1. Gas Exchange about the exchange of gases at the interface between the alveoli and capillaries WAL: All Most Some What are the essential features of exchange surfaces? Why is the alveoli such an important structure in gas exchange? How are gases exchanged in the alveoli of humans?

2. Today we are covering from the specification: Pages 78 & 79 of your textbook

3. Essential features of gas-exchange surfaces To enable efficient transfer of materials across the gas exchange surfaces via diffusion or active transport, the gas exchange surfaces have the following essential features.....

4. Essential features of gas-exchange surfaces They have a large surface area to volume ratio – to speed up the rate of change. They are very thin – to keep the diffusion pathway short and so allow materials to cross rapidly. They are partially permeable – to allow selected materials to diffuse easily. There is movement of the internal medium, e.g blood – to maintain a diffusion gradient.

5. Total Recall: Fick’s Law of Diffusion

6. Diffusion is proportional to: surface area x difference in concentration length of diffusion path

7. To do now: Read pages 78 & 79. Answer summary question 1 in the peachy/orangey/apricot looking box.

8. The role of the alveoli

9. To do now: 1.Complete the summary sections on your sheet 2.Complete the questions on your sheet 3.Make a plasticine model of gas exchange at the alveolus. – You should be able to move some of the bits around to help you explain to the person next to you. – Use the diagram on page 79 to help you. – I will be coming round to see how you are getting on.

10. Exam question, June 2010 Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them. (5 marks)

11. Mark scheme – self-assessment

12. Lungs Question 1 (a) P - Trachea Q – Bronchus 1 (b) – Increase volume of lungs – Lowers pressure of lungs – Air pushed out down pressure gradient 1(c) Tidal volume and ventilation rate