Introduction to Cell Transport

Lesson Plan - Get It!

Audio:

"Mosaic" is a term meaning "made of different components."

In this first lesson of the Cell Transport series, you will learn why the cell membrane is called the "fluid mosaic model."

• Based on the definition of mosaic, what would you predict is true about the cell membrane?

If you guessed that it is made up of different substances, you guessed correctly! The cell membrane has a couple different types of pieces that work together to allow material to move into and out of the cell. Notice where the cell membrane can be found in a cell — surrounding all the internal structures!

The image of a cell membrane shows the different components of the cell membrane. You will learn about each type in-depth as you progress through the lesson.

The main component of the cell membrane is a double layered phospholipid. Phospholipids are fat-like molecules with extra phosphorus atoms attached. These molecules have two parts: a head and a tail. The diagram below shows how the phospholipids are arranged in the cell membrane. The blue head, the part touching the inside of the cell, is considered water-loving, while the tail, shown in red, wants to avoid contact with water. These structures are the reason cells aren't constantly losing water to their environment.

Phospholipids are made up of phosphorus, carbon, hydrogen, and oxygen in a determined ratio. They are an integral part of the cell membrane. Cell membranes are called semi-permeable because they selectively allow substances to move across the membrane in and out of the cell. You might also see the term "selectively permeable," which means that the membrane is responsible for choosing what materials move through it. This is how cells gain water and lose waste. The phospholipids promote a lot of this movement, but are assisted by different kinds of proteins.

Proteins can be embedded in the membrane or create a pore in the membrane to facilitate transport.

As you look at the image above, you will notice lots of different kinds of proteins. They each have a unique job, spanning from cellular communication to hormone regulation to facilitating cell transport.

You might also notice how cholesterol and carbohydrates are part of the membrane. These substances give cell membranes structure and support, allowing them to support the cell shape.

The membrane is called "fluid" because it moves — it can expand as cells take in more water and shrink as they release water. Cell membranes are very flexible, which helps cells from becoming damaged during different processes. Cell membranes are a critical part of all cells, and play a very important role in the transport of materials.

• How do you think phospholipids and proteins are different? How are they similar?
• What do you think would happen to the membrane without cholesterol or carbohydrates?

Discuss what you have learned with a parent or teacher before moving to the Got It? section for a review activity.