All living organisms are made up of cells. Thus, the cell is the structural unit of life. Each living cell has the capacity to perform certain basic functions, that are characteristics of all living forms. Each cell acquired distinct structure and function, due to the organisation of its membrane and cytoplasmic organelles in a specific way. Each kind of cell organelle performs a special function, such as making new materials in the cell (e.g. chloroplast, ribosomes), clearing up the waste materials from the cells (e.g. lysosomes), utilisation of oxygen, oxidation of food and energy production (e.g. mitochondria), movement (microtubules containing spindle, cilia flagella), etc. A cell is able to live and perform all its functions because of these organelles. These organelles together constitute the basic unit called ‘cell’.