The 6 characteristics of living beings

These are the aspects that characterize living beings, whether they are animals or plants, fungi, etc.

Defining what is a living being is something complex, a subject of wide debate that science today is not too sure if it is clear or not.

Since we only know of life forms on Earth, the features we consider to be those that delimit what is alive from what is not are not extrapolable to the rest of the universe, but they are the best we have for now.

Next we will discover what are the 6 main characteristics of the alive beings.

The 6 characteristics of living things (explained and summarized)

What is life? This question has a complex answer, since seeking definitions of life is as complicated as trying to find out exactly where the human soul is located. It is not possible to give a simple definition of what life is without resorting to arbitrariness, debates and discussions.

However, although it incurs in certain subjectivity, not establishing a limit between what is considered alive and what is not can make us commit the error of thinking that either everything is alive or nothing is.

It is difficult to define in words what is alivebut it seems that our common sense finds it a very simple task to identify it. For example, when we walk down the street and see a stray cat, a tree, a dog walking with its owner or even a cockroach, we know that they are all living beings, Biological organisms that harbor what we call life. On the other hand, the stones on the road, the clouds in the sky, a car on the road or a street lamp, we know very well that they are not alive.

Everything we know that is alive comes from our planet, something that makes it impossible for us to generalize it to the rest of the Universe.. Until we know of an extraterrestrial civilization, the current definition of what is alive can only be based on our small terrestrial experience. For now, it is considered that living beings are those that meet a set of characteristics, which distinguish them from inanimate objects and that we will see in depth below.

Organization and complexity

According to cell theory, which is one of the unifying concepts of biology, the structural unit of all organisms is the cell. In themselves, cells have a specific organization, all have particular sizes and shapes but are sufficiently generic to facilitate their recognition.

Some organisms are made up of a single cell, called unicellular, while others are more complex, composed of several cells and are called multicellular. In multicellular organisms, the cells that compose them work in a coordinated manner and are organized into complex structures such as tissues, organs and systems. as tissues, organs and systems.

Living beings show a high degree of organization and complexity. Life is structured in different levels of organization, where each one of them is based on the previous level and constitutes the foundation for the next level. For example, in multicellular organisms we have tissues, subdivided into cells which, in turn, are subdivided into organelles.

2. Growth and development

All living organisms grow at some point in their life cycle. When we speak of growth in a biological sense, we refer to an increase in cell size, cell number, or both. Even the smallest organisms, such as bacteria, grow by doubling in size before dividing again.

Growth is a phenomenon that can vary greatly from species to species.. There are organisms, such as many trees, in which growth occurs throughout life, while in others it is restricted to a certain stage or until a certain height has been reached, as in the case of human beings.

Development includes any change that occurs during the life of an organism since it was conceived.. In the case of the human species, we can say that this process begins once the ovum has been fertilized, following the different stages of embryonic development.

3. Homeostasis

In the universe, there is a natural tendency to the loss of order called entropy. Living structures, organized and complex, are victims of this tendency, which is why, in order to stay alive and function properly, organisms must maintain the constancy of order, organisms must maintain the constancy of their internal environment.. This process is homeostasis.

There are several conditions of the organism that need to be regulated. These include body temperature, pH, electrolyte concentration, water content, etc. The maintenance of the organism is a very costly process, which is why it is so important to maintain a constant internal environment. a large part of the energy that a living being obtains from its environment is used to maintain its internal environment within homeostatic limits..

4. Irritability

When we speak of irritability as one of the characteristics of living beings, we mean that life is capable of detecting and responding to the stimuli it receives. capable of detecting and responding to the stimuli it receives.. These stimuli are physical and chemical changes, both from the external and internal environment. Among these stimuli we can find:

• Light: intensity, color change, direction or duration of light-dark cycles.
• Pressure
• Temperature
• Chemical composition of the surrounding soil, water or air.

In unicellular organisms, being composed of a single cell that performs all vital functions, it is the whole individual that responds to these stimuli.In single-celled organisms, it is the whole individual that responds to the stimulus. In more complex organisms, on the other hand, there are cells that are responsible for detecting certain stimuli.

For example, humans detect light by means of specialized cells in our ocular retina, called cones (detect colors) and rods (detect light intensity).

5. Metabolism

To maintain their high degree of complexity, organization, growth and reproduction, organisms need materials from the external environment and transform them into others that can serve them. All the chemical reactions that take place in the cells of living beings and that allow their growth, conservation and repair are called metabolism.

On the one hand we have anabolism, the process by which the simplest substances are transformed into more complex ones, synthesizing new substances by expending energy. An example of this is synthesis of carbohydrates, lipids and proteins which, in turn, help to form cells and tissues and are responsible for growth. and are responsible for growth.

On the other hand, we have catabolism, which is the process in which complex substances are broken down into simpler ones, degrading substances and obtaining energy. An example of catabolic process is digestion, in which food is degraded into simpler compounds such as sugars, amino acids and fatty acids.

6. Reproduction

One of the main premises in biology is that every cell comes from another cell, so there must be some kind of reproduction that brought it into the world. There are two types of reproduction: asexual and sexual.

Asexual reproduction is reproduction that takes place without the participation of gametes or reproductive cells.. This type of reproduction is typical of simpler organisms, such as bacteria or protozoa, although it is true that there are animal and plant species that carry it out.

Of animals with asexual reproduction we have jellyfish, anemones, snails and starfish, and of plants with this type of reproduction we find tulips, dandelions, onions and gladiolus. The methods used by organisms with asexual reproduction are many, among which we can find parthenogenesis, stolons, grafting, cuttings, gemmation, spores...

Sexual reproduction is the one that occurs with the participation of gametes, one female and one male.. When these cells are combined, they produce a fertilized egg or zygote, which, as time goes by and given the ideal conditions, will become a new living organism.

Sexual reproduction is the one that occurs in the human species, in which the female egg is fertilized with a male sperm that gives rise to a zygote that, about nine months later, will become a baby. It is a type of reproduction found in most mammals, birds, fish and also in plants such as cacti, dahlias or violets.

Sexual reproduction has the advantage that it contributes to the variation of traits within a species, a fact that Charles Darwin and Alfred Wallace already recognized with their studies of biological inheritance.

Most living beings use a molecule called DNA or deoxyribonucleic acid, which is the physical support of the hereditary information they contain. There are entities, whose classification as living beings is debatable, that make use of other types of molecules, as is the case of retroviruses that use RNA or ribonucleic acid as the physical support of their hereditary information.

Reproduction and evolution: fundamental characteristics for life.

In most debates about where to draw the line between what is living and what is not, the ability to reproduce autonomously is considered the essential characteristic for establishing that something is a living thing.. One possible definition for life is anything that is capable of reproducing by some mechanism and responds to evolutionary pressure.

The genetic characteristics of a single organism are the same throughout its life as an individual, but the genetic composition of the species changes throughout its existence thanks to processes of recombination and mutations. These phenomena contribute to genetic variability, causing the species to change with the passing of generations and, therefore, to evolve constantly.

What most determines the survival of a species as a whole is natural selection. Individuals that have favorable characteristics for survival in the environment in which they live are more likely to reach reproductive age, have offspring and have their genes passed on to the next generation. In contrast, organisms with maladaptive traits are less likely to be able to survive and reproduce, which makes their genetic load more difficult to carry.This means that their genetic load is reduced from generation to generation.

Based on this, it can be seen that the fundamental pillars for a species to remain alive are reproduction and evolution, insofar as it involves the ability to adapt to the demands of the environment. Any species, eukaryotic or prokaryotic, animal or plant, uni or multicellular, will be considered a life form if it is capable of reproducing on its own and responding to the demands of the environment.

Are viruses living beings?

In principle, viruses are not considered to be living beings. Among the main counterarguments to those who did consider them to be organisms are that they are not cells and, therefore, cannot fulfill all the vital functions discussed above: organization and complexity, growth and development, metabolism, homeostasis, irritability, and reproduction and adaptation.

Viruses cannot be included in the phylogenetic tree of lifeViruses cannot be included in the phylogenetic tree of life: they do not contain ribosomes, they lack a nucleic acid, they have no fossil record and there is not even a shared gene among most of the viral groups, since they are newly synthesized as most of their genes are mixed with those of the cellular organisms they parasitize and, therefore, viral particles do not have a common ancestor, which makes them a polyphyletic group, having several origins.

But in spite of this, several arguments have continued to be put forward to defend that viruses are alive. One of them is that they are complex entities that are able to multiply, contain genes and evolve, as is the case of the COVID-19 variants. However, it is considered that these same arguments can be easily refuted by looking at viral behavior and taking into account evolutionary data.

For some researchers, viruses resemble mobile genetic elements such as plasmids, transposons, viroids and prions, subviral agents that are not considered living things. In addition, viruses cannot be considered complex entities because they lack cell membranes, chromosomes, ribosomes and organelles, but are rather inert particles composed of some type of nucleic acid and proteins.

Particles identical to viruses but without a genome have been found to function as organelles of bacteria and archaea, such as bacterial microcompartments, a single-celled organelle that performs metabolic and nutritional functions.The "free" viruses, once they enter the cell they invade, disintegrate completely, dividing themselves into smaller particles, such as bacterial microcompartments, an organelle of unicellular organisms that performs metabolic and nutritional functions. Free" viruses, once they enter the cell they invade, disintegrate completely, splitting into nucleic acids and proteins that will begin to be passed through the host's molecular synthesizing process, replicating.

It is for this reason that viruses replicate, a more correct term than "reproduce". They are replicated in part by the host's polymerases, ribosomes and messenger RNA, but not by their own means or because they do so voluntarily. This process has been called the virion factory, referring to the fact that viruses are manufactured by the cellular machinery. In fact, viruses can only multiply and evolve in cells. Without them, they are completely inanimate organic matter.