Living things can interact with their environment.  In order to do this they must first be aware of it.  They can sense it.  Humans and most vertebrates have five main senses - sight, hearing, smell, taste and touch.   There are others - the ability to detect the direction of the pull of gravity, some snakes can sense infrared, some birds can sense magnetic fields.  These sensing abilities allow living things to react to their environment and even change it.

Micro-organisms also sense their environment and can react to it.  This interactive ability is known as irritability. They can respond to various forms of sensory stimuli such as light, flow of their environmental media around them, and the properties of that environment - temperature, acidity, salinity etc.

Additionally, living things can communicate with others of their own species and even other living things.  This can take many forms, from speech and reading at the human level, right down to nervous electrical impulses and hormonal chemical messages at a cellular level.  Even plants communicate by releasing chemical "markers" into the air, which other plants can detect.


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