AS & A Level Biology - 9700 Paper 4 2012 Winter Zone 1

(a) Nerve impulses have to cross synapses. The events that enable a nerve impulse to cross a cholinergic synapse are listed in Table 1.1.
The events are not listed in the correct order.

Table 1.1

[Table_1]

Complete Table 1.2 to show the events in the correct order.
Two of the events have been done for you.

Table 1.2

[Table_2]

(b) Synapses have many roles in nervous coordination in mammals.
(i) Explain how synapses ensure one-way transmission of nerve impulses.
....................................................................................................................................................................................................................................................
....................................................................................................................................................................................................................................................[2]

(ii) In a learning activity, it is believed that the number of synapses between brain neurones increases. Suggest the advantages of this increased number of synapses.
....................................................................................................................................................................................................................................................
....................................................................................................................................................................................................................................................
....................................................................................................................................................................................................................................................
....................................................................................................................................................................................................................................................
....................................................................................................................................................................................................................................................[2]

(a) Penicillin belongs to a group of antibiotics known as $\beta$ lactams, which all act in the same way on bacteria.

Describe how penicillin kills non-resistant bacteria.
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
................................................................................................................................................................................................. [4]

(b) One of the ways in which a bacterium may be resistant to an antibiotic, such as a $\beta$ lactam, is by having protein pumps in its cell surface membrane which expel the antibiotic from the bacterium.

The gene coding for such an efflux pump is carried on a plasmid.

Outline how the bacterium produces an efflux pump from a gene on a plasmid.
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
................................................................................................................................................................................................. [3]

(c) A strain of the bacterium ​Pseudomonas aeruginosa​, strain R, has a gene coding for an efflux pump and is resistant to a $\beta$ lactam antibiotic.

The minimum inhibitory concentration (MIC) of the $\beta$ lactam for strain R was determined. The MIC is the lowest concentration of antibiotic that prevents a colony of the bacterium from growing.

The MICs were also determined for two mutant strains derived from strain R, mutant strain 1 and mutant strain 2. Each of these strains differs from strain R in the expression of the gene coding for the efflux pump.

The MICs for the three strains of ​P. aeruginosa​ are shown in Table 2.1.

Table 2.1

strain of​ P. aeruginosa​	MIC of $\beta$ lactam / $\mu$g cm$^{-3}$
resistant strain R	64
mutant strain 1	0.5
mutant strain 2	256

With reference to Table 2.1, suggest:

(i) why the MICs for mutant strains 1 and 2 differ from that for strain R

​mutant strain 1​ .................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................

​mutant strain 2​ .................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
................................................................................................................................................................................................. [4]

(ii) how a population of strain R of ​P. aeruginosa​ could be replaced by mutant strain 2.
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
.................................................................................................................................................................................................
................................................................................................................................................................................................. [4]

Green fluorescent protein (GFP) is a small protein that emits bright green fluorescence in blue light. It was first isolated from the jellyfish, Aequorea victoria.
The gene coding for GFP can be expressed in bacteria, such as Escherichia coli, and so it is often used as a marker to show successful uptake of a gene by the bacterium.
(a) (i) Outline how a gene from another species can be inserted into E. coli.
.................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
.................................................................................................................................................. [3]
(ii) Explain how a marker gene, such as the gene for GFP, is used to show successful uptake of a gene for a wanted protein.
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
.................................................................................................................................................. [3]

(ii) A wild relative of maize, called teosinte, grows in Mexico. There are concerns that pollen from genetically-modified maize could pollinate wild teosinte and transfer new genes to it.
Suggest how the results shown in Fig. 5.1 could be used to devise strategies that would reduce the possibility of this happening.
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
..................................................................................................................................................
.................................................................................................................................................. [2]

(a) Fig. 4.1 shows the stages in spermatogenesis in a mammal.
(i) State the letter(s) of the arrow or arrows that represent mitosis. [1]
(ii) Name the cells W, X and Y.
W .........................................................................................
X .........................................................................................
Y ......................................................................................... [3]
(b) Fig. 4.2 is a light micrograph of a transverse section through a seminiferous tubule in a mammalian testis.
On the sector indicated on Fig. 4.2, use label lines and letters to label:
G a cell in the germinal epithelium
M a maturing sperm cell
Y an area where spermatids are found. [3]
(c) In all animals so far studied, the production of fully functional sperm is sensitive to temperature. In the nematode worm, Caenorhabditis elegans, spermatogenesis takes place in a similar way to mammals. Two proteins known as argonaute proteins are important in the development of sperm. They are coded for by the genes alg-3 and alg-4. Table 4.1 shows the effect of mutations in one or both of these genes on the fertility of male worms, at temperatures of 20°C and 25°C. Fertility was measured as the mean number of offspring produced when the male worms mated with normal females.
[Table_1]
(i) Describe the effect of increased temperature on the fertility of normal male worms. ........................................................................... [2]
(ii) Compare the effect of increased temperature on the fertility of alg-3 mutant male worms with the effect on fertility of alg-4 mutant male worms. ........................................................................... [2]
(iii) An investigation showed that at 20°C the number of spermatids produced in worms with both mutations, in alg-3 and alg-4, was the same as in normal worms. However, at 25°C, these mutant worms produced 29% fewer spermatids than the normal worms. Microscopic examination of their testes showed that many of the secondary spermatocytes had failed to complete meiosis. Use this information to state the letter of one arrow on Fig. 4.1 that represents a stage of spermatogenesis affected by mutations in both the alg-3 and alg-4 genes. ......................................... [1]
(iv) Table 4.2 shows the effect of temperature on the percentage of spermatids that developed full motility at 20°C and 25°C in normal worms and in worms with mutations in both alg-3 and alg-4. [Table_2]
With reference to Table 4.2, and the information in (iii), state the cause or causes of reduced fertility in these mutant worms at each temperature.
at 20°C ........................................................................... at 25°C ........................................................................... [2]

Flowers are the organs of sexual reproduction in plants. Before fertilisation and seed development can take place, pollination must occur. This can be either self-pollination or cross-pollination, and can be carried out by insects or by wind.

(a) Explain the meaning of the term self-pollination.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................[2]

(b) Explain why cross-pollination may be more beneficial to a species than self-pollination.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................[3]

(c) In maize, wind pollination occurs. An investigation was carried out to find out how the length of time that maize pollen is in the air affects its ability to bring about fertilisation in a female flower.
• Pollen grains were removed from maize flowers and left exposed to the air for varying times.
• The pollen grains were then placed onto groups of female flowers.
• The groups of fertilised flowers developed into ‘ears’, each containing many seeds. The number of seeds per ear was counted.
The results are shown in Fig. 5.1.

(i) Describe the effect of exposure to the air on maize pollen.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................[2]

(ii) A wild relative of maize, called teosinte, grows in Mexico. There are concerns that pollen from genetically-modified maize could pollinate wild teosinte and transfer new genes to it.
Suggest how the results shown in Fig. 5.1 could be used to devise strategies that would reduce the possibility of this happening.
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................
..........................................................................................................................[2]

A group of plants, known as Rapid Cycling Brassicas (RCBs), has been developed for use in schools and colleges for genetics experiments.

When RCB seedlings develop they can have either purple stems or non-purple stems. Their seed leaves can be either green or yellow-green.

Purple stems and green seed leaves are controlled by dominant alleles.

The genes for stem colour and seed-leaf colour are located on separate chromosomes.

(a) Explain what is meant by a dominant allele.

allele .......................................................................................................................................................
......................................................................................................................................................................
dominant ..................................................................................................................................................
....................................................................................................................................................................... [2]

(b) Draw a genetic diagram to show the likely outcome of a cross between two RCB plants which are heterozygous for both stem colour and seed-leaf colour.

Use the symbols A / a for stem colour and B / b for seed leaf colour. [6]

(a) Corals, although they are animals, are sometimes mistaken for members of the plant kingdom. State two ways in which corals differ from plants. ................................................................................................................................................................................................ ................................................................................................................................................................................................ ................................................................................................................................................................................................ .................................................................................................................................[2]
(b) Outline what is meant by the term ecosystem. ................................................................................................................................................................................................ ................................................................................................................................................................................................ ................................................................................................................................................................................................ .................................................................................................................................[2]

(c) Coral reefs are at risk of damage due to human activities. All the coral reefs in three regions were classified as being at low, medium or high risk of damage. Table 7.1 shows the areas of coral reef at risk of damage in these three regions.

Table 7.1

[Table_1]

(i) Complete Table 7.1, giving your answers to the nearest whole number. [1]
(ii) Suggest how human activities could damage coral reefs. ................................................................................................................................................................................................ ................................................................................................................................................................................................ ................................................................................................................................................................................................ ................................................................................................................................................................................................ .................................................................................................................................[3]

(a) Fig. 8.1 is an electronmicrograph of a section through a mitochondrion.

Name X and Y.

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

(b) Fig. 8.2 outlines the early stages of respiration.

With reference to Fig. 8.2:

(i) explain why ATP is needed at the start of glycolysis
....................................................................................................
....................................................................................................
....................................................................................................
.................................................................................................... [1]

(ii) state the role of NAD in glycolysis
....................................................................................................
....................................................................................................
.................................................................................................... [1]

(iii) state how many molecules of ATP are produced from one molecule of glucose during glycolysis
.................................................................................................... [1]

(iv) name the two types of reaction that occur during the conversion of pyruvate to acetyl CoA in the link reaction
1. ...................................................................................................
2. ................................................................................................... [2]

(v) name the location, in the mitochondrion, of the link reaction
.................................................................................................... [1]

(vi) describe what happens to the hydrogen released during the link reaction.
....................................................................................................
....................................................................................................
....................................................................................................
....................................................................................................
.................................................................................................... [2]

(c) Explain why ATP is regarded as the universal energy currency in organisms.
....................................................................................................
....................................................................................................
....................................................................................................
....................................................................................................
....................................................................................................
....................................................................................................
.................................................................................................... [5]

(a) Describe the first division of meiosis (meiosis I) in animal cells. [6]
(b) Discuss the link between the frequency of sickle cell anaemia and the number of cases of malaria. [9]

10 (a) Describe the arrangement and location of chloroplast pigments and discuss their effect on absorption spectra. [8]
(b) Describe the part played by auxins in apical dominance in a plant shoot. [7]