IB DP Biology- C1.2 Cell respiration - IB Style Questions For SL Paper 2 - FA 2025
▶️ Answer/Explanation
(a)
Light intensity (controlled by changing the distance of the light source from the plant)
(b)
- Temperature of the water — because temperature affects enzyme activity involved in photosynthesis.
- Carbon dioxide concentration — as it’s a reactant in photosynthesis and will affect the rate.
(c)
Set up the same experiment without any light (in complete darkness) to show that light is necessary for oxygen production/photosynthesis.
(d)
- The bubbles are oxygen, which is a product of photosynthesis.
- In the presence of light, the plant carries out photosynthesis, converting carbon dioxide and water into glucose, with oxygen released as a byproduct.
- The equation for photosynthesis:
6\mathrm{CO}_2 + 6\mathrm{H}_2\mathrm{O} \xrightarrow{\text{light}} \mathrm{C}_6\mathrm{H}_{12}\mathrm{O}_6 + 6\mathrm{O}_2
Markscheme:
(a) To check there is no carbon dioxide (left in the air)/show any carbon dioxide present;
(b) Soil releases \(\mathrm{CO}_2\) from microorganisms/decomposers/bacteria/fungi
OR
Respiration by microorganisms may affect the result;
(c) Using the same apparatus without a plant
OR
Cover the whole plant with a plastic bag;
(d) No change/limewater stays clear
OR
Because plant takes in carbon dioxide by photosynthesis;