The object which are self-regulating, evolving and self-replicating in nature are termed to be living.

It refers to organised state of molecules which are able to show growth, development, response to external stimuli.

The 4 defining characteristics are-

i) Growth

ii) Reproduction

iii) Metabolism

iv) Consciousness

i) Growth:

- It refers to an irreversible process of increase in size [either increase in mass, volume or in number of an individual].

- May be of 2 types:

a) Extrinsic growth –deposition of material on the outer surface.

b) Intrinsic growth – inside the body/cell.

Intrinsic growth occurs due to addition of material & formation of cells inside body – this is called intussusception.

However, in non-living things, similar materials get deposited on their outer surface. This is called accretion.

In unicellular organism increase in number of organism is equivalent to growth.

[Due to binary fission]� each member splits into 2.

ii) Reproduction:

- Biological process in which an organism give rise to individuals similar to themselves.

- Reproduction is of two types:

i) Asexual reproduction

• Uniparental

• With or without the involvement of gametes.

• Identical progeny’s produced

• E.g.- cell division

Budding

Regeneration

Fragmentation

Binary fission

Etc.

ii) Sexual reproduction

• Bi-Parental

• Involves formation & fusion of gametes.

• Brings out variation.

iii) Metabolism:

It is the sum total of all chemical & biological reactions occurring simultaneously inside the cells.

- It is of 2 types

i) Catabolism – involves break down of Biomolecules

ii) Anabolism – involves building up of Biomolecules.

It plays vital role in functioning of the living forms.

iv) Consciousness

• Ability of the body to sense & respond to the external stimuli.

• It can also be explained as self-awareness in humans.

• Plants can sense physical stimulus like light, water, temperature etc.

• Photoperiod affects reproduction in seasonal breeders.