Question

plant A is kept in the dark or a black box for 72 hours (3days) Plant B is kept in sunlight iodine tes is conducted ith the leaves of the both plants which plant leaf tests positive for starch and why

Answer 1

Answer:

Plant B will test positive for starch because it is kept in sunlight so the process of photosynthesis will continue to take place and produce glucose which will be stored in the form of starch by the process of polymerisation. While plant A is kept in dark so no photosynthesis will take place the starch present in the leaf will be used for the metabolic processes so no starch will be left.

Explanation:

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Answer 2

Activity 6.2 of chapter number 6 NCERT science book

Aim:

To show that carbon dioxide is necessary for photosynthesis.

Procedure:

1. Take a plant with destarched leaves.
2. Insert one of its leaves in a conical flask containing potassium hydroxide.
3. Leave the plant in sunlight.
4. After a few hours, test the particular leaf and some other leaf of the same plant for the presence of starch.

Observation:

Leaf of plant kept without potassium hydroxide turn blue with iodine solution.

The plant with potassium hydroxide does not turn blue.

Explanation:

Potassium hydroxide is a highly reactive compound. It reacts with the carbon dioxide of the bell and forms its carbonate.

KOH + CO2 —————>K2CO3 + H2O

As a result, no carbon dioxide is available for the plant. In the absence of Carbon dioxide plant is unable to do photosynthesize and form starch. So, iodine does not turn the leaf blue.

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