Module 3 - Transport in animals

Question 1

Explain why large multicellular animals need a circulatory system, whereas single-celled organisms do not? (2 marks)

Answer 1

Single-celled organisms have a large SA : V ratio, so diffusion is sufficient to meet their metabolic needs, whereas for large multicellular animals have a small SA :V ratio and higher metabolic demands, so diffusion alone is too slow and inefficient.

Question 2

State and explain three reasons why a large, active animal needs a specialised transport system? (3 marks)

Answer 2

• They have a low SA:V ratio, so diffusion alone won’t be sufficient over large distances.
• Higher metabolic rates, so requires more O2 and nutrients
• Waste products need to be removed efficiently to avoid toxicity.