Question

A healthy cotton plant bearing variegated leaves was kept in a dark cupboard to destarch it, after which it was placed in sunlight for a few hours. One of the leaves was then plucked and an outline of the leaf making the green and non-green region were drowned. The leaf was then tested for starch. Using the above information, answer the following question.
State the aim of the above experiment.

Answer 1

Hint: The process by which the organisms, bearing photosynthetic pigment (chlorophyll) are capable of synthesizing their food in presence of water, sunlight, and carbon dioxide is called photosynthesis. Photosynthesis produces organic compounds and converts solar energy into chemical energy.

Complete answer: In the given question a healthy cotton plant with variegated leaves first kept in a dark cupboard destarching. Then the plant was kept in the sunlight. After some time one of the leaves was plucked and separated the green region and white region by outlining. Then the starch test was performed in the leaf. This experiment was done to prove that chlorophyll is a necessary component for photosynthesis.
The steps of the experiment are given below:
First, a healthy variegated plant (cotton plant) is kept in the darkness for some time.
Then the plant is exposed to the sunlight and kept for some hours.
Then a leaf is plucked from the plant and outlined the green area so that the white area and green area of the leaf can be separately visible.
After that, the leaf is placed in boiling water for 60 seconds.
From the boiling water, the leaf is transferred to boiling ethanol for two minutes.
After two minutes the leaf is placed in a shallow dish. Then the iodine is given to the leaf.
Then the leaf is washed with water to remove excess iodine.
Result of the experiment: After adding iodine the portion of the leaf which was white turns reddish-brown color and the green area of the leaf turns black-blue color. Black Blue color is an indication of the presence of starch. The white area of the leaf does not perform photosynthesis that results in absence of starch. Thus starch is present only in the green area which contains the chlorophyll pigment. So it can be said that chlorophyll is the essential component of photosynthesis.
So, the correct answer is “Option A”.

Note: Variegated plants are those which comprise different colors in the leaves and stems. Normally plant leaves are green but variegated plant leaves possess leaves in a combination of white and green. The white part lacks chlorophyll and the green part bears chlorophyll. In this experiment variegated plants are chosen to prove that plants need chlorophyll for performing photosynthesis.