The body of living organisms is organised, i.e., several
components and sub-components cooperate with each
other for the functioning of whole body.
Physical and Biological Hierarchies
There is a physical (non-living) hierarchy and biological
(living) hierarchy in the organisation of living body.
In physical hierarchy, various non-living components
(atoms and molecules) aggregate to form compounds, which
finally enter the living world in the form of cells. Each cell is
made up of many compartmentalised cell organelles, each of
which has specific intracellular function. These cells organise
to form tissues, that form organs and several organs
combine to form organ systems. Finally, many organ
systems organise and form a living organism.
The properties of tissues are not present in the constituent
cells, but arise as a result of interactions among the
constituent cells. For example, bone is a hard tissue, which
provides framework to the body, but the cells present inside
it do not have this property. This phenomenon of
interactions between various components of the body results
in the hierarchy of organisation.
The various life processes are the result of this interaction
and coordination. The complexity in organisation enables
living organisms to self-replicate, evolve, self-regulate and
respond to external stimuli. All living organisms along
with their ancestors and descendants are linked to one
another by sharing of common genetic material in the
form of DNA in varying degrees. This DNA is responsible
for the expression of specific traits in organisms.

the
All living organisms, from the simplest prokaryotes to
most complex eukaryotes, have excellent ability to sense their
environment. They respond to various physical, chemical and
biological stimuli.
The various external factors to which living organisms respond
are light, water, temperature, pollutants, other organisms,
Light duration or photoperiod affects many seasonal
breeders, plants as well as animals. All living things respond
to chemicals entering their bodies. Humans are superior to
all living things as they have an additional ability of
self-consciousness. Therefore, consciousness can be
considered as a defining property of living organisms.
However, in human beings, it is difficult to define living
state, in certain situations like if patients lying in coma
supported by machines that replace heart and lungs are
brain-dead with no self-consciousness.
6. Body Organisation
The body of living organisms is organised, i.e., several
components and sub-components cooperate with each
other for the functioning of whole body.

Metabolism is an another characteristic and defining feature of
all living things. All living organisms are made of chemicak
which are constantly being formed or changed into some other
biomolecules.
The sum total of anabolic or constructive reactiom
(anabolism) and catabolic or destructive reactiotu
(catabolism) continuously occurring inside the body is called
metabolism.
Metabolism = Anabolism + Catabolism
Metabolism occurs in all unicellular and multicelluhr
organisms. Its two stages include, i.e., anabolism, the
of building up or synthesis of complex substances from
simpler ones, e.g., photosynthesis and catabolism, the proces
of breakdown of complex substances into simpler substance
e.g., respiration, releasing waste outside.
Metabolic reactions cannot be demonstrated outside the
of
Hence, metabolism can be considered as a defining feature
all living organisms without exception. No non-living
exbibits metabolism.
The important differences between anabolism and
catabolism are