The Question is from neet-botany , and it was created by the author B VENKAT

Question

A researcher exposes two genetically identical plants to different light intensities. Plant A receives high intensity monochromatic red light, while Plant B receives low intensity polychromatic light. Assuming all other factors are optimal, which statement is MOST likely true regarding the quantum yield of photosystem II (ΦPSII)?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: B
## CONCEPT FRAMEWORK
	**Primary Concept**: Quantum yield of Photosystem II (ΦPSII)
	**Related Topics**: Photosynthesis, Light intensity, Photoinhibition, Light absorption
	**Prerequisites**: Understanding of light reactions in photosynthesis and the definition of quantum yield.
## SOLUTION PATHWAY
**Given Information**:
	Plant A: High intensity monochromatic red light.
	Plant B: Low intensity polychromatic light.
**Method & Steps**:
	1. **Understanding ΦPSII**: ΦPSII represents the efficiency of photosystem II in converting absorbed light energy into chemical energy.  It's the ratio of oxygen molecules evolved to photons absorbed by PSII.
		Reasoning: Higher ΦPSII means higher efficiency of light utilization.
	2. **Effect of High Light Intensity**:  At very high light intensities, the rate of damage to the photosynthetic apparatus, particularly PSII (photoinhibition), can exceed the rate of repair. This leads to a decrease in ΦPSII.
		Working: Excess light energy can lead to the formation of reactive oxygen species, damaging PSII.
		Key Point:  While some red light is essential for photosynthesis, excessive amounts can be detrimental.
	3. **Effect of Low Light Intensity**: At low light intensities, the light reactions are light-limited.  Almost all absorbed photons are used efficiently for photochemistry, resulting in a high ΦPSII.
		Result: Plant B, exposed to low light intensity, will likely operate at a higher ΦPSII.
		Verification: This aligns with the principle that under low light, plants maximize light utilization, leading to higher quantum yield.
## OPTION ANALYSIS
[A] :x: Plant A will likely have a higher ΦPSII than Plant B.  High light intensities can cause photoinhibition, reducing ΦPSII.
[B] ✓: Plant B will likely have a higher ΦPSII than Plant A. Low light intensities lead to higher ΦPSII due to efficient light utilization.
[C] :x: The ΦPSII will be approximately equal in both plants. Light intensity significantly affects ΦPSII.
[D] :x: The ΦPSII will be zero in both plants due to the different light conditions.  Plants exposed to light, even monochromatic or polychromatic, will have a non-zero ΦPSII as long as the light is within the photosynthetically active radiation (PAR) range.
## LEARNING AIDS
	**Common Mistakes**:
		1. Assuming higher light intensity always leads to higher photosynthetic rates:  Ignoring the impact of photoinhibition at high light intensities.
		2. Confusing light absorption with light utilization:  Not all absorbed light contributes to photochemistry.  ΦPSII reflects the efficiency of utilization.
	**Quick Tips**:
		1. Think of ΦPSII as 'light use efficiency' of PSII.
		2. Remember that photoinhibition reduces efficiency at high light intensities.

B VENKAT · Answer

Plant A will likely have a higher ΦPSII than Plant B.

B VENKAT · Answer

The correct Option is "Plant B will likely have a higher ΦPSII than Plant A."

B VENKAT · Answer

The ΦPSII will be approximately equal in both plants.

B VENKAT · Answer

The ΦPSII will be zero in both plants due to the different light conditions.

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