Lesson 6 ·Class 9 · The Respiratory System · Flow Lab
Gas Transport and Exchange
From alveolus to tissue and back.
Follow one oxygen molecule from a breath of air into a working muscle cell.
→ → → → →
🫧 Step 1 of 6 · In the alveolus
Air in the alveolus has a high oxygen concentration; the blood arriving is low in oxygen.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
Every step is diffusion down a concentration gradient — the gradient simply reverses between lung and tissue.
What this lesson covers
Challenges to clear
- Advance to how oxygen is actually carried.
- Reach the point where oxygen is handed over to the cells.
- Follow the whole round trip.
The task
Follow one oxygen molecule from a breath of air into a working muscle cell.
What this lesson covers
- In the alveolus — Air in the alveolus has a high oxygen concentration; the blood arriving is low in oxygen.
- Oxygen diffuses in — Oxygen crosses the thin alveolar wall and capillary wall into the blood, down its concentration gradient.
- Carried by haemoglobin — Oxygen binds to haemoglobin in red blood cells as oxyhaemoglobin — a loose, reversible bond.
- Reaching the tissue — At a respiring tissue, oxygen is low and carbon dioxide is high — the opposite of the lung.
- Oxygen released — Oxyhaemoglobin breaks down and releases oxygen to the cells. This is tissue respiration.
- Carbon dioxide returns — CO₂ diffuses into the blood, is carried mostly as bicarbonate, and is breathed out at the alveoli.
Hint
Every step is diffusion down a concentration gradient — the gradient simply reverses between lung and tissue.