AS & A Level Biology - 9700 Paper 2 2010 Summer Zone 3

Fig. 1.1 shows part of an animal cell viewed with an electron microscope.

(a) Name the structures A to C.
A ..............................................................................................................................
B ..............................................................................................................................
C ..............................................................................................................................[3]
(b) (i) State the function of structure C.
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(ii) Explain why structure C cannot be seen using a light microscope.
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(c) Suggest one disadvantage of the electron microscope compared to the light microscope for the study of cells.
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(d) Calculate the magnification of the image in Fig. 1.1.
Show your working and give your answer to the nearest whole number.
Answer = ...................................................[2]

Fig. 2.1 shows a diagram of a section through a human heart.


(a) State the name and function of the circled structure labelled X.
name ................................................................................................................
function ..............................................................................................................
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(b) Explain why the region labelled Y is thicker than the region labelled Z.
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(c) Cardiac muscle is described as myogenic as it naturally contracts and relaxes. With reference to the structures and tissues within the heart, describe how the cardiac cycle is initiated and coordinated.
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(a) With reference to Fig. 3.1, state
(i) which two levels of protein structure are shown
1. .................................................................................................................................
2. ................................................................................................................................. [2]
(ii) the name of the structures responsible for holding the two polypeptide chains together.
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(b) Many people with diabetes need to take regular injections of insulin. Insulin in the form shown in Fig. 3.1 cannot be taken by mouth as it would be hydrolysed by proteases in the gut.
In the space below, draw a diagram to show how the peptide bond between glutamine 15 and leucine 16 in polypeptide chain A could be hydrolysed and show the products of the hydrolysis.

Describe one method of controlling the spread of malaria by targeting its vector and explain its effect.

Explain why it has been difficult to develop an effective vaccine for malaria.

Another method of preventing malaria is to take drugs, such as chloroquine, but resistance to these drugs among certain species of the malarial parasite is increasing. New drugs are being developed. A laboratory investigation was carried out to determine the effect of a new drug on two strains of the malarial parasite Plasmodium falciparum. The results are shown in Fig. 4.1. With reference to Fig. 4.1, compare the effect of increasing the concentration of the drug on the chloroquine-resistant and chloroquine-sensitive strains of P. falciparum.

When a person becomes infected with the Human Immunodeficiency Virus (HIV) they become more susceptible to infection by the malarial parasite. Fig. 4.2 shows maps of Africa produced by the WHO. Fig. 4.2a shows the percentage population of each country testing positive for HIV Fig. 4.2b shows the percentage increase in malaria as a result of HIV infection in each country. (i) Explain how the information in Fig. 4.2 supports the idea that there is a link between HIV infection and susceptibility to malaria. [2] (ii) Suggest how HIV infection may have led to an increase in malarial infections in these countries. [2]

(a) Some bacteria, such as Rhizobium, carry out nitrogen fixation, which is an important process in the nitrogen cycle.
Explain what is meant by the term nitrogen fixation.
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(b) An important enzyme in the nitrogen cycle is urease, which catalyses the hydrolysis of urea to ammonia. This reaction is shown below:
$(NH_2)_2CO + H_2O \xrightarrow{\text{urease}} 2NH_3 + CO_2$
(i) State the name of this process in the nitrogen cycle.
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(ii) Explain the importance of this process in making nitrogen from animals available for uptake by plants.
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(c) The enzyme urease is known to be affected by competitive inhibitors. A student carried out an investigation to determine the percentage of urea hydrolysed by urease at various time intervals
• without any inhibitor
• with a competitive inhibitor.
The experiment was carried out in test tubes set up as follows:
Tube A – 1 cm³ of urease solution, 10 cm³ pH 7.5 buffer solution, 1 cm³ urea solution.
Tube B – 1 cm³ urease solution, 9 cm³ pH 7.5 buffer solution, 1 cm³ inhibitor, 1 cm³ urea solution.
Tube C – 1 cm³ water, 10 cm³ pH 7.5 buffer solution, 1 cm³ urea solution.
The results are shown in the table below.
[Table]
| time / min | percentage of urea remaining | | | Tube A | Tube B | Tube C |
| 0 | 100 | 100 | 100 |
| 5 | 55 | 99 | 100 |
| 10 | 29 | 98 | 100 |
| 15 | 14 | 96 | 100 |
| 20 | 8 | 95 | 100 |
| 25 | 5 | 92 | 100 |
| 30 | 3 | 90 | 100 |
(i) State how Tube C acts as a control for this investigation.
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(ii) Explain the difference in results between Tube A and Tube B.
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Various structures in the human gas exchange system are adapted in different ways to perform their specific functions.
(a) Complete the table below using a tick ✓ or cross ✗ in each box to show whether or not the structure shows the particular feature.
Two boxes have been completed for you.

[Table_1]

trachea
bronchus
bronchiole
alveolus


(b) State the two ways in which the concentration gradients of oxygen and carbon dioxide are maintained for efficient gas exchange.
1. ..........................................................
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2. ..........................................................
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(c) The alveoli in the lungs have elastic fibres in their walls.
(i) State one function of the elastic fibres.
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(ii) Name the medical condition caused by breakdown of the elastic fibres.
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(d) Cigarette smoke contains tar, a substance which has several harmful effects on the cells lining the gas exchange system.
Outline three of these effects.
1. ................................................................
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2. ................................................................
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3. ................................................................
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