which behavior of stomata increases the rate of photorespiration?

Question

they open at night, allowing CO2 to enter


they close at night, conserving water


they open during day, allowing CO2 to enter


they close during day, conserving water.

Answer 1

D. closing during the day to conserve water

Answer 2

Photorespiration refers to the alternate pathway for production of Glyceraldehyde 3-phosphate (G3P) by Rubisco, the main enzyme of the Dark reactions of photosynthesis (also known as the Calvin cycle or the Primary Carbon Reduction (PCR) cycle). Although Rubisco favors carbon dioxide to oxygen,(approximately 3 carboxylations per oxygenation), oxygenation of Rubisco occurs frequently, producing a glycolate and a glycerate. This usually occurs when oxygen levels are high; for example, when the stomata (tiny pores on the leaf) are closed to prevent water loss on dry days. It involves three cellular organelles: chloroplasts, peroxisomes, and mitochondria. Photorespiration produces no ATP.

The Oxidative photosynthetic carbon cycle reaction is catalyzed by RuBP oxygenase activity:

RuBP + O2 → Phosphoglycolate + 3-Phosphoglycerate
The phosphoglycolate is salvaged by a series of reactions in the peroxisome, mitochondria, and again in the peroxisome where it is converted into serine and later glycerate. Glycerate reenters the chloroplast and subsequently the Calvin cycle by the same transporter that exports glycolate. A cost of 1 ATP is associated with conversion to 3-phosphoglycerate (PGA) (Phosphorylation), within the chloroplast, which is then free to reenter the PCR cycle. One carbon dioxide molecule is produced for every 2 molecules of O2 that are taken up by Rubisco.

Photorespiration is a wasteful process because G3P is created at a reduced rate and higher metabolic cost (2ATP and one NAD(P)H]) compared with RuBP carboxylase activity. G3P produced in the chloroplast is used to create "nearly all" of the food and structures in the plant. While Photorespiratory carbon cycling results in G3P eventually, it also produces waste ammonia that must be detoxified at a substantial cost to the cell in ATP and reducing equivalents.

Answer 3

They close during day, conserving water. I think it is a mode of photosynthesis when there is not enough CO2 and too much O2.