AS & A Level Biology - 9700 Paper 2 2024 Summer Zone 1

(a) (i) State the approximate thickness of the membrane as shown by the line G–H.
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(ii) Complete Table 1.1 to show:
• the names and functions of the components of the cell surface membrane
• the letters of the labels in Fig. 1.1 that identify each component.



Table 1.1
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component function letter on Fig. 1.1
channel protein
phospholipid
receptor for cell signalling F
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[4]

(b) Fig. 1.2 is a drawing of a transmission electron micrograph (TEM) of a cell from the palisade mesophyll of a leaf.
The drawing does not show all of the organelles visible in a transmission electron micrograph.



(i) Complete Fig. 1.2 by drawing and labelling:
• a mitochondrion
• rough endoplasmic reticulum
• smooth endoplasmic reticulum.
Your drawings should show the detail that can be seen in a transmission electron micrograph. [3]

(ii) Identify the organelle labelled X and state one function of this organelle.
name .............................................................................................................................
function ..........................................................................................................................
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(a) Water is the main component of blood. Explain how the properties of water make it suitable as the main component of blood. ................................................................................................................................................
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(b) Fig. 2.1 is a diagram of the circulation in a mammal.
(i) Complete Fig. 2.1 by naming P and Q. Write your answers on Fig. 2.1. [1]
(ii) Describe the functions of P and Q. ................................................................................................................
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(iii) Explain why the mammalian circulation is described as a closed, double circulation. ................................................................................................................................................
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(c) Fig. 2.2 is a transmission electron micrograph of a cross-section of an arteriole. Blood flows from muscular arteries through arterioles into capillary networks. The lining of the arteriole is folded because the arteriole has constricted. This constriction causes the blood pressure to decrease from 12.7 kPa in the muscular artery to 2.7 kPa at the end of the arteriole.
(i) Explain why it is important that the pressure of blood decreases as it passes through arterioles. ................................................................................................................................................
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(ii) Compare the structure of a muscular artery with the structure of the arteriole shown in Fig. 2.2. ................................................................................................................................................
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(a) A class of students was studying the features of some human pathogens. One of the students constructed a flow chart to identify four different human pathogens. The student used information about the structure and mode of transmission of each of these pathogens.

Fig. 3.1 shows the partially completed flow chart.



Complete the flow chart in Fig. 3.1 by identifying:
• the modes of transmission
• the scientific names of the pathogens
• the name of one of the diseases.

(b) HIV has a nucleic acid core of RNA. The virus also contains the enzyme reverse transcriptase.

After HIV enters T-lymphocytes, reverse transcriptase catalyses the formation of DNA using activated DNA nucleotides with the viral RNA as a template.

Some drugs, such as tenofovir, have been developed to inhibit the action of reverse transcriptase.

The structure of tenofovir is similar to the structure of deoxyribose adenosine monophosphate, as shown in Fig. 3.2.



After tenofovir is absorbed into cells it is phosphorylated twice and can be used by reverse transcriptase in the synthesis of DNA.

When a tenofovir molecule is added to the DNA strand being synthesised, the process stops.

Suggest the mechanism of action of tenofovir to prevent the synthesis of DNA by reverse transcriptase. Use the information in Fig. 3.2 in your answer.

(c) Pre-exposure prophylaxis (PrEP) is the use of therapeutic drugs to prevent the replication of HIV in the body following infection. The drugs are taken by people who are at risk of becoming infected. Tenofovir is one of these therapeutic drugs.

In 2016, the United Nations (UN) set a global target of 3 million PrEP users by 2020.

Table 3.1 shows the number of people across the world who received a therapeutic drug for PrEP in each of the years between 2012 and 2019.

[Table_1]

(i) Calculate the percentage of people who received PrEP in 2019 as a percentage of the target set by the UN in 2016.
Give your answer to the nearest whole number.
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(ii) PrEP does not prevent transmission of HIV.
State and explain how health authorities can reduce the transmission of HIV.

(a) (i) Name the cells labelled A and B in Fig. 4.1.
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(ii) Describe how the tissue shown in Fig. 4.1 is adapted to its function in the gas exchange system.
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(b) (i) The structures labelled X in Fig. 4.1 have a characteristic internal appearance, as seen in Fig. 4.2. Describe the internal appearance of the structures labelled X.
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(ii) Explain how Fig. 4.2 shows that each of the structures labelled X are intracellular.
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(c) Stem cells are found in the lining of the bronchi. Describe the function of centrioles and explain how they are involved in the cell cycle of a stem cell.
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(a) Compare the results of the two species shown in Fig. 5.1. [3]

(b) Fig. 5.2 shows part of a plant of N. oleander.



Fig. 5.3 shows a cross-section of part of an oleander leaf.



Fig. 5.4 is a drawing of a high-power view of region N on Fig. 5.3.



State and explain two adaptations shown by the leaves of N. oleander that are visible in Fig. 5.3 and Fig. 5.4.

one adaptation visible in Fig. 5.3 ......................................................................................................

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explanation .............................................................................................................................................

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one adaptation visible in Fig. 5.4 ...................................................................................................

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explanation .............................................................................................................................................

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(a) (i) Explain how the structure of an antigen-binding site makes it specific to a particular antigen, as shown in Fig. 6.1.
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(ii) State the function of the hinge region of the antibody shown in Fig. 6.1.
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(iii) Antibodies can bind to membrane receptors on cells of the immune system, such as macrophages.
Suggest an advantage of antibodies binding to receptors on macrophages.
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Fig. 6.1 shows antigens bound to antigen-binding sites of an antibody molecule.

(b) It is estimated that the immune system of each person can make enough antibodies to bind to over $10^{12}$ different antigens.
When plasma cells make antibody molecules they combine the polypeptides produced by the expression of genes for heavy chains and the genes for light chains.
Research has shown that producing this very large number of antibodies is only possible by modifying the primary transcripts of the genes that code for heavy chains and the genes that code for light chains.
Suggest how this modification of the primary transcripts occurs in plasma cells.
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