Cells

Cells are the basic building blocks of all living organisms. The human body is composed of trillions of cells that perform specific functions. There are many different types of cells in the human body, each with a unique function.

Cells are constantly dividing to produce new cells, which is necessary for growth and repair. When cells become damaged or die, new cells must be produced to take their place.

Cells are very small; the largest ones are only about 0.1 millimeters in diameter. Most cells are much smaller than this. The smallest cells are called bacteria, and they are only about one-thousandth of a millimeter in diameter.

Cells are organized into tissues, which are groups of cells that perform similar functions. For example, muscle cells are organized into muscle tissue, and skin cells are organized into skin tissue.

Cells are held together by cell junctions, which are special proteins that act like glue. Cell junctions help to hold cells in place and to keep them from moving around too much.

The inside of a cell is called the cytoplasm, and it is filled with many different types of molecules, including proteins, carbohydrates, fats, and DNA. The cytoplasm also contains organelles, which are small structures that have specific functions.

The cell membrane is a thin layer of molecules that surrounds the cytoplasm and provides protection for the cell. The cell membrane is selectively permeable, which means that it allows some molecules to enter and exit the cell, but it prevents other molecules from entering.

The nucleus is the largest organelle in the cell, and it contains the cell's DNA. The DNA is responsible for encoding the instructions for all of the cell's activities.

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