Living beings are all organisms made up of one or many cells that have the ability to carry out special functions such as breathing, growing and developing, reproducing, feeding, interacting with and responding to their environment.
It is not always easy to define living beings, because on our planet there are a huge number of organisms, all very different from each other.
Humans, crabs, cows, giraffes, whales, snails, robins, worms, sharks, lichens, plants, mosses, fungi, corals, and microscopic bacteria are all beings. alive.
All living beings share a set of fundamental characteristics that help us to differentiate them from those ‘things’ that are not alive, such as river rocks, wind or water, for example.
Characteristics of living beings
The irritability is characteristic of living beings having to do with their ability to interact with the environment around them and respond to stimuli they receive from it.
It is a very important characteristic, since no living being lives isolated on the planet, so it is constantly receiving stimuli to which it often needs to respond.
Due to irritability, living beings can respond to stimuli such as increases or decreases in temperature, the amount of light, water, etc.
A good example of irritability is what happens when we exercise on a very hot day, as our heart beats faster to pump enough blood to our muscles and our body cools itself through sweating.
When we talk about adaptation we say that it is the characteristic of living beings to cope with some aspects of the environment that surrounds them and survive the possible changes that they could find in their natural environment.
It can be presented as the ability to “readjust” some of its characteristics to survive and adaptation can be at a physiological, structural, biochemical, behavioral level or a combination of all these.
For example, amphibians like frogs have long tongues that allow them to catch the insects they feed on.
Zebra fur stripes, on the other hand, are thought to be an adaptation that allows them to ‘escape’ the sight of their predators.
There are other animals that are able to camouflage themselves with the environment that surrounds them to go unnoticed in front of their predators, such as chameleons.
Reproduction is the process by which an organism forms another equal or very similar, always of the same species. By this process the species are maintained and perpetuated over time and it can occur in two ways: asexually or sexually.
– Sexual reproduction
Sexual reproduction is a complex process that is carried out in multicellular organisms and is exclusive to beings formed by eukaryotic cells .
It usually involves two organisms of opposite ‘sex’: a female and a male, which produce a type of cells specialized in reproduction: eggs and sperm, respectively.
Sexual reproduction consists of both the production of these cells and the process by which both cells meet, fuse, fuse their nuclei and genetic material, and produce a new cell – the zygote – with shared characteristics of both parents.
– Asexual reproduction
Asexual reproduction, in its different presentations, is the formation of genetically clonal organisms, that is, from one organism two organisms equal to the original are formed.
It is a type of reproduction that characterizes many microbes such as bacteria, archaea, and eukaryotic single-celled parasites, although it can also occur in some fungi and in part of the life cycle of many plants.
Metabolism is defined as the set of chemical reactions that take place within all cells. Through these reactions, living beings can take advantage of the energy and nutrients derived from food to carry out their activities, grow, interact with the environment, etc.
Metabolic reactions are essential for any living being to continue to be alive, since all its characteristics depend on them.
These reactions are classified into two groups: anabolic reactions (anabolism) and catabolic reactions (catabolism). Let’s see what each one is about:
Through anabolic reactions, cells and multicellular organisms “manufacture” the materials they need to grow and perform their functions.
It has to do with the joining of small molecules to form more complex entities, for which energy is needed .
Protein synthesis and the production of lipids, carbohydrates, and nucleic acids are good examples of anabolic processes that take place in every cell on planet Earth.
We can also say that anabolic reactions are what make it possible for us to “produce” something like, for example, muscle tissue.
It is for this reason that anabolism is related to bodybuilders, for example, since they adjust their metabolism for the production of large muscles.
Catabolism, on the other hand, has to do with the production of energy that is used during anabolism and to carry out other cellular processes.
We can say that it is the opposite, that is: the disintegration of large molecules to obtain smaller molecules and a certain amount of energy that can be used by cells.
Cellular catabolic reactions are many, but we could say that glycolysis and fatty acid oxidation are good examples of catabolic reactions.
All living things are capable of growth. Growth is the ability of an organism to increase in size until it reaches a defined size for its species and this is possible thanks to the fact that it uses the nutrients that it feeds on for this purpose.
For unicellular organisms, growth implies an increase in cell size. When a cell divides, generally two slightly smaller daughter cells are formed, which progressively increase in size, that is, they grow .
For multicellular organisms, growth is both an increase in the size of the cells and an increase in the number of cells, which are organized to form complex structures such as organs and tissues with different functions.
Let’s think about the seed of a plant: at first it consists of a small embryo made up of a few cells, protected by a special structure.
When germinating, the cells of the embryo “wake up” and activate their internal processes, at the same time that they begin to divide and activate their metabolism. The cells are forming tissues and the tissues are forming the organs of a very small seedling, with a stem and a root.
As the seedling feeds thanks to photosynthesis and the water it collects from the soil, it grows and becomes an adult plant.
The same happens with human beings: babies at birth are very small and thanks to the food provided by mothers, they grow and can develop to, over time, form children, young people, adults and the elderly.
All living beings are characterized by being able to maintain certain optimal internal conditions to continue doing that: being alive.
This proper ‘maintenance’ or balance of internal conditions is what we know as homeostasis and is a set of fundamental life processes.
Homeostasis mechanisms, for example, allow the activation or inhibition of metabolic or anabolic pathways whenever the cell needs or does not need some type of molecule. In other words, homeostasis is the way that living things control or regulate metabolism.