AS & A Level Biology - 9700 Paper 2 2017 Winter Zone 2

(a) Fig. 1.1 is an image of the root tip of Allium as observed using a microscope with a low-power objective lens.



State which region, B, C, or D, should be chosen in order to observe the highest proportion of cells in stages of mitosis. ....................................................................................................................................................................................[1]

(b) (i) Draw a labelled diagram to show the structure of a chromosome at late prophase of mitosis.[3]

(ii) Describe the behaviour of the nuclear envelope during mitosis.
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Triglycerides and phospholipids are types of lipid.
Fig. 2.1 shows the structure of one type of phospholipid known as phosphatidylcholine.
F1 and F2 are fatty acid residues.

(a) Phospholipase is an enzyme that can break down phospholipids. This enzyme is found in the venom of some insects, such as bees.
Bee venom can destroy red blood cells, a condition known as haemolysis.
Suggest how bee venom destroys red blood cells.
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(b) Compare, stating similarities and differences, the structure of the phosphatidylcholine shown in Fig. 2.1 with the structure of a triglyceride molecule.
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(c) Name and describe the cell structure in which the synthesis of triglycerides and other lipids takes place.
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(a) State the term used to describe an enzyme that functions within the cell. .................................................................................................................................................................[1]

(b) The rates of reaction of two different hydrolytic enzymes, enzyme G and enzyme H, were measured at different substrate concentrations. The results are shown in Fig. 3.1. The two enzymes have different values of the Michaelis–Menten constant ($K_{m}$).
[Image_1: Fig. 3.1] (i) The $K_{m}$ value of enzyme G is 5 m mol dm$^{-3}$. Use Fig. 3.1 to derive the $K_{m}$ value for enzyme H. Show your working. ................................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. .................................................................................................................................................................[2] (ii) With reference to Fig. 3.1, explain how the values of $K_{m}$ for these enzymes provide information about the relationship between the enzyme and their substrates. ................................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. .................................................................................................................................................................[2]

(c) Name the vesicles in the cell that contain hydrolytic enzymes. .................................................................................................................................................................[1]

(d) The cell has internal chemical messengers that signal when an old or damaged mitochondrion should be broken down. Suggest one feature involving mitochondrial structure or function that could lead to the release of these internal signals. ................................................................................................................................................................. .................................................................................................................................................................[1]

(e) Glucocerebrosidase is an enzyme synthesised by macrophages to hydrolyse glucocerebroside, a glycolipid found in cell membranes. The $GBA$ gene codes for glucocerebrosidase. There are a number of different mutations of the $GBA$ gene. Some mutations result in a single amino acid change in the enzyme molecule produced, and this causes a disorder known as Gaucher’s disease. Two of these mutations, at different positions in the $GBA$ gene, are shown in Table 3.1. [Table_1: Table 3.1] With reference to Table 3.1, - outline how a mutation leads to a single amino acid change in the enzyme glucocerebrosidase and - suggest why the two different amino acid changes, Asn to Ser and Leu to Pro, will result in differences in the tertiary structure of the enzyme. ................................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. ................................................................................................................................................................. .................................................................................................................................................................[5]

(a) Explain how a loss of chloride ions and sodium ions from the intestinal epithelial cell will cause a loss of water from the cell.

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(b) The main treatment for cholera is oral rehydration therapy (ORT) using oral rehydration salts (ORS). This involves drinking a solution of electrolytes (mineral ions) and glucose.

Fig. 4.2 summarises the movement of glucose and sodium ions across an intestinal epithelial cell.

Fig. 4.2 includes three different types of cell surface membrane proteins:
• SGLT1 is a cotransporter protein
• GLUT2 and Na⁺/K⁺ pump are two types of carrier protein.



The first rehydrating solution developed for the treatment of cholera did not contain glucose. Using ORS, patients absorb a higher concentration of sodium ions and there is an increase in water uptake.

With reference to Fig. 4.2:
• outline the transport mechanisms that result in the movement of glucose and sodium ions across the intestinal epithelial cell
• suggest how the movement of glucose and sodium ions increases water uptake by the cell.

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(c) In severe cases of cholera, the rehydrating solution is given intravenously, as a drip directly into a vein.

Suggest one reason why the rehydrating solution is given as a drip directly into a vein rather than into an artery.

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(d) Tetracycline binds to a ribosomal subunit.

Suggest what effect this will have on the metabolism of V. cholerae.

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(e) A study was carried out to compare the effectiveness of the antibiotic tetracycline in the treatment of 118 patients with cholera. The patients were divided into four different treatment groups:

• Group A, given one dose of 1 g tetracycline
• Group B, given one dose of 2 g tetracycline
• Group C, given a multiple dose (one dose of 500 mg tetracycline every 6 hours for 24 hours)
• Group D, no antibiotic given.

Following treatment, the volume of diarrhoea collected from each patient was measured every 16 hours for 128 hours. Fig. 4.3 shows the mean volume collected for each group.



(i) Describe the trends shown in Fig. 4.3.

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(ii) Explain whether the results support, or do not support, treating very severe cases of cholera with tetracycline.

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(f) Some strains of V. cholerae are antibiotic resistant.

Explain why this means that medical practitioners prefer to treat cholera with a single dose of antibiotic, rather than a multiple dose of the same antibiotic.

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(g) Most people who have recovered from cholera rarely become ill again from the disease. In these people, antibodies have been identified that will bind either to the cholera toxin, or to the bacterial flagellum, or to the main bacterial cell.

Explain why the antibodies are different, each one specific to its target.

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(h) Evidence suggests that newborn babies of mothers who have had cholera have immunity to the disease.

State precisely the type of immunity these babies are likely to have.

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(a) Descriptions A, B and C relate to the movement of water from the soil to the xylem in roots.
State the correct term to match each of the descriptions A, B and C.
A The specialised root epidermal cell that provides a large surface area for the uptake of water from the soil.
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B The band of suberin in the cell walls of the endodermis that prevents the movement of water by the apoplastic pathway.
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C The cell structures that allow water to pass from one cell to the next as part of the symplastic pathway.
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(b) Explain, with reference to the structure of xylem vessel elements, why water does not take a symplastic pathway in the xylem to the leaves.
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(c) Explain why the rate of movement of water in the xylem may slow down at night.
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Fig. 6.1 is a diagram of a vertical section through the mammalian heart. The labels Q to X represent valves and blood vessels of the heart.

(a) (i) State which label represents the valve that prevents the backflow of blood from the aorta into the ventricle.
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(ii) Name the blood vessel that carries oxygenated blood from the lungs to the heart and state which label represents this blood vessel.

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(b) State precisely where the sinoatrial node is located.
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(c) Explain the role of the atrioventricular node in the coordination of heart action.
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