Chapter 5 · Question 12
How is oxygen and carbon dioxide transported in human beings?
Q12
How is oxygen and carbon dioxide transported in human beings?
Answer Revealed
Direct Answer:
Oxygen is transported by haemoglobin in red blood cells, and CO2 is transported as dissolved gas, as bicarbonate ions, and bound to haemoglobin.
Simple Explanation
In our blood, oxygen is carried by a special protein called haemoglobin inside red blood cells. Carbon dioxide goes back to the lungs dissolved in the blood and also in the form of bicarbonate.
Exam-Ready Structure
Transport of oxygen: Oxygen from the lungs diffuses into the blood and binds with haemoglobin (a respiratory pigment present in red blood cells) to form oxyhaemoglobin. This reversible binding allows oxygen to be released at tissues where oxygen concentration is low. Transport of carbon dioxide: CO2 is more soluble in water than oxygen and is transported in three ways: 1. Dissolved in plasma (about 5-7%). 2. As bicarbonate ions (HCO3-) in plasma (about 70%) — CO2 reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions. 3. Bound to haemoglobin as carbamino-haemoglobin (about 23%). At the lungs, CO2 is released and exhaled.
Key Points
- Oxygen is carried by haemoglobin as oxyhaemoglobin
- CO2 is transported mainly as bicarbonate ions
- CO2 is also transported dissolved in plasma
- CO2 binds to haemoglobin as carbamino-haemoglobin
Common Mistakes
- Saying oxygen is simply dissolved in blood
- Not naming haemoglobin as the oxygen carrier
Answer Sources
- Transport of oxygen and carbon dioxidetextbook section | Science | Life Processes | Respiration and blood transport | Pages 12-14