AS & A Level Biology - 9700 Paper 4 2014 Winter Zone 3

(a) (i) In people without PKU, excess phenylalanine is converted to the amino acid tyrosine by the enzyme phenylalanine hydroxylase (PAH). One of the mutations that can lead to PKU is caused by a base substitution in the gene coding for PAH. This results in the replacement of the amino acid arginine by the amino acid glutamine.

Table 1.1 shows the triplet base codes for arginine and glutamine.

Table 1.1

[Table_1]

Using the information in Table 1.1, explain how a single base substitution can replace arginine with glutamine in PAH.
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(ii) Suggest the consequence to the structure of PAH as a result of a single base substitution in its gene.
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(b) For some genetic diseases, the proportion of individuals that have the disease can vary in different parts of the world. Sometimes this is due to different environmental conditions. The number of cases of PKU is approximately ten times higher in Europe than in Sub-Saharan Africa.

• Individuals who are carriers of the recessive allele for PKU are more resistant to ochratoxin A, produced by a fungus found on contaminated grain products.
• Ochratoxin A has been linked to a form of renal cancer.
• The fungi that produce ochratoxin A are less common in dry regions such as Sub-Saharan Africa.

Suggest and explain the mechanism which has resulted in the different number of cases of PKU in European and Sub-Saharan populations.
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The endangered Californian condor, Gymnogyps californianus, is the largest flying bird in North America. Condors feed on dead bodies of large mammals, such as cattle and deer. Fig. 2.1 shows the Californian condor.



The population of these condors fell to just 22 in 1982 and this led to the California Condor Recovery Program (CCRP), a captive breeding programme, being set up in different zoos in the United States and Mexico. Owing to the success of the captive breeding programme there are now over 300 condors. Many of these have been released as part of the programme.

(a) Outline the advantages of captive breeding programmes such as CCRP. [4]

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(b) Suggest why animals in captive breeding programmes may not always breed successfully. [2]

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(c) When animals that have been bred in captivity are released, their survival rate is low.

Suggest two reasons why many of these animals are unable to survive in the wild. [2]

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(d) Bullets containing lead are commonly used by hunters. Hunting for pleasure means that hunters often leave the killed animals, such as deer, bears and antelopes, in the area where they have been shot.

Suggest why this is a threat, rather than an advantage, to the Californian condor. [1]

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(a) The diagram outlines how a gene coding for human insulin is produced by genetic engineering techniques.

step 1: mRNA for human insulin gene isolated
X
step 2: single strand of complementary DNA (cDNA) produced
Y
step 3: single-stranded DNA made into double-stranded DNA
step 4: additional non-coding DNA added

Fig. 3.1

(i) Name the enzymes X and Y.

X ............................................
Y ............................................ [2]

(ii) Explain why the starting point in this procedure is mRNA.

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(b) Suggest why some methods of manufacturing genetically engineered insulin use eukaryotic yeast cells rather than prokaryotic bacterial cells.

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(c) State three advantages of using human insulin produced by genetic engineering.

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(a) All living organisms require a continuous supply of energy.
Outline the need for energy in living organisms.
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(b) Fig. 4.1 is a diagram of ATP.

(i) Name A and B.
A ............................................
B ............................................
(ii) Describe how the structure of ATP is related to its role as energy currency.
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(c) Thermus thermophilus is a bacterium found in geothermal environments, such as hot springs.
The bacterium respires aerobically, even though at high temperatures the solubility of oxygen in water is low.
(i) Explain how aerobic respiration may be affected by a decrease in oxygen availability.
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(ii) One strain of T. thermophilus, HB8, has an enzyme, nitrate reductase, which allows nitrate to be used as the final electron acceptor in the electron transport chain (ETC).
Suggest an advantage to the bacterium of this adaptation.
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(d) A mutant strain of HB8 (HB8 mutant) was made by adding an insertion mutation to the gene that codes for the enzyme nitrate reductase.
An investigation was carried out into population growth of HB8 and of HB8 mutant in aerobic and in anaerobic conditions. In each experiment, a flask containing bacterial culture medium was incubated. Table 4.1 shows how the flasks were set up.
The number of bacteria of each strain per cm³ was calculated after 20 hours.
[Table_1]
The results are shown in Fig. 4.2.

(i) Compare the growth of the two strains of bacteria in aerobic and anaerobic conditions in separate cultures.
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(ii) Compare the growth of the two strains of bacteria in aerobic and anaerobic conditions in mixed cultures.
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(iii) Suggest an explanation for the results shown in flask 6.
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(a) The pollutants in waste water from the textile industry may include azo-dyes, which give colour to textiles. Azo-dyes are organic pollutants that can be carcinogenic.

White-rot fungi are useful for the treatment of environmental pollution as they produce extracellular enzymes that are able to break down a number of organic pollutants, such as azo-dyes.

The extracellular enzymes produced by white-rot fungi are primary metabolites that are mass produced by continuous culture.

(i) Outline the main operating conditions of continuous culture.
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(ii) State three advantages of using continuous culture and not batch culture, for the mass production of these enzymes.
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(b) (i) The ability of the white-rot fungi to break down azo-dyes was investigated. A suspension of the intact fungal cells was added to water contaminated with various concentrations of an azo-dye.

The results are shown in Table 5.1.

[Table_1]

Describe the results shown in Table 5.1.
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(b) (ii) When a similar experiment was performed using the free enzymes from the white-rot fungal cells, all concentrations of azo-dye shown in Table 5.1 were broken down within 12 hours.

Suggest why free enzymes break down the azo-dye more quickly than intact white-rot fungal cells.
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(c) These extracellular enzymes may be immobilised on an inert support.

Outline the advantages of using immobilised enzymes in the treatment of textile waste water.
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(a) The shoots are usually cooked and then eaten hot or cold. Asparagus contains many mineral ions which have important roles in the bodies of mammals.
Complete Table 6.1 to summarise some of these roles.

Table 6.1

| ion | role | type of cell |
|-----|------------------------------|--------------------|
| Fe^{2+} | .........................................
........................................ | red blood cell |
| Na^{+} | co-transport in the kidney | ..........................................
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| Ca^{2+} | .........................................
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(b) When asparagus is digested, some of the compounds produced pass quickly into the urine to give a characteristic odour that only 22\% of people can detect. The compounds bind to specific chemoreceptors in the nasal cavities of these people.
Complete the sentence below by using the most appropriate scientific term.
The chemoreceptors will send impulses to the brain only if the ........................................ potential is reached. [1]

(c) Outline how molecules, such as the compounds from the digestion of asparagus, pass from the blood to become part of the glomerular filtrate.
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The ABO blood grouping system in humans is determined by a single gene with three alleles: $I^A$, $I^B$ and $I^0$.

(a) Distinguish between the terms gene and allele.

gene ......................................................................................................................................................
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allele .................................................................................................................................................................
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(b) Fig. 7.1 shows a pedigree diagram of the inheritance of the ABO blood group system. The blood group of some of the individuals is given in the pedigree.



Use the information in Fig. 7.1 and the genetic symbols $I^A$, $I^B$ and $I^0$, to complete the table.

[Table_1]

individual | phenotype | genotype
1
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[4]

Fig. 8.1 is a diagram of a palisade cell from a leaf.

Using label lines and the letters X, Y and Z, identify a structure in Fig. 8.1 that:
• contains RuBP – X
• is fully permeable – Y
• is made mainly of phospholipids – Z

(b) An experiment was carried out to investigate the effect of light intensity on the rate of photosynthesis in an aquatic plant using the apparatus shown in Fig. 8.2.

As photosynthesis took place, the oxygen produced formed a bubble of gas which moved along the scale in the capillary tube. The distance moved by the bubble in a fixed period of time was used to calculate the rate of photosynthesis.
The light intensity was varied by altering the distance, d, between the lamp and the photosynthesising plant.
The results are shown in Table 8.1.
[Table_1]
i) Using the data in Table 8.1, draw a graph to show the relationship between light intensity and the rate of photosynthesis. [3]
ii) Explain the shape of the graph you have drawn, with reference to limiting factors. [3]

(c) Fig. 8.3 shows the absorption spectra of the photosynthetic pigments of a flowering plant.

i) Name the accessory pigment(s) shown in Fig. 8.3. [1]
ii) Outline the role of the accessory pigments in photosynthesis. [3]
iii) Very little light of wavelength 550 nm is absorbed by the photosynthetic pigments. State what happens to most of this light. [1]
iv) A graph can also be drawn to show the relationship between the wavelength of light and the rate of photosynthesis. State the name of this type of graph. [1]

(a) Describe how the vitamin A content of rice can be enhanced by genetic modification. [8]
(b) Outline the disadvantages of using plants that have been genetically modified. [7]

(a) Outline the technique of in-vitro fertilisation (IVF). [8]
(b) Discuss the ethical implications of IVF. [7]