What is living ?

WHAT IS LIVING ?

Life is a unique ,complex organization of molecules expressing itself through chemical reactions(metabolism) which lead to growth,development,responsiveness,adaption and reproduction,Hence, “the object by itself exhibiting the growth,development,death,consciousness,reproduction etc is designated as living being”.

 

CHARACTERISTICS OF LIVING BEINGS

1)      GROWTH

Increase in mass and increase in number of cells are twin characteristics of growth,It is irreversible increase in mass or overall size of a tissue,an organism or its parts, It occurs due to synthesis of two types of substances ,protoplasmic and apoplasmic. 

Protoplasmic substances are components of living matter like cytoplasm and nucleus.Apoplasmic substances are non living materials formed by the cells and which become components of tissues ,Growth is the result of the difference between anabolism and catabolism,there will be no increase in mass of cells or organism. Hence growth will be absent. Degrowth or negative growth will occur when catabolism exceeds anabolism,it will decrease the mass of body.

Growth be cell division occurs continuously in plants, While in animals this can be seen only upto a certain age. Unicellular organisms also grow by cell division. In majority of higher animals and plants,growth and reproduction are mutually exclusive events,but in unicelled organisms like Amoeba,reproduction is synonymous with growth i.e increase in number of cells.

Non living objects also grow if we take increase in body mass as a criterion of growth.But in these objects extrinsic growth is present i.e increase in the mass of body from outside eg : mountains,boulders and sand mounds.Growth therefore,cannot be taken as a defining property of living organisms.

2)      REPRODUCTION

Reproduction is the formation of new individuals of similar kind, It is however required for survival of the population as it compensates for the loss of life due to death, Reproduction is of two types asexual and sexual . Asexual reproduction is uniparental multiplication that occurs through binary fission,multiple fission,spore formation,fragmentation and vegetative multiplication. Fungi multiplies by asexual spores,yeast and hydra show budding,Planaria exhibits true regeneration.

Fungi,Filamentous algae,protonema of mosses easily multiplies by fragmentation. But when we notice single celled organisms like bacteria,unicellular algae and Amoeba, we are not clear about the usage of these two terms – growth and reproduction , Hence reproduction also cannot be an all inclusive property of living organisms. Still no non living object is capable of reproducing or replicating by itself,Further there are some organisms which do not reproduce at all eg : worker bees,mules..etc

3)      METABOLISM

Life is a never ending flow of energy and materials , The latter are required by all living cells for building and functioning of their living matter. Metabolism is the sum total of all chemical reactions occurring in an organism due to specific interactions amongst different types of molecules within the interior of cells. It involves exchange of matter and energy between an organism and its environment and transformation of matter and energy within an organism.

Despite vast differences occurring in structure and functioning of cells in different organisms,metabolic reactions are unusually similar.Metabolic reactions can be demonstrated outside the body in cell free systems,An isolated metabolic reaction in a test tube is neither living nor non living, Hence while metabolism is a defining feature of living organisms without exception, isolated metabolic reactions in vitro are not living things but surely living reactions.

4)      CELLULAR STRUCTURE

Body of organism cosists of cells and their products. Hence cellular organization of the body is the defining feature of life forms.

5)      CONSCIOUSNESS

All living beings,plants and animals,are aware of their environment, All organisms sense their surroundings and respond to sudden or smooth changes in it,All organisms from prokaryota to eukaryote can sense and respond. Humans also have self consciousness hence,this becomes the defining property of living beings.

The forgetting discussion ,nevertheless concludes that living beings are organized,self replicating,evolving and self regulating interactive systems, with consciousness at the head of all.

A question may arise whether a man living in coma on the life support systems is living or non living ? . the answer lies in the quantitative presence of consciousness in the living being in that particular state.Infact,the person in coma has lost the requisite quantity of consciousness to exhibit the features of living being,but still exhibits life.If the requisite consciousness is restored,the person may again start to be a living being or die otherwise.Other characteristics of living beings are adaptation,life span,homeostasis,healing and repair,movement and variation.