In the leaves are tiny openings called stomata. There are about 9,000 to 72,000 stomata per square centimeter of surface area. Photosynthesis happens when the sunlight hits the leaves. This makes the leaves a very important part of making food for the plant. Food and energy Plants make their own food because they have chlorophyll.
Photosynthesis is the chemical change that produces food for the plant.
In photosynthesis, carbon dioxide, gas and water are mixed to make sugar and oxygen. Sunlight is the energy it needs for the chemical reaction. Because of the earth's gravity, the roots grow down and the stem grows up. The gravity is a stimulus. Geotropism is the plant's way of responding.