Practical Assessment (A Level Only) (AQA A Level Biology)

Exam Questions

57 mins6 questions
1a3 marks

An experiment was conducted to investigate amylase activity. The contents from a section of gut from a mouse were obtained and then added to a starch solution (which was at pH 6.9 and kept in a 30°C water bath). Every three minutes samples were removed and added to separate test tubes containing a diluted iodine solution. The colour intensity for each sample was determined. Figure 1 below shows the results.

 Figure 1Y9YVP_l8_1

 

Describe and explain the results seen in Figure 1.

1b2 marks

Sketch two labelled curves on Figure 1 to show the predicted results of the experiment if it was carried out at:

i)
pH 1.8

ii)
45°C
1c4 marks

Explain how lowering the pH affects the activity of the enzyme amylase.

1d3 marks

Explain how increasing the temperature to 40 °C affects the activity of the enzyme amylase.

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2a3 marks

A biology student wanted to investigate the stages of mitosis in onion root tips. To do this they prepared a stained squashed sample of onion root tip cells. They used the following method:

  • Cut first 4-6 mm from onion root tip and place on glass slide (shown in Figure 1)
  • Add stain solution to the tip and lay cover slip over tip
  • Press down firmly on cover slip

 Figure 1fr2tNQSu_2

Explain why the student:

i)
only used the first 4-6 mm of onion root tip.

ii)
added stain solution to the onion root tip.

iii)
pressed down firmly on the cover slip.
2b2 marks

The biology student looked at their stained squash of onion root tip cells under the microscope and obtained the data shown in Table 1.

 Table 1

 

Stage of mitosis Number of cells observed
Interphase 521
Prophase 63
Metaphase 19
Anaphase 12
Telophase 4

 

Calculate the percentage of cells in which the chromosomes are visible and are lined up along the middle of the cell. Show your working.

2c2 marks

The biology student wanted to repeat the procedure in parts (a) and (b) with more onion root tips (from genetically identical onion plants) to check the accuracy of their results in part (b).

Suggest two variables that the student should control to ensure similar root growth in the other onion plants. For each variable, explain why it should be controlled.

2d2 marks

The student in parts (a), (b) and (c) conducted further studies on different sections of onion roots. They found that the proportion of dividing cells decreased with increasing distance from the root tip.

Explain why they found this result.

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3a2 marks

A biologist was investigating the effect of three types of antibiotic on the growth of Streptococcus bacteria. The student biologist carried out the following procedure:

  • Boil the agar before pouring the agar plates
  • Flood agar plates with a liquid culture of Streptococcus
  • Place four sterile paper discs, A, B, C and D onto the agar plates (three soaked in different antibiotics, one in sterile water)
  • Incubate agar plates at 37°C for three days

Explain why the biologist:

i)
Boiled the agar.

ii)
Soaked one of the paper discs in sterile water.
3b4 marks

The biologist in part (a) should use aseptic techniques to transfer the liquid culture of Streptococcus onto the agar plate.

Describe two aseptic techniques that the biologist should use and for each, explain why these techniques are important.

3c2 marks

Certain factors can affect the rate at which the antibiotics from each paper disc diffuse through the agar.

State two of these factors and for each one, describe the effect it would have on the rate of diffusion through the agar.

3d1 mark

By what process do bacterial cells divide?

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4a2 marks

A biologist carried out an investigation to find the water potential of carrot tissue. The biologist started with a carrot and 100 cm3 of a 1.0 mol dm−3 sucrose solution. They made a series of different concentrations of sucrose solution using the 1.0 mol dm−3 solution. They cut and weighed cylinders of carrot tissue and left them in the sucrose solutions for a set time. They then removed the carrot cylinders and blotted them dry
before reweighing them.

Explain why the biologist blotted the carrot cylinders dry before reweighing them.

4b2 marks

Describe how the biologist in part (a) could use a 1.0 mol dm−3 solution of sucrose to produce 60 cm3 of a 0.30 mol dm−3 solution of sucrose. Show your working.

4c2 marks

The biologist presented the results of their investigation from part (a) in Table 1 below:

 Table 1 

Concentration of sucrose solution / mol dm−3 Percentage change in mass of carrot cylinder
0.30 +3.6
0.40 +2.9
0.50 +1.1
0.60 -0.6
0.70 -2.4

 

Describe how the biologist could use their results in Table 1 to find the water potential of the carrot tissue.

4d2 marks

The biologist in part (a) calculated the percentage change in mass rather than just the change in mass. Explain why it might have been advantageous to do this.

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5a5 marks

Betalains are pigments found in the cell vacuole of beetroot cells and are responsible for the dark purple-red colour of beetroot tissue. A student wanted to investigate how alcohol concentration affected the loss of these pigments from beetroot tissue. They obtained the results shown in Table 1 below:

 Table 1

Alcohol concentration / % Absorbance / AU
0 0.36
20 0.48
40 0.72
60 0.95
80 1.08
100 1.22

 

Suggest a suitable method that the student could use to obtain these results.

5b2 marks

What conclusions can you draw from the results shown in Table 1?

5c2 marks

Another student wanted to investigate the effect of temperature on the loss of pigment from beetroot. They put beetroot discs into test tubes containing water and placed the tubes in water baths at a different temperature. After 40 minutes, they measured the percentage of light passing through the water in each tube.

Explain why it was important that the student made sure each test tube contained the same volume of water to begin with.

5d2 marks

The student in part (c) found that the higher the temperature, the more pigment was released from the beetroot and the lower the percentage of light passing through the water in each tube.

Suggest how an increase in the temperature of the water caused pigment to be released from the beetroot.

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6a2 marks

Insects have a system of very small air-filled pipes called tracheae which they use for gas exchange. A student wants to dissect a grasshopper to view the tracheae.

Give two safety precautions the student should take when carrying out this dissection.

6b1 mark

Describe one ethical issue involved in the dissection of animals for scientific purposes.

6c3 marks

The tracheal system of the grasshopper that the student dissected in part (a) is adapted for efficient gas exchange. Explain how.

6d2 marks

Insect spiracles have valves that enable them to be closed by the insect. In many insect species, the spiracles are also surrounded by tiny hairs. Suggest the advantage of each of these features for an insect in hot weather.

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