Biology is the story of life on earth. Biology is the story of evolution of living organisms on earth. The living world comprises an amazing diversity of living organisms. The living world is wonderful. Living organisms reside in extraordinary habitats (place where organism lives). It may be cold mountains, deciduous forests, oceans, fresh water lakes, deserts or hot springs. When we try to define ‘living’, we conventionally look for distinctive characteristics exhibited by living organisms. Growth, reproduction, ability to sense environment and mount a suitable response are some of the unique features of living organisms.
All the living things have some common characteristics (or features) which make them different from non-living things. The characteristics of living things are given below
(i) They are made up of cells.
(ii) They need food, air and water.
(iii) They can grow.
(iv) They can move by themselves.
(v) They can respond to stimuli (or changes around them). They are sensitive.
(vi) They respire (release energy from food).
(vii) They excrete (get rid of waste materials from their body).
(viii) They can reproduce.
(ix) They have a definite life-span (after which they die).
(x) They show adaptability.
Biodiversity refers to all the diverse plants, animals and micro-organisms on the earth.
Life began on earth about 4.2 million years ago since then it has undergone numerous changes and diversification. Today there are more than 5 million types of living organisms on earth. Every living organism is unique in itself. This uniqueness of individuals is the diversity in life forms. Despite their unimaginable diversification, the living organisms are inter-related structurally and functionally because of their common origin. It has been proved that complex organisms evolved from simple ones by slow and gradual changes.
(Session 2025 - 26)