AS & A Level Biology - 9700 Paper 2 2012 Summer Zone 2

One role of the cell surface membrane is to control the entry and exit of substances.
(a) Complete Table 1.1 to show the transport mechanisms across cell surface membranes and examples of materials transported.

Table 1.1
[Table_1: A table listing transport mechanisms across the cell surface membrane and examples of materials transported. Entries include:
- transport mechanism across cell surface membrane: active transport, facilitated diffusion, exocytosis, osmosis.
- example of material transported across membrane: sodium ions, oxygen molecules, bacteria (for exocytosis: mucin for mucus).]
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(b) Each transport mechanism across cell surface membranes has a characteristic set of features.
In each of the boxes below, state one example of a transport mechanism that matches the pathway shown.
[Image_1: A flowchart showing pathways with nodes 'specific transport protein involved' leading to passive, active, etc.]
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[Total: 6]

Fig. 2.1 is a transmission electron micrograph of a plasma cell. Plasma cells are antibody-secreting cells that are formed from B-lymphocytes.

[Image_1: Fig. 2.1]

(a) Complete Table 2.1 to:
• name in full, structures A, B and C
• outline how each structure functions to contribute to the specific role of the plasma cell.

[Table_1: Table 2.1]

structure | name of structure | function of structure within plasma cell
A | |
B | |
C | |

[6 marks]

(b) An activated B-lymphocyte divides repeatedly by mitosis to produce many identical plasma cells.

(i) Explain why it is important that many identical plasma cells are produced.
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(ii) B-lymphocytes have centrioles and a spindle that can be observed during mitosis.

Describe and explain how the behaviour of the centrioles and spindle of a cell dividing by mitosis is associated with the behaviour of the chromosomes.

You may use the space below for labelled diagrams.
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(a) With reference to the structure of a leaf, explain the difference between evaporation and transpiration. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [4]
(b) Apple, $Pyrus \ malus$, sour cherry, $Prunus \ cerasus$, and peach, $Prunus \ persica$, are dicotyledonous trees that are of importance to commercial growers for the fruit that they produce.
A student chose a small area of land where all three species of fruit tree were growing. Leaf samples were removed and, using a microscope, the mean number of stomata per square millimetre was estimated for each species.
The rate of transpiration of each species was then measured on each of three separate occasions. The student performed the investigation outside where the trees were located and recorded the weather conditions on each day.
The mean transpiration rate was calculated per unit area of leaf.
The results are shown in Table 3.1.
[Table_1]
(i) With reference to Table 3.1, describe and explain the results of the investigation. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [4]
(ii) The mean transpiration rate of each species was calculated over a 24 hour period. Describe how the transpiration rate during the night would differ from the transpiration rate during the day. Explain your answer. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [3]
(iii) Suggest which of the three species of fruit tree has been described as 'drought-resistant' and would be economical to grow in areas where water is scarce. ................................................................................................................................................ [1]
(c) Many fruits are thought to have beneficial health effects. Sour cherries and peaches may contribute to improved health for tobacco smokers.
Read the following statements. For each, explain how the fruit contributes to protecting smokers from smoking-related diseases.
(i) Glutathione is a protein known to be involved in the repair of damaged DNA. Regularly eating sour cherries increases the level of glutathione in the body. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [2]
(ii) A diet rich in peaches can help reduce inflammation of the bronchi and bronchioles. ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ ................................................................................................................................................ [2]

DNA and RNA are important biological molecules that are involved in the production of polypeptides.

(a) Fig. 4.1 shows two nucleotides joined by a covalent bond.

(i) Fig. 4.1 represents part of a DNA molecule, not part of an RNA molecule. Explain why.
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(ii) Name the covalent bond between the two nucleotides.
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(iii) Name component X.
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(b) Outline the role of transfer RNA (tRNA) in the production of a polypeptide.
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(c) Describe how a peptide bond is formed between two amino acids during polypeptide production.
You may use the space below to help with your answer.
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(a) State the name of the organism that causes cholera.
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(b) NQR is an important respiratory enzyme located in the cell surface membrane of the bacterium that causes cholera.
A student suggested that an inhibitor of the enzyme NQR could be used as a drug in the prevention and control of cholera.
Suggest and explain how this inhibitor would function.
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(c) Table 5.1 shows the statistics for cholera reported to the World Health Organization (WHO) in four regions of the world in 2008.

!(Table 5.1)
| region | number of cases | number of deaths | fatality rate / % |
|---------------|-----------------|------------------|------------------|
| Africa | 179323 | 5074 | 2.83 |
| Asia | 10778 | 69 | 0.64 |
| Europe | 22 | 0 | 0.00 |
| North America | 7 | 0 | 0.00 |
| Total | 190130 | 5143 | |

(i) Calculate the total cholera fatality rate for 2008.
Show your working.
answer ....................................... % [2]
(ii) Apart from differences in total population size in each of the regions, suggest explanations for the differences shown in Table 5.1.
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Microorganisms play an important role in the cycling of nitrogen in ecosystems.

Fig. 6.1 is a diagram of a nitrogen cycle.


(a) Read the information below about four different species of soil bacteria. In the box provided, write the appropriate letter that matches each microorganism to its corresponding stage in the nitrogen cycle in Fig. 6.1.

• Nitrosomonas europaea is an ammonia-oxidising bacterium.
• Bacillus cereus is a denitrifying bacterium.
• Azospirillum lipoferum lives in the roots of some cereals and grasses and supplies fixed nitrogen to plants.
• Streptomyces coelicolor is a bacterium that secretes powerful hydrolases to break down compounds such as proteins and cellulose.

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(b) Some fungi form beneficial associations with plant roots. They enable the plant to increase the uptake of nutrients, such as phosphates, which are not readily available to the plants from the soil.
Suggest how increasing phosphate ion uptake will lead to increased plant growth.
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