01 Passive and Active Transport

All living things are made of tiny u nits called cells,which are surrounded by a covering called a membrane.The membrane controls what moves in and out of the cell.

In order to thrive, cells need many kinds of material.For example, they must have water, oxygen, glucose, sodium, potassium, and many other minerals. The body needs to have a delivery system to get these materials to where they need to go. Cells also produce waste material that they need to get rid of, so the body has to have a method of waste collection and disposal. There are two types of transport: active transport and passive transport.

Passive transport is quite easy because the cells don't need to use any energy to make it happen. Diffusion is the simplest and most common form of passive transport. During diffusion, tiny particles of the materials that need to be delivered to the cells are spread through either a gas like oxygen, or a liquid like water.

Active transport is used when the concentration of materials inside the cell is high, and the cell needs to push materials to areas of low concentration. This causes the cell to use energy. An example of this is how nerve cells work. They pump sodium out and pull potassium in. Although they use a lot of energy doing this, they must do it in order to thrive.

Word List

thrive : do very well

method : a way to do something

You Practice

I. Answer the following questions.

1) What are some things that cells need in order to thrive?

2) Why is passive transport easier than active transport?

3) What happens during diffusion?

4) How do nerve cells work?

5) What is the main difference between active and passive transport?

II. What's the word? Using the clues, write the correct words from the reading.

1) cell covering: m _ _ _ _ _ _ _

2) glucose and sodium, for example: m _ _ _ _ _ _ _

3) delivering things to where they need to go: t _ _ _ _ _ _ _ _

4) not active: p _ _ _ _ _ _

5) a kind of passive transport: d _ _ _ _ _ _ _ _

III. Word power—Use these words from the reading in sentences of your own.

1) membrane____________________________________________

2) thrive________________________________________________

3) passive_______________________________________________

4) diffusion______________________________________________

5) concentration__________________________________________