The diagram shows an experiment to investigate the effect of increasing light intensity on the rate of photosynthesis in an aquatic plant.
The rate is found by measuring the rate of bubble release by the plant.
As the light intensity increases, the rate of bubble release increases and then becomes constant.
Which statement describes why the rate of bubble release becomes constant at high light intensities?
A) Carbon dioxide concentration becomes a limiting factor.
B) Light intensity becomes a limiting factor.
C) Oxygen availability becomes a limiting factor.
D) Water availability becomes a limiting factor.
▶️ Answer/Explanation
Ans: A
At high light intensities, photosynthesis initially increases due to greater energy availability. However, when the rate of bubble release (oxygen production) plateaus, it indicates another factor is limiting. Since carbon dioxide is a key reactant in photosynthesis, its limited availability (A) restricts further increase in the rate, even if light intensity continues to rise.
Light intensity (B) cannot be the limiting factor here because the rate stops increasing despite more light. Oxygen (C) is a product, not a limiting reactant, and water (D) is typically abundant in aquatic experiments. Thus, the correct answer is A (Carbon dioxide concentration becomes a limiting factor).
In an investigation, the rate of photosynthesis in a plant is measured at different temperatures. The investigation is carried out at three different light intensities. The results are shown.
What is the limiting factor for the rate of photosynthesis at point X?
▶️ Answer/Explanation
Ans: C
At point X, the rate of photosynthesis plateaus despite increasing light intensity, indicating that another factor is limiting. Since the experiment varies temperature, and the graph shows that higher temperatures increase the rate, temperature (C) is the limiting factor at X.
Light intensity (B) is not limiting here because increasing it does not raise the rate further. Carbon dioxide (A) and oxygen (D) are not mentioned as variables, making them irrelevant in this context. Thus, the correct answer is C (Temperature).