The main advantage for an organism to have tissue level organization is the division of labour. A cell is the basic unit of the body. In multicellular organisms, there are different levels of organization. The cells with similar structure and function form tissue to perform a specific activity.Humans have four basic tissues: connective, epithelial, muscle and nerve. Groups of two or more tissues that work together to perform specific function form an organ. For e.g. heart, brain, lungs etc. Different organs form systems like the circulatory system, respiratory system etc. Systems carry out separate functions independently and simultaneously. Thus when the lung is purifying the blood, circulatory system is distributing blood throughout the body. In this way, the work or body functions are allotted to different tissues or organs for survival.Single cell type cannot carry out complex functions of organs efficiently.