Question

Photorespiration is an alternative process that some plants undergo under stressful environmental conditions. Which of the following best describes conditions that would most likely lead to a plant undergoing photorespiration?

• A. High temperature and open stomata which leads to a build up of carbon dioxide in the leaf.
• B. High temperatures and closed stomata which leads to a build up of oxygen gas in the leaf.
• C. High temperature and closed stomata which leads to a build up of water and carbon dioxide in the leaf.
• D. Low temperature and closed stomata which leads to a build up of water and oxygen gas in the leaf.
• E. Low temperature and open stomata which leads to a build up of oxygen gas in the leaf.

Answer 1

The correct option is B High temperatures and closed stomata which leads to a build up of oxygen gas in the leaf.

In C3 plants, when there is high O₂ concentration and temperature, RuBisCO binds with O₂ instead of CO₂ and form one molecule of phosphoglycerate and phosphoglycolate in a pathway called photorespiration. The process can be understood in following steps:

1. Oxygen binds with RuBP oxygenase to form phosphoglycolate in chloroplast which gets converted to glycolate and transported to peroxisomes.

2. In peroxisomes it forms glyoxylate and then glycine.

3. Glycine then enters mitochondrion and looses NH4 and CO₂ in a reaction and form serine.

4. Serine is transported to peroxisomes and in a series of reaction it form glycerate which gets converted to phosphoglyceric acid (PGA) and then RuBP in the chloroplast.

Hence, the conditions that lead a plant to undergo photorespiration are high oxygen concentration which can build up when stomata are closed and high temperature.

So, the correct answer is 'High temperatures and closed stomata which leads to a build up of oxygen gas in the leaf'.