2.51, 2.52 Transport

Why do multicellular organisms need transport systems?

Multicellular animals have high metabolic demand - they require lots of oxygen and food and produce lots of waste.

Why can simple unicellular organisms rely on diffusion for movement of substances in and out of cells?

It has a large SA:V ratio, therefore diffusion is fast and efficient due to the short distances required substances have to travel.

Substances can diffuse directly into and out of the cell across the cell membrane, and the swiftness allows the cell to stay alive.

Why do multicellular organisms need transport systems?

They have a small SA:V ratio meaning diffusion would be slow and inefficient because of the long distances that would be required to reach every cell and the organism's cells wouldn't get required substances (e.g. water, mineral ions and sugars) fast enough and would die.

Multicellular organisms therefore need transport systems to move substances to and from cells quickly.

Name 5 things which may need to be transported around the body of a multicellular organism

Hormones
Enzymes
Products of digestion
Waste
Mineral ions