gas exchnage unit 3

Question 1

Tidal volume is the volume of air inhaled and exhaled during a single breath when a person
is resting. The tidal volume in a person with emphysema is reduced compared with the tidal
volume in a healthy person.
Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide
between the blood and the alveoli. (3 marks)

Answer 1

A reduced tidal volume leads to impaired carbon dioxide exchange because:
- Less fresh air enters the alveoli which means more Co2 build up in the alveoli and lungs
- This means upon exhalation, less Co2 is being removed from the blood this means it reduces the concentration gradient

Question 2

  Explain the advantage for larger animals of having a specialised system that facilitates
oxygen uptake. (2 marks)

Answer 2

• Larger animals have smaller surface area to volume ration
• This overcomes long diffusion pathway
  (Explainations: Normal diffusion is only effective over short distances. Specialised strcutures like alveoli in lungs reduces diffusion distance.

Question 3

Suggest why some animals have specialised structures outside their body e.g. gills in a fish compared to specialised structure inside the body e.g. alveoli in lungs

Answer 3

• Water has a lower partial pressure of oxygen so
• Having gills on the outside decreases the diffusion distances between the blood and water.

Question 4

Explain how the counter-current principle allows efficient oxygen uptake in the fish gas
exchange system.

Answer 4

Blood and water flow in opposite directions so
concentration gradient maintained across the whole length of the lamellae

Question 5

Describe and explain the mechanism that causes lungs to fill with air. - 3 marks

Answer 5

• Diaphragm contracts and flattens
• External intercostal muscles contracts
• Volume of thoracic activity increases
• Pressure decreases
• Air moves down a concentration gradient.

Question 6

Describe and explain the advantage of the counter-current principle in gas exchange
across a fish gill.

Answer 6

• Water and blood flowing in the opposite direction
• maintains concentration gradient of oxygen
• across the whole length of the lamellae

Question 7

Describe the pathway taken by an oxygen molecule from an alveolus to the blood.

Answer 7

-Oxygen dissolves into the most fluid lining of the alveolar epithelium
- Oxygen molecule diffuses across flattened epithelial cells
- Oxygen molecule diffuses across capillary endothelium
- Oxygens enters plasma and binds to haemoglobin in red blood cells

Question 8

Explain how one feature of an alveolus allows efficient gas exchange to occur.

Answer 8

Alveolar epithelium is one cell thick creating a short diffusion pathway.

Question 9

Breathing out as hard as you can is called forced expiration.
(a) Describe and explain the mechanism that causes forced expiration.

Answer 9

1. Contraction of internal intercostal muscles;
2. Relaxation of diaphragm muscles / of external intercostal muscles;
3. Causes decrease in volume of chest / thoracic cavity;
4. Air pushed down pressure gradient.