Chlorophyll and Starch in Leaves

On the 24/7/08, Tuesday. Our Grade 10 FIB class, 10RRa learnt a new topic for biology lesson, photosynthesis. To allow us to have a better understanding of how photosynthesis occurs, Dr Hjorth engaged us in an experiment which requires us to test for starch in a piece of leaf.

Our class was then divided into several groups. Whereby we then obtained leaves from various plants and begin on our experiment.
Our group consisted of Yvette, Nicole and Sunshine. Dr Hjorth gave us a piece of leaf that looked distinctively different from the ordinary green leaves. The colour of the leaf was as of such, from the centre, pink, pale yellow, to the edges which are green. According to our knowledge, only the green parts of the leaves contain starch. Yet now we have a leaf with 3 shades, would the coloured parts possibly test positive to starch?

Step 1: First we had to place the leaf in boiling water for a minute to soften it.

Step 2: Once that is done, we place the leaf into a new test-tube with ethanol. Stand the test-tube in a beaker of hot water for around 10 minutes.

Step 3: Wash the leaf in cold water

Step 4: Spread the leaf flat on the Petri dish and cover it with iodine solution. If the leaf turns blue-black, it means starch is present.

After conducting the required steps, we obtained the following results:



As you can see, the places which were green turned blue-black, indicating starch was present where chlorophyll was. The pale coloured parts of the leaf stayed the colour they were, indicating starch was absent. So we can conlude that chlorophyll is involved in photosynthesis producing starch. The reason why a substance like starch is used for storage in plants is because it is insoluble, and does not cause problems like osmosis, unlike glucose.