The Question is from neet-botany plant-physiology transpiration-and-photosynthesis-compromise, and it was created by the author K SURESH KUMAR

Question

A researcher observes that a plant species exhibits a lower transpiration rate and higher water use efficiency (WUE) under high light intensity compared to low light.  Which physiological adaptation BEST explains this observation?

K SURESH KUMAR · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Plant Physiology, specifically stomatal regulation and water use efficiency (WUE).
	**Related Topics**: Photosynthesis, transpiration, plant adaptations to light.
	**Prerequisites**: Understanding of stomatal function, transpiration, and the relationship between photosynthesis and water use.
## SOLUTION PATHWAY
**Given Information**:
	Lower transpiration rate and higher WUE under high light intensity.
**Method & Steps**:
	1. **Analyze the relationship between transpiration, WUE, and light intensity**.
		Reasoning:  WUE is the ratio of carbon gained through photosynthesis to water lost through transpiration.  High light generally increases photosynthesis. If transpiration decreases while photosynthesis increases or remains constant, WUE will increase.
	2. **Consider the role of stomata**.
		Working: Stomata are pores on the leaf surface that regulate gas exchange, including the uptake of $CO_2$ for photosynthesis and the release of water vapor (transpiration).  Partial closure of stomata reduces transpiration.
	3. **Connect stomatal behavior to the given observation**.
		Result: Partial stomatal closure under high light allows the plant to conserve water while still photosynthesizing efficiently, leading to lower transpiration and higher WUE.
		Verification: This aligns with the observed lower transpiration rate and higher WUE under high light.
 ## OPTION ANALYSIS
[A] :x: Increased leaf thickness: While increased leaf thickness can enhance water storage, it doesn't directly explain the lower transpiration rate and higher WUE under high light.  It might even slightly increase transpiration due to a larger surface area for evaporation (although this effect is usually minor compared to stomatal control).
[B] :x: Deeper root system: A deeper root system improves access to water, but it doesn't directly influence the rate of transpiration or WUE under different light conditions.  It primarily helps the plant survive drought, not necessarily improve WUE under high light.
[C] :x: Increased chlorophyll content: Increased chlorophyll can enhance light absorption and potentially increase photosynthesis. However, it doesn't directly explain a lower transpiration rate.  If photosynthesis increases without a corresponding decrease in transpiration, WUE might increase, but the question states a lower transpiration rate, which increased chlorophyll alone wouldn't cause.
[D] ✓: Partial stomatal closure: This directly reduces water loss through transpiration while allowing $CO_2$ uptake for photosynthesis to continue, albeit potentially at a slightly reduced rate.  This is the most direct and effective way for a plant to increase WUE under high light.
 ## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing water storage with water use efficiency:  While adaptations like increased leaf thickness or deeper roots can improve a plant's drought tolerance, they don't directly influence WUE under varying light conditions.
		2.  Ignoring the role of stomata: Stomatal regulation is the primary mechanism controlling transpiration and is crucial for understanding plant responses to light intensity.
	**Quick Tips**:
		1. Remember that WUE is about the balance between carbon gain and water loss, and stomata are the key regulators of this balance.
		2.  High light can lead to photoinhibition (damage from excessive light), and partial stomatal closure can help mitigate this by reducing water loss and thus maintaining leaf temperature.

K SURESH KUMAR · Answer

Increased leaf thickness

K SURESH KUMAR · Answer

Deeper root system

K SURESH KUMAR · Answer

Increased chlorophyll content

K SURESH KUMAR · Answer

The correct Option is "Partial stomatal closure"

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