Plants use sunlight to chemically join carbon dioxide gas from the air with water to make sugary food. The process is called photosynthesis.
Photosynthesis occurs in leaves in two special kinds of cell: palisade and spongy cells.
Inside the palisade and spongy cells are tiny packages called chloroplasts. A chloroplast is like a little bag with a double skin or membrane. Each is filled with a jelly-like substance called the stroma in which float various structures, such as lamellae. The jelly contains a chemical called chlorophyll which makes leaves green.
The leaf draws in air containing the gas carbon dioxide through pores called stomata. It also draws water up from the ground through the stem and veins.
When the sun is shining, the chlorophyll soaks up its energy and uses it to split water into hydrogen and oxygen. The hydrogen released from the water combines with the carbon dioxide to make sugar; the oxygen goes out through the stomata.
Sugar is transported around the plant to where it is needed. Some sugar is burned up at once, leaving behind carbon dioxide and water. This process is called respiration.
Some sugar is combined into large molecules called starches, which are easy for the plant to store. The plant breaks these starches down into sugars again whenever they are needed as fuel.
Starch from plants is the main nutrient we get when we eat food such as bread, rice and potatoes. When we eat fruits, cakes or anything else sweet, the sweetness comes from sugar made by photosynthesis.
Together all the world’s plants produce about 150 billion tons of sugar each day.