Why do animals have to consume food?
Animals have to consume food as they cannot make their own food
yes! In most cases, yes, but much of how much food an animal of any size needs to live is determined by the nutrients in the food they consume the most. Though this is not true 100% of the time, many herbivores, for instance, tend to consume more because the food they eat is not overly nutrient rich.
They are called producers, because they produce the food for the animals. The next ones are consumers, these are usually animals that consume the plant or other animals. The last type are called decomposers, these are fungi, or mould or earthworms, these decompose dead remains of plants and animals.
An autotroph such as a photosynthetic cell produces it's own food. Once produced through photosynthesis, the food needs to be used as in cellular respiration. Hetertroph, such as animals do not produce their own food. They must consume the food produced by the autotrophs or consume the heterotrophs that have consumed the food produced by the autotrophs.
One reason why is because they are able to produce their own food using energy from the environment, and therefore have no need to consume any other plants or bacteria. They provide food to a variety of living species including animals, protozoa, bacteria and fungi. They are consumed, but do not consume.