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 some time. It was later found that part of leaf, which was exposed to air tested positive for starch. This indicates that

• A. light is essential for photosynthesis
• B. oxygen is liberated in photosynthesis
• C. water is essential for photosynthesis because in $KOH$ soaked leaf, starch synthesis does not occur as water reacts with $KOH$ and it become unavailable for photosynthesis
• D. carbon dioxide is essential for photosynthesis because in $KOH$ soaked leaf, starch synthesis does not occur as $CO _{2}$ is absorbed by $KOH$ and not available for photosynthesis

Answer 1

Answer: (D)

Half leaf experiment demonstrates that $CO _{2}$ is essential for photosynthesis. In this experiment, a part of a leaf is enclosed in a test tube containing some $KOH$ soaked cotton (which absorbs $CO _{2}$ ) and the other half part is exposed to air. The setup is then placed in light for some time.
On testing for starch later in the two halves of the leaf, the exposed part of the leaf tested positive for starch, while the portion that was in the tube, tested negative. This showed that $CO _{2}$ is required for photosynthesis.