Importance of Biochemistry

What is the simple definition of life?

Life characteristics?


What is the simple definition of life?

Definition of life:life

Definition of life and it’s characteristics are discussed here in detail.Biology is the science concerned with the study of things and living things. This definition is very simple, but it opens the door to more difficult and interesting questions:


What is life? What does it mean to be alive?

You are alive and I am too, the dog I hear is alive, and the tree that I see from my window is also, but the snow falling from the clouds is not alive, and the computer that you use to read this article is not alive, and the chair that you are sitting on is as well, the parts of the chair made of wood were alive Previously, if you wanted to burn wood, fire was not alive either.

What defines life? And when can we say that this is a living being and this is not living?

Most people have an intuitive understanding of what it means to be alive, however it is difficult to come up with an accurate definition of life.

For this reason, many of our definitions of life are practical definitions, that is, they allow us to separate living things from non-living things, but they do not define what life is?

To define this class, we have to create a list of distinct and unique characteristics that are limited to living things only.

Life characteristics:

Biologists have identified many diverse features common to all living things we know. Although some non-living bodies may possess some of these traits, they do not collectively.

1- Regulation:

Living things are highly organized, which means that they have specialized and coordinated parts. All living things consist of one or more cells, with the cell being the basic unit of life.

Complexity extends to single-celled organisms! Within each cell, the atoms make up the molecules, which in turn form the organelles and cell structures.

In multicellular organisms, similar cells form tissues, tissues in turn collaborate to form organs, and organs then work together to form body systems.

Multicellular organisms consist of many cells, as cells specialize to perform different functions, and they are organized into tissues, such as connective tissues, epithelial tissues, muscles and nerve tissues, and then the organ tissues, such as the heart and lungs, are formed to perform specific functions that the organism needs.


2- Metabolism:

Life depends on a tremendous number of intertwined chemical reactions, as living organisms can do their work with these reactions, such as movement and catching prey in addition to growth, reproduction and maintaining the structure of their bodies.

Living things must use energy and consume nutrients to carry out life-sustaining chemical reactions. The sum total of the biochemical (biochemical) reactions taking place in an organism is called; Metabolism.

It divides metabolism into two parts, catabolism and anabolic. In the process of construction, living things form complex molecules from simple molecules, but in the process of demolition, the opposite happens.

Building processes usually consume energy, while demolition processes store energy.

3- Homeostasis:

Living things regulate their internal environment to maintain a relatively narrow range of conditions required for cell functioning, for example, your body must maintain a temperature of around 37 degrees Celsius.

The process of maintaining the stability of the internal environment in the face of changes in the external environment is known as homeostasis.

4- Growth:

Organisms undergo a regular growth process, as individual cells increase in size, and cells divide in multicellular organisms to form many cells through the process of cell division.

You were formerly a single cell, but now you are made of tens of trillions of cells! Growth depends on the building blocks that make up large and complex molecules such as proteins, chromosomal DNA, matter and genetics.

5- Reproduction:

Living things can reproduce to create new organisms, reproduction may be asexual, resulting in a living being from one parent, or it is sexual that requires two parents. Single-celled organisms can reproduce by dividing into two parts like bacteria.

Definition of life.Image on the right: fertilization - image on the left: splitting of bacteria

Image on the right: fertilization – image on the left: splitting of bacteria

In sexual reproduction, the parents produce sperm and egg cells, each containing half the genetic information, and these cells fuse to form a new individual with a complete genetic set. This process is known as fertilization.

6- Response:

Living things show signs of response, which means that they respond to stimuli and changes in their environment.

For example, people quickly pull their hands from a fire, many plants turn toward the sun, and single-celled organisms migrate toward the food source or away from harmful chemicals.

7- Evolution:

Groups of organisms may undergo evolution, which means the genetic makeup of a particular group changes over time.

In some cases, evolution includes natural selection, as a specific hereditary trait, such as the color of dark fur or a pointed beak, gives certain organisms chances of survival and provides them with better reproduction in a particular environment.

With the passage of generations, the genetic trait that provides the advantage of validity may increase in spread between groups, making the groups better suited to their environment, this process is called adaptation.

Is this list critical?

Living organisms have many different characteristics related to their life, and it may be difficult to accurately determine the characteristics that give the best definition of life, for this reason different thinkers have developed different lists of the characteristics of life, for example, movement in some lists is one of the defining characteristics of life, and other lists say that living things carry Its genetic information is in the form of DNA, and some assert that life depends on carbon.

The mentioned list is subject to error. For example, there is an organism from the offspring of a female horse and a male donkey called a mule, which is unable to reproduce, but people and most biologists consider it a living being.

However, the aforementioned list provides a reasonable set of properties to help us distinguish between living and non-living things.

The separation between living and non-living things:

To what extent do the aforementioned characteristics allow us to determine whether or not this thing is alive?

Let us review the living and non-living things that we mentioned in the introduction, for example, that the living things mentioned, which included humans, dogs and trees, easily achieve the seven characteristics that we mentioned, as humans, dogs and trees consist of cells, and each of them has a metabolism, homeostasis, growth and response to surrounding factors , And all of them can reproduce, and they also undergo a process of biological evolution.

Inanimate objects may exhibit some characteristics of life. For example, snow crystals are regular, although they do not contain cells, and they may increase in size but do not possess other life characteristics.

Likewise, fire can grow and reproduce by creating new fires and responding to specific stimuli. We can say that it performs the metabolism process, but the fire is not regular and does not maintain homeostasis and lacks the genetic information required for the evolution process.

Living things may preserve some of the characteristics of life when they become inanimate. For example, if you look at a chair made of wood under a microscope, you may see traces of the cells that make up the living tree, however, the wood is no longer alive after turning into a chair, and it can no longer grow, maintain homeostasis, respond or reproduce. .

Whether the thing is alive is still a matter of debate:

The question about the meaning of life remains unanswered. For example, viruses possess many characteristics of life and are made up of bodies containing small proteins and nucleic acid structures that can only reproduce within a host cell, but they do not possess a cytoskeleton and cannot reproduce without a host.

Likewise, it is not clear that they maintain homeostasis or metabolize them.

structure of virus:

Virus structure
Structure of virus

For these reasons, viruses are not living organisms, yet not everyone agrees with this conclusion, as they think that life is still a topic of debate.

Some of the simpler molecules possess some of the properties of life, such as self-replicating proteins such as the prions that cause mad cow disease, and self-replicating RNA enzymes.

In addition, all of the characteristics of life that we discussed are limited to life on planet Earth, so if there is life outside the planet, it may or may not share the same characteristics.

NASA defines Life:

NASA defines life in practice as “a stand-alone system capable of Darwinian evolution,” which opens the door to many possibilities that go beyond the specified criteria mentioned above, but based on that definition we cannot quickly judge whether an object is considered alive or not?

As more biological entities are discovered on or off Earth, we may be asked to rethink what it means to be a living thing, and future discoveries may require a review and extension of the definition of life.

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