Gas Exchange

Question 1

Draw a simple diagram of the gas exchange system in humans.

5 marks

Answer 1

trachea
lungs
bronchi
bronchioles
lungs (2 must be shown)
intercostal muscles between ribs
diaphragm

Question 2

Describe the mechanism of ventilation in the human lung.

5 marks SL

Answer 2

consists of inhaling and exhaling air / exchanging stale air with fresh air (with the environment)
external intercostal muscles contract moving the rib cage up/out
diaphragm contracts
increaes volume of thorax / lowers lung pressure relative to air pressure / pulls air in
diaphragm relaxes
abdominal muscles contract
internal intercostal muscles contract moving the rib cage down/in
force air out / decreases volume of thorax / raise lung pressure relative to air pressure

Question 3

Describe the need for a ventilation system.

6 marks SL

Answer 3

• (small) animals obtain oxygen (by diffusion) through skin / in humans (large) animals skin is ineffective for ventilation
• humans are large / have a small ratio of surface area:volume
  so need ventilation system to increase surface area
  to maintain a concentration gradient in alveoli
• as oxygen is used in respiration (and carbon dioxide is produced)
• gaseous exchange occurs between air in alveoli and blood capillaries
• alveoli have high ratio of surface area:volume (to facilitate ventilation)
• to bring in fresh air (and remove stale air)

Question 4

Explain the need for, and mechanism of, ventillation of the lungs in humans.

8 marks SL

Answer 4

draws fresh air / oxygen into the lungs
removal / excretion of carbon dioxide
maintains concentration gradient of oxygen / carbon dioxide / respiratory gases
diaphragm contracts
(external) intercostal muscles contract
increased bolume (of thorax / thoracic cavity)
decreasing air pressure in lungs
air rushes in down air pressure gradient
converse of the above causes exhalation
abdominal muscles contract during active exhalation
elastic recoil of lungs helps exhalation

Question 5

Many processes in living organisms, including ventilation and gas exchange, involve moving materials. State the differences between ventilation and gas exchange in humans.

4 marks SL

Answer 5

ventiallation: 2 max
movement of air
movement in and out of the lungs
caused by muscles
an active process
involves mass flow / involves flow along air passages

gas exchange 2 max
movement of carbon dioxide and oxygen
(occurs when) oxygen moves from lungs / alveoli to red blood cells / carbon dioxide moves to lungs / alveoli from red blood cells
(occurs when) oxygen moves from red blood cells to tissues / carbon cioxide moves to red blood cells from tissues
a passive process / diffusion
takes place across a surface