Chapter 5 · Question 4
Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
Q4
Why is diffusion insufficient to meet the oxygen requirements of multicellular organisms like humans?
Answer Revealed
Direct Answer:
Diffusion is too slow to transport oxygen to all cells in large multicellular organisms because the distance between the body surface and deepest cells is too large.
Simple Explanation
In large organisms like humans, cells deep inside the body are too far from the surface for oxygen to reach them quickly enough by simple diffusion. So we need a special transport system.
Exam-Ready Structure
In multicellular organisms like humans, the entire body is not in direct contact with the environment. Every cell needs oxygen for respiration, but cells deep inside the body are far from the body surface. Diffusion is a slow process and cannot transport oxygen quickly over such large distances. Moreover, the oxygen demand of all body cells is very high. Therefore, a specialised respiratory system with a large surface area (lungs) and a transport system (blood) are required to supply oxygen efficiently to every cell.
Key Points
- Diffusion is too slow over large distances
- Not all cells are near the body surface
- Oxygen demand of all cells is very high
- Specialised respiratory and transport systems are needed
Common Mistakes
- Saying diffusion does not occur in humans (it does, but is insufficient alone)
- Not mentioning the large distance between body surface and internal cells
Answer Sources
- Limits of diffusion in large organismstextbook section | Science | Life Processes | Respiration and transport need | Pages 10-12