Living matter is the one able to carry out the three so called vital functions:
- Nutrition, which consists of taking in matter and energy in order to grow, survive and reproduce; waste matter and waste energy are produced as by-products. If a living being feeds directly off other living beings (such as animals, fungi and protozoa) it is called a consumer or heterotroph; but if it takes the matter and the energy that it needs from the inert matter (such as plants and algae) then it is a consumer or autotroph. Another way to express this difference is that consumers take in both organic and inorganic molecules, while the producers only feed on inorganic substances.
- Interaction is (a) the ability to perceive what is going on in both the environment and the inside of the organism itself, and (b) the ability to produce responses coherent with the information that was perceived. It usually goes as follows: an stimulus is perceived by a receptor → a control centre analyses the stimulus and generates a response order → an effector performs the response.
- Reproduction, the ability to produce living beings similar to the parental organisms. It may be sexual (when there is only one parental organism, as in bacteria) or sexual (when two different types of individuals, male and female, are required).
Every living being, and every cell in the multicellular living beings, is able to carry out these three vital functions.