1. THE LIVING WORLD
Life is a unique, complex organization of molecules, expressing through chemical reactions which lead to growth, development, responsiveness, adaptation & reproduction.
A living
organism is self-replicating, evolving and
self-regulating interactive system capable
of responding to external stimuli.
PROPERTIES OF LIVING ORGANISMS
1. Growth
· It is the increase in number & mass of cells by cell
division.
·
In plants, growth continues
throughout their lifespan.
·
In animals, growth is only
up to a certain age. However, cell division occurs to replace lost cells.
·
Basically,
growth is the increase in mass & size. Thus non-living objects also grow (surface
accumulation of material). So growth is not a
defining property of living organisms.
·
In living organisms, growth
is from inside.
2. Reproduction
·
It is the production of progeny
having features similar to those of parents.
·
Organisms reproduce
asexually and sexually.
·
In
unicellular organisms, growth & reproduction are same because they
reproduce by cell division.
·
Many organisms do not
reproduce (e.g. mules, worker bees, infertile human couples, etc). Hence,
reproduction is not a perfect defining property of living organisms.
3. Metabolism
·
It is the sum total of
all biochemical reactions taking place inside a living system.
·
It is the defining
feature of living organisms.
·
Metabolic reactions can
be demonstrated outside the body in cell-free systems. Isolated metabolic
reactions in vitro are not living things but are living reactions.
4. Cellular organization
·
Organisms are made up of
one or more cells.
·
It is the defining
feature of living organisms.
5. Consciousness
·
It is the ability of
organisms to sense their environment and
respond to environmental stimuli (like light, water, temperature, other organisms, chemicals, pollutants, etc).
·
All organisms
are ‘aware’ of their surroundings. So, it is the
defining property of living organisms.
· Human is the only organism having self-consciousness.
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