Video Lab: A Sign of Photosynthesis

By means of photosynthesis, plants convert carbon dioxide and water into glucose, which is their food. As soon as glucose molecules have been produced, they are grouped and converted into a substance called starch.

Starch is made up of tightly packed glucose molecules, and acts as a food reserve for plant cells. If the leaves of a plant contain starch, we can say that the plant has been performing photosynthesis.

Watch the following video, in which a leaf is tested for starch using iodine. Iodine reacts chemically with the starch in the leaf and turns from brown to green. To ensure that the iodine penetrates into the plant cells and that the change in color is visible, the leaf must be boiled and its pigments extracted using alcohol.

This video belongs to an interactive activity in the Explain section of the "Nutrition" 5E Unit.