Do Animal Cells Have a Cell Membrane

Instructor: Dominic Corsini
What are cell membranes and what do they do? Better yet, do animal cells even have them? This lesson answers those questions through an investigation into cell membranes. A lesson summary and brief quiz are included.

What is a Cell Membrane?

All living things are made from cells. Some of these cells belong to plants, others to animals, and even more to bacteria. No matter their origin, each cell contains a cell membrane. The cell membrane is the semi-permeable membrane surrounding the outside of the cell. Semi-permeable means that some things can pass through, while other things cannot.

Cells are somewhat analogous to water balloons. The balloon itself represents the cell membrane and the water inside the balloon represents the interior of the cell. As you can see in Figure A, cell membranes outline the outside of the cell.

Figure A: Cell Membranes
Cell Membrane

Animal Cell Membrane's Function

So what does the animal cell membrane actually do? Well, our initial definition said that the cell membrane was semi-permeable, and that it surrounded the cell. Its semi-permeable nature means the membrane can serve two primary functions: 1) forming an outer boundary of the cell and therefore holding the cell together, and 2) allowing certain substances to pass through it while prohibiting others from doing so.

The first of these functions is fairly straightforward. Just like the water balloon itself holds water inside, the cell membrane holds all cellular components inside - no big surprise there. So, rather than focus on the obvious function, let's look at the second job: controlling entry and exit from the cell. By controlling what gets into and out of the cell, the membrane is really acting as a regulatory structure. Examples of substances that it regulates include (but are not limited to) sodium, potassium, sugar, and amino acids. Each of these interacts with the animal cell membrane in similar ways.

Controlling Entry and Exit

How does a cell membrane control what moves in and out of the cell? To find out, we must first understand what the membrane is made of.

Figure B: Cell Membrane Proteins
Cell Membrane Proteins

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