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Cell Membrane

The cell membrane is a thin biological layer that contains the cytoplasm and all organelles of the cell.   The cell membrane’s main purpose is to protect the cell and control the movement of materials entering and leaving the cell.  Think of the membrane as a wall with security guards controlling who is allowed to enter and who is allowed to leave.

The cell membrane helps protect the cell.

Animal Cell Membrane

Found in both plant and animal cells, the cell membrane is the outside wall of a cell.  In animal cells, the membrane contains a chemical called cholesterol.  This chemical makes the membrane harder.

Plant Cell Membrane and Cell Wall

In plant cells, the membrane is the second wall and is found just inside the cell wall.   The cell wall is the main protector of the cell as it is a very rigid structure.  The membrane is right behind the cell wall a form of extra protection.   Unlike animal cell membranes, plant cells do not need cholesterol because they have a hard cell wall.  As a result, their membranes are much softer.

Cell Membrane Function

Cells have openings to bring in food and remove waste.In order for a cell to remain healthy, the cell needs to be able to bring in food, and get rid of waste.  Look closely at this picture. You will notice that the cell membrane has small openings or doorways. These openings allow the cells to move materials in and out of the cell.

But the cell membrane doesn’t let just any material to enter into the cell.  Instead, the membrane is selectively permeable.  Which basically means it regulates what substances are allowed into the cell.  If the membrane does its job correctly, it should keep out anything that may be harmful to the cell.  Therefore, the cell membrane is crucial to the cell’s survival.


A cell membrane protects a cell, just like a building's walls protect it from outside forces.

Think of your home or school. On the outside of the building are walls. These walls protect the building from danger and from the weather. At various locations, the building has small openings that allow food, people, electricity, and water to enter. There are also openings that allow things to leave, including waste. Without these openings, the building would not be much use.





Written by: Lauren Lacey