Test for the Presence of Starch in a Leaf

Materials:

Two leaves, petri dish, iodine solution, boiling water, test tubes, alcohol, white tile, Bunsen burner

Method:

i. Remove two green leaves from a plant that has been in the sun for some hours.

ii. Put one of the leaves into a petri dish and add a few drops of iodine solution.

iii. Place the other leaf into a boiling water for five minutes to kill the living cells in the leaf.

iv. Half fill a large test tube with alcohol

v. Put the test tube containing the alcohol in the beaker of hot water.

vi. Remove the leaf from the hot water and put it in the alcohol. This removes the green colouring (chlorophyll) in the leaf.

This step should be done severally until there is no colour change in the alcohol.

vii. Remove the leaf from the alcohol and feel it.

viii. The leaf is then dipped in cold water to wash away the alcohol.

ix. The leaf is dipped in boiling water for about five seconds to make it soft.

x. Remove it and spread it out on a white tile. Add a few drops of iodine solution.

Observation:

The leaf turns blue-black

Conclusion:

The blue-black colour change of the leaf when iodine solution was added shows the presence of starch in the leaf.

The colour of the first leaf when iodine solution was added to it was still the same. No change was recorded. This was because, the starch was locked up in the cells of the leaf.