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Paper 2 Specimen (set 1) - Q4

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Questions
4) Figure 7 shows the equipment used for measuring respiration in peas.
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  • Respirometer A contains germinating peas.
  • Respirometer B contains peas that are not germinating.
  • Respirometer C contains glass beads.

All three respirometers are placed in a water bath at 25°C for 30 minutes. The reduction in oxygen levels in each respirometer is measured using a data logger.

(a) Explain why the respirometers are placed in a water bath at 25°C. [2 marks]

(b) A student recorded the change in oxygen levels in the germinating peas over a 30-minute period. The results are shown below.
A 10 mins (−0.8) ml, 20 mins (−1.6) ml, 30 mins (−2.4) ml
B 10 mins (−0.1) ml, 20 mins (−0.1) ml, 30 mins (−0.1) ml
C No change

(i) Complete the table for these results. [2 marks]
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(ii) Calculate the rate of oxygen consumption per second for the results in respirometer A. [2 marks]
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........................................ ml/second
​
(iii) Explain why respirometer A has the highest rate of oxygen consumption. [2 marks]

(c) Some respirometers read the movement of a bubble along capillary tubing.
Carbon dioxide can affect the measuring of oxygen used in this type of respirometer.
State a chemical that could be placed in the respirometer that would stop carbon dioxide affecting the experiment. [1 mark] 

(Total for Question 4 = 9 marks)​
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