AS & A Level Biology - 9700 Paper 2 2023 Summer Zone 1

(a) (i) State the evidence from Fig. 1.1 that shows that the cell is from the stem of S. pectinata and not from the mesophyll of a leaf.
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(ii) Complete each row in Table 1.1 to identify a cell structure shown in Fig. 1.1 that carries out the function listed.

Table 1.1

function	name of cell structure	letter on Fig. 1.1
gas exchange
production of subunits of ribosomes
active transport of ions
aerobic respiration

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(b) Plant vacuoles develop when vesicles fuse together. The vacuoles increase in size as more vesicles fuse.

Fig. 1.2 shows the movement of vesicles within a plant cell during the development of a vacuole.


(i) Name the process that is occurring at X.
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(ii) Some of the vesicles formed by the Golgi body pass to the vacuole. These vesicles contain proteins that have been folded correctly and some that have not folded into their correct shapes. The proteins that have not folded correctly pass to the vacuole where they are broken down.

Explain how proteins that have not folded correctly are broken down in the vacuole.
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(c) Small vacuoles in S. pectinata may have roles similar to lysosomes in animal cells.

Describe the role of lysosomes in animal cells in defence against pathogens.
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(a) Describe three ways, visible in Fig. 2.1, in which the molecule of glycogen differs from the molecule of cellulose.

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(b) Glycogen is found in the form of granules in mammalian liver and muscle cells. Fig. 2.2 is a diagram of part of a molecule of glycogen isolated from a glycogen granule.



Explain how the structure of glycogen is related to its function in cells.

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(c) Explain how the arrangement of cellulose molecules in plant cell walls is related to their function.

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Fig. 3.1 shows some fruits (grapes) of the grapevine, Vitis vinifera.



Fig. 3.1
Sucrose is transported in the phloem of the grapevine to the fruits. In the fruits, sucrose is hydrolysed by the enzyme sucrase, which is found in cell walls. The glucose and fructose produced by the hydrolysis of sucrose pass through membrane proteins, known as hexose transporters, into the cytoplasm of the fruit cells.

(a) State why membrane proteins are required for the movement of molecules, such as glucose, across cell surface membranes into cells.
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Researchers investigated one type of hexose transporter, known as VvHT1, which is found in the fruit cells of V. vinifera. They used a mutant strain of yeast that has very few hexose transporters in its cell surface membranes to investigate the properties of VvHT1. The researchers inserted molecules of VvHT1 into the cell surface membranes of the mutant strain of yeast.

• Equal volumes of mutant yeast cells with VvHT1 were kept in eight different concentrations of glucose solution.
• The rate of uptake of glucose by the yeast cells in each solution was determined.
• All the solutions were kept at the same temperature and pH.

The results are shown in Fig. 3.2.



Fig. 3.2
(b) (i) The researchers concluded that VvHT1 is responsible for the facilitated diffusion of glucose into the cells.
Explain how the results in Fig. 3.2 provide evidence to support this conclusion.
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(ii) The researchers thought that grapevines could be modified to have more hexose transporters to increase the size and quality of grapes.
Explain why increasing the number of hexose transporters could be commercially important to growers of grapevines.
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Fig. 3.3 is a diagram of a protein in the cell surface membrane of a macrophage from a mouse.
Macrophages use these proteins in antigen presentation. Non-self antigens bind to the proteins and are involved in the activation of specific T-lymphocytes during the immune response.



Fig. 3.3
(c) (i) State what is meant by a non-self antigen.
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(ii) Some pathogens enter human cells. Macrophages partially digest these pathogens and present antigens to T-lymphocytes during immune responses.
With reference to Fig. 3.3, explain how T-lymphocytes respond to infection by a specific type of pathogen.
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The gene for the enzyme catalase is on chromosome 11 in humans.

(a) Explain the meaning of the term gene.

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(b) Two enzymes, DNA polymerase and DNA ligase, are involved in the replication of DNA.

Fig. 4.1 shows the replication of part of human chromosome 11 by DNA polymerase. The arrows show the direction of synthesis of the new polynucleotides by DNA polymerase.

[Image_1: Diagram showing DNA polymerase action with arrows indicating synthesis direction]

(i) Describe the roles of DNA polymerase and DNA ligase in the replication of DNA.

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(ii) State the name of the stage of interphase in the cell cycle when DNA replication occurs.

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(c) Fig. 4.2 is a diagram of chromosome 11 at metaphase of mitosis.

[Image_2: Diagram showing chromosome 11 with labels A and B]

(i) State the names and functions of structures A and B.

structure A ................................................................................................................
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structure B ................................................................................................................
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(ii) Complete Fig. 4.3 to show what happens to chromosome 11 in anaphase, so that the daughter nuclei are genetically identical.

[Image_3: Incomplete diagram showing cell with chromosomes]

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Fig. 5.1 is a longitudinal section of a capillary in muscle tissue as viewed with a transmission electron microscope.

(a) State the evidence, visible in Fig. 5.1, that identifies the cells inside the capillary as red blood cells.
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(b) Explain how the structure of the capillary wall is related to its functions.
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(c) Fig. 5.2 is a diagram showing some of the events that occur as blood flows through a capillary in a respiring tissue.

(i) An increase in respiration results in an increase in the carbon dioxide concentration in the blood and the release of more oxygen from red blood cells to tissues.
Explain how an increase in carbon dioxide in the blood leads to the release of more oxygen from red blood cells.
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(ii) Chloride ions are a constituent of blood plasma. The concentration of chloride ions in the plasma of deoxygenated blood is between 2–4 mmol dm$^{-3}$ lower than in the plasma of oxygenated blood.
Explain why the concentration of chloride ions in the blood plasma of deoxygenated blood is lower than in the plasma of oxygenated blood.
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Fig. 6.1 is a diagram showing the passage of water through the tissues of a flowering plant from the soil to the atmosphere. The arrows show the direction of water movement.

(a) The structure labelled X is part of the symplast pathway. State the name of structure X.
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(b) The structure labelled Y in the cell wall is a barrier to the apoplast pathway. State the name of structure Y.
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(c) With reference to Fig. 6.1, complete the statements about the movement of water in the flowering plant.
Water moves from the soil solution to the cytoplasm of root hair cells by ...........................
Water moves from the xylem in the root to the leaf by ........................................
Water moves from mesophyll cell walls to intercellular air spaces by ..................................
Water vapour moves from intercellular air spaces to the atmosphere outside the leaf by ................................ [4]