What Is the Outside Boundary of an Animal Cell?

Cells are the basic building blocks of life within organisms. Some organisms are composed entirely of a single cell, while animals are composed of numerous cells that perform specific functions. Within an animal cell are various organelles, similar to organs within an animal body, that perform specific functions for the cell. Surrounding these organelles is a fluid called cytoplasm which is in term surrounded by the cell's outer boundary, known as the cell membrane.

Animal Cells

• Animal cells are the basic building block of organisms falling under the animal classification. Each cell can be thought of as a self-contained unit that combines with other similar cells to form tissue and organs. There are a variety of different cells contributing to different parts of the animal's body. For example, there are brain cells, blood cells, liver cells, skins cells and various other types. While these different types of cells have different roles, they all have some characteristics in common, such as the cell membrane and cytoplasm.

Cell Membrane

• The cell membrane is the outermost boundary of a cell. It is composed of a thin layer of protein and fat. To the extent that an animal cell can be thought of as a miniature organism, the cell membrane can be thought of as the skin of that miniature organism.

Cell Membrane Functions

• The cell membrane is semipermeable. This means that the membrane allows some substances to move in and out of the cell while blocking others. For example, cell membranes allow waste to exit cells and permit nutrients to enter the cell. This gatekeeper function is the basic role of the membrane within the overall function of the cell.

Cytoplasm

• Cytoplasm is a fluid substance that fills the spaces between the organelles within a cell and within the boundary of the cell membrane. Many important biochemical reactions take place within the cytoplasm. Additionally, the cytoplasm's fluid and expandable nature allow cells to grow without necessarily requiring a corresponding growth of the organelles within the cell. Cytoplasm also supports the movement of substances within the cell.