In nature there is a constant flow of energy and organic matter that is essential for the maintenance of life. All living organisms participate in these processes through the food chains, whether they are autotrophic and produce their own food, or heterotrophic and consume other organisms.
Autotrophic Beings
Autotrophic beings are living beings that obtain nutrients and energy, taking advantage of sunlight, through photosynthesis. As they produce their own food, they do not need to consume other organisms, and participate as main producers (base) of the food chains. They are generally green organisms because they contain a pigment called chlorophyll, but others like blue algae or cyanobacteria also contain other pigments, which make them bluish. Examples of autotrophic beings are plants, algae and cyanobacteria.
More rarely, energy can be obtained in the absence of sunlight, through chemical oxidation. This process, called chemosynthesis, produces organic matter through inorganic substances, such as iron, sulfur and nitrogen. Some species of bacteria are capable of carrying out this process, examples are Nitrosomonas and Nitrobacter that participate in the nitrogen cycle and Thiobacillus that oxidize sulfur .
Heterotrophic Beings
Heterotrophic beings are living beings that obtain nutrients and energy, consuming other living beings. Heterotrophs take advantage of carbon sources that are part of other organisms. In the food chains they act as consumers, depending directly or indirectly on autotrophic beings.
If they are herbivores (primary consumers) they feed directly on producers, and if they are carnivores (secondary consumers), they feed on herbivores. Thus, for example: the frog is a secondary consumer since it feeds on insects, but indirectly depends on the plants (producer) that serve as food for insects.
The type of food varies widely among heterotrophs. An animal can eat both vegetables and animals and therefore be omnivorous (bat, skunk, human being); it can feed on the remains of dead animals, being called detritivore (vultures, flies, hyenas) or feed only on the blood of an animal, called hematophagous (parasites such as lice, fleas, ticks).
To learn even more, also read about omnivores .
Did you know that carnivorous plants are autotrophic and heterotrophic beings? Because it does not absorb all the necessary nutrients during photosynthesis, it complements its diet with the ingestion of small animals.