1. Settler
Describe and explain the 2 features that make an exchange surface efficient (4 marks)
Students to feedback answers – check understanding from previous lesson

2. Exam Question
Explain why large, active organisms need specialised surfaces for exchange.
(3 marks)
Large mammals have a high demand for oxygen for respiration, which can’t be met by diffusion alone as their surface area : volume ratio is too low. A specialised exchange surface gives a greater area, so more oxygen can be absorbed and more carbon dioxide can be removed.
Explain in terms of surface area to volume ratio how multicellular organisms are different to unicellular organisms
(Grade B – A)

3. Module 3 Exchange and transport
7.2– Mammalian gas exchange system

4. Starter Activity
In pairs talk for 30 seconds on how to breathe

5. Outline the mechanism of breathing
Learning Objectives
Success Criteria
Label the lungs and each features importance
(Grade E – D)
Describe the features of an efficient exchange surface (Grade C – B)
Outline the mechanism of breathing in mammals, with reference to the function of the ribcage, intercostal muscles and diaphragm (Grade B – A)
Describe how the features of the lung structure that allow it to be an efficient gas exchange surface
Outline the mechanism of breathing

6. add onto your diagram briefly the importance of each structure
LUNGS
Label the lungs and each features importance
(Grade D – C)
Trachea
Intercostal muscle
Bronchus
Bronchiole
Rib
Pleural membrane
Hand out sheet for students to label
Diaphragm
add onto your diagram briefly the importance of each structure

7. Lung dissection Demonstration
Discuss worksheet answers

8. Lung dissection
1. What structure makes the windpipe stay open, but able to bend? 
2. Are the lungs hollow bags or spongy? What does the lung tissue look like where you cut into it? What happens when you put this tissue into water?
3. What are the lungs like when full of air? Do you have to squeeze them to push the air out again?
4. In a living animal, what body movements draw air into the lungs?
5. In a living animal, what body movements force air from the lungs?

9. Dissection answers
1 Horseshoe-shaped rings of cartilage make the windpipe stay open, but able to bend. 2 The lung tissue is spongy. When you cut into it you can see that it is permeated with air-filled tubes and blood vessels. A small piece will float in water. 3 When full of air, the lungs expand but are still soft to the touch. If left to rest, some of the air comes out as the lung tissue relaxes down 4 In a living animal, the lungs are surrounded by a pleural membrane that keep the outside surface in contact with the inner surface of the rib cage. The diaphragm (muscle at the bottom of the thorax) contracts and flattens, and the ribcage moves upwards and outwards. Both of these movements increase the volume of the ribcage, reducing the air pressure and so air is drawn into the lungs to equalise the pressure. 5 In a living animal, the diaphragm relaxes and domes up into the bottom of the thorax, and the ribcage moves down and in. Both these movements reduce the volume of the ribcage, increasing the air pressure and forcing air out of the lungs to equalise the pressure.

10. How lungs are adapted for gaseous exchange
Describe the features of an efficient exchange surface (Grade B – C)
Task – Use page 46/47
4 features of a good exchange surface?
1)large surface area
2)thin barrier
3)fresh supply of molecules on one side to keep concentration high
4)Removal of required molecules on the other side to keep concentration low
In pairs,
Person 1 explain how number 1) and 2) would apply to the lungs
Person 2 Explain how number 3) and 4) would apply to the lungs.
Teach each other what you have found

11. How they are adapted for exchange
Large surface Area = more space for molecules to pass through
Alveoli = µm
Many of them
Total surface area = 70m2
Permeable to oxygen and Carbon Dioxide
Plasma membrane allows diffusion of both these molecules
Thin barrier to reduce diffusion distance

12. How they are adapted for exchange
Maintaining the diffusion gradient
Steep diffusion gradient is needed
Achieved by the blood transport system and the ventilation movements
Blood Transport System
Blood brings Carbon dioxide to the lungs
Carries oxygen away
Breathing Movements
Replace used air with fresh air
Ensures concentration of oxygen is higher than in the blood
Removes air containing carbon dioxide
Ensure concentration of carbon dioxide is lower than in the blood

13. A mobile ribcage?
This means that the rib cage must also be able to change position.
Take your hands and place them flat on your chest just above your hips on each side of your body. Now breathe in and out very deeply. Whilst you do this, watch to see what happens to your hands.
You should notice the following things…..

14. Mechanism of breathing

15. Make a table like this:
Step
Breathing in (Inspiration)
Breathing out (expiration) 1 2 3 4 5 6
Complete the table by writing the sentences on the next slide in the correct order.
Outline the mechanism of breathing in mammals, with reference to the function of the ribcage, intercostal muscles and diaphragm (Grade A – B)

16. Breathing in and out Pressure in lungs decreases.
Volume of chest cavity decreases
Diaphragm relaxes and is pushed upwards by displaced organs underneath
External intercostal muscles relax and ribs fall
Pressure in lungs increases.
Air moves out of the lungs.
Diaphragm contracts to become flatter and pushes digestive organs down
Volume of chest cavity increases
External intercostal muscles contract to raise ribs
Air moves into the lungs.

17. Breathing in and out Breathing in Breathing out
Energy using process
Breathing out
Passive process
1. External intercostal muscles contract to raise ribs
1. External intercostal muscles relax and ribs fall
2. Diaphragm contracts to become flatter and pushes digestive organs down
2. Diaphragm relaxes and is pushed upwards by displaced organs underneath
3. Volume of chest cavity increases
3. Volume of chest cavity decreases
4. Pressure in lungs decreases.
4. Pressure in lungs increases.
5. Air moves into the lungs.
5. Air moves out of the lungs.

18. Task
Complete questions 1-3 on p47

19. Plenary Activity Alveolus Intercostal muscles Inspiration Expiration
Diaphragm
Squamous Tissue
Capillary
Trachea
Bronchi
Bronchioles
Ribs
Lungs
Surfactant
Volume
Pressure
Plenary Activity