specimen_qp_paper_2_aqa_biology_a_level., Exams of Nursing

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SPECIMEN MATERIAL

A-level

BIOLOGY

(7402/2)

Paper 2

Specimen 2014 Session Time allowed: 2 hours

Materials

For this paper you must have:

• a ruler with millimetre measurements
• a calculator.

Instructions

• Use black ink or black ball-point pen.
• Fill in the boxes at the bottom of this page.
• Answer all questions.

Information

• The marks for questions are shown in brackets.
• The maximum mark for this paper is 91. Please write clearly, in block capitals, to allow character computer recognition. Centre number Candidate number Surname Forename(s) Candidate signature

Answer all questions in the spaces provided.

Turn over  1 Figure 1 shows the apparatus used for measuring the rate of oxygen consumption in aerobic respiration by seeds.

. 1 For the first 10 minutes, the tap attached to tube A was left open and the syringe from tube B was removed. Suggest three reasons why the apparatus was left for 10 minutes. [3 marks] 1 2 3

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2 Suggest and explain why the chosen temperature was 20 °C for this experiment. [2 marks] Question 1 continues on the next page

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After 10 minutes, the tap attached to tube A was closed and the syringe was attached to tube B. Every minute, the syringe plunger was moved until the levels in the U-tube were the same. The reading on the syringe volume scale was then recorded. The results are shown in Table 1. Table 1 Time / minutes Reading on syringe volume scale / cm^3 0 0. 1 0. 2 0. 3 0. 4 0. 5 0. 6 0. 7 0. 8 0. 9 0. 10 0. 0 1

During the experiment, the coloured liquid in the tubing moved towards tube B. Explain what caused this. [3 marks] [Extra space]

Turn over  The mass of the seeds was 1.6 g. Use the information in Table 1 to calculate the rate of oxygen consumption in cm 3 g

• 1 hour - 1 by the seeds. Show your working. [2 marks] Turn over for the next question

cm 3 g

• 1 hour - 1 Rate =

There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED

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1 Describe the roles of calcium ions and ATP in the contraction of a myofibril. [5 marks]

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[Extra space] 2 ATP is an energy source used in many cell processes. Give two ways in which ATP is a suitable energy source for cells to use. [2 marks] 1 2

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1 In fruit flies, the genes for body colour and wing length are linked. Explain what this means. [1 mark] A scientist investigated linkage between the genes for body colour and wing length. He carried out crosses between fruit flies with grey bodies and long wings and fruit flies with black bodies and short wings. Figure 2 shows his crosses and the results.

• G represents the dominant allele for grey body and g represents the recessive allele for black body.
• N represents the dominant allele for long wings and n represents the recessive allele for short wings. Figure 2 Phenotype of parents grey body, × black body, long wings short wings Genotype of parents GGNN ggnn Genotype of offspring GgNn Phenotype of offspring all grey body, long wings These offspring were crossed with flies homozygous for black body and short wings. The scientist’s results are shown in Figure 3. Figure 3 GgNn crossed with ggnn Grey body, long wings Black body, short wings Grey body, short wings Black body, long wings Number of offspring^975 963 186

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2 Use your knowledge of gene linkage to explain these results.

[4 marks] [Extra space] 3 If these genes were not linked, what ratio of phenotypes would the scientist have expected to obtain in the offspring? [1 mark]

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4 Which statistical test could the scientist use to determine whether his observed results were significantly different from the expected results? Give the reason for your choice of statistical test. [2 marks]

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A biologist investigated the stimulation of a Pacinian corpuscle in the skin of a fingertip. She used microelectrodes to measure the maximum membrane potential of a Pacinian corpuscle and its sensory neurone when different pressures were applied to the fingertip. Figure 4 shows the Pacinian corpuscle, its sensory neurone and the position of the microelectrodes. Figure 4 Table 2 shows some of the biologist’s results. Table 2 Pressure applied to the fingertip Membrane potential at P / millivolts Membrane potential at Q / millivolts None – 70 – 70 Light – 50 – 70 Medium +30 + Heavy +40 + Explain how the resting potential of – 70 mV is maintained in the sensory neurone when (^0 4) no pressure is applied.

[2 marks] 0 4 0 4

Explain how applying pressure to the Pacinian corpuscle produces the changes in membrane potential recorded by microelectrode P. [3 marks] [Extra space] The membrane potential at Q was the same whether medium or heavy pressure was applied to the finger tip. Explain why. [2 marks]

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Multiple sclerosis is a disease in which parts of the myelin sheaths surrounding neurones are destroyed. Explain how this results in slower responses to stimuli. [2 marks] 0 4.

Turn over  Scientists have produced genetically modified (GM) silkworms that contain a gene Silkworms secrete silk fibres, which are harvested and used to manufacture silk fabric.

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Step 1 Isolate gene from spider. Step 2 Insert spider gene into a plasmid with a marker gene, called EGFP. This gene codes for a protein that glows brightly in ultraviolet (UV) light. Step 3 Inject copies of this plasmid into many eggs of silkworms. Step 4 Allow silkworm eggs that have taken up the plasmid to grow and produce spider silk.

from a spider. The GM silkworms secrete fibres made of spider web protein (spider silk), which is stronger than normal silk fibre protein. The method the scientists used is shown in Figure 5. Figure 5 1 Suggest why the plasmids were injected into the eggs of silkworms, rather than into the silkworms.

Turn over  0 5. [2 marks] 2 Suggest why the scientists used a marker gene and why they used the EGFP gene. [2 marks] The scientists ensured the spider gene was expressed only in cells within the silk glands. 3 What would the scientists have inserted into the plasmid along with the spider gene to ensure that the spider gene was only expressed in the silk glands of the silkworms? [1 mark]

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4 Suggest two reasons why it was important that the spider gene was expressed only in the silk glands of the silkworms. [2 marks] 1 2 6 0 Malaria is a disease that is spread by insects called mosquitoes. In Africa, DDT is a pesticide used to kill mosquitoes, to try to control the spread of malaria. Mosquitoes have a gene called KDR. Today, some mosquitoes have an allele of this gene, KDR minus , that gives them resistance to DDT. The other allele, KDR plus , does not give resistance. Scientists investigated the frequency of the KDR minus allele in a population of mosquitoes in an African country over a period of 10 years. 6. 1 Use the Hardy–Weinberg equation to calculate the frequency of mosquitoes Figure 6 shows the scientists’ results.

Turn over  heterozygous for the KDR gene in this population in 2003. Show your working. [2 marks] Frequency of heterozygotes in population in 2003 2 Suggest an explanation for the results in Figure 6.