What are the factors that affect the photosynthesis of plants? In Y9 Science, students tested the starch content of four different leaves: normal leaves, variegated leaves, partially-covered leaves, and carbon dioxide starved leaves. After stripping the leaves of their green chlorophyll, a few drops of iodine on the leaf turns it black if starch is present. Since photosynthesis makes starch, if starch is still in the leaf, then the plant it came from must have been photosynthesizing fairly recently. Can you guess which leaves had starch and which ones didn’t? If you know a Y9 DC student, ask him or her to find out the answer.