Cell Structure: There are many different types, sizes, and shapes of cells in the body. For descriptive purposes, the concept of a generalized cell is introduced. It includes features from all cell types. A cell consists of three parts: the cell membrane, the nucleus, and the cytoplasm.

The cell membrane (plasma membrane) is a thin semi-permeable membrane that surrounds the cytoplasm of a cell . Its function is to protect the integrity of the interior of the cell by allowing certain substances into the cell, while keeping other substances out.

Cytoplasm is the fluid that fills a cell. Scientists used to call the fluid protoplasm. Early on, they didn't know about the many different types of fluids in the cell. There is special fluid in the mitochondria, endoplasmic reticulum, Golgi apparatus, and nucleus.