Organisms can be classified into three main types: plants, animals, and microorganisms. Plants are living things that produce their own food through a process called photosynthesis. They are essential for life on Earth as they provide oxygen and food for other organisms. Animals are organisms that consume other living things for energy. They can be further divided into groups like mammals, birds, reptiles, and insects. Microorganisms, such as bacteria and fungi, are tiny organisms that can only be seen under a microscope. They play crucial roles in ecosystems, including decomposition and nutrient cycling.