CIE Biology - Gaseous Exchange

[Dania]

State two ways in which the concentration gradients of oxygen and carbon dioxide are maintained for efficient gas exchange?

The answer in the mark scheme says "Good blood supply & good ventilation" which I find to be rather vague.

Help, please

[Freaked12]

The steep concentration gradient across the respiratory surface is maintained in two ways: by blood flow on one side and by air flow on the other side. The ventilation system replaces diffuses oxygen (keeping the concentration high) and removes carbon dioxide (keeping the concentration low).

This means oxygen can always diffuse down its concentration gradient from the air to the blood, while at the same time carbon dioxide can diffuse down its concentration gradient from the blood to the air.

[Deadly_king]

State two ways in which the concentration gradients of oxygen and carbon dioxide are maintained for efficient gas exchange?

The answer in the mark scheme says "Good blood supply & good ventilation" which I find to be rather vague.

Help, please

Gaseous exchange......I guess you must be meaning the diffusion of gases in the lungs.

Good blood supply : Deoxygenated blood from the right side of the heart is pumped to the lungs via the pulmonary artery. There is a continuous flow of blood in the blood vessel which passes besides the alveoli of the lungs. This blood is rich in carbon dioxide but defficient of oxygen(only a little amount is present).

Good ventilation : Breathing brings much oxygen gas into the lungs, more precisely the alveoli and as you must be aware breathing never stops. So there is a continuous input of oxygen into the lungs while at the same time carbon dioxide is expelled from the body.

I believe that the word continuous us important since it indicates that blood is constantly deprived of oxygen and also alveolar air deprived of carbon dioxide. This will result in an unchanged steep concentration gradient.

So both these mechanisms are necessary to maintain a steep concentration gradient between the alveolar gases(high O₂ concentration but low CO₂ concentration) and those in the blood(high CO₂ but low O₂). Therefore the two gases diffuse efficiently down their concentration gradients respectively.

Oxygen moves into the blood while carbon dioxide takes the opposite route.

Hope it helps