Photo AI
Heat stress decreases the light-dependent reaction of photosynthesis - AQA - A-Level Biology - Question 1 - 2018 - Paper 2
Question 1
Heat stress decreases the light-dependent reaction of photosynthesis. Explain why this leads to a decrease in the light-independent reaction. Another effect of he... show full transcript
Worked Solution & Example Answer:Heat stress decreases the light-dependent reaction of photosynthesis - AQA - A-Level Biology - Question 1 - 2018 - Paper 2
Step 1
Explain why this leads to a decrease in the light-independent reaction.
Answer
In this process, light energy is converted into chemical energy, producing ATP and NADPH. These products are crucial for the light-independent reactions, also known as the Calvin cycle, where carbon dioxide is fixed into glucose. Heat stress can lead to reduced ATP and NADPH levels, thereby limiting the energy and reducing the carbon fixation occurring in the Calvin cycle.
Step 2
Explain why.
Answer
Rubisco, the enzyme responsible for catalyzing the first step of the Calvin cycle, is essential for the conversion of carbon dioxide into organic molecules. If the activity of rubisco decreases, the rate at which carbon dioxide is fixed into sugars is reduced. Consequently, this limits the overall rate of photosynthesis, as the production of glucose is closely tied to the activity of rubisco.
Step 3
Step 4
Use all the information to evaluate their conclusion.
Answer
The scientists' conclusion that heat stress reduces the activity of rubisco by affecting rubisco activase is valid. The data shows that rubisco activity increases with temperature until a maximum, after which it decreases due to denaturation. This suggests that when temperatures exceed optimal levels, rubisco's efficiency decreases significantly. Moreover, it is likely that the activase, which regulates rubisco activation, also becomes less effective at higher temperatures, further impairing rubisco function. This twofold effect of heat stress ultimately leads to reduced photosynthetic efficiency in plants.