When we talk about living beings, we immediately remember animals, however, plants, fungi, protozoa, algae and bacteria are also considered living beings. Although quite distinct, they all have characteristics that allow them to be classified as such.
→ What characteristics allow us to say that an organism is alive?
To be considered alive, the researchers analyze some very simple criteria, such as:
Reproduction: Living beings are capable of leaving descendants, that is, they are capable of reproducing. Initially, it was believed that microorganisms, such as bacteria, arose by abiogenesis. Today, however, it is known that even these small organisms reproduce. In the case of bacteria, the main type of reproduction is binary division or cissiparity, a type of asexual reproduction.
Evolution:Evolution is a process that acts on all living beings, modifying them over time. At this point, it is important to highlight natural selection, which ends up selecting the organisms that have the greatest chances of survival in a given environment. The most adapted organisms survive longer in the environment and, consequently, pass on their advantageous characteristics to their descendants.
Metabolism:Living beings have metabolism, that is, within their cells, chemical reactions occur that guarantee their survival. This metabolism ensures, for example, that living beings acquire energy to carry out activities such as reproduction and locomotion.
Response to stimulus: Living beings are able to respond to stimuli, which ensures that they interact with the environment. A pain stimulus, for example, can cause an animal to move away from an area. Another example is the light stimulus, which makes plants grow towards the light.
Carnivorous plants can respond to touch and capture their prey
Cell: It is generally accepted that living beings have cells, which are considered the structural and functional unit of an organism. Some beings are formed by several cells (multicellular); others, however, have only one (single cell).
Genetic material: All living beings have DNA and/or RNA, the material responsible for controlling their metabolism and ensuring that characteristics are passed on to the next generation (heredity).
→ What about viruses?
As we all know, the virus they are acellular beings that do not have their own metabolism. Because of these characteristics, classifying viruses as living beings is not an easy task, and opinions in the scientific community are quite divergent. There are researchers who do not consider viruses as living beings due to the absence of cells and metabolism, being considered by many only chemical products. Others, however, claim that they are, indeed, living organisms, as they manage to use the machinery of the infected cell to their advantage, reproduce and undergo evolution.
Curiosity: Did you know that the world has approximately 8.7 million species of living things?
By Ma. Vanessa dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/o-que-e/biologia/o-que-e-um-ser-vivo.htm