Life manifests itself from the simplest one-celled microbe to the more complex full bodied organisms. And is characterised by irritability and the search for food, water and a place to exist. This earmarks its tendency to become more complex and subtle as one goes up the evolutionary ladder.

Those organisms which have more needs to satisfy has a system of retrieval. In other words the move to locate a supply of nourishment takes place and given importance. So that there is a frenzy of activity at this point. By securing nutrients it guarantees a longer life span provided there is no competitors nearby.

Water is the key element for any existence and without it there is no chance of survival. It is zero in the case where this has dried up leaving the organism to fend for itself. So finding a source of liquid takes priority and other factors are given lesser considerations. For it to flourish water becomes necessary as a base and quickly turns into a life-and-death struggle.

There is also the fact that a place to exist in safety is important in any scheme of things. Its importance increases if there is a large number of individual organisms living within the same space. Because of this some may venture out to seek more favourable habitat. The matter does not end here for it has to be secure and relatively free from predators.

In any case the movement to finding a location forms the basis of life Life is considered a phenomena because it comprises so many details that go into its making. The question of irritability crops up in anything related to it. This is in response to stimulis received and regarded as a criteria for any act to take place. Where before there was only a reaction now it is replaced by a full fledged mass movement either towards it or away from it.

Because life deals with a number of requirements it becomes imperative to be on the look out for them. More than this cannot be said as the fact speaks for itself — the immediate concerns may mean losing out the fight to survive. So that there is a felt need to continue to exist in a suitable medium

Life is also speaking in gross terms sometimes observed as a full grown realization — those that exhibit nervousness have a better chance of survival. Evolutionary patterns dictate which organism will go on surviving and those that will perish.