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Practical skills assessed in a written examination

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Question 26

An investigation was carried out to measure the rate of respiration of yeast cells under anaerobic conditions at different glucose concentrations using a simple micro-respirometer.

  • A yeast-glucose suspension was placed in a respirometer. To establish a baseline (control), yeast in a glucose-free water solution was kept at 30∘C30^\circ\text{C}30∘C for six hours.
  • The distance moved by the fluid in the capillary tube during this time was 7.5 mm.
  • In separate trials containing glucose, the yeast was exposed to different glucose concentrations for six hours at a time, and the distance moved by the fluid was recorded:
    • At 2% glucose concentration: 4.5 mm
    • At 5% glucose concentration: 11.7 mm
a.

The diameter of the capillary tubing was 0.4 mm. The volume of a cylinder can be calculated using the formula:

volume of cylinder=πr2l \text{volume of cylinder} = \pi r^2 l volume of cylinder=πr2l

Calculate the rate of gas production by the yeast in the glucose-free control in mm3 h−1\text{mm}^3\text{ h}^{-1}mm3 h−1. Give your answer to two significant figures. Show your working.

[4]
b.

Calculate the percentage increase in gas production by the yeast between 2% glucose and 5% glucose concentrations. Show your working.

[3]

Practical skills assessed in a written examination Questions

  1. A Level
  2. /Biology
  3. /Practical skills assessed in a written examination