Walnut tree leaves are known as compound leaves because they have a number of blades on the same stalk or petiole. Unlike animals, plants make their own food by absorbing sunlight in a process called photosynthesis. The Sun gives the plant energy to convert carbon dioxide from the air and water into food. Inside each are tiny packages called chloroplasts that contain a green substance called chlorophyll, which makes leaves green. Carbon dioxide is drawn from the air through tiny holes called stomata, on the underside of each leaf.
Water is drawn up from the ground through the stem.
When the Sun shines, the chlorophyll soaks up energy and changes water into hydrogen and oxygen. The hydrogen joins with the carbon in carbon dioxide to make sugar. The oxygen goes out through the stomata. The newly made sugar is carried away through the veins to where it is needed. There it is converted into fats and starches for storage or is burned up at once, leaving carbon dioxide and water.