This Worksheet Is Designed to Be Completed Alongside the Lesson

This worksheet is designed to be completed alongside the lesson.

The icons on the left tell you which pages of the lesson the questions relate to.

You breathe to get oxygen from the air into your blood. This oxygen is used in respiration to produce energy out of food, and carbon dioxide is made as a waste product. As you breathe out you get rid of carbon dioxide from your blood into the air. Your lungs are mostly made up of millions of tiny air sacs called alveoli. Each alveolus cleverly allows you to exchange these gases at just the rate you need. You are going to investigate how they do this.

/ 1. / a. / What happens to the size of each alveolus as the person breathes in and out?
b. / What is the name of the type of tiny blood vessels round the alveoli?
c. / What are the round cells that move in the blood capillary called?
/ 2. / a. / On the diagram below there are six numbered bars, each of which represents the level of either oxygen or carbon dioxide.
Point A is where the capillary first touches the alveolus and point B is where the capillary last touches the alveolus.
Label each bar with the correct gas (either O2 or CO2).

b. / Using the animation and the diagram above, describe how the amount of each gas in the blood changes as the blood flows around the alveolus between points A and B.
c. / Compare the amount of each of the gases in the blood at point A with the amount in the alveolus.
d. / Complete the following sentence:
Diffusion is the random movement of particles from a region of ______concentration to a region of ______concentration.

Version 2.0 1

e. / Choose the correct statement from the following and explain why it is correct:
· More oxygen molecules diffuse from the capillaries into the alveoli than the other way.
· More carbon dioxide molecules diffuse from the alveoli into the capillaries than the other way.
· Oxygen and carbon dioxide molecules diffuse in mainly opposite directions. They are exchanged.
f. / How is the oxygen level in the alveolus kept higher than in the capillary?
g. / How is the carbon dioxide level in the alveolus kept lower than in the capillary?
h. / How does the thickness of the alveolus wall and the capillary wall help gas exchange?
/ 3. / a. / How does the fact that there are many blood capillaries round each alveolus in our lungs help exchange?
b. / How does the large surface area of the alveoli help gas exchange?
/ 4. / a. / Complete the flow chart using the words in the box.
You may use each word more than once or not at all.
faster slower more less oxygen carbon dioxide

Version 2.0 1

b. / How and why do changes to breathing and blood flow during exercise affect the rate of gas exchange?
/ 5. / a. / Under what circumstances might you need to hold your breath?
b. / Describe what happens to the gas levels during the two minutes while the person holds their breath.
c. / When does oxygen diffuse fastest into the blood during these two minutes? Explain why.
d. / When does carbon dioxide diffuse fastest from the blood during these two minutes? Explain why.
e. / Some divers train to hold their breath for a long time.
Use your knowledge of gas exchange to explain what changes will enable them to hold their breath for longer. Give reasons for your answers.

Version 2.0 1