The cell is the basic functional and structural unit of life. Many organisms are single-celled like amoeba and bacteria. Rest, are multi-celled with billions and trillions of cells that make up an animal body. Cells are covered in a protective membrane. At the center of the cell is the cell nucleus which contains the genetic code (DNA). Apart from the nucleus, there are many small structures inside the cell like ribosomes, mitochondria, lysosomes etc. each performing one or more vital functions that make life possible.