Cells are the structural units of life. All living things are made up of tiny cells. In the human body, different types of cells specialize to perform different functions; humans have skin cells, lung cells, brain cells, and hair cells.
The cells found in the human body are called eukaryotic cells. Eukaryotic cells contain a nucleus which is a compartment that stores genetic information. Another characteristic of eukaryotic cells is that they contain their own organ-like structures called organelles. Organelles carry out functions for the cell much like organs in a person.
Bacteria cells are a different type of cell called a prokaryotic cell. Prokaryotes are the oldest type of cells. These ancient cells don't have a nucleus to contain their genetic information and are much smaller than eukaryotic cells. Prokaryotic cells are almost always single celled organisms and don't make up larger organisms like humans.