Living beings: what they are, characteristics, classification, examples

What are living things?

The living beings they are all complex molecular structures or systems that fulfill essential functions such as food, development, reproduction and interactions with other organisms, including energy exchange with the surrounding environment.

For what an organism or being alive can be cataloged as such, it requires at least one cell in its structure.

Characteristics of living beings

Although there is a wide diversity of living beings, they all share certain characteristics:

Living beings have levels of organization

All living things are characterized by having a cellular structure. What varies is the number of cells, since some organisms have only one (unicellular organisms), while others may have more than one (multicellular organisms).

This structure has several levels of organization, ranging from biomolecules to the tissues, bones and organs of the most complex living beings.

All living organisms fulfill metabolic functions

All living organisms comply with a process of absorption, transformation and release of energy called metabolism, which allows them to fulfill their essential functions.

The metabolism has two phases:

  • Anabolism: is the transformation of nutrients into new organic sub products, such as amino acids.
  • Catabolism: is the transformation of nutrients into energy.

Living things develop and reproduce

Living organisms comply with a development cycle that involves a series of internal and external changes (increase in size, weight, shape, etc.).

At one point in their development they are ready to reproduce, either sexually or asexually.

Organisms respond to stimuli

Every living being has the ability to receive stimuli from the environment, process it and take that information to generate a short or long term response.

An animal that flees when listening to its predators is responding to a stimulus.

A living being is able to self-regulate

All organisms have the ability to internally compensate for changes that occur in the environment. This ability is known as homeostasis and is vital for survival.

Osmotic pressure regulation is an example of homeostasis.

All living things evolve

Any living organism has the ability to adapt to the surrounding environment and evolve. In this way it ensures the survival of its species.

Classification of living things

In principle, living things are classified into three large groups called domains:

  • Bacterium: are unicellular organisms whose DNA is not surrounded by a cell wall.
  • Archaea: are unicellular organisms whose DNA is separated from the rest of the structure by a cell wall.
  • Eukarya: also called eukaryotic, they are all organisms whose DNA is in the nucleus of the cell.

Each domain, in turn, is made up of other subdivisions called kingdoms In the Eukarya domain is the kingdom with the best known life forms, hence the classification of the most popular living beings. However, this does not mean that they are the only living organisms.

The most accepted classification by kingdoms in the Eukarya domain includes four groups:

  • Eubacteria: all bacterial microorganisms.

A kingdom example Eubacteria is the Escherichia coli, a bacterium found in the intestinal tract of the human being,

  • Plant: is the kingdom composed of red and green algae and land plants with and without flowers.

A example of an organism of the kingdom Plant it’s the orchid (Orchidaceae).

  • Fungi: It is the kingdom composed of all fungi, which are organisms that, although they resemble plants, cannot perform photosynthesis.

An example of a living being from the Fungi kingdom is the Penicillium chrysogenum , the fungus from which penicillin is extracted.

  • Animals: in this kingdom are all animals whose embryonic development is generated from a zygote.

Examples of living beings from the Animalia kingdom they are the birds, the mammals, the reptiles and the human being

Chemical Composition of living being

Living beings share a chemical composition consisting of about 60 elements, which in turn are divided into two large groups:

  • Primary chemical elements: carbon, oxygen, hydrogen, phosphorus, sulfur and nitrogen. These elements are indispensable for life on Earth.
  • Secondary chemical elements: sodium, calcium, potassium, iodine, iron, magnesium, silicon, copper, fluorine, manganese, boron and chlorine.