6.4 Gas Exchange
Respiratory System
Why do we need to breathe?
To intake oxygen
To exhale carbon dioxide
What is oxygen used for?
Aerobic respiration
And what is aerobic respiration used for?
Energy production (ATP!)
Definitions: Ventilation, Gas
Exchange, and Cell Respiration
Ventilation
The process of inhaling and exhaling, with oxygen
entering the alveoli (large surface area)
Gas Exchange
The process of exchanging one gas for the other
between alveoli and capillaries (carbon dioxide for
oxygen)
Cell Respiration
The chemical process occurring in mitochondria
where energy is released as ATP
What composes the human respiratory system?
Mouth
Nose
Trachea
Bronchi
Bronchioles
Lungs
Alveoli
Identify the respiratory components.
6
1
7
3
2
3
4
5
Be able to draw something like this.
Why are alveoli shaped like they are?
Small alveoli increase surface area of tissue
exposed to open air
Gases only have to go through
one layer of cells (thin capillary
wall) to get into blood vessel
There are so many capillaries
blood easily diffuses
How is air drawn into the lungs?
Diaphragm muscle contracts
Intercostal muscles
between ribs contract
Lungs can open up more
More volume with same
amount of gas = decreased
air pressure
Air rushes into lungs to
balance pressure
How is air pushed out of the lungs?
Diaphragm muscle relaxes
Pushes on lungs to
“deflate”
Intercostal muscles relax
Chest cavity gets smaller
Pushes air out of lungs
Air is exhaled
IB Exam Question
1. State the difference between ventilation,
gas exchange, and cell respiration. (3 marks)
Ventilation
The process of inhaling and exhaling, with oxygen
entering the alveoli (large surface area)
Gas Exchange
The process of exchanging one gas for the other
between alveoli and capillaries (carbon dioxide for
oxygen)
Cell Respiration
The chemical process occurring in mitochondria
where energy is released as ATP
IB Exam Question
2. Draw a diagram of the human gas
exchange system.
(5 marks)
Award [1] for each of the following structures clearly
drawn and labelled.
mouth / nose;
trachea;
bronchi;
bronchioles;
lungs;
alveoli;
diaphragm;
ribs / rib eye / intercostal muscles;
IB Exam Question
3. List the features of the alveoli that
adapt them to gas exchange.
(3 marks)
Alveoli increase surface area between blood
and respiratory gases
Single layer of cells allows for short diffusion
distance of gas into blood
Dense network of capillaries near the surface
increases absorption
IB Exam Question
4. Explain the need for, and the mechanism
of, ventilation of the lungs in humans.
(8 marks)
draws fresh air / oxygen into the lungs;
removal / excretion of CO2;
maintains concentration gradient of O2 / CO2 /
respiratory gases;
diaphragm contracts;
intercostal muscles contract;
increased volume (of thorax / thoracic cavity);
decreasing air pressure in lungs;
air rushes in down air pressure gradient;
opposite of the above causes exhalation;
abdominal muscles contract during active exhalation;
elastic recoil of lungs helps exhalation;