Characteristics of Living Beings

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

What is a living being?

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

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

• Nutrition that is, taking from the environment (or other beings) the materials necessary to perpetuate one's own existence.
• The interaction that is, the establishment of links of all kinds with other living beings and with the environment, whether by way of competition, cooperation, symbiosis or antagonism.
• The reproduction that is, the formation of new individuals of the same species, which remain once the organism completes its life cycle.
• death Finally, it is the return to the environment of the matter and energy that was used to exist, and the inevitable end of all life.

Living beings are the fundamental object of study of biology, and are (according to the most accepted hypothesis) the fruit 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 beings are the result of a very rigorous organization of the matter that makes them up, and The basic unit of organization of life is the cell. This means that from the most complex beings (like mammals) to the simplest (like 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:

• single-celled living beings 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 ceasing to be unique, unicellular organisms at any time. For example: amoebas and paramecia, free-living microscopic organisms.
• Multicellular living beings 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, perform different tasks and therefore have different compositions, shapes and organelles.

2. They maintain internal order or homeostasis

So that living beings can continue living, Their bodies must regulate their vital functions and maintain a delicate internal balance. Ingesting too much (or too little) of a certain nutrient, losing too much temperature or having too little water are some examples of situations that can break this balance and endanger the continuity of existence.

For this, the organizations They have developed different mechanisms that allow them to counteract the effect of the environment on their bodies and adapt to situations to preserve their inner balance.

For example, when it is very hot, our skin sweats to hydrate itself and so that the evaporation of sweat cools us; 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 thing occurs at the cellular level: the cells of our body are maintained at a level of acidity slightly higher than that of plasma, since this is conducive to their fundamental chemical reactions. To ensure that this pH is maintained, they release or seize ions and salts from the environment depending on what is convenient at the time.

3. They react to environmental stimuli

Living beings do not exist in a vacuum, but rather 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, perceive the stimuli around them and orient themselves in the environment according to what is best for them just as we do when it's sunny and we look for shade.

For this, living beings have different sensory apparatuses that communicate the outside of the body with the inside of the body and are able to recognize environmental stimuli such as sound, light, smell, pH, etc., and subsequently react to them in an appropriate way. In this way, living beings adapt to their environment to preserve themselves.

For example, certain plants have a mechanism of positive phototropism, 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 (essential for photosynthesis).

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

4. They go through a life cycle

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 must go through from birth to death. Life cycles can be very different from each other, and that is the reason why some living beings are long-lived and lead slow lives, while others live frenetically and become extinct quickly.

Every life cycle is made up of the following stages:

• Birth, the appearance of a new individual of a species in the world, either by being expelled from the mother's womb, hatching from an egg, or emerging from an ancestor cell.
• Growth, a stage of accumulation of resources from the environment to invest them in the expansion of the body itself, that is, to increase in size and complexity, develop new organs or prepare for a metamorphosis.
• Reproduction, stage in which individuals reach their peak of growth, change and mature, and prepare to bring new members of the species into the world.
• Senescence and death a 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

All living beings need matter and energy to keep their biochemical cycles running, as well as to repair, move, grow or undergo metamorphosis.

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

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

For example, the human body requires organic matter to decompose and obtain glucose, a type of sugar that is very chemically useful. Said sugar is then oxidized (that is, made to react with oxygen taken from the environment when breathing) and subjected to different biochemical processes.

As a result, Adenosine Triphosphate (ATP) molecules are obtained, a molecule of pure chemical energy that can be used for very diverse purposes.

There are two fundamental metabolic processes:

• Anabolism which consists of composing complex substances from simpler ones, as plants do when combining water, sunlight and atmospheric carbon dioxide to compose a wide range of sugars and starches, essential to keep the body going.
• Catabolism which consists of the reverse process: breaking down complex substances into simpler ones, generally with the help of specialized proteins called enzymes, just as we do with the organic matter that we ingest when eating, 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 intended 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 intended to obtain energy to keep the body moving 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 decomposed to recover the energy contained in its molecules.

6. They nourish and excrete

To keep the metabolism going, living beings must obtain 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 to them or that are dangerous to them, that is, excrete.

• Nutrition. It consists of taking the necessary materials from the environment 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 that 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 can also be primary consumers (they feed on autotrophic beings), secondary consumers (they feed on primary consumers or other secondary consumers) or detritophages (they feed on waste and waste).
• The excretion. The excretion process consists of the release into the environment of those substances produced during the metabolism chain, 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 breathing and, along with other substances, expelled from the body through urine. Naturally, the excretion of certain organisms can serve as nutrients for others.

7. They reproduce

Life exists based on its reproduction: All living things come from other living things that existed before them whether we are talking about human beings, fungi, plants, etc. Life generates new life, and to do so it can resort to processes of a different nature, such as:

• asexual reproduction in which an organism gives life to another genetically identical (or very similar, if random mutations occur) to the parent, through cell division and replication of the genetic material. This is the oldest method of reproduction that exists, and is characteristic of the most primitive unicellular beings, such as bacteria. A bacteria feeds on the environment, reaches the proper size and then divides into two bacteria, which will begin the cycle again.
• 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 its own DNA, 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

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

Evolution is responsible for the fact that the same community of living beings, distributed in two different environments, ends up producing two different species after numerous generations. That is the reason, for example, that the fauna and flora are different on each of the continents, despite the fact that many species present very similar traits to each other, given that they are evolutionarily related.

References

• “Living beings” on Wikipedia.
• “Main characteristics of living beings” on Wikipedia.
• “Characteristics of living beings” in the Ministry of Education of Argentina.
• “Characteristics of living beings” at the National University of Mar del Plata (Argentina).
• “Characteristics of living beings” by María Isabel Pérez Aguilar at the Autonomous University of the State of Hidalgo (Mexico).