Biology 2023 Oct/Nov | Past Paper

Q2

Short Answer 1 mark

Keratin is the structural protein in feathers of birds. Keratin polypeptides are composed of a high proportion of cysteine amino acids, which have sulfur-containing R groups. Keratin polypeptides form filaments. The two main types of keratin in feathers are α-keratin, which consists of many α-helices, and β-keratin, consisting of many β-pleated sheets.

Q2(a)

Short Answer 1 mark

Keratin can be classified as α-keratin or β-keratin based on a study of protein structure. Suggest the level of protein structure used to classify a protein as α-keratin or β-keratin.

Q2(b)

Short Answer 1 mark

Protease enzymes hydrolyse proteins. Many proteases are able to hydrolyse more than one type of protein. Suggest why it is possible for a protease to act on different types of protein.

Q2(c)

Short Answer 1 mark

Proteases known as keratinases vary in the extent to which they can hydrolyse keratin. Feathers are not easily degraded (broken down) because keratin is a very stable protein. Suggest features of keratin structure that contribute to its stability. Keratinases are used to degrade the large quantities of waste feathers from chickens and turkeys that are processed in the food industry. The products of feather degradation can be used in animal feed. Scientists investigated whether three different keratinases, K12, A22 and P3, were suitable as industrial enzymes. These enzymes were extracted from three different soil bacteria. The effects of temperature and pH on the activity of each keratinase were investigated. The results are shown in Fig. 2.1 and Fig. 2.2. 20 30 40 50 temperature / °C 60 70 80 relative activity/ %Key K12 = A22 = 5.0 6.0 7.0 8.0 9.0 10.0 relative activity/ %

Q2(d)

Structured 4 marks

To degrade feather waste from industry, it is an advantage to use keratinases that show at least 60% relative activity in conditions where temperature and pH can vary widely. Table 2.1 shows, for each keratinase, the working range of temperature and pH where at least 60% relative activity is obtained. Use Fig. 2.1 and Fig. 2.2 to complete Table 2.1 and use the completed table to: Table 2.1 keratinase temperature range with at least 60% relative activity / °C pH range with at least 60% relative activityK12 41-63A22 6.0-9.0 29-56 5.3-7.5 Keratinase with a relative activity of at least 60% that has:

Q2(e)

Short Answer 1 mark

Some detergents contain proteases to remove stains from clothes. These enzymes have a high relative activity in alkaline conditions. The scientists reported that K12 and A22 could be suitable for use in the detergent industry. With reference to Fig. 2.1 and Fig. 2.2, discuss the advantages and disadvantages of using K12 and A22 in the detergent industry. [Total: 12]

Q3

Short Answer 1 mark

The liver receives blood from the hepatic artery and from the hepatic portal vein. The hepatic portal vein transports blood from the digestive system. Hepatocytes are the main cell type of the liver. They have a wide range of functions, including:

Q3(a)

Short Answer 1 mark

The hepatic artery branches from the main artery that transports blood from the heart. Name the main artery that transports blood to the hepatic artery.

Q3(b)

Short Answer 1 mark

Blood arriving at the liver enters specialised blood vessels known as sinusoids. Fig. 3.1 is a diagram of part of a sinusoid and surrounding hepatocytes. A second type of cell found in the liver, a Kupffer cell, is also shown. Kupffer cells are phagocytic cells of the immune system. sinusoid large gap between endothelial cells Kupffer cell hepatocyte

Q3(i)

Short Answer 1 mark

Suggest one advantage of having large gaps between the endothelial cells of the sinusoid, as shown in Fig. 3.1.

Q3(ii)

Short Answer 1 mark

In addition to removing bacteria present in the blood inside the sinusoid, Kupffer cells are also able to remove old or damaged red blood cells. Describe the mode of action of a Kupffer cell in removing and breaking down a damaged red blood cell.

Q3(c)

Short Answer 1 mark

Fig. 3.2 is a transmission electron micrograph of part of a hepatocyte showing some cell structures. The peroxisome shown in Fig. 3.2 is a spherical organelle bound by a single membrane. It carries out a variety of enzyme-catalysed metabolic reactions, including detoxification. Some of these reactions require oxygen. peroxisome glycogen granules lipid droplet

Q3(i)

Short Answer 1 mark

Describe the evidence visible in Fig. 3.2, apart from the presence of a peroxisome, that indicates some of the functions of a hepatocyte. Add labels to Fig. 3.2 to identify the location of any cell structures, if not already labelled, that are part of your evidence.

Q3(ii)

Short Answer 1 mark

The mitochondria in Fig. 3.2 are larger than the peroxisome. State one other difference, visible in Fig. 3.2, between a peroxisome and a mitochondrion.

Q3(iii)

Short Answer 1 mark

Some of the enzymes used within mitochondria can be synthesised by the organelle. Peroxisomes cannot synthesise any of the enzymes that they contain. Suggest why a mitochondrion can synthesise enzymes, but a peroxisome cannot synthesise enzymes.

Q3(iv)

Short Answer 1 mark

One of the enzymes present in peroxisomes is catalase. This enzyme catalyses the breakdown of hydrogen peroxide to harmless products. Suggest why it is useful to the cell for this reaction to take place within peroxisomes. [Total: 14]

Q4

Short Answer 1 mark

The alveoli of the lungs are the main gas exchange surface in humans.

Q4(a)

Short Answer 1 mark

Explain how blood flow through the alveolar capillaries helps to maintain steep diffusion gradients for gas exchange.

Q4(b)

Short Answer 1 mark

Ventilation of the lungs is the process of inhalation and exhalation. Ventilation helps to maintain steep diffusion gradients. Explain the role of elastic fibres in the alveolar wall during ventilation.

Q4(c)

Short Answer 1 mark

Some cells in the alveolar wall are specialised to secrete surfactant to prevent collapse of the alveoli at the end of exhalation. In these cells, surfactant is stored in membrane-bound organelles known as lamellar bodies. Surfactant is a mixture of lipids, mainly phospholipids, and some proteins. A protein known as ATP-binding cassette transporter A3 (ABCA3) is needed to move surfactant phospholipids into lamellar bodies from the surrounding cytosol (fluid part of cytoplasm). Suggest and explain the features of protein ABCA3 that make it suited to its function.

Q4(d)

Short Answer 1 mark

The gene ABCA3 codes for protein ABCA3. The gene is 80 kb (80 000 base pairs) long and is composed of introns and exons. Protein ABCA3 is composed of 1704 amino acids.

Q4(i)

Short Answer 2 marks

Fig. 4.1 shows the flow of genetic information in the production of ABCA3. gene ABCA3 primary transcript RNAmessenger RNA (mRNA)polypeptide ABCA3protein ABCA3 Complete Fig. 4.1 to name the processes occurring at X and Y.

Q4(ii)

Short Answer 1 mark

A triplet of bases codes for one amino acid. This fact only partly explains how the activity of gene ABCA3, which is 80 kb long, can result in the protein ABCA3, which is only 1704 amino acids long. Suggest other reasons to explain the difference in the number of base pairs in gene ABCA3 compared with the number of amino acids in protein ABCA3. [Total: 12]

Q5

Short Answer 1 mark

Tuberculosis (TB) is an infectious disease caused by a bacterium. In the majority of people, only the lungs are affected. In most cases, the transmission of TB from an infected person to an uninfected person involves Mycobacterium tuberculosis. A different species of bacterium is involved in the transmission of TB from cattle, such as dairy cows, to humans.

Q5(a)

Short Answer 1 mark

Name the species of bacterium causing the transmission of TB from dairy cows to humans.

Q5(b)

Short Answer 1 mark

In some areas, cattle cannot be regularly tested or treated for TB. In these areas, milk and dairy products from infected dairy cattle may enter the human food chain. Outline a control measure that can be taken to protect people that consume milk and dairy products from these infected cattle.

Q5(c)

Short Answer 1 mark

Cattle are not usually affected by M. tuberculosis, but the pathogen can cause disease in other animals. A few cases of transmission of TB from people to animals have been reported. Explain the most likely mode of transmission of TB from an infected person to an animal.

Q5(d)

Short Answer 1 mark

In most people, the response of the immune system to the infection of lung tissue by M. tuberculosis can prevent the spread of the bacterium to other organs of the body. The bacterium is contained in the lungs in a dormant state. This is known as latent TB. Outline the treatment that is used to kill M. tuberculosis in latent TB infections.

Q5(e)

Short Answer 1 mark

M. tuberculosis can spread in the blood and lymph to other organs in the body. In very rare cases, a disease known as mycotic aneurysm can be caused by infection of the arterial wall, particularly in elastic arteries. The damage caused by the pathogen can lead to a rupture (bursting) of the artery. With reference to the structure of the wall of elastic arteries, suggest how damage caused by M. tuberculosis infection can lead to the rupture of the artery. You may draw a diagram if you wish. Space for diagram [3] [Total: 9]

Q6

Short Answer 1 mark

Water that is absorbed from the soil solution by the roots of a plant enters xylem vessels and is transported to the leaves and buds. Fig. 6.1 shows four important requirements for the efficient transport of water from the roots to the leaves of a plant. requirements for the efficient transport of water tension needs to be created in xylem vessels water in xylem vessels must be in continuous, unbroken columns there should be minimum resistance to the flow of water xylem vessels must be able to cope with the tensions created by the movement of water

Q6(a)

Short Answer 1 mark

Name the specialised cells that are arranged end to end to form xylem vessels.

Q6(b)

Short Answer 1 mark

Explain how tension is created in the xylem vessels.

Q6(c)

Short Answer 1 mark

Fig. 6.1 highlights how the structure of xylem vessels must be related to their function. This means that during the development of xylem vessels changes need to occur to the cells forming the vessels.

Q6(i)

Short Answer 1 mark

The walls of the cells forming the xylem vessel walls become lignified during development. Explain how this feature is important for the efficient transport of water.

Q6(ii)

Short Answer 1 mark

During the development of xylem vessels, the end walls of the cells forming the vessels break down. This contributes to minimising resistance to the flow of water. Describe one other main change that needs to occur to these cells so that their structure becomes suited to their function. [Total: 6] 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. Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort 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. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge 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.

Board	CAIE
Level	A Level
Subject	Biology
Code	`9700`
Year	2023
Session	Oct/Nov
Q&A	35 questions

Biology 2023 · Oct/Nov

Questions & Model Answers 35 Qs

Paper Details