Woodlice are small invertebrates that live in cool, damp places under wood and stones. Some students determined the respiration rate of woodlice at different temperatures. [Figure 1.1] shows a single woodlouse. The students tested the hypothesis: For each 10°C increase in temperature the volume of oxygen absorbed will double. [Figure 1.2] shows the respirometer that the students used.

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. 1(a)(i) independent variable: temperature;
2. dependent variable: distance travelled by liquid / volume of oxygen taken up ;
3. 1(a)(ii) 1 (because) these are temperatures at which, enzymes are expected to be functioning / woodlice may survive;
4. 2 (intervals of) 5 °C / 3°C / 2 °C ;
5. 1(a)(iii) inert material / glass beads, of same volume (as woodlice); A dead (sterilised) woodlice
6. 1(a)(iv) idea that absorption of carbon dioxide allows measurement of uptake in oxygen / AW ;
7. 1(a)(v) any 1 from:
8. 1 movement of woodlice;
9. 2 size/age/ sex, of woodlice ;
10. 3 AVP;
11. 1(b)(i) allow in context of using the same respirometer for each temperature, or separate respirometers set up in the same way for each temperature
12. any 7 of:
13. 1 idea of adding a fixed volume of carbon dioxide absorbent solution;
14. 2 idea of adding fixed, number / mass, of woodlice to tube ;
15. 3 idea of method of adding dye solution to capillary tube ;
16. 4 idea of attaching tubes and making airtight;
17. 5 idea of placing respirometer tube into a water-bath at a stated temperature ;
18. 6 idea of leaving apparatus to equilibrate with tap open ;
19. 7 idea of closing the tap and, marking/recording, position of liquid ;
20. 8 idea of measuring movement of dye on the scale for, 5 minutes / a set time;
21. 9 idea of re-opening tap / using syringe, to allow liquid to equalise and then closing to take another measurement ;
22. 10 idea of a minimum of three measurements (in sequence) and taking a mean;
23. 11 idea of repeating experiment at each temperature, e.g. 5 °C, 10 °C, 15 °C, etc ;
24. 12 low risk experiment or medium risk experiment due to (named) carbon dioxide absorbent is harmful and wear gloves ;
25. 13 AVP;
26. 1(b)(ii) 1 idea of converting the distance in cm to mm³ by multiplying by 10 ;
27. 2 volume calculated = volume of oxygen absorbed by woodlice;
28. 3 divide each of the volumes by time (oxygen uptake per unit time = rate of respiration) ;
29. 1(b)(iii) 1 axes correctly orientated with labels ;
30. 2 axes have units ;
31. 3 line shows (exponential) increase as temperature increases ;
32. e.g. volume of oxygen absorbed / mm³ per unit time (y-axis label)
33. temperature / °C (x-axis label)
34. 1(c) woodlice are using mostly carbohydrate as their energy source ;
35. A using a mixed energy source
36. A using, protein / lipid, under anaerobic conditions
37. R using, protein / fat only