• what is a living being?
• Characteristics of living beings

We explain what living beings are and what are the shared characteristics that differentiate them from inert matter.

All living beings have common basic and elemental characteristics.

what is a living being?

From the point of view of biology, the living beings or living beings, also known as organisms, are very complex forms of organization of matter, capable of functioning as a system that is perpetuated over time, exchanging energy and matter with your environment.

These forms of life differ from the inert matter in that they comply with the elementary processes of existence, which are:

• The nutrition, that is, take from environment (or from other beings) the necessary materials to perpetuate its own existence.
• The interaction, that is, the establishment of bonds of all kinds with other living beings and with the environment, either by way of competition, of cooperation, of symbiosis or of antagonism.
• The reproduction, that is, the formation of new individuals Of the same species, which remain after the organism fulfills its life cycle.
• The death, finally, is the return to the environment of the matter and the Energy that were used to exist, and the inevitable end of all life.

Living beings are the fundamental object of study in biology, and they are (according to the most accepted hypothesis) the result of complex chemical processes that occurred on our planet in its primitive stages of geological formation.

Finally, all living beings have common basic and elemental characteristics, which we will describe in detail below.

Characteristics of living beings

1.They have a certain degree of cellular organization

All living things are made up of cells.

All living beings are the result of a very rigorous organization of the matter that makes them up, and the basic unit of the organization of life is the cell. That means that from more complex beings (such as mammals) to the simplest (such as bacteria), we are all made up of cells.

In fact, depending on how many there are, we can talk about two types of living beings:

• living beings unicellular, whose bodies are made up of a single cell. These organisms can exist individually and freely, or form colonies of organisms that live together, without ever ceasing to be single and unicellular organisms. For example: the amoebas and the paramecia, microscopic organisms of free life
• living beings multicellular, whose bodies are made up of lots of cells of various types, organized at such a complex level that they constitute tissues, organs, etc. In the case of these organisms, the cells sacrifice their autonomy to form a much more complex whole, so that none can survive without the rest. For example: chickens, trees, mushrooms and Humans.

All living beings are made up of cells, although their respective cells have different levels of complexity: some are simple and have few organelles, others are more complex and carry out various specialized biochemical processes: epidermal cells, bone cells and muscle cells, for example, they perform different tasks and therefore have different compositions, shapes, and organelles.

2. They maintain an internal order or homeostasis

Mechanisms such as sweat allow living beings to maintain their internal balance.

In order for living things to continue living, their bodies must regulate their vital functions and maintain a delicate Balance internal. Getting too much (or too little) of a certain nutrient, losing too much temperature or having very little water are some examples of situations that can break this balance and endanger the continuity of existence.

To do this, organisms have developed different mechanisms that allow them to counteract the effect of the environment on their bodies and adapt to situations to preserve their internal balance.

For example, when it is very hot, our skin sweats to hydrate itself and so that the evaporation of sweat cools us down; On the other hand, when it is very cold, our body shivers so that the movement of the muscles generates heat. These measures try to counteract the effect of environmental temperature on our bodies.

The same occurs at the cellular level: the cells of our body are maintained with a slightly higher level of acidity than that of plasma, since this is conducive to their chemical reactions fundamental. To ensure that said pH be preserved, released or hoarded ions and you leave the environment depending on what is convenient at the time.

3. They react to environmental stimuli

Living things adapt to their environment to preserve themselves.

Living beings do not exist in a vacuum, but proliferate in an environment that they share with other forms of life and with different processes, dynamics and natural mechanisms, many of which have a certain impact on homeostasis.

For this reason, living beings relate to the environment, that is, they perceive the stimuli around them and orient themselves in the environment according to what suits them best, just as we do when it is sunny and we look for a shade.

To do this, living beings have different sensory devices that communicate the outside of the body with the inside of the body, and are capable of recognizing environmental stimuli such as sound, light, odor, pH, etc., and then react to them in an appropriate way. In this way, living beings adapt to their environment to preserve themselves.

For example, certain floors They have a positive phototropism mechanism, that is, they change the position of their leaves and stems depending on the presence of the sun, in order to expose them to the greatest possible amount of sunlight. sunlight (essential for photosynthesis).

Other plants, less in need of sunlight, on the other hand, have negative phototropism and tend to flee from the sun, limiting or moderating the amount of light that their leaves receive. In this way, the plants adapt to the amount and orientation of the surrounding sunlight, depending on what suits them best.

4. They go through a life cycle

The life cycles of different species can be very different from each other.

Every living being is at some point in its respective life cycle or circuit, that is, in the set of stages or vital moments that it must go through from birth to death. Life cycles can be very different from each other, and that is the reason why some living things are long-lived and lead slow lives, while others live frantically and die quickly.

Every life cycle consists of the following stages:

• Birth, the appearance of a new individual of a species in the world, either by being expelled from the womb, hatching an egg or arising from an ancestor cell.
• Increase, a stage of accumulation of resources from the environment to invest them in the expansion of the body itself, that is, in increasing size and complexity, developing new organs or preparing for a metamorphosis.
• Reproduction, stage in which individuals reach their maximum point of growth, change and mature, and prepare to bring new members of the species into the world.
• senescence and death, stage of gradual loss of internal balance and weakening of vital functions, which ends in one way or another in death.

5. They have a metabolism

Metabolism allows living beings to take advantage of matter and energy.

All living beings need matter and energy to keep their biochemical cycles going, as well as to repair themselves, move, grow or undertake a metamorphosis.

This energy and matter needs to come from somewhere, and for this there is the metabolism, that is, the ability to process nutrients from the environment and store them to undertake subsequent tasks. Otherwise, we would have to be eating all day to sustain ourselves.

There are many forms of metabolism, depending on each form of life, but in general they consist of chains of chemical reactions that occur inside the body in a controlled and specific way, from certain substances that are taken from the environment and that When transformed, they serve as fuel for the body.

For example, the human body requires organic material to break down and thus obtain glucose, a type of sugar that is very useful chemically. Said sugar is then oxidized (that is, it reacts with the oxygen taken from the environment when breathing) and subjected to different biochemical processes.

As a result, the molecules of Adenosine Triphosphate (ATP), a molecule of pure chemical energy which can be used for many different purposes.

There are two fundamental metabolic processes:

• The anabolism, which consists of composing substances complex from simpler ones, as plants do by combining water, sunlight, and carbon dioxide atmospheric to compose a wide range of sugars and starches, essential to keep the body running.
• The catabolism, which consists of the reverse process: breaking down complex substances into simpler ones, generally with the help of proteins specialized calls enzymes, just as we do with the organic matter that we ingest when we eat, and that we break down into the different nutrients that we need to absorb during digestion.

Similarly, metabolisms comprise two types of cycle, which are:

• The material cycle, that is, the one destined to obtain material nutrients that serve to build new tissue, especially in growth or repair phases, or to manufacture substances with a specific purpose, such as reproductive cells.
• The energy cycle, that is, the one destined to obtain energy to keep the body running or to undertake other tasks later. For the latter, energy must be conserved in some way, generally by manufacturing substances (such as fat) that can then be broken down to recover the energy contained in its contents. molecules.

6. They are nourished and excreted

Every living being takes nutrients from the environment and discards substances that it does not need.

To keep the metabolism going, living things must get matter and energy from the environment, and this can be done in many different ways. But once the matter is obtained and processed, however, their bodies must also discard the compounds that are not useful or that are dangerous to them, that is, excrete.

• The nutrition. It consists of taking from the environment the necessary materials to start the metabolism. This includes the intake of organic and inorganic matter, to feed different metabolic processes such as respiration or photosynthesis. Beings capable of making their own food, such as plants, are known as autotrophs; Those who instead take food from other living beings or from substances released by them, as is the case with animals, are known as heterotrophs. The latter, in addition, can be primary consumers (they feed on autotrophic beings), secondary consumers (they feed on primary consumers or other secondary ones) or detritophagous (they feed on waste and debris).
• excretion. The excretion process consists in the release into the environment of those substances produced during the chain of metabolism, but which are useless or dangerous for the body. For example, in the case of humans, the excretory system is responsible for collecting ammonia (NH4) generated during respiration and, along with other substances, expelling it from the body through urine. Naturally, the excretion of certain organisms can serve as a nutrient for others.

7. They reproduce

Life begets new life, but through different processes.

Life exists based on its reproduction: all living beings come from other living beings that existed before them, whether we talk about human beings, mushrooms, plants, etc Life generates new life, and for this it can resort to processes of a different nature, such as:

• The asexual reproduction, in which an organism gives life to another genetically identical (or very similar, if produced mutations random) to progenitor, through cell division and replication of genetic material. This is the oldest method of reproduction that exists, and is characteristic of the most primitive unicellular beings, such as bacteria. A bacterium feeds on the environment, grows to size, and then splits into two bacteria, which will restart the cycle.
• The sexual reproduction, more complex than the asexual and typical of multicellular living beings, requires the cooperation of two living beings of the same species (one female and one male) to join their sexual cells or gametes and combine half of their Genetic information. Thus, a totally new individual is produced, provided with a DNA own, the result of the random fusion of the DNA of its parents. This is how human beings reproduce: after the fusion of an egg and a sperm, a new member of the species comes into the world.

8. They evolve

Evolution does not affect a single individual but the species as a whole.

evolve is adapt in the long term to the environment. It is a process that living beings do not actually carry out individually, but that affects the species as a whole, as the offspring present certain traits that are beneficial for them to deal with the environment and compete more advantageously with other rival living beings. .

The evolution it is responsible for the fact that the same community of living beings, spread over two different environments, ends up producing two different species after many generations have elapsed. That is the reason, for example, that The fauna and the flora are different in each of the continents, despite the fact that many species have very similar traits, since they are evolutionarily related.