CBSE Quick Revision Notes (Class-11 Biology)
CHAPTER-01 THE LIVING WORLD
Life is a unique, complex organization of molecules that expresses itself through
chemical reactions which lead to growth, development, responsiveness, adaptation and
reproduction.
The objects exhibiting growth, development, reproduction, respiration, responsiveness
and other characteristics of life are designated as living beings.
Unique features of living organism:-
(a) Growth- Living organisms grow in mass and number. A multicellular organism
increases its mass by cell division. In plants growth continuous throughout life in
their meristemtic area but in animals, growth occurs to a certain age. Unicellular
organisms also grow by cell division. Living organisms show internal growth due to
addition of materials and formation of cells inside the body. Non living organism like
mountains, boulders, crystals also grow but due to addition of similar materials to
their outer surface.
(b) Reproduction- It is the formation of new individuals of the similar kind. Reproduction
is not essential for survival of the individuals. It is required for perpetuation of the
population. In sexual reproduction two parents are involved to produce more or less
similar kinds of individuals. In asexual reproduction single parent is involved and
individual is copy of the parent. Asexual reproduction may occurs by fission,
fermentation, regeneration, vegetative propagation etc. In unicellular organism,
growth and reproduction are synonyms. Many organisms like mules, sterile worker
bees, infertile human couples. Therefore, reproduction is not an all-inclusive
characteristic of living organism. However, no nonliving object has the power to
reproduce or replicate.
(c) Metabolism- The sum total of all types of chemical reactions occurring in an
individual due to specific interactions amongst different types of molecules in the
interior of cells is called metabolism. All activities of an organism including growth,
movements, development, reproduction etc. are due to metabolism. There are two
types of metabolism- Catabolism and Anabolism. Anabolism includes all the building
up reactions to increase the mass of the organism like photosynthesis. In catabolism
breakdown reactions are involved, such as respiration, digestion etc. no nonliving
object show metabolism.
(d) Consciousness- It is the awareness of the surroundings and responding to external
stimuli. External stimuli may be physical, chemical or biological. Plants also responds
to stimuli like light, water, gravitation, pollution etc. All living organisms prokaryotic
to eukaryotic responds to different kinds of stimuli. Human being is only organism
who is aware of himself. Consciousness therefore, becomes the defining property of
living organisms.
(e) Life span- every living organism has a definite life span of birth, growth, maturity,
senesce and death.
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