Answer: Photosynthesis rate equals respiration rate (net gas exchange = 0).
- A Mitochondrial respiration reaches its absolute maximum measured rate
- B Photosynthesis rate equals respiration rate (net gas exchange = 0)
- C Guard cells fully close the stomatal pore, halting all gas exchange
- D Ambient temperature reaches the optimum for Rubisco carboxylase activity
Correct answer: B. Photosynthesis rate equals respiration rate (net gas exchange = 0)
Explanation: Compensation point: light intensity at which CO<sub>2</sub> fixed by photosynthesis = CO<sub>2</sub> released by respiration. Net gas exchange is zero.
Simplified photosynthesis diagram: light energy, CO2, and H2O enter the leaf and are converted in the chloroplast into glucose and O2.
Concept context
Light reactions, the Calvin cycle, C 3 /C 4 /CAM pathways, photorespiration, and factors affecting the rate of photosynthesis. One of the highest-yield NEET chapters.