What is meant by living? Give any four defining features of life forms.

(N/A) $\rightarrow$ An organism is said to be living if it shows certain characteristic features that distinguish it from non-living things.
$\rightarrow$ The following are the defining features of life forms:
$(1)$ Metabolism: It is the sum total of all chemical reactions occurring inside the body of a living organism. It is a defining feature because no non-living object exhibits metabolism.
$(2)$ Cellular organization: All living organisms are made up of one or more cells,which are the structural and functional units of life.
$(3)$ Consciousness: The ability to sense the environment and respond to environmental stimuli is a defining property of all living organisms.
$(4)$ Self-replication/Self-organization: Living organisms possess the ability to self-replicate and self-organize,which is a unique characteristic of life.