Living Things: Concept, Characteristics and Life Cycle

We explain what living beings are, their characteristics and how their life cycle is. In addition, the vital functions and the types of living beings.

Living beings
Living things are diverse in complexity, size, and intelligence.

What are living things?

When we speak of living beings or living beings we refer to the various forms that life assumes throughout its historyFrom the simplest and most microscopic beings to complex life forms, including human beings themselves.

Living beings are tremendously diverse in complexity, size, intelligence, and other characteristics differentiating, which allow them to adapt to different environments and compete with other living beings for access to the necessary resources to continue living and reproduce their species, transmitting these characteristics, anatomical or behavioral, to their offspring. This is the adaptation and evolution of species.

It is not very well known how life originated, and this is a matter of debate, since the bodies of living beings are composed of exactly the same elements as inanimate matterthough arranged in entirely different ways. In fact, in the body of living beings it is possible to find various doses of metals and inorganic elements.

Even so, living beings are distinguished from inert matter in that they try by all means to maintain their balanced chemical and biological structure, that is, to stay alive, and at the same time perpetuate the species.

If they fail to maintain their internal balance, living things die, and their bodies break down to their constituent elements.

Characteristics of living beings

Living beings
Living beings interact with their environment and are capable of modifying it.

Living beings share, within their immense variety, the following elemental characteristics:

  • They maintain their homeostasis. This term means the internal balance of matter and energy, essential for the organism to operate in a coordinated and not chaotic manner.
  • They are deadly and they reproduce. All forms of life that exist die, eventually, since in the end disorder (entropy) is imposed on the system after enough time, or when accidents and sudden changes occur that do not allow it to adapt in time. Life’s response to this inevitable reality is to reproduce: to create new living beings that perpetuate the species and contain the genetic information of their parents.
  • Consume energy. Life requires energy expenditure to operate, and this energy is obtained from the environment through various mechanisms, which introduce matter into the body and subject it to chemical reactions.
  • They react to their environment. One of the characteristics of living beings is that they do not exist apart from their environment and respond to its conditions, that is, they interact with it in different ways, and consequently also modify it.


All living beings have a limited time of existence, during which they fulfill various stages of the call cycle of life, which will be repeated in their descendants. These stages are:

  • Birth. Living beings are generated in various ways by their parents and come into the world in different stages of maturity, that is, of preparation for life.
  • Feeding. Once born, living beings must feed themselves for the rest of their existence, since it is the only method of obtaining the necessary energy to continue existing and to undertake the changes of growth and maturation.
  • Increase and maturation. Once a certain feeding point has been reached, living beings grow, that is, they enlarge their structures and gradually reach maturity, that is, the point necessary to reproduce.
  • Reproduction. Either sexually or asexually, living beings reproduce and give rise to new individuals of the species, whose life cycles will begin at that precise moment.
  • Aging and death. After the necessary time, living beings will age, which means that their vital functions will deteriorate over time, until they stop operating correctly and die.

Vital functions

Living beings
Living things need nourishment to have energy and stay alive.

Living beings fulfill three minimum vital functions throughout their life cycles, which are:

  • Nutrition. Nutrition consists of obtaining matter and energy to stay alive, repair the body and make it grow. Accordingly, there are two types of living beings: autotrophs (they make their own food) and heterotrophs (they feed on the environment).
  • Relationship. Living beings interact with the environment and with other living beings, being able to flee from dangers and feed themselves.
  • Reproduction. Once a certain well-being has been achieved, living beings proceed to reproduce and perpetuate the species.

Types of living things

Living beings are classified based on a system of kingdoms, grouped by their common characteristics. These kingdoms are:

  • Animals (Animalia). These are living beings with voluntary movement, mostly heterotrophs, and which can be mammals, reptiles, birds, fish or amphibians.
  • Vegetable (Plantae). Non-mobile living beings, usually autotrophs and that carry out their food through photosynthesis, taking advantage of sunlight and water.
  • Mushrooms (Fungi). They can be considered an intermediate between plants and vegetables, since they are immobile and feed on decomposing organic matter, even going so far as to parasitize other living beings.
  • Protista (Proctist). Single-celled living beings of a very varied nature, which are primitive forms of life. This includes algae and protozoa.
  • Bacteria (bacteria). The smallest and simplest living beings of all, that inhabit the environment and many of which lead an infectious life, within the body of other living beings.