Question

A healthy croton 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 any outline of the leaf making the green and non-green regions were drawn. The leaf was then tested for starch. Using the above information, answer the following question
What change is seen on the leaf after the starch test?

Answer 1

Starch is one form of the carbohydrates and it is also the by-product of the photosynthesis of the plants, where it is produced and usually stored by the plants for their future use and they store it in seeds.

Complete answer:
The important things that require in order to explain the changes that takes place in the leaves are given below that are

Healthy croton plant as given above
Glass beaker, stove, ethyl alcohol
Iodine, hot water and also tweezers.
Procedure:
At first a healthy croton plant should be placed in a dark room for 24hrs and later it should be placed in sunlight for about 2 hours.
At the same time glass beakers should be filled with ethyl alcohol and it should start heating. i
And any one of the leaves of the plant which we are using in this experiment is plucked and where the green and non green areas are marked in that leaf. Now that leaf should be placed in heated ethyl alcohol for 2 minutes.
Due to this color of the leaf changed to white, now iodine should be dropped on the leaf and wait for the observation.
Observation :
The heated ethyl alcohol used here makes the leaf white by breaking it chlorophyll and at the same time iodine which is used here turns any starch that present on leaves turns to blue black color, and non starch part of the leaf to reddish brown color.
The part of the leaf which turns blue black is starch containing green part, whereas the other non green part of the leaf turns to reddish color.
So chloroplast is required for photosynthesis, and photosynthesis is required for the production starch.

Note: The main reason for using the ethyl alcohol in this experiment is to break the green color due to the presence of chloroplast. The existing green color may mislead the experiment, so it is better to remove the chloroplast.