Biology 2025 May/June Paper 22 | Past Paper

Q1

Short Answer 1 mark

Root hair cells are specialised plant cells located in the outer layer of young roots of plants. Root hair cells have an essential role in the uptake of water and dissolved mineral ions from the soil solution. The transport of water across the root to reach the central xylem tissue can occur by the symplast pathway or apoplast pathway.

Q1(a)

Short Answer 3 marks

Fig. 1.1 is a diagram of a photomicrograph of a root hair cell. cytoplasm Z X Y On Fig. 1.1, name cell structures X, Y and Z.

Q1(b)

Short Answer 1 mark

In the symplast pathway , water passes through the cells of the dif ferent tissues in the root before entering the xylem vessels of xylem tissue. Name the tissues of the root, in the correct sequence, through which water passes in the symplast pathway.

Q1(c)

Short Answer 1 mark

In the apoplast pathway , water passes along the cell walls of adjacent plant cells and through the intercellular spaces. This is more efficient than the symplast pathway. Explain the structural features of plant cell walls that make the apoplast pathway an ef ficient pathway for the transport of water.

Q1(d)

Short Answer 1 mark

Root hair cells also synthesise and secrete substances into the soil. Electron microscopy of the structure of root hairs has identified endoplasmic reticulum (ER), a number of small Golgi bodies, and numerous vesicles. catalyse the release of inorganic phosphate ions from organic phosphates in the soil. sorgoleone, which slows down the growth of neighbouring plants.

Q1(i)

Short Answer 1 mark

Explain why the proportion of rough ER to smooth ER may be dif ferent in the root hair cells of barley plants compared with the root hair cells of sorghum plants.

Q1(ii)

Short Answer 1 mark

Student X stated that acid phosphatases and sorgoleone could be transported out of root hair cells using the same process. Student Y stated that acid phosphatases and sorgoleone are transported out of root hair cells using different processes. Suggest the reasons given by student X and by student Y to support their statements. student X student Y [4] [Total: 14] * 0000800000003 *

Q2

Short Answer 1 mark

The transport of respiratory gases involves blood plasma and red blood cells. Red blood cells contain the globular protein, haemoglobin.

Q2(a)

Short Answer 1 mark

Describe features of a haemoglobin molecule that are typical of a globular protein, other than having an approximately spherical shape.

Q2(b)

Short Answer 1 mark

A number of substances are involved in the transport of respiratory gases. Complete Table 2.1 by stating the name of the substance that matches the description of its role in the transport of respiratory gases. The first row has been completed for you. Table 2.1 substance role in the transport of respiratory gases carbon dioxide In the capillaries of respiring tissues, this combines with water to form carbonic acid. In the capillaries of respiring tissues, this enters red blood cells through a membrane transport protein. In red blood cells, this is formed when carbon dioxide binds to haemoglobin. In alveolar capillaries, this combines with a hydrogen ion in red blood cells to form carbonic acid. In alveolar capillaries, this is formed in red blood cells as a result of oxygen binding to a haem group. In red blood cells, this combines with haemoglobin to form haemoglobinic acid. [5] [Total: 7] * 0000800000004 *

Q3

Short Answer 1 mark

Carrots are root vegetables of the carrot plant. The carrot plant is an important food crop that is grown throughout the world. Carrots have a sweet taste because sugars form a proportion of the total carbohydrate present. Plant breeding has produced many dif ferent varieties of carrot, with different levels of sweetness.

Q3(a)

Short Answer 1 mark

One of the sugars found in carrots is galactose. Galactose has the same molecular formula, C Fig. 3.1 shows the molecular structure of galactose found in carrots. This is similar , but not In Fig. 3.1, the six carbon atoms are numbered 1 to 6.OHH State the dif ferences between the molecular structure of galactose, shown in Fig. 3.1, and the

Q3(b)

MCQ 3 marks

An investigation was carried out to determine the sugar content of mature carrots produced by different local varieties of carrot plants that are grown in Tunisia, North Africa. Carrot plants were grown from seed under standardised conditions. When mature, the carrots were harvested. The dif ferent sugars present in the carrots were identified. Measurements of sugar content for each of the sugars were made. T able 3.1 shows the results for five different local varieties of carrot plant, A to E. Table 3.1 local variety sugar content of carrots / mg g of dry weight fructose galactose glucose sucrose A 183.04 1.43 173.28 73.73 B 194.43 1.13 188.18 46.20 C 200.15 5.99 125.19 85.93 D 157.35 4.88 137.28 89.57 E 170.38 4.54 133.57 60.27 After studying the results shown in Table 3.1, a student concluded that the carrots from the local varieties contain the same four sugars. The student made three other conclusions from the data in Table 3.1. conclusion 2 There are monosaccharide and disaccharide sugars in the carrots. conclusion 3 The carrots have the same pattern of results. * 0000800000006 * Explain the evidence in Table 3.1 that supports these three other conclusions. conclusion 1 conclusion 2 conclusion 3

A

183.04 1.43 173.28 73.73

B

194.43 1.13 188.18 46.20

C

200.15 5.99 125.19 85.93

D

157.35 4.88 137.28 89.57

Q3(c)

Short Answer 1 mark

Carbohydrates that are not sugars are also present in carrots. Name one carbohydrate that is present in carrots and that is not a sugar .

Q3(d)

Short Answer 3 marks

Each carrot plant produces a carrot in the first year of growth. If the carrot is not removed from the plant after it matures, the plant passes through a dormant period and shoots develop from the carrot in the second year of growth. This allows flowers to be produced and seed formation to occur before the plant dies. Explain, with reference to the life cycle of the carrot plant, when the carrot acts as a source and when the carrot acts as a sink. source sink

Q3(e)

Short Answer 1 mark

Carrot virus Y is a pathogen of carrot plants. The virus, which belongs to a group known as Potyvirus, replicates its viral nucleic acid and proteins within host carrot cells. The general structure of potyviruses is shown in Fig. 3.2. capsidRNA The synthesis of viral proteins in host carrot cells only involves the process of translation. The process of transcription does not occur . Suggest why translation occurs in host carrot cells during the synthesis of viral proteins, but transcription does not occur . [Total: 10] * 0000800000008 *

Q4

Short Answer 1 mark

Tuberculosis (TB) is an infectious disease that is caused by a bacterial pathogen. The pathogen has mechanisms to avoid digestion by phagocytes. Macrophages may engulf the bacteria, but in some cases the bacteria remain alive within the cells instead of being killed.

Q4(a)

Short Answer 1 mark

Although there are two main species of bacterium causing TB, it is rare for the species that causes bovine TB in cattle to infect humans. Name the species of bacterium that is the main cause of TB in humans.

Q4(b)

Short Answer 1 mark

Explain how the pathogen named in

Q4(b)(a)

Short Answer 1 mark

is transmitted from a person with the disease to a person who is uninfected.

Q4(c)

Short Answer 1 mark

State the type of therapeutic drug used to treat TB.

Q4(d)

Short Answer 1 mark

Fig. 4.1 is a photomicrograph of a section of lung tissue taken from a person who has not been infected with the bacterial pathogen and who does not have TB. Blood vessels and some structures of the gas exchange system are visible in Fig. 4.1. On Fig. 4.1, use a label line and label: [3] * 0000800000010 *

Q4(e)

Short Answer 1 mark

In some people with TB, areas known as granulomas may form in lung tissue as part of an immune response to the pathogen. Fig. 4.2 is a photomicrograph of a granuloma in lung tissue. granuloma darkly staining white blood cells in outer area of granuloma dead cells and infected cells (mainly macrophages) multinucleated giant cells, formed by the fusion of many macrophages With reference to Fig. 4.1 and Fig. 4.2, describe and explain how the changes that occur as a result of granuloma formation: [Total: 12] * 0000800000011 *

Q5

Short Answer 1 mark

There is a global shortage of blood for transfusions. Researchers can culture bone marrow stem cells in the laboratory to manufacture red blood cells for potential use as an artificial blood product. The researchers collect bone marrow stem cells that are present in small quantities in blood, rather than extracting them from bone marrow. be collected.

Q5(a)

Short Answer 1 mark

The antibodies are attached to the beads so that the sites used for binding to specific molecules on the bone marrow stem cells are left exposed. Name the term given to the specific molecules on the bone marrow stem cells that attach to the antibody binding sites.

Q5(b)

Short Answer 1 mark

Suggest and explain the advantages of using bone marrow stem cells from the blood sam ple to manufacture artificial red blood cells.

Q5(c)

Short Answer 1 mark

One desirable feature of artificial blood products, such as artificial red blood cells, is that they should be economical to produce. Suggest other desirable features of artificial blood products. [Total: 7] * 0000800000012 *

Q6

Short Answer 1 mark

Horseradish peroxidase (HRP) is an enzyme that can be ex tracted from the roots of the horseradish plant, Armoracia rusticana. HRP is used extensively in industry and technology. In the reaction catalysed by HRP , hydrogen peroxide (H ) is used to oxidise an organic substrate. This is summarised in Fig. 6.1.HRP organic substrate + hydrogen peroxide oxidised substrate + water

Q6(a)

Short Answer 2 marks

Inhibitors can have an ef fect on Vmax , the maximum rate of reaction, and K , the Michaelis - Menten constant, of HRP. Fig. 6.2 shows the ef fect of substrate concentration on the rate of reaction of HRP. 0.30.20.10.0 initial rate of reaction / arbitrary units substrate concentration / mmol dm will affect the rate of reaction of HRP. Use the curve you have drawn to obtain an estimate of K =

Q6(b)

Short Answer 1 mark

Scientists can design synthetic DNA nucleotide sequences to produce a synthetic HRP gene. These sequences will include a start codon and a stop codon so that translation of messenger RNA (mRNA) can occur. Explain what is meant by a start codon and a stop codon.

Q6(c)

Short Answer 1 mark

HRP is used in an immunological test known as a sandwich ELISA. One use of the test is to diagnose disease. Fig. 6.3 outlines the main steps in a sandwich ELISA in which a toxin released by a pathogen is detected in a sample of body fluid taken from a person who is ill. The test involves two types of monoclonal antibody that can bind to the toxin, a capture antibody and a detection antibody. test well capture antibody toxin toxinHRP detection antibody step 1 step 2 step 3 Prepare a test well by immobilising the capture monoclonal antibody to the support surface. Remove a sample of the body fluid from the person who is ill and add the sample to the test well. Wash out the test well to remove any substances not bound to the capture antibody. step 4Add detection antibody to the test. step 5Wash out the test well to remove any detection antibody that is not bound to the toxin. step 6Add substrates for catalysis by HRP and add acid after a set time to stop the reaction.

Q6(i)

Short Answer 1 mark

Complete Fig. 6.4 to show the situation in the test well after step 5. [1] * 0000800000014 *

Q6(ii)

Short Answer 1 mark

With reference to Fig. 6.3, describe one dif ference between the capture antibody and the detection antibody.

Q6(iii)

Short Answer 1 mark

Fig. 6.5 outlines the reaction catalysed by HRP in step 6. The organic substrate, TMB, is in excess and changes colour when it is oxidised. This indicates a positive test result.HRPTMB colourless + H oxidised TMB + water A student suggested that: positive result quantitative result and help to avoid this error. With reference to Fig. 6.5, explain why using a colorimeter would provide a quantitative measurement for detection of a low concentration of the toxin and help to confirm a positive result. [Total: 10] * 0000800000015 * 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. * 0000800000016 *

Board	CAIE
Level	A Level
Subject	Biology
Code	`9700`
Year	2025
Session	May/June
Paper No.	Paper 22
Total Marks	2025
Duration	75 minutes
Q&A	34 questions

Biology 2025 · May/June · Paper 22

Questions & Model Answers 34 Qs

Paper Details