User:Rohan nikoshe

Introduction :-

The living world is wonderful. We find living organisms in all types of habitats, like cold mountains, forests, oceans, fresh water lakes, deserts and even hot springs, the diversity is amazing. Life exists everywhere on earth. What is life? What is the purpose of life? The second question is philosophical as a biology student, let us learn what is life or "Living"?

what is "living" :-

You have already studied characteristics of living organisms. Growth, reproduction, metabolism, ability to sense environment and respond to it and cellular organization are unique features of living organisms. Let us see how to define "living".

Growth :- is exhibited by all living organisms. Increase in body mass is considered as growth. Non-living objects also grow. Mountains and sand mounds show growth. However, the growth exhibited by non-living objects is by accumulation of material on the surface, while in living organisms growth cannot be taken as a defining property of living organism.

Reproduction :- is a characteristic of living organisms. Organisms reproduce asexually or sexually, and produce their own kind. However, there are living organisms which do not reproduce e.g. mules, sterile worker bees, infertile human couples etc. Hence, reproduction also cannot be the defining characteristic of living organisms.

Metabolism :- is another characteristic of living organisms. There are various bio-chemical reactions which occurs simultaneously inside all living organisms. The sum total of all the reactions occurring in the body of an organism is called metabolism. Non-living objects do not show metabolism but, metabolism reactions can be demonstrated in cell-free system (in vitro). Hence metabolism and cellular organization of the body is defining feature of life form.

Technically complicated feature of all living organisms is irritability i.e. there ability to sense their environment  and respond to it. Both plants and animals respond to environmental factors like, light, temperature water etc. All organisms are "aware" of their surroundings. Consciousness therefore is the defining property of living organisms.

'''Thus, living organisms are self-replicating, evolving, and self regulating interacting systems capable of responding to external stimuli. Biology is the story of life on earth. It is an interesting life-science.'''