Immobilized algal beads containing photosynthetic Chlorella cells are commonly used to investigate photosynthesis. When placed in a beaker containing sodium hydrogencarbonate solution, the beads initially sink. As the algae photosynthesize and release oxygen gas, tiny bubbles become trapped on the surface of the alginate beads, causing them to rise to the top.
Fig. 22.1 shows how the algal beads rise in the presence of light.
Fig. 22.1
A group of students introduces an inhibitor chemical to the solution. This chemical blocks a specific metabolic pathway within the chloroplasts. Even when exposed to high-intensity light, none of the algal beads rise to the surface.
Which biological process is targeted and blocked by this inhibitor? Tick (✓\checkmark✓) one box.
[ ] Active transport [ ] Aerobic respiration [ ] Photosynthesis [ ] Transpiration
Explain why the algal beads fail to rise in the presence of this inhibitor.
The students then investigate how light exposure over a 40-minute period affects the buoyancy of 12 algal beads.
- In Trial A, the beads are exposed to 20 minutes of light, followed by 20 minutes of darkness.
- In Trial B, the beads are exposed to continuous light for the full 40 minutes.
They record the number of floating algal beads over time. Their results are shown in Fig. 22.2.
Fig. 22.2
State what conclusion can be made from Trial A about the relationship between light exposure and the floating of the algal beads.
Suggest an explanation for the difference in the trends observed between Trial A and Trial B after 20 minutes.
Temperature is another environmental factor that affects the rate of photosynthesis. Explain how increasing the temperature of the solution from 15∘C15^\circ\text{C}15∘C to 50∘C50^\circ\text{C}50∘C affects plant processes like photosynthesis.