What is inside of a leaf?

This is what our teacher taught us a few days back.

we all know chlorophyll creates food for the plant as there are chloroplasts in them. let me show you a experiment to prove it.

Aim : To investigate the type of food stored in a green leaf.

Hypothesis : I will use iodine to test if the leaf has starch in it. As iodine turns from brown to blue when it comes in contact will starch, it is the best candidate to test for starch in a leaf.

Theory : Leaf has chloroplasts in them hence, starch will be created as when leaf undergo photosynthesis, they produce oxygen and glucose. The excess glucose is converted to starch which is stored in flowers or fruits. EG. A potato, strawberry.

Materials : A beaker, water, leaf, bunsen burner, alcohol( denatured ethanol ), gauze mat, tripod, test tube.

Steps :

1) Firstly boil the leaf in a beaker of water for about 5 minutes

2) Set up the apparatus as shown above. (methylated spirits also know as alcohol )

3) Boil the leaf for about 10 minutes

* After this stage the leaf will be very brittle so carefully remove the leaf from the beaker to avoid breaking the leaf

4) Dip the leaf in a beaker of hot water to soften the the dehydrated leaf.

5)Next add a few drops of iodine on the leaf

Results : The iodine turned from dark brown to blue.

Our opinion : The results show that when a plants photosynthesize the produce starch.

Further explanation : This is because starch is composed of polymers of glucose. Long linear chains are amylose. Amylopectin is similar but contains a branch point about every 25th glucose or so. Amylose coils into a helical secondary structure resembling a tube with a hollow core. Certain molecules including fatty acids and iodine can lodge inside the core as already mentioned. The complex of iodine stuck inside the amylose coil produces a characteristic blue-black colour. The starch itself is not altered. Starch-iodine complex becomes unstable at temperatures above 35 °C. This complex in presence of an oxidizing agent the solution turns blue, in the presence of reducing agent, the blue color disappears because trioxide ions break up into three iodide ions, disassembling the complex. So starch turns into glucose molecules. Therefore the blue black colour disappears. However, when it cools down again, then the glucose macromolecules bonded up together again in a long chain, becoming starch. That is why it tested positive for starch and turns back into blue-black colour. Hence i can conclude that iodine change colours when it come in contact with starch.

Better Theory : One of the product of photosynthesis is Starch.When the iodine comes in contact with the leaf the iodine turns blue as the starch is reacting with the iodine.

Our opinion :The content inside the leaf is starch.

Conclusion :

My hypothesis was confirmed. I concluded this as when my teacher taught us how to do the experiment i checked the results of my friends and all of them have the same result.

Overall : My results generalize that leafs do produce starch.