An organism needs raw materials from outside are mainly.

(a) Food: Usually carbon based compounds to supply energy, materials like minerals, vitamins etc. for working and maintenance of cells/tissues.
(b) Water: To provide medium in the body to live and carry out all the metabolic reactions necessary for life.
(c) Oxygen: For respiration.

Processes essential for maintaining life are:
(i) Nutrition (ii) Respiration
(iii) Transportation (iv) Excretion.