Question

Explain an activity to test the presence of starch in a leaf.

Answer 1

Hint: Starch is one of the products of the photosynthesis of plants which is stored in the seeds for future nutrition, it is a white powdery substance that contains glucose molecules in it. And starch granules are also observed in stroma, and cytosol, etc.

Complete answer:
In order to explain the presence of starch in the leaves, the test is done with different substances, and the requirements of the test are:
- 2 plants
- Glass jar or beaker.
- Stove and pan.
- Ethyl alcohol.
- Iodine.
- Hot water and tweezer.

> Procedure:
- Before the test begins, two plants are taken and placed in 2 different rooms, one is under sunlight and another one is in a dark room for 24 hours.
- After 24 hrs, ethyl alcohol is taken to fill the glass jar or beaker and place this jar on the pan, place them on the stove and start heating the ethyl alcohol.
- And in the meantime, the leaves of both plants are cut and placed in the hot water with the help of a tweezer.
- Now the leaves are again placed in ethyl alcohol for 120 seconds.
- Because of the ethyl alcohol, the leaves are turned to white color, and now the iodine solution is dropped on the leaves and wait for the observation.

> Observation:
- The ethyl alcohol breaks the chlorophyll in the leaves and makes them white in color, and iodine turns the starch into a blue-black color.
- So the leaves which contain starch are turned into blue-black, and the leaf without starch is turned to reddish-brown color.
- The leaf which turned blue-black is a leaf which is placed in sunlight, and photosynthesis occurred and starch was produced.
- So photosynthesis is required for the starch to produce.

Note: In this experiment, the main reason for the removal of chlorophyll from the leaves is, their presence may mask the color produced by the iodine and may mislead the experiment, so it is very important to decolorize the leaves for this starch experiment.