then risk of extinction increases ;
4 use of paired figures ; e.g. quote % germination and risk of extinction for each of:
high v low [mp1]
2 points on low survival line [mp2]
2 points on high survival line [mp3]
allow ± one grid square for figures
(ii) yes
1 (scraping) increases germination ;
2 more germination lowers risk of extinction ; ora
3 if seeds don’t survive long/ for low survival value seeds, scraping is good ;
no
4 if seeds do survive long-term/ for high survival value seeds, a store of seeds remains in soil ;
5 (avoid risk of) all germinating at once and perhaps all dying ;
Question 10
(a) Fig. 6.1 shows the concentration of four hormones in a woman’s blood during one menstrual cycle.
(i) With reference to Fig. 6.1, explain why there is a large increase in LH at around day 12.[1]
(ii) State how Fig. 6.1 shows that the woman did not become pregnant during this cycle.[1]
(b) The combined oral contraceptive pill contains oestrogen and progesterone.
(i) Explain how this combined contraceptive pill works to prevent pregnancy.[4]
(ii) Suggest why some women take the combined contraceptive pill for just the first 21 days of their cycles.[1]
(iii) Some women have a contraceptive device inserted under the skin. This releases hormones into the blood and can last for up to three years.
Suggest one advantage of using such a device rather than taking contraceptive pills.[1] [Total: 8]
Answer/Explanation
Ans:
6(a)(i) high concentration of oestrogen (causes surge in LH concentration)
or
(surge in LH concentration) causes ovulation to occur ;
6(a)(ii) progesterone concentration falls (towards end of cycle) ;
6(b)(i) four from
1 (acts on) anterior pituitary gland ;
2 FSH secretion inhibited ; I FSH inhibited
3 Graafian / dominant, follicle does not develop ;
4 LH secretion inhibited ; I LH inhibited
5 ovulation prevented /AW ;
6 ref. to negative feedback ;
7 cervical mucus thickens ;
8 ref. to thin endometrium ;
6(b)(ii) to allow menstruation to occur/idea of mimicking the body’s natural cycle ;
6(b)(iii) one from
1 no need to take contraceptive pill every day ;
2 maintains steady concentration of hormones / no hormonal imbalance ;
3 AVP ; e.g. no menstruation / fewer side effects