4.7 Core practical: rate of respiration
6 exam questions worth 11 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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What is the function of the soda lime in the respirometer?
Mark scheme
absorbs carbon dioxide
Model answer
It absorbs the carbon dioxide given out by the organisms.
Explain why the coloured liquid moves towards the woodlice.
Mark scheme
- woodlice take in / use oxygen (for respiration) (1)
- carbon dioxide produced is absorbed by soda lime (1)
- so volume / pressure of gas in the tube decreases (pulling the liquid) (1)
Model answer
The woodlice use oxygen for respiration. The carbon dioxide they give out is absorbed by the soda lime, so the volume of gas in the tube falls and the liquid is pulled towards them.
A control tube contains glass beads instead of woodlice. Explain why.
Mark scheme
- to show that the movement is caused by the organisms / respiration (1)
- and not by changes in temperature / pressure (1)
Model answer
It shows that any movement of the liquid is caused by the respiration of the woodlice and not by other factors such as temperature changes.
At 20 °C the liquid moved 18 mm in 6 minutes.
Calculate the rate of movement in mm per minute.
Mark scheme
- 18 ÷ 6 (1)
- = 3 (mm per minute) (1)
Model answer
rate = 18 ÷ 6 = 3 mm per minute.
Predict how the rate would change at 30 °C and explain your prediction.
Mark scheme
- rate increases / liquid moves faster (1)
- enzymes (for respiration) work faster at higher temperature (1)
Model answer
The rate would increase, because the enzymes that control respiration work faster at a higher temperature.
Give one ethical precaution when using woodlice in this experiment.
Mark scheme
stop them touching the soda lime / use gauze / handle carefully / return them to their habitat / keep time short
Model answer
Use a gauze so the woodlice cannot touch the soda lime, and return them to their habitat afterwards.
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