Cambridge IGCSE Biology

1. Gas exchange

2. LO
• List the features of gas exchange surfaces in
humans
• Name and identify the lungs, diaphragm, ribs,
intercostal muscles, larynx, trachea, bronchi,
bronchioles, alveoli and associated capillaries
• Explain the role of goblet cells, mucus and
ciliated cells in protecting the gas exchange
system from pathogens and particles

3. Functions
• Taking in the oxygen
• Getting rid of carbon dioxide
= gas exchange

4. Gas exchange system in humans
Made up of:
• Respiratory surface = membranes lining the
alveoli
• A set of tubes – allow the air to reach the
respiratory surface
• Blood supply – to carry dissolved gases to and
from the respiratory system
• Ventilation system – to keep the flow of air

5. Respiratory surface = gas exchange surface
• Thin
• Large surface area
• Moist
• Well ventilated
• Close to a blood supply

6. • Mucous membrane – lines the whole
bronchial tree

7. Set of tubes = bronchial tree

9. • Larynx (voice box)
– Vocal cords
– Produces sounds

10. • Trachea (windpipe)
– Tube that carries air
towards the lungs
– Made of C-shaped rings
that prevents it from
collapse

11. • Bronchus
- first branch
from the
trachea
- contains
cartilage plates
- one pair

12. • Bronchiole
– Final, very fine
branch
– Leading into alveolus
– No cartilage

13. • Alveoli
– Air sacs
– Lined by the membranes where the gas exchange
takes place
– The surface is moist, thin
– Surface area as big as tennis court

16. LO
• Explain the role of the ribs, the internal and
external intercostal muscles and the
diaphragm in producing volume and pressure
changes in the thorax leading to the
ventilation of the lungs
• Explain the differences in composition
between inspired and expired air

17. Additional organs
• Intercostal muscles
– Contract and pull the rib cage upwards and
outwards while breathing in
– Relax and rib cage falls downwards and inwards
while breathing out

19. • Diaphragm
– A thin sheet of muscle under the lungs
• Pleural membrane
– Stick the outside of the lungs to the inside of the
chest cavity

21. Breathing in
• Intercostal muscles contract and pull the rig cage
upwards and outwards
• Diaphragm muscles contract and diaphragm
moves down
• Lung volume increases and the pressure falls
• Air rushes in to fill the extra space and equalise
the pressure

22. Breathing out
• Intercostal muscles relax and rib cage falls
downwards and inwards
• Diaphragm muscles relax and diaphragm returns
to its dome shape
• Lung volume decreases
• Air is forced out

25. The air
Component of air inspired expired reason
Oxygen 21% 18% Oxygen has diffused from the air in
the alveoli into the blood
Carbon dioxide 0.04% 3% Carbon dioxide has diffused from
the blood into the air in the alveoli
Nitrogen 78% 78% Nitrogen gas is not used by the
body
Water vapor Very variable saturated Water evaporates from surface in
the alveoli
Temperature Very variable 37°C Heat is lost to the air from the lung
surfaces

26. Efficiency of the lungs
• Spirometer
– Measures
the amount
of air that
enters and
leaves the
lungs
– Graph =
spirogram

27. • Homework 2:
– Explain the link between physical activity and rate
and depth of breathing in terms of changes in the
rate at which tissues respire and therefore of
carbon dioxide concentration and pH in tissues
and in the blood
• Hand in in written form on Monday
– P. 126 - 127