Why Transport Systems Are Needed

IGCSE Edexcel Biology
2.51-2.52 Transport in Organisms
Key Concept: Diffusion alone is sufficient in unicellular organisms but too slow for large multicellular organisms.

Section A: Diffusion

1. Explain why unicellular organisms can rely on diffusion. [3]

Section B: Transport Systems

2. Explain why multicellular organisms need transport systems. [3]
3. Give two substances that must be transported around the body. [2]
Total marks: 8

Mark Scheme

1. They have a large surface area to volume ratio and short diffusion distances [3]
2. Large size gives small surface area to volume ratio and long diffusion distances, so diffusion is too slow [3]
3. Any two: oxygen, glucose, amino acids, carbon dioxide, urea, hormones [2]