Cell Biology: Function of the Cell Membrane

When you tutor high school biology, cell biology is a mainstay.  The particular role of the cell membrane sometimes gets neglected.

Membranes are very important in the construction of organisms.  Every membrane has the basic function of keeping materials separate or else keeping them where they are.  Every cell has a membrane surrounding (enveloping) it.  Some people call it the cell membrane; others call it the plasma membrane.

The role of the cell membrane is sometimes described as protection – that it shelters the cell from its environment.  To some extent you could argue that’s true, but really the cell membrane’s function is to control the movement of materials in and out of the cell.

You can think of the cell as a factory.  It has valuable things inside that need to be there.  Some of those valuables are destined to leave, but only under the correct circumstances.  Until the appropriate time of departure, those valuables must remain safe inside.

The factory, however, can’t just be locked up until someone comes to take delivery of the merchandise.  New supplies are arriving all the time, and need to be taken in.  However, anything (and anyone) not meant to be there is stopped at the door.

A busy factory probably has its doors open all day, yet the movement of goods in and out of it is carefully controlled.  Foremen watch the crews and the doors to make sure the right shipments leave at the right times.  New shipments that arrive are confirmed before they are brought in.  Securing the movement of the goods is a constant, involved process.

With a cell, the conduction of goods in and out is much the same.  Water, oxygen and carbon dioxide can pass through the cell membrane freely, but many important molecules and ions need to be allowed in – or even brought in – by the membrane.  Otherwise, they can’t enter.  With exiting, it’s the same situation.

The cell “decides” what to let in at any given instant based on what it needs to maintain the composition of its cytoplasm.  The cytoplasm is the nonspecific, jelly-like “body” of the cell.  It’s a complex mix of water, ions, proteins, lipids, sugars, and other biological compounds.  Cytoplasm’s precise mix comprises the “living condition” of the cell.  If the mix goes wrong, the cell dies.  Cytoplasm can only be found in a living cell.

Therefore, the cell membrane maintains the “living” mix of the cytoplasm by controlling what enters and leaves the cell.  It’s a function that may not sound specific at first, but might be the most important of any the cell does.  Just how the cell membrane manages its role will be discussed in future posts.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.

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