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This lesson focuses on the cell membrane. We’ll go over what the cell membrane is and look at several analogies to help understand it further, then you can test your knowledge with a short quiz.

What Is the Cell Membrane?

Cells are the basic units of life. They were actually named cells because, under the microscope, they look like tiny rooms. Much like rooms make up a building, cells make up our bodies and every other living thing. Cells are, in fact, required for something to be considered alive. Each type of cell in our body is a little different and does a specific job. For example, cardiomyocytes, or heart cells, beat on their own and keep the heart pumping.

To do these special jobs, cells need to be protected from the environment, which is the function of a thin, movable barrier called the cell membrane.Let’s explore some analogies of cell membranes to better understand this important cell protector.

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Classroom Analogy

Let’s go back to the idea of a cell as a room and, in particular, a classroom.

When in a classroom, students need to be undisturbed and ready to learn, and the noisy kids walking through the hall on their way back from lunch need to be kept out. The age-old solution is to put up walls. The walls keep the classroom protected and all the parts inside the classroom, like the teacher and the students working. In this way, the walls are like the cell membrane.But we’re not fenced in the classroom forever. Windows and doors let people come and go, and this is also an important part of the cell membrane. The cell membrane is selectively permeable, meaning it only lets certain things in and out of the cell as needed.

Students late to class come in, and students needing a sip of water go out. Administrators come in, and maybe some bugs fly out the window. The cell only lets things it needs in and gets rid of things it doesn’t need.

Circus Tent Analogy

Next, let’s use something a little more fun to compare to the cell membrane: a circus! The circus is a fantastic place with working parts all swirling around inside. There are cotton candy vendors, trapeze artists, jugglers, and more. Each of these players are analogous to the parts that work inside the cell. The cell membrane of the circus is the flexible tent separating it from the outside.

Like the classroom walls, the tent keeps out wildlife as well as people that didn’t buy tickets. Salespeople at the doors monitor the patrons and only let them in if they have their tickets ready, just as the plasma membrane selectively lets substances into the cell. Waste, like trash, can also leave the circus, just like waste leaves the cell.

Water Balloon Analogy

This time, let’s get a little more into how the plasma membrane moves. The inside of the cell is made of a thick goo called cytoplasm. The cytoplasm is mainly made of water, with some salt and sugars mixed in. It’s where all the parts of the cell hang out.

Since it’s made of water, a water balloon lends itself to an analogy easily. In this example, the water is like the cytoplasm. The thin plastic covering of the balloon is the cell membrane. Until you really throw the balloon, the plastic shifts with it. This is like the membrane, which is flexible, moving with the cell when it has to move.

Ocean Analogy

Although the ocean is incredibly vast and doesn’t have a cover that’s visible to the human eye, it nicely parallels the cell membrane. First, the ocean is fluid.

If boats are not tied down, they float over the ocean, traveling with the current. Although the cell membrane is a tough barrier, it is actually quite fluid. The fats, or phospholipids, that make up the membrane drift around like a sea. Proteins and carbohydrates also float along the phospholipid sea, drifting unless they are anchored to the membrane.The fish, coral and plants in the ocean are analogous to the parts inside a cell. The ocean is made of water, just like the inside of our cell, and the boats and buoys dotting the surface of the ocean make a great example of the membrane’s mosaic nature. The larger cell membrane is made from many tiny parts, including lipids, carbohydrates and proteins.

In our ocean analogy, the boats and buoys are the lipids, carbohydrate, and proteins.

Lesson Summary

In summary, cells are the basic units of life. They are covered by a thin, fluid, and flexible barrier called the cell membrane. The cell membrane protects the cell through selective permeability, only letting certain things in and out of the cell, like doors in a classroom.

Like a water balloon, the cell membrane is flexible, moving with the inside of the cell. It is made of a mosaic of substances, like lipids, proteins, and carbohydrates, which drift freely as if floating on an ocean.


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