In this chapter, students learn the complex animal tissues which are arranged in a particular proportion and pattern for the formation of an organ. These organs, in turn, carry out a similar functionality by their physical and chemical interaction which constitutes for the organ system. Cells, tissues, organs and organ system divide their work in such a way that exhibits division of labour, contributing to the survival of the body.
In unicellular organisms, all functions like digestion, respiration and reproduction are performed by a single cell. In the complex body of multicellular animals, the same basic functions are carried out by different groups of cells in a well-organised manner. All complex animals consist of only four basic types of tissues. These tissues are organised in specific locations to form organs – such as the stomach, lung, heart and kidney.