3.2-Gas Exchange

Question 1

1. Complete the equation of Fick’s law:

Answer 1

Rate of diffusion  Surface area x Concentration Gradient

Thickness of diffusion pathway

Question 2

2. How does gas exchange take place in single celled organisms and small thin organisms such as flat worms?

Answer 2

Simple diffusion

Question 3

3. Small organisms obtain enough oxygen without a specialised gas-exchange system. Why is this possible?
   Why do larger organisms need a gas-exchange and transport system?

Answer 3

Small organisms have large surface/volume ratio;
All cells are close to the gas exchange surface
So diffusion/exchange can take place over the whole body surface/skin;

But cells of larger organisms are a long way from gas exchange surface;
and because diffusion is a slow process;
gases (and other substances) must be supplied by transport system/circulatory system/blood;

Question 4

4. Label this diagram of the lungs with the key parts

Answer 4

0

Question 5

5. What makes the alveoli well adapted for gas exchange (diffusion)

Answer 5

• Many alveoli provide a large surface area
• Many capillaries provide a large surface area
• Alveoli and capillary walls are thin
• This is due to the squamous (flattened) epithelial cells
• So there is a short diffusion pathway between the alveoli and the blood
• Ventilation brings fresh air into the lungs containing a high concentration of oxygen and removes air with a low concentration of oxygen
• Circulation keeps the blood moving so there is deoxygenated blood in contact with the alveoli
• This maintains a concentration gradient between the alveoli and the blood

• So fast rate of diffusion

Question 6

6. Complete the table below:

Answer 6

Inhaled Air (%) Exhaled Air (%)
Oxygen 21 17
Carbon dioxide 0.04 4
Nitrogen 78 78

Question 7

7. Describe the path that oxygen takes from the alveoli to the blood

Answer 7

Through the alveolar epithelium

Through the capillary endothelium to the blood

Question 8

8. Write the equation for pulmonary ventilation and rearrange it to calculate tidal volume and ventilation rate (include units)

Answer 8

Pulmonary ventilation = breathing rate x tidal volume

dm3min-1 min-1 dm3

Question 9

9. How can breathing rate be calculated if you know time taken for one breath?

Answer 9

Breathing rate = 60 / time taken for one breath

Question 10

10. Complete this table:

Answer 10

Intercostal muscles Diaphragm Volume Pressure Air moves…
Inhaling • Externals contract
• Internals relax Contracts and flattens Increases Decreases In
Exhaling • Externals relax
• Internals relax (unless vigerous exercise, in which case the internals contract) Relax and becomes dome shaped Decreases Increases out