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Heat stress decreases the light-dependent reaction of photosynthesis - AQA - A-Level Biology - Question 1 - 2018 - Paper 1
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 hea... show full transcript
Worked Solution & Example Answer:Heat stress decreases the light-dependent reaction of photosynthesis - AQA - A-Level Biology - Question 1 - 2018 - Paper 1
Step 1
Explain why this leads to a decrease in the light-independent reaction.
Answer
The decrease in light-dependent reactions due to heat stress results in lower ATP and NADPH production, which are essential for the light-independent reactions (Calvin cycle). Without sufficient ATP to provide energy and NADPH to supply reducing power, the light-independent reactions become limited in their capacity to fix carbon dioxide into glucose.
Step 2
Explain why.
Answer
Rubisco facilitates the carboxylation of ribulose bisphosphate (RuBP) to form 3-phosphoglycerate (3-PGA). If the enzyme rubisco is less active due to heat stress, the rate of this reaction diminishes. Consequently, lower levels of 3-PGA mean that fewer carbohydrates are synthesized, thereby limiting overall photosynthesis.
Step 3
Step 4
Use all the information to evaluate their conclusion.
Answer
The conclusion that heat stress reduces rubisco activity via the action of rubisco activase is supported by the data. Rubisco activase plays a critical role in ensuring rubisco remains functional. If heat stress denatures rubisco activase or reduces its activity, it would lead to decreased rubisco function. Moreover, the research suggests that enzyme activity tends to decrease at higher temperatures, further corroborating this conclusion. Therefore, the conclusion is valid given the presented evidence regarding the effects of temperature on enzyme activity.