Biology 2025 Oct/Nov | Past Paper

Q1

Short Answer 1 mark

Rice, Oryza sativa, is a crop plant that has adapted to grow in flooded fields. Fig. 1.1 outlines the effects on rice plants of growing in flooded fields. flooded fields lower concentration of mineral ions and A in the soil available for absorption compared to non-flooded fields presence of tissue C in stems and roots production of ethylene (ethene) breakdown of abscisic acid (ABA) high concentration of waste product B in root cells

Q1(a)

Short Answer 3 marks

With reference to Fig. 1.1, name: substance A substance B tissue C

Q1(b)

Short Answer 1 mark

Describe how root cells respond to a high concentration of substance B.

Q1(c)

Short Answer 1 mark

Gibberellin is involved in the growth of stems in rice plants. Fig. 1.2 shows the ef fect of gibberellin concentration on the length of stems in rice plants. concentration of gibberellin / arbitrary units 2 3 4 5 length of stem / mm

Q1(i)

Short Answer 1 mark

Describe the relationship shown in Fig. 1.2.

Q1(ii)

Short Answer 1 mark

ABA in rice plant cells inhibits the action of gibberellin. With reference to Fig. 1.1 and Fig. 1.2, explain the importance of ethylene production for the growth of rice plants in flooded fields. [Total: 9] * 0000800000003 *

Q2(a)

Short Answer 3 marks

Explain the terms gene, genotype and phenotype. gene genotype phenotype

Q2(b)

Short Answer 1 mark

A monohybrid genetic cross can be carried out to produce an F1 and an F2 generation. F2 generation. Assume that the inheritance pattern is for autosomal dominant and recessive alleles. [Total: 8] * 0000800000004 * Question 3 starts on page 6. * 0000800000005 *

Q3

Short Answer 1 mark

The lac operon is present in the genome of the bacterium Escherichia coli. When glucose is not available, the presence of lactose in the extracellular environment leads to the expression of the genes of the lac operon. This leads to an increase in the uptake and metabolism of lactose. When glucose and lactose are available in the extracellular medium, lactose is prevented from entering the bacterial cell. Fig. 3.1 shows what happens when glucose enters a bacterial cell. glucose lactose extracellular environmentlactose permease cell surface membrane cytoplasm glucose 6-phosphate lacI lacZ repressor lacYlacAPO Fig. 3.1 * 0000800000006 *

Q3(a)

Short Answer 1 mark

(i) With reference to Fig. 3.1, suggest and explain how the presence of glucose in the extracellular environment prevents lactose entering the bacterial cell.

Q3(ii)

Short Answer 1 mark

Suggest the advantages for the bacterial cell in preventing the entry of lactose when glucose is present in the extracellular environment. Outline the events that occur in glycolysis following the production of

Q3(b)

Short Answer 1 mark

E. coli is present in the gut (intestines) of young mammals. The diet of young mammals contains lactose which is present in the milk they consume. Scientists carried out an experiment using E. coli with a lac operon (lac E. coli) and E. coli without a lac operon (lac E. coli). The experiment was carried out to determine whether the presence of a lac operon gives E. coli a selective advantage. E. coli and lac E. coli were given to 8 mice to allow the bacteria to colonise the gut. E. coli. E. coli that were in the gut of each mouse was determ ined every day for 6 days. The results are shown in Fig. 3.2. 1 2 3 4 5 6 time / days percentage of E.coli that arelac lactose lactose Fig. 3.2 * 0000800000008 *

Q3(i)

Short Answer 1 mark

With reference to Fig. 3.2, describe the ef fect of the dif ferent diets on the percentage of E. coli that are lac

Q3(ii)

Short Answer 1 mark

The scientists concluded that lac E. coli had a selective advantage when colonising the gut, but only in the presence of lactose. Suggest why the presence of lactose caused lac E. coli to have a selective advantage. [Total: 12] * 0000800000009 *

Q4

Short Answer 1 mark

The evolution of antibiotic resistance in bacteria has occurred as a result of natural selection.

Q4(a)

Short Answer 1 mark

Name two ways in which a bacterium can become resistant to an antibiotic.

Q4(b)

Short Answer 1 mark

The World Health Organisation regularly analyses bacterial DNA sequence data. Suggest one way in which this contributes to solving the problem of antibiotic resistance in bacteria.

Q4(c)

Short Answer 1 mark

Some infectious bacterial diseases are treated with the antibiotic streptomycin. If a person does not finish the prescribed course of streptomycin, bacteria are more likely to become resistant to the antibiotic. natural selection when a person does not complete the prescribed course of antibiotics. [Total: 6] * 0000800000010 * [ 0 Question 5 starts on page 12. * 0000800000011 * [[0

Q5

Short Answer 1 mark

Metachromatic leukodystrophy (MLD) is a genetic disease that af fects the nervous system. MLD is caused by mutations in the ARSA gene located on chromosome 22. The ARSA gene, which is 3150 base pairs (bp) in length, includes 8 exons and is shown in Fig. 5.1. 3.15 kb exon A genetic test using DNA sequencing is available to identify mutations associated with MLD in the ARSA gene. The sequencing method can only work if a DNA fragment size is less than 1000 bp. The test involves a number of dif ferent stages: of the ARSA gene. Table 5.1 shows the length of the DNA fragments and the exons present in each DNA fragment. Table 5.1 fragment number DNA fragment length / bp exons in DNA fragment 1 405 1 [T0

Q5(a)

Short Answer 1 mark

Genomic DNA and primers are added to the PCR machine. Name two other substances that are added to the PCR machine, and explain why each substance is added. [u0

Q5(b)

Short Answer 1 mark

Gel electrophoresis is carried out on the 5 dif ferent DNA fragments produced as a result of PCR. Each DNA fragment is put into a loading well on the gel. The final lane on the electrophoresis gel contains a DNA ladder of known lengths of DNA. Fig. 5.2 shows the results of the gel electrophoresis. fragment fragment fragment fragment fragmentDNA ladder

Q5(i)

Short Answer 1 mark

Suggest the role of the DNA ladder.

Q5(ii)

Short Answer 1 mark

In the genetic test for MLD, PCR and gel electrophoresis are carried out before DNA sequencing. Suggest and explain reasons why PCR and gel electrophoresis are carried out before DNA sequencing. [r0

Q5(c)

Short Answer 1 mark

Calculate the number of copies of DNA that are obtained if PCR is run for 35 cycles. Assume that there is only 1 copy of DNA at the start of PCR. Give your answer in standard form to two significant figures. number of copies

Q5(d)

Short Answer 1 mark

MLD is a rare autosomal recessive disease. It is estimated that there is one case of MLD in every 40 000 births worldwide. Children with MLD have a reduced life expectancy. was to provide pain relief. A new gene therapy treatment known as Libmeldy® became available in a number of countries in 2022. The treatment must start before symptoms are present. Although the treatment may provide a cure for MLD, a single dose is extremely expensive. Blood samples from newborn babies are screened for a number of rare genetic diseases (neonatal screening) in most countries of the world, but none include screening for MLD. Discuss the social and ethical considerations of including screening for MLD when carrying out neonatal screening in a country where gene therapy for MLD is available. [Total: 14] * 0000800000015 * [n0 regulation of blood glucose concentration. receptor insulin glucose cell surface membrane activation PI3KPKB vesicle GLUT4 transport protein cytoplasm T ype 2 diabetes mellitus is a common disease. Some people with type 2 diabetes have a low concentration of PI3K in their muscle cells and cannot maintain their blood glucose concentration within normal limits. With reference to Fig. 6.1, suggest why a low concentration of PI3K can lead to type 2 diabetes. [o0

Q5(b)

Short Answer 1 mark

Describe how a biosensor can be used to measure blood glucose concentration. [Total: 11] * 0000800000017 * [v0

Q7(a)

Short Answer 1 mark

The V enus fly trap, Dionaea muscipula, is a plant that can capture insects. Each leaf of a Venus fly trap is modified to form 2 lobes. Fig. 7.1 shows how the leaf of a V enus fly trap appears folded (closed) when an insect has been captured.

Q7(i)

Short Answer 1 mark

Suggest a reason why the V enus fly trap needs to capture insects, even though it carries out photosynthesis.

Q7(ii)

Short Answer 1 mark

The leaves are specialised to form 2 lobes. The lobes are red on the upper surface. Suggest why the lobes are red.

Q7(iii)

Short Answer 1 mark

The lobes have sensory hairs. Touching 1 sensory hair will not cause a response by the leaf. At least 2 sensory hairs need to be touched within 20 seconds to cause a response in the leaves. State the advantage to the plant of producing a response only when 2 sensory hairs are touched within 20 seconds. [e0

Q7(iv)

Short Answer 1 mark

When an insect has been trapped, the leaves have to remain closed for a number of days. Suggest why this needs to happen.

Q7(b)

Short Answer 1 mark

Action potentials are produced by the V enus fly trap during the closure of a leaf. Each action potential is also associated with a refractory period. This is similar to the action potential and refractory period observed in a mammalian neurone during nerve impulse transmission. Explain the role played by the refractory period in the transmission of an impulse in a mammalian neurone. [Total: 7] * 0000800000019 * [C0

Q8(a)

Short Answer 1 mark

Palm oil is the most widely used vegetable oil. It is obtained from the African oil palm, Elaeis guineensis. Oil palms are the highest yielding vegetable oil crop, needing only 10% of the land area required by other crops to produce the same quantity of oil. On the island of Borneo, tropical rainforests are cut down and cleared to create oil palm plantations. This has a large effect on biodiversity. The Bornean orangutan, Pongo pygmaeus, is only found on the island of Borneo and is classified as critically endangered on the International Union for Conservation of Nature Fig. 8.1 shows Bornean orangutans. Suggest ways in which the Bornean orangutan may be conserved. T 0

Q8(b)

Short Answer 1 mark

Biodiversity can be assessed at different levels. Outline the main levels at which biodiversity can be assessed. T[0

Q8(c)

Short Answer 1 mark

The biodiversity of a habitat can be measured by calculating Simpson' s index of diversity (D). The formula for Simpson' s index of diversity (D) is: R=-c`jm Key to symbols: n = number of individuals of each type present in the sample N = the total number of all individuals of all types present in the sample A survey of shrubs and trees in a temperate woodland was carried out. The results are shown in Table 8.1. Table 8.1 common name nN N maple 807 0.196 0.0384 alder 6 0.001 0.0000 hazel 1856 0.451 hawthorn 82 0.020 0.0004 blackthorn 40 0.010 0.0001 willow 101 0.025 0.0006 birch 78 0.019 0.0004 wild rose 84 0.020 0.0004 oak 1036 0.252 0.0635 dogwood 29 0.007 0.0000 N = 4119 Total =

Q8(i)

Short Answer 2 marks

Complete T able 8.1.

Q8(ii)

Short Answer 1 mark

Calculate the value for Simpson's index of diversity (D). D =

Q8(iii)

Short Answer 1 mark

Using your value for D, comment on the biodiversity of this temperate woodland. [Total: 12] * 0000800000022 * TT0

Q9(a)

Short Answer 1 mark

Fig. 9.1 shows an absorption spectrum for chlorophyll a and the corresponding action spectrum for a species of plant. 400 500 600 700 absorption spectrum action spectrum wavelength of light / nm

Q9(i)

Short Answer 1 mark

Explain what is meant by an absorption spectrum and an action spectrum.

Q9(ii)

Short Answer 1 mark

Suggest and explain why the curve shown in Fig. 9.1 for the absorption spectrum is different from the curve for the action spectrum for wavelengths of light between 450 nm and 550 nm. Tu0

Q9(b)

Short Answer 1 mark

Scientists investigated the ef fect of temperature on the rate of photosynthesis and the rate of respiration of the trailing azalea, Kalmia procumbens, at a high light intensity . Fig. 9.2 shows the results of this investigation. 0.0 1.0 2.0 rate of photosynthesis (uptake of carbon dioxide) / mg g rate of respiration (production of carbon dioxide) / mg g 3.0 4.0 100 20 30 temperature / °C 40 50 0.0 0.5 1.0 1.5 2.0

Q9(i)

Short Answer 1 mark

With reference to Fig. 9.2, describe and explain the ef fect of temperature on the rate of photosynthesis for K. procumbens. Tr0

Q9(ii)

Short Answer 1 mark

The rate of photosynthesis in this investigation was obtained by measuring the uptake of carbon dioxide from the atmosphere. It did not take into account the use of carbon diox ide produced by respiration. Using Fig. 9.2, calculate the rate of photosynthesis at 20 °C when the carbon dioxide produced by respiration is taken into account. rate of photosynthesis [2] [Total: 11] * 0000800000025 * Tn0

Q10(a)

Short Answer 1 mark

Nerve impulses can be transmitted along a myelinated motor neurone to a neuromuscular junction at fast speeds of up to 100 m s Outline how a transmission speed of 100 m s is achieved by the neurone.

Q10(b)

Short Answer 1 mark

When a nerve impulse reaches the neuromuscular junction, acetylcholine is released and diffuses to the sarcolemma. Describe how the release of acetylcholine can result in the binding of calcium ions to troponin in the sarcomere. To0

Q10(c)

Short Answer 1 mark

Muscle contraction can be affected by a low blood glucose concentration. Suggest how a low blood glucose concentration would af fect the functioning of the sarcomere. [Total: 10] * 0000800000027 * Tv0 The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country , territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries. reasonable ef fort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. Assessment International Education Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cambridgeinternational.org after the live examination series. Local Examinations Syndicate (UCLES), which is a department of the University of Cambridge. BLANK PAGE * 0000800000028 * Te0

Board	CAIE
Level	A Level
Subject	Biology
Code	`9700`
Year	2025
Session	Oct/Nov
Q&A	47 questions

Biology 2025 · Oct/Nov

Questions & Model Answers 47 Qs

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