AS & A Level Biology - 9700 Paper 4 2010 Summer Zone 2

The American crocodile, Crocodylus acutus, was classified as an endangered species by the USA in 1975. It is found in estuarine regions of southern Florida.
Fig. 1.1 shows an American crocodile.

Fig. 1.1
The salinity of the water was thought to play a part in the distribution of the American crocodile.
Fig. 1.2 shows the number of American crocodile nest sites in areas with water of varying salinity in southern Florida.

Fig. 1.2
(a) Describe the results shown in Fig. 1.2.
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(b) Much conservation work has been done in the Everglades National Park in Florida, which is a large wetland area. As a result the number of nest sites has increased from 8 in 1975 to 31 in 2000. This has led to a rise in the number of crocodiles.
(i) Calculate the percentage increase in nest sites between 1975 and 2000.
Show your working.
answer ...................................................... % [2]
(ii) Suggest two reasons why the population of crocodiles in the Everglades National Park has increased.
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Follicle stimulating hormone (FSH) and luteinising hormone (LH) both consist of two polypeptide chains, the α and β chains.
• The α chains of FSH and LH are identical.
• The β chain of FSH has 111 amino acids and that of LH 121 amino acids.
• FSH and LH bind to different receptors in the cell surface membranes of their target cells.
• This binding leads to steroid synthesis by the target cells.

(a) Explain why FSH does not bind to a LH receptor.
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(b) Name the cells of a human female that carry
(i) FSH receptors .........................................................................................................
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(ii) LH receptors ..............................................................................................................
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(c) Describe what happens when FSH binds to its receptors on its target cells.
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(a) With reference to Fig. 3.1, explain the effect of penicillin V on bacterium A. [3]

(b) With reference to Fig. 3.1 and Fig. 3.2
(i) describe how the outer layers of bacterium B differ from those of bacterium A [2]
(ii) explain the different effects of penicillin V on bacteria A and B [2]
(iii) suggest how the synthetic penicillin, carboxypenicillin, is able to affect the growth of bacterium B. [2]

(c) Distinguish between batch culture and continuous culture of microorganisms. [3]

(d) Explain why batch culture rather than continuous culture is used in the production of penicillin. [3]

Cereal crops, such as sorghum and rice, are a major source of nutrients all over the world.
(a) Explain why cereal crops are important components of many people’s diets.
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(b) Alpha amylase is an enzyme produced in germinating seeds, where it hydrolyses starch. Fig. 4.1 shows the effect of temperature on alpha amylase in germinating seeds of sorghum and rice.



(i) Name the part of the seed that contains starch.
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(ii) With reference to Fig. 4.1, compare the effects of temperature on alpha amylase in sorghum and rice.
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(iii) With reference to the types of bonding in proteins, suggest how differences in the tertiary structure of alpha amylase in rice and sorghum could explain the differences in their activities shown in Fig. 4.1.
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(c) Sorghum does not grow well at low temperatures. An investigation was carried out into the response of sorghum to low temperatures at different light intensities.
• Sorghum plants were kept at 25°C in a light intensity of 215Wm⁻² for several weeks, and then at 10°C for three days.
• The temperature was then increased to 25°C again for seven days.
• The investigation was repeated at light intensities of 170Wm⁻² and 50Wm⁻².
• Day length and carbon dioxide concentration were kept constant throughout.

The uptake of carbon dioxide, as mg $CO_2$ absorbed per gram of leaf dry mass, was measured
• at 25°C before cooling
• at on each of the three days at 10°C
• for seven days at 25°C.

The results are shown in Table 4.1.

[Table_1]

With reference to Table 4.1
(i) describe and explain the effect of light intensity on the rate of carbon dioxide uptake before cooling
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(ii) describe the effect of light intensity on the ability of sorghum plants to survive cooling.
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The fruitfly, _Drosophila_, has many different species. Three of these species, _Drosophila pseudoobscura_, _D. persimilis_ and _D. miranda_, are thought to be closely related.

Samples of these three species were collected from the western United States of America. Fig. 5.1 shows where these species naturally occur.


The base sequences of four regions of DNA of each species were sequenced. The divergence of these base sequences in _D. pseudoobscura_ and _D. persimilis_ from the sequences in _D. miranda_ was calculated. The results are shown in Table 5.1.
[Table_1]

(a) With reference to Table 5.1, describe the evidence that _D. miranda_ may be more closely related to _D. persimilis_ than to _D. pseudoobscura_.
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(b) Suggest why there is more divergence in some regions of DNA than in others.
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(c) The area where _D. pseudoobscura_ is found is separated from the areas where the other two species are found by a high range of mountains.
Explain how the species _D. pseudoobscura_ could have evolved from a population of _D. miranda_.
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In humans a rare, sex-linked, recessive allele results in a change in the shape of the iris in the eye. This condition is known as cleft iris (CI).
(a) Explain what is meant by the term $sex \ linkage$.
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(b) Using suitable symbols complete the genetic diagram below.

Key to symbols
recessive allele ..........................................
dominant allele ..........................................

parental phenotypes male with CI       X       normal female
parental phenotypes                         
gametes                                              [Image]

offspring genotypes ..................................................................................................................................................
offspring phenotypes .................................................................................................................................................. [5]

(c) A woman who is heterozygous for CI becomes pregnant by a man with a normal iris.
State the probability that their child will have CI.
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Fig. 7.1 is an outline diagram of the Krebs cycle. A two carbon acetyl group enters the cycle by combining with a molecule of oxaloacetate. A molecule of citrate is formed which is decarboxylated and dehydrogenated to regenerate the oxaloacetate. The letters P to V are steps in the cycle.


(a) (i) Explain what is meant by the following terms:
decarboxylation ......................................................................................................................
dehydrogenation ......................................................................................................................
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(ii) Using the letters in the cycle, state where decarboxylation is taking place.
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(b) Fig. 7.1 shows that fatty acids can be converted into acetyl coenzyme A (acetyl CoA) by a process known as oxidation. Both this process and the Krebs cycle require NAD. The hydrogen atoms released reduce the NAD molecules.
(i) State the number of reduced NAD molecules that are formed in the Krebs cycle from one acetyl group that enters the cycle from acetyl CoA.
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(ii) State where the reduced NAD molecules are re-oxidised and describe what happens to the hydrogen atoms.
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(c) Describe the role of reduced NAD in respiring yeast cells in the absence of oxygen.
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(d) Describe how the production of lactate in muscle tissue differs from anaerobic respiration in yeast.
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Gene technology has many uses including the production of substances such as insulin.

(a) (i) Outline what is meant by gene technology.
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(ii) Explain why genes for enzymes that produce fluorescent substances are used as markers in gene technology.
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(b) There is much controversy throughout the world regarding the use of genetically modified (GM) crops.

(i) Suggest two advantages of growing GM rice with an enhanced vitamin A content.
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(ii) Suggest two disadvantages of growing GM crops.
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(a) Describe the structure of photosystems and explain how a photosystem functions in cyclic photophosphorylation. [8]
(b) Explain briefly how reduced NADP is formed in the light-dependent stage and how it is used in the light-independent stage. [7]

(a) Describe the structure of a myelinated sensory neurone. [7]
(b) Explain how an action potential is transmitted along a sensory neurone. [8]
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