Leaf discs cut from spinach leaves are frequently used in laboratory investigations to study photosynthesis. Before the experiment, the air is removed from the intercellular spaces of the leaf discs using a vacuum syringe containing a dilute sodium hydrogencarbonate solution. This causes the leaf discs to sink. When exposed to light, the leaf discs begin to rise to the surface.
Scientists run an experiment where they add a metabolic inhibitor (DCMU) to the solution. This chemical specifically blocks the flow of electrons in photosystem II, and they observe that the leaf discs do not rise.
Which biological process is affected by this chemical?
- Active transport
- Aerobic respiration
- Photosynthesis
- Transpiration
Explain why the leaf discs did not rise to the surface after the chemical inhibitor was added.
The scientists then investigate how light exposure affects the buoyancy of these leaf discs over time.
- In Experiment X, 10 leaf discs are exposed to 6 hours of light followed by 18 hours of darkness.
- In Experiment Y, 10 leaf discs are exposed to continuous light for 24 hours.
They record the number of floating leaf discs at regular intervals over a 24-hour period. The results are shown in the graphs below:
What conclusion can be made from Experiment X about the effect of light on the buoyancy of the leaf discs?
Suggest an explanation for the differences in the number of floating leaf discs between the two experiments after 12 hours.
Light is one environmental factor that affects plants. Explain how increasing the temperature from 15∘C15^\circ\text{C}15∘C to 50∘C50^\circ\text{C}50∘C can affect the rate of photosynthesis in these spinach leaf discs.