Question

Vegetable crops like tomatoes and bell pepper, allowed growing in a carbon dioxide rich environment, showed higher yields because:

• A. C4 pathway for carbon fixation at high carbon dioxide is the limiting factor in such plants.
• B. These showed an increased rate of photosynthesis at higher carbon dioxide concentrations.
• C. These can respond to high carbon dioxide conditions even in low light conditions.
• D. Only carbon dioxide is the limiting factor in such plants.

Hint:

Remember tomato and bell pepper are C3 crops, and think about what extra CO2 does to RuBisCO's two competing reactions.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
Tomato and bell pepper are C3 plants. The question asks why growing them in a CO2 enriched environment raises their yield.

Step 2: Key Formula or Approach:
In C3 plants, the enzyme RuBisCO can either fix CO2 (photosynthesis) or fix oxygen (photorespiration), and under normal atmospheric CO2 levels a good share of RuBisCO activity is wasted on the oxygen reaction. Raising CO2 around the leaf pushes RuBisCO towards more carboxylation and less oxygenation.

Step 3: Detailed Explanation:
Option 1 talks about the C4 pathway, but tomato and bell pepper are C3 crops, they do not run a C4 pathway, so this option does not apply to them.
Option 2 says these crops showed a higher rate of photosynthesis at higher CO2. This matches the known CO2 fertilisation effect in C3 plants: more CO2 means RuBisCO carries out more carboxylation and less wasteful oxygenation, so net photosynthesis and dry matter production go up, which raises yield.
Option 3 claims these crops respond to high CO2 even in low light. Photosynthesis still needs enough light to generate ATP and NADPH in the light reactions, so CO2 enrichment cannot fully replace light as a requirement, making this an overstatement.
Option 4 says CO2 is the only limiting factor, but real crop yield also depends on light, water, temperature and nutrients, so this absolute claim does not hold.

Step 4: Final Answer:
The higher yield comes from a genuine increase in the photosynthesis rate once more CO2 is available, so option 2 is correct.