Plants can be classified into three groups: grasses, bushes, and trees. Grasses have soft, thin stems and are usually short, while bushes are taller and have many woody stems and branches. Trees have thick, woody trunks. Deciduous trees lose their leaves in autumn, while evergreen trees keep their leaves year-round. Photosynthesis is the process by which plants make their own food, using water, minerals, carbon dioxide, and sunlight.