1. Metabolism is the sum of the chemical reactions that take place within each cell of a living organism and provide energy for vital processes and for synthesizing new organic material. 

2. It involves continuous process of breakdown and synthesis of biomolecules through chemical reactions. 

3. Each of the metabolic reaction results in a transformation of biomolecules. 

4. Most of these metabolic reactions do not occur in isolation but are always linked with some other reactions. 

5. In cells, metabolism involves two following types of pathways: 

a. Catabolic pathways 

This involves formation of simpler structure from a complex biomolecule. For e.g. when we eat wheat, bread or chapati, our gastrointestinal tract digests (hydrolyses) the starch to glucose units with help of enzymes and releases energy in form of ATP (Adenosine triphosphate). 

b. Anabolic pathway 

It is also called as biosynthetic pathway that involves formation of a more complex biomolecules from a simpler structure Fone.g., synthesis of glycogen from glucose and protein from amino acids. These pathways consume energy.