Cells can also be classified according to how they obtain their energy. Some cells have the ability to use light or chemical energy found in the outside environment to manufacture their own sugars, fats, and proteins. We call these types of cells autotrophs . All 400,000 species of plants and a few species of bacteria use sunlight and the process of photosynthesis to obtain their energy. Some bacteria breakdown molecules found in the environment to release chemical energy to sustain their life.
Organisms can also obtain their energy by consuming other organisms.
These organisms are called heterotrophs . Heterotrophs include most types of bacteria and all of the animal and fungi species. However, most organisms are multi-cellular . Within multi-cellular organisms, groups of cells can become specialized to carry out a certain function. We call these functional groups of cells a tissue .