When we see an animal, we know it's a living being, don't we? But, after all, what defines a being as a living organism? What characteristic must an organism have to be classified as a form of life? These answers, despite appearing simple, are much more complex than we can imagine, since certain organisms do not fit into certain requirements even if they behave as a form of life.
Below we list some of the main requirements for an organism to be considered a living being.
→ Chemical composition
All living organisms have certain types of chemical elements. Are they: carbon, hydrogen, oxygen and nitrogen. In addition to these elements, we also find phosphorus and sulfur, but in smaller amounts.
→ cells
At cells they are the functional and structural units of living beings, being present in all living organisms, with the exception of viruses. In a simplified way, we can say that cells have plasma membrane, cytoplasm and genetic material. This genetic material may be dispersed in the cytoplasm (
prokaryotic cells) or be delimited by a membrane (eukaryotic cell). Organisms made up of just one cell are called unicellular, and those made up of multiple cells are called multicellular.→ Genetic material
All living beings have genetic material, which is responsible for transmitting the characteristics of a living being to the next generation (heredity) and control the activities that will be carried out by the cell. The genetic material is made up of one or two types of nucleic acids (DNA and RNA).
→ Metabolism
Living beings have chemical reactions inside their bodies, which are necessary for the most varied activities, such as obtaining energy. The set of these chemical reactions is called metabolism. There are reactions that are related to the synthesis or construction of molecules, these processes being called anabolism. There is still the catabolism, which consists in the destruction of particles for the release of simpler substances.
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It is important to point out that viruses do not have their own metabolism and, therefore, they must parasitize a cell in order for them to reproduce.
→ Nutrition
Living organisms need energy to carry out their activities, and this energy is obtained through nutrition. Living organisms can be divided, based on nutrition criteria, into autotrophic and heterotrophic. Autotrophs obtain energy through processes such as photosynthesis, and heterotrophs obtain energy from the breakdown of products from other living beings. In a simplified way, we can say that the autotrophic beings are capable of producing their own food, and heterotrophs are not.
After nutrition, organisms carry out chemical reactions so that energy is obtained and used later. The energy production process is calledcellular respiration.
→ reproduction
Living beings are capable of reproducing, that is, producing offspring. Reproduction can occur sexually or asexual. In the sexual form, gametes are involved; in asexual, no.
→ Ability to respond to stimuli
Living beings are able to respond to stimuli from the environment, a property known as irritability. As an example, we can mention the closing of the leaflets of the touch-sensitive plant or even the escape of an animal in the face of imminent danger.
→ Evolution
All living beings are subject to the evolutionary processes, that is, they undergo changes over time. One of the factors that cause evolution is the emergence of mutations, modifications that occur in the DNA molecule and lead to the appearance of new characteristics in an organism. These modifications can be passed on to descendants.
By Ma. Vanessa dos Santos
Would you like to reference this text in a school or academic work? Look:
SANTOS, Vanessa Sardinha dos. "General characteristics of living beings"; Brazil School. Available in: https://brasilescola.uol.com.br/biologia/caracteristicas-dos-seres-vivos.htm. Accessed on June 27, 2021.
