The Question is from neet-botany photosynthesis-in-higher-plants factors-affect-photosynthesis, and it was created by the author K SURESH KUMAR

Question

A C4 plant and a CAM plant are grown under identical environmental conditions. Which statement BEST describes their relative water use efficiency (WUE) and photosynthetic rates under prolonged high light intensity and high temperature?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: Photosynthetic pathways and adaptations to arid environments.
	**Related Topics**: C4 photosynthesis, CAM photosynthesis, Water Use Efficiency (WUE), Photorespiration, Stomata
	**Prerequisites**: Understanding of basic plant physiology and the different photosynthetic pathways.
## SOLUTION PATHWAY
**Given Information**:
	- C4 and CAM plants are compared.
	- Environmental conditions: prolonged high light intensity and high temperature.
**Method & Steps**:
	1. **C4 Plants**: 
		Reasoning: C4 plants minimize photorespiration by concentrating CO2 around Rubisco. This allows them to maintain high photosynthetic rates, especially under high light and temperature conditions. However, they achieve this by using energy to pump CO2, and they also need to open their stomata to some extent to take in CO2, leading to water loss through transpiration.
		Key Point: High photosynthetic rate, moderate WUE.
	2. **CAM Plants**: 
		Working: CAM plants open their stomata at night to take in CO2 and store it as malic acid. During the day, they close their stomata and use the stored CO2 for photosynthesis. This minimizes water loss through transpiration, especially in hot and dry conditions.
		Key Point: Low photosynthetic rate (due to limitations in CO2 storage capacity), high WUE.
	3. **Comparison**: 
		Result: C4 plants have higher photosynthetic rates due to their efficient CO2 concentrating mechanism. CAM plants have higher WUE because they minimize water loss by closing stomata during the day.
		Verification: This aligns with the adaptations of these plants to different environmental conditions. C4 plants thrive in hot, sunny environments with moderate water availability, while CAM plants are adapted to arid environments.
## OPTION ANALYSIS
[A] :x: Incorrect. C4 plants have higher photosynthetic rates but not necessarily higher WUE than CAM plants.
[B] ✓: Correct. CAM plants have higher WUE, while C4 plants have higher photosynthetic rates.
[C] :x: Incorrect. C4 plants have higher photosynthetic rates, not CAM plants.
[D] :x: Incorrect. CAM plants have higher WUE, not higher photosynthetic rates.
## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing the functions of C4 and CAM pathways: Remember that both mechanisms increase CO2 concentration around Rubisco, but they achieve this through different temporal and spatial separations.
		2. Assuming higher photosynthetic rate automatically means higher WUE: WUE considers both carbon gain and water loss. CAM plants sacrifice photosynthetic rate for water conservation.
	**Quick Tips**:
		1. C4 - think 'Concentrate CO2'; CAM - think 'Conserve water'.
		2. WUE = Carbon assimilation / Water transpired.

K SURESH KUMAR · Answer

The C4 plant will have both higher WUE and a higher photosynthetic rate than the CAM plant.

K SURESH KUMAR · Answer

The correct Option is "The CAM plant will have higher WUE than the C4 plant, but the C4 plant will have a higher photosynthetic rate."

K SURESH KUMAR · Answer

The C4 plant will have higher WUE than the CAM plant, but the CAM plant will have a higher photosynthetic rate.

K SURESH KUMAR · Answer

The CAM plant will have both higher WUE and a higher photosynthetic rate than the C4 plant.

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