What – it’s doomed! Even in your own

What are cell membranes and why do cells have them? Better yet, are they even important? This lesson answers those questions through an investigation into the cell membrane and its function.

What Is a Cell Membrane?

As you may know, all living things are made from cells. Each of these cells, be they plant, animal, fungus, or bacteria, has a cell membrane. The cell membrane is the semipermeable covering that surrounds all cells. To say something is semipermeable means that it will allow certain substances to pass through it, while prohibiting the passage of others.

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Check out this illustration depicting the location of the cell membrane in both animal and bacterial cells.

Cell Membranes


So what do cell membranes actually do, and why do they matter? Remember that our definition said that cell membranes were semipermeable and that they surrounded the cell. This leads us to two reasons for the membrane’s importance:FlexibilityFirst, the membrane forms an outer boundary of the cell and, as such, holds the cell together.

The membrane is also pliable, which means it can move and flex in response to the surrounding environment. The fluid nature of the membrane is important because it allows the cell to survive in various environments. For example, if your skin cells are exposed to water for a long period of time (such as in a bath), what happens? Your fingertips shrivel up because water is able to move through the cell membrane and exit the cell. When it does, the cell membranes flex inward, causing the skin to shrivel.

The skin cells on your fingertips do not die. Instead, the flexible nature of their membranes allows them to survive and eventually return to normal.SemipermeabilityThe second reason for the membrane’s importance is that cell membranes allow certain substances to pass through, while prohibiting others from doing so. For example, your cells are constantly attempting to expel sodium (think salt), while simultaneously importing potassium (think bananas). To achieve this, membranes use specialized proteins embedded within them.

Proteins are the gatekeepers of cells. They control what gets in and what gets out. Notice the green structures in the image – they’re proteins helping to import or export material from the cell.

Cell Membrane Proteins

Controlling what enters or exits the cell is important for survival purposes. For example, if a cell cannot rid itself of waste, it will not survive. Inversely, if a cell cannot ingest nutrients, it, too, will perish.

Imagine a bacteria cell that cannot feed on decomposing material – it’s doomed! Even in your own body, the immune system relies on the ability of membranes to bring materials into the cell. White blood cells consume invading pathogens and destroy them, thus keeping you healthy. This process cannot occur without help from the cell membrane.

Lesson Summary

All living cells contain a cell membrane, the semipermeable structure that surrounds the cell. Something that is semipermeable will allow specific substances to pass through it, while preventing the passage of other substances. Cell membranes are important for a variety of reasons. First, the semipermeable nature of the cell membrane aids in cellular survival.

This semipermeability is created by protein embedded in the membrane. Proteins are the regulatory structures that control entry and exit of certain material from the cell. Second, cell membranes are pliable. In other words, they flex.

This flexible ability is important because it allows the cell to survive in differing environments, such as when immersed in water over long periods of time.


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