The Question is from neet-botany photosynthesis-in-higher-plants , and it was created by the author Mr. NARESH KUMAR K

Question

In half leaf experiment, a part of a leaf is enclosed in a test tube containing KOH soaked cotton, while the other half is exposed to air and then setup is placed in light for sometime. It was latter found that part of leaf which was exposed to air tested positive for starch. This indicates that

Mr. NARESH KUMAR K · Accepted Answer

## CORE INFORMATION
✓ **Answer**: D
## CONCEPT FRAMEWORK
**Primary Concept**: The role of carbon dioxide in photosynthesis
**Related Topics**: Photosynthesis, Starch synthesis, KOH absorption, Experimental controls
**Prerequisites**: Understanding of photosynthesis, the role of CO2, and the half leaf experiment.
## SOLUTION PATHWAY
**Given Information**:
* Half leaf experiment setup with one part exposed to air and the other in a test tube with KOH.
* The exposed part tests positive for starch.
* KOH absorbs CO2.
**Method & Steps**:
1. **Understand the purpose of KOH:** KOH is used to absorb carbon dioxide (CO2). In the experiment, it ensures that the leaf part inside the tube does not have access to CO2.
Reasoning:  KOH removes CO2 from the air.
2. **Analyze the starch test results:** The part of the leaf exposed to air tested positive for starch, indicating photosynthesis occurred.
Reasoning: Starch is a product of photosynthesis.
3. **Relate the results to CO2:** The part enclosed with KOH did not make starch because it lacked CO2, which is essential for photosynthesis.
Reasoning: Absence of CO2 prevents photosynthesis and starch synthesis.
4. **Conclude the role of CO2:** The experiment demonstrates that CO2 is necessary for photosynthesis since the leaf part deprived of it was unable to produce starch.
Result: CO2 is essential for photosynthesis.
Verification: The result aligns with the established knowledge about photosynthesis.
## OPTION ANALYSIS
[A] :x: While light is necessary for photosynthesis, this experiment primarily shows the role of CO2, not light.
[B] :x: Oxygen production is not being tested in this particular setup.
[C] :x: The experiment's focus is not on water, and the KOH doesn't directly interact with the water in the leaf. Its primary function is CO2 absorption.
[D] ✓: This is the correct explanation as the KOH absorbs the CO2, preventing photosynthesis in that part of the leaf.
## LEARNING AIDS
**Common Mistakes**:
1. Confusing the purpose of KOH: Mistaking KOH's role for something other than CO2 absorption.
How to avoid: Remember KOH is a CO2 absorber.
2. Misinterpreting the control group: Not understanding the purpose of comparing the part exposed to air with the part enclosed with KOH.
How to avoid: Always identify the control and experimental variables.
**Quick Tips**:
1. Remember that starch is a product of photosynthesis, and the absence of starch indicates the absence of photosynthesis.
2. Think of KOH as a CO2 scavenger in these experiments.

Mr. NARESH KUMAR K · Answer

Light is essential for photosynthesis

Mr. NARESH KUMAR K · Answer

Oxygen is liberated in photosynthesis

Mr. NARESH KUMAR K · Answer

Water is essential for photosynthesis because in KOH soaked leaf, starch synthesis do not occurs as water reacts with KOH and it become unavailable for photosynthesis

Mr. NARESH KUMAR K · Answer

The correct Option is "Carbon dioxide is essential for photosynthesis because in KOH soaked leaf, starch synthesis do not occurs as $C{O_2}$ is absorbed by, so $C{O_2}$ is not available for photosynthesis"

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