The Plantae kingdom is the only kingdom that is entirely autotrophic; Eubacteria, Protista and Archeabacteria contain some autotrophs. Kingdoms Fungi and Animalia are solely heterotrophic. Living things that are autotrophic can make their own energy, while heterotrophic organisms must look to other organisms for food to use as energy.
Plants are considered autotrophic because they can convert sunlight into a food source for energy in a process known as photosynthesis. Other organisms, such as certain types of bacteria, can also make their own energy from sunlight, chemicals or other inorganic materials. Organisms such as animals do not have these biological processes. Instead, they feed on other organisms to take in the proteins, fats and carbohydrates needed to make energy.