Passive Cell Transport

Lesson Plan - Get It!

Audio:

You have learned how cell membranes are organized to allow for transport of materials into and out of the cell.

If you missed or want a refresher on the previous Cell Transport lesson, check it out under Related Lessons in the right-hand sidebar.

Remember that cell membranes are made up of different components such as phospholipids, proteins, carbohydrates, and cholesterol. All these pieces work together to create a membrane that functions to support cellular processes.

In this lesson, you will learn about passive transport. Passive transport is the movement of materials across the cell membrane without using energy!

Think about what happens when you put Kool-Aid in water — the color slowly moves throughout the entire glass or pitcher.

Passive transport works in a very similar way, moving substances from areas of high concentration to low concentration.

Concentration is a measure of how much of something you have in a given area. There is a high concentration of sugar in ice cream, which makes it so good!

Think of the Kool-Aid packet as having a high concentration and the surrounding water having a lower concentration. Another example is perfume or cologne being sprayed from a bottle. The bottle represents a high concentration moving in spray form into an area of lower concentration in the surrounding air.

Another name for passive transport is diffusion, as pictured above. Notice how the pinkmolecules move and equally distribute through the sample of blue molecules.

Water diffuses across the cell membrane to keep a healthy water balance. When water diffuses, it is called osmosis. Look at how the water level changes in the image below:

In the image above, the pink line represents a semi-permeable membrane.

• Do you remember what semi-permeable means?

That means membranes can select which substances are able to move into and out of the cell.

The last type of passive transport is called facilitated diffusion.

• What does the word facilitate mean?

If you said, "to assist or help," you are right!

Facilitated diffusion occurs when proteins help substances move across the cell membrane. Facilitated diffusion is used when larger molecules need to move into or out of the cell and cannot fit between the phospholipids. Even though proteins are used, there is no energy input!

Passive transport is constantly occurring in cells throughout your body. Cells are required to maintain nutrient and water balance in order to continue to function.

In passive transport, materials move across the cell membrane without energy. There are three types of passive transport: diffusion, osmosis, and facilitated diffusion.

• How is osmosis unique?
• What helps larger molecules move across the cell membrane?
• What do you think would happen if cells were not able to carry out passive transport?

In the Got It? section, you will review types of passive transport.