ABSTRACT
The basis of the human body is atoms. One or several atoms form molecules, which perform different functions in the human body or form various types of cells. There are more than 200 different types of cells in the human body. Cells contain several molecules and are the smallest units of life. Depending on the type, cells may function independently, e.g., macrophages police the body to eliminate pathogens. Other cells group together (or work together) and form tissues. There are four types of tissues which are as follows:
1. Epithelial tissue: these cover body surfaces exposed to the environ ment, body cavities, etc., e.g., the gastrointestinal tract is covered with epitheliaum.
