Essential Characteristics of Living Organisms
The biological definition of life is when a living matter, or any matter that shows certain attributes which include responsiveness, growth, metabolism, energy transformation, and also reproduction.
Life comprises living beings, and they are segregated into groups known as taxonomy. Each individual is composed of one or more than one minimal living unit, known as cells. Some studies state that life began as early as 4.1 billion years ago. It can be traced to fossils dated billions of years ago.
Biological Definition of Life
The nonliving things might show some of these characteristic traits, but the living things show all of them mentioned below:
1. Organization
Living things are highly organized, which means they contain specialized, and co-ordinated parts. All living organisms on this planet are made up of either one or more than one cell. Cells are considered to be the most fundamental units of life.
Even unicellular organisms are peculiar and complex. Inside each cell, the atoms make up molecules, which then makeup cell organelles and also structures. In multicellular organisms, those similar cells form tissues which in turn, collaborate to create organs. Organs are body structures with distinct functions and they work together to form organ systems.
Multicellular organisms like humans are made up of many cells. The cells in multicellular organisms are specialized to do different jobs. These cells are organized into tissues, such as the connective tissue, the epithelial tissue, the muscle, and the nervous tissue. The tissues make up organs, such as the heart or the lungs that carry out specific functions when needed by the organism.
2. Metabolism
Life on earth depends on a various number of interlocking chemical reactions. These reactions make it possible for all the organisms on this planet to do work like moving around or catching prey, growing, reproducing, and also maintaining the structure of their respective bodies. Living things use energy and consume nutrients to carry out the chemical reactions that help them to sustain their life. The total of the biochemical reactions that occur in an organism is known as its metabolism.
Metabolism is further subdivided into anabolism as well as catabolism. In anabolism, the organisms make complex molecules from simpler ones. In catabolism, they are just the reverse of anabolism. Anabolic processes always consume energy, whereas the catabolic processes can make the stored energy available.
3. Homeostasis
All living organisms on this planet regulate their internal environment to maintain the relatively narrow range of conditions needed for their cellular function. This maintenance of a stable internal environment, of the living organism even in the face of a changing external environment, is called homeostasis.
4. Growth
Every living organism on this planet undergoes regulated growth. The individual cells become larger, whereas multicellular organisms accumulate many cells through the cell division. You have started as a single cell and then the growth depends on anabolic pathways which build large, complex molecules such as the proteins and the DNA. The DNA is the genetic material.
5. Reproduction
All living organisms can reproduce themselves to create new organisms. Reproduction can be either asexual which involves a single parent organism or can be sexual, which requires two parents. Single-celled organisms, such as the dividing bacterium, can reproduce themselves simply by splitting in two.
In sexual reproduction, two-parent organisms produce sperm and egg cells that contain half of their genetic information. These cells fuse to form a new individual from them with a full genetic set. This process is called fertilization.
6. Response
Living organisms show “irritability,” which means that they respond to stimuli or change according to their environment. For example, people pull their hands away as fast as possible when coming in contact with a flame. Many plants turn towards the sun like sunflowers. There are unicellular organisms that may migrate towards a source of nutrients or even away from a noxious chemical.
7. Evolution
Populations of living organisms can undergo evolution according to the situation. This means the genetic makeup of a population may change over time. In some cases, evolution involves natural selection.
Over the generations, a heritable trait that provides a fitness advantage might become more common in the population, and making the population better suited to its environment. This process is known as adaptation.
FAQs on What Is Life in Biology?
1. What is the biological definition of 'life'?
From a biological standpoint, 'life' is not a substance but a complex process. It is a unique characteristic that distinguishes physical entities possessing biological processes from those that do not. An entity is considered living if it exhibits a combination of specific traits, including growth, reproduction, metabolism, cellular organisation, and consciousness or the ability to respond to stimuli.
2. What are the key characteristics that collectively define a living organism?
The key characteristics that living organisms exhibit are:
Growth: A permanent increase in size and mass, which is intrinsic (from the inside).
Reproduction: The ability to produce new individuals of the same kind, either sexually or asexually.
Metabolism: The sum of all chemical reactions occurring in the body, including anabolism (building up) and catabolism (breaking down).
Cellular Organisation: Being composed of one or more cells, which are the basic structural and functional units of life.
Consciousness: The ability to sense the surrounding environment and respond to external stimuli.
3. How does growth in living beings differ from the growth observed in non-living objects?
The primary difference lies in the mechanism of growth. In living organisms, growth is intrinsic, meaning it occurs from within the body through processes like cell division and an increase in cell size. In contrast, non-living objects like mountains or crystals 'grow' through extrinsic means, which is the accumulation of material on their external surface. Therefore, only intrinsic growth is considered a true characteristic of life.
4. What is metabolism and what are its main types?
Metabolism refers to the total sum of all biochemical reactions that occur within a living organism to sustain life. These reactions are crucial for growth, maintenance, and functioning. Metabolism has two main types:
Anabolism: Constructive processes where simpler substances are combined to form complex ones, such as the synthesis of proteins from amino acids. This process requires energy.
Catabolism: Destructive processes where complex substances are broken down into simpler ones, such as the breakdown of glucose during respiration to release energy.
5. Why isn't reproduction considered an all-inclusive, defining characteristic of life?
While reproduction is a fundamental characteristic of most living species, it is not considered a defining, all-inclusive property of every single living individual. This is because there are many examples of organisms that are undoubtedly alive but cannot reproduce. These include sterile individuals like mules (a hybrid of a donkey and a horse), sterile worker bees, and infertile human couples. Since life exists without the capacity for reproduction in these individual cases, it cannot be used as the sole defining feature of life.
6. What is the importance of consciousness for a living organism?
Consciousness, or the ability to sense and respond to environmental stimuli, is arguably the most complex and defining property of life. It allows an organism to interact with its surroundings, find food, avoid predators, and respond to changes in light, temperature, or chemicals. This responsiveness is crucial for survival and maintaining homeostasis (a stable internal environment). Humans are unique in possessing self-consciousness, the awareness of oneself.
7. Based on the characteristics of life, is a virus considered a living organism?
A virus exists on the borderline between living and non-living. It is not considered truly living because it lacks a cellular structure and cannot carry out metabolic processes or reproduce on its own. It is an inert, crystalline structure outside of a host cell. However, once it infects a living host, it takes over the host's cellular machinery to replicate itself, thereby showing a characteristic of life. Because of this dual nature, viruses are often referred to as 'organisms at the edge of life'.
