The simplest, functioning part of an organism is a cell. Although cells are small in size, they contain all the necessary information to keep an organism alive. There are trillions of cells in the human body. Many cells are necessary to carry out the specialized functions of the body. There are also organisms that are made up of just one cell.

There are many types of cells. Every organism contains cells that are unique to that organism. Animals, plants, and bacteria all have specialized cells. Of the three types, plant cells are easiest to recognize because they contain a very distinctive cell wall around each one. There are even some organisms made of just one large cell but this cell has multiple nuclei that help run the entire cell.

Cells of prokaryotic organisms (organisms that contain cells with a nucleus) are made of many cell parts called organelles. The organelles present are dependent upon the specific cell type. Organelles are responsible for carrying out certain functions within the cell. These functions include making protein, providing the cell with energy, and riding the cell of waste.

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