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

Question

Which one of the following is not true about the light reactions of photosynthesis?

B VENKAT · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
	**Primary Concept**: Light-dependent reactions of photosynthesis
	**Related Topics**: Photosynthesis, Chloroplasts, ATP synthesis, NADPH, Electron transport chain
	**Prerequisites**: Basic understanding of photosynthesis and its two stages (light-dependent and light-independent).
## SOLUTION PATHWAY
**Given Information**:
	The question asks about what is *not true* regarding the light reactions of photosynthesis.
**Method & Steps**:
	1. **Recall the purpose of light reactions**: The light reactions capture light energy and convert it into chemical energy in the form of ATP and NADPH.  These energy-carrying molecules are then used in the Calvin cycle (light-independent reactions).
		Reasoning: Light reactions are the energy-capturing phase of photosynthesis.
	2. **Remember the role of water**: Water molecules are split (photolysis) during the light reactions, releasing oxygen as a byproduct and providing electrons for the electron transport chain.
		Working: The electrons from water replace the electrons lost by chlorophyll in photosystem II.
		Key Point: Oxygen is a byproduct of the light reactions.
	3. **Understand the products**:  ATP and NADPH are the main products of the light reactions. These molecules carry the energy captured from light.
		Result: Light reactions produce ATP and NADPH.
	4. **Consider the role of carbon dioxide**: Carbon dioxide is *not* involved in the light reactions. It is used in the Calvin cycle (light-independent reactions) to build organic molecules (sugars).
		Verification: Carbon dioxide fixation occurs in the stroma of the chloroplast during the Calvin cycle, not during the light reactions which occur in the thylakoid membranes.
 ## OPTION ANALYSIS
[A] ✓: Light energy is converted into chemical energy (ATP and NADPH) during the light reactions. This is true.
[B] ✓: Water molecules are split during the light reactions (photolysis). This is true.
[C] ✓: ATP and NADPH are produced during the light reactions. This is true.
[D] :x: Carbon dioxide is *not* incorporated into organic molecules during the light reactions. This occurs during the Calvin cycle (light-independent reactions). This is false, making it the correct answer to the question.
 ## LEARNING AIDS
	**Common Mistakes**:
		1. Confusing the roles of light reactions and the Calvin cycle: Remember that light reactions capture energy, while the Calvin cycle uses that energy to fix carbon dioxide.
		2. Forgetting the source of oxygen in photosynthesis: Oxygen is released from water during the light reactions, not from carbon dioxide.
	**Quick Tips**:
		1. Light reactions = Light energy in, chemical energy (ATP and NADPH) out.
		2. Calvin cycle = Carbon dioxide in, sugar out.

B VENKAT · Answer

Light energy is converted into chemical energy.

B VENKAT · Answer

Water molecules are split.

B VENKAT · Answer

ATP and NADPH are produced.

B VENKAT · Answer

The correct Option is "Carbon dioxide is incorporated into organic molecules."

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