Photosynthesis is a process that results in the synthesis of complex organic molecules. Respiration is a process that involves the breakdown of complex organic molecules.

Mark scheme

Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.

1. [1] (a) cyclic involves (only) PS1 and non-cyclic involves PS1 and PS2 ;
2. [1] (a) cyclic produces only ATP and non-cyclic produces ATP and reduced NADP ;
3. [1] (a) cyclic does not involve photolysis of water and non-cyclic does involve photolysis of water; A photolysis only occurs in non-cyclic
4. [1] (b)(i) as a, control / reference tube, for comparison ; R control variable
5. [1] (b)(ii) tube 2 changes to blue 1 (plant carries out) photosynthesis ;
6. [1] (b)(ii) 2 uses up CO2 in the, Calvin cycle / light independent stage or less CO2 causes pH to increase ; I oxygen
7. [1] (b)(ii) tube 3 changes to yellow 3 (snail carries out) respiration ;
8. [1] (b)(ii) 4 produces CO2 in, the link reaction / Krebs cycle or more CO2 causes pH to decrease ; A more CO2 acidifies solution I oxygen
9. [1] (b)(ii) tube 4 stays green 5 both photosynthesis and respiration or CO2 produced in respiration is used in photosynthesis or oxygen produced in photosynthesis is used in respiration ;
10. [1] (b)(iii) no/less, photosynthesis, so, no/less, CO2 used ;
11. [1] (b)(iii) detail; e.g. no light dependent stage / no non-cyclic photophosphorylation no/less, Calvin cycle / light independent stage / carbon (dioxide)fixation
12. [1] (b)(iii) respiration occurs producing CO2;
13. [1] (b)(iii) respiration rate slower, in aquatic plants / test-tube 6, than, pond snails / test-tube 7;
14. [1] (b)(iii) (so) slight decrease in pH ;