High School

In most plants, carbon is fixed through photosynthesis when the enzyme Rubisco attaches carbon dioxide molecules to RuBP. However, under high oxygen concentrations, Rubisco can also attach oxygen molecules to RuBP, initiating a process called photorespiration.

Select all of the statements that accurately describe photorespiration.

1. Photorespiration prevents the production of PGA in the Calvin cycle.
2. Photorespiration reduces the output of products from the light reactions.
3. Photorespiration reduces the rate at which sugar is produced by the Calvin cycle.
4. Photorespiration is metabolically expensive.
5. Photorespiration releases CO₂.

Answer :

Final answer:

Photorespiration is a less efficient process compared to the Calvin cycle in photosynthesis, caused by Rubisco binding oxygen to RuBP. It is metabolically expensive and reduces sugar production while releasing CO2.

Explanation:

The question asks for an accurate description of photorespiration, a process that occurs when the enzyme Rubisco attaches oxygen molecules to RuBP instead of carbon dioxide during photosynthesis. This event initiates several reactions that are generally considered less efficient than the standard Calvin cycle.

  • Photorespiration prevents the production of PGA in the Calvin cycle because it diverts RuBP and energy to processes that recover from the initial mistake of oxygenation instead of carboxylation.
  • Photorespiration does not directly reduce the output of products from the light reactions; these reactions are primarily concerned with converting light energy to chemical energy (ATP and NADPH) and proceed independently of the Calvin cycle and photorespiration.
  • Photorespiration reduces the rate at which sugar is produced by the Calvin cycle by consuming ATP and reducing NADP+, without producing sugar, rendering the process metabolically expensive.
  • Photorespiration is metabolically expensive because it utilizes ATP and other resources without producing sugars or other useful end products of the Calvin cycle.
  • Photorespiration releases CO₂, contrasting with the primary goal of photosynthesis to fix carbon dioxide into organic molecules.