Exchanging materials – the lungs

p.220

Requirements

• Lung/alveolus diagrams• Lungs to dissect

Outcomes

• Most students should be able to:• describe the features of exchange surfaces that make

them effective• describe the function of the alveoli• explain how the alveoli are adapted for the efficient

exchange of gases. • Some students should also be able to:• evaluate the importance of adaptations which give

increased surface area to the effectiveness of gas exchange.

Objectives

• Students should learn:• that many organ systems are specialised for

exchanging materials• that exchange surfaces in humans and other

organisms are adapted to maximise effectiveness• that the lungs are especially adapted for the

exchange of gases• that the alveoli provide a large surface area over

which gases can readily diffuse into and out of the blood.

Specification • Many organ systems are specialised for exchanging materials. The

effectiveness of an exchange surface is increased by:• – having a large surface area.• – being thin, to provide a short diffusion path.• – (in animals) having an efficient blood supply.• – (in animals, for gaseous exchange) being ventilated. [B3.1.1 h)]• Gas and solute exchange surfaces in humans and other organisms

are adapted to maximise effectiveness. [B3.1.1 i)]• The size and complexity of an organism increases the difficulty of

exchanging materials. [B3.1.1 j)]• In humans:• – the surface area of the lungs is increased by the alveoli. [B3.1.1 k)]

Workbook

• P. 105-6

Gas exchange mechanismschoose from body skin /gills /lungs /mesophyll cells

Letter Organism How it exchanges Oxygen and carbon dioxide

A Fish

B Frog

C Tadpole

D Amoeba

E Plant

F Locust

G Snail

H Worm

A

B

C

D

E

F

G

H

For each letter record how the organism exchanges its gases

Question

• What do you notice about the difficulty of gas exchange in a more complex organism?

• It is more difficult/requires better adapted exchange surface

Adaptations of a gas exchange surface

• Make a list of 4• Learn them!!

• Person is ~1.5 m tall and ~0.08 m3.• Skin is ~2 m2, so person as a box is ~1 m2 × 0.1 m thick.• Lung is ~100 m2 and ~0.01 m3, so lung as a sheet is ~7 m2 × ~10-4 m thick.• Intestine is ~300 m2 and ~0.01 m3, so intestine as a sheet is (~12 m2 x ~10-4m thick.

lung

intestine

The human breathing system How an alveolus is adapted for gas exchange

Alveolus on next slide and in book

Label your diagram carefullyUse page 224 in text book to help you1

2

3

4

5

6

7

8

9

10

11

B3 1.2 gas exchange in the lungs

Q2 and 3 p.221

2. Gas exchange is the exchange of oxygen and carbon dioxide in the lungs in humans. Vital to supply oxygen to the red cells in the blood which is transported to tissues for respiration, and to get rid of the waste product of carbon dioxide from respiration carried back to lungs by the plasma in the blood

Q3

• Many alveoli combined have a large surface area for gas exchange

• Alveoli have a rich blood supply maintaining the concentration gradients of oxygen and carbon dioxide

• Ventilation refreshes the gases in the alveoli maintaining the concentration gradients

• The alveolar and capillary cells are flattened so there is a short diffusion pathway for the gases

Lung dissection

• Or video if you wish