In Biology, an entity is considered a living being when it is able to perform processes such as growth and reproduction and when it is able to respond to internal and external stimuli. Living beings are divided into prokaryotes, eukaryotes, autotrophs, and heterotrophs.
Prokaryotes and eukaryotes
Considering the cellular organization, living beings can be divided into two groups. One is composed of prokaryoticbeings , possessing cells with simple organization, that is, cells devoid of nuclear envelope, or library, and very simple cytoplasm with few structures. As examples of living prokaryotes we have bacteria and cyanobacteria , which have been called blue algae.
Another group of living beings are eukaryotes, which have more complex cells, with the presence of nuclear envelope and many cytoplasmic organelles such as mitochondria, endoplasmic reticulum, ribosomes, golgiense complex, etc. In this group we find a great variety of organisms that differ in form, size and degree of development. Examples of eukaryotes include protozoa, algae, fungi, plants and animals.
However, there is another group of living beings that can not be classified as prokaryotes or eukaryotes due to their organization. These are viruses, acellular organisms , without their own metabolism and only have molecular organization. These organisms are considered living beings because they have reproductive capacity and genetic material.
Autotrophic and heterotrophic beings
Another way of dividing living things is to take into account the type of nutrition of each species. In this division, we have the organisms that are called autotrophs and the organisms that are called heterotrophs. The autotrophs are those who can produce their own food, and most do through the process of photosynthesis and is represented by plants, algae and cyanobacteria.
However, heterotrophic organisms are those that can not produce their own food and must feed on other organisms or matter present in the environment. Examples of heterotrophic organisms are fungi, animals and most bacteria.