AS & A Level Biology - 9700 Paper 2 2019 Winter Zone 2

Fig. 1.1 is a photomicrograph of a transverse section through the stem of creeping buttercup, Ranunculus repens.

(a) Draw one label line on Fig. 1.1 to indicate one precise location where phloem sieve tubes occur. [1]
(b) State the role of phloem sieve tubes. [2]
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(c) A good quality plan diagram of Fig. 1.1 will show only the tissues in the stem in their correct location and in the correct proportions.
(i) State the name of the tissue that forms the outer layer of the stem section of $R. repens$ in Fig. 1.1. [1]
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(ii) State the piece of equipment that can be used in the light microscope to work out the correct proportions of the tissues. [1]
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(d) Draw a diagram in the space provided to show the structure of a typical plant cell.
Label your diagram with the name of any structures that are found only in plant cells.
Do not label any structures that are also found in animal cells. [5]

(a) With reference to Fig. 2.1, list the two WHO regions where smokers are at the highest risk of developing diseases of the gas exchange or cardiovascular systems.
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(b) With reference to Fig. 2.1, explain why smoking a popular brand of cigarette from the AFRO region is more likely to increase the risk of blood clots forming than smoking a popular brand of cigarette from the EURO region.
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(c) One short-term effect of cigarette smoking is a decrease in the supply of oxygen to body tissues.
Describe and explain why cigarette smoking leads to a decrease in the supply of oxygen to body tissues.
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A red blood cell goes through a number of stages in the bone marrow before it is released into the circulation to carry out its role of oxygen transport.

Fig. 3.1 is a transmission electron micrograph of developing red blood cells in the bone marrow. Each cell is known as an erythroblast.


(a) Fig. 3.1 shows erythroblasts at a higher magnification than can be obtained using the light microscope.

Explain the advantages of using an electron microscope to obtain images such as that in Fig. 3.1.
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(b) Describe the differences between an erythroblast and a mature red blood cell.
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(c) The maturing red blood cell synthesises haemoglobin and other proteins.

(i) Complete Table 3.1 to:

• name three organelles (cell structures) that are involved in the synthesis of a fully functioning protein
• state one way in which the named organelle is involved in protein synthesis.

[Table_1]
[3]

(ii) Fig. 3.2 shows a reversible reaction that takes place within red blood cells.
$$\text{CO}_2 + \text{H}_2\text{O} \leftrightarrow \text{H}_2\text{CO}_3$$

Fig. 3.2

Name the protein that catalyses the reaction shown in Fig. 3.2.
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The \textit{SPTB} gene codes for a protein that provides stability and support to the cell surface membrane of the red blood cell.

Mutations in \textit{SPTB} result in red blood cells that are spherical in shape. This mutation leads to a disease known as spherocytosis type 2.

(d) Suggest why a person with spherocytosis type 2 has a reduced ability to take up oxygen in the pulmonary capillaries compared with a person who has normal red blood cells.
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(e) Increases in the water potential of the blood plasma have greater effects on red blood cells in people with spherocytosis type 2 than on normal red blood cells.

Compare and explain the effects of an \textbf{increase} in the water potential of blood plasma on spherocytosis type 2 red blood cells and normal red blood cells.
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(a) A polymer is a large molecule composed of smaller repeating molecules known as monomers.

Complete Table 4.1 to produce a summary of some named biological polymers.

[Table_4.1]
| polymer | constituent monomer | type of bond between monomers |
|------------|---------------------|------------------------------|
| amylose | glucose | |
| cellulose | glucose | |
| collagen | peptide | |
| DNA | DNA nucleotide | |
| glycogen | | glycosidic |

[4]

(b) Explain why an amylose molecule and a cellulose molecule have very different structures, even though they both have glucose as the constituent monomer.

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[2]

(c) Polymerisation of DNA nucleotides occurs during the semi-conservative replication of a molecule of DNA during interphase.

Describe the semi-conservative replication of DNA.

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[5]

(b) Name one of the four species of Plasmodium that can cause malaria. .......................................................................................................................................................

(c) The male Anopheles mosquito does not feed on blood and so does not act as a vector. Suggest why there is a difference in this feeding behaviour between male and female Anopheles.

(d) Research has shown that Plasmodium is not always transmitted to uninfected people. Two main reasons for this have been suggested. • The immune system of mosquitoes kills Plasmodium while it is still in the gut. • Bacteria living in the gut of mosquitoes compete with Plasmodium so it does not survive to continue its life cycle. A study was carried out to see if taking antibiotics affects the risk of transmission of malaria. Some observations and results of the study are summarised in Fig. 5.1. [Image] Suggest explanations for the results shown in Fig. 5.1 and comment on the importance of these results for doctors working in countries that have malaria and a high number of bacterial infections.

(e) After many years of intense research and development, WHO reported in 2016 that a pilot vaccination programme would be trialled between 2017 and 2020. The programme uses a vaccine acting against the most widespread species of Plasmodium. Explain the difficulties faced by researchers in developing a malaria vaccine.

Telomerase is an enzyme that is important in maintaining the telomeres that are located at the ends of chromosomes.
(a) Explain the importance of telomeres.
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(b) Suggest why telomerase is present in much higher quantities in stem cells and cancer cells than in other cell types.
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(c) Studies suggest that telomerase is a flexible molecule when binding its substrate. The active site changes its shape slightly to allow the formation of the enzyme-substrate complex.
Name the theory that describes this mode of enzyme action.
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(d) An investigation was carried out into the effect of substrate concentration on the activity of telomerase.
The results are shown in Fig. 6.1.

With reference to Fig. 6.1, explain the difference in the rates of reaction obtained for telomerase at a substrate concentration of $0.2\text{ }\mu\text{mol dm}^{-3}$ compared with a substrate concentration of $1.6\text{ }\mu\text{mol dm}^{-3}$.
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