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

What are living things?

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

For an organism or living being to be classified 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 things 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 (single-celled organisms), while others can 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 undergo a process of absorption, transformation, and release of energy called metabolism, which enables them to fulfill their essential functions.

The metabolism has two phases:

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

Living things develop and reproduce

Living organisms go through 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 runs away when listening to its predators is responding to a stimulus.

A living being is capable of self-regulation

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.

Regulation of osmotic pressure is an example of homeostasis.

All living things evolve

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

Classification of living things

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

• Bacterium. Archaea. Eukarya.

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 most popular classification of 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:

• Protista: it is the kingdom of protozoa, which are single-celled microscopic organisms.

An example of the Protista kingdom is the amoebas.

• Plantae : it is the kingdom made up of red and green algae and terrestrial plants with and without flowers.

An example of an organism from the Plantae kingdom is the orchid ( Orchidaceae).

• Fungi : it is the kingdom made up of all fungi, which are organisms that, although they are similar to plants, cannot photosynthesize.

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

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

Examples of living things in the Animalia kingdom are birds, mammals, reptiles and humans.

See also:

• Kingdom Protista .Reino Plantae .Reino Fungi .Reino Animalia.

chemical composition of living being

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

• Primary chemical elements: carbon, oxygen, hydrogen, phosphorous, 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.