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A system that moves substances between exchange surfaces and cells elsewhere in a multicellular organism.

A system that carries substances between exchange surfaces and cells in different parts of a multicellular organism.

A transport system moves substances in bulk between exchange surfaces and internal cells. For example, a circulatory system carries oxygen and nutrients towards cells and carries waste products away. Its network brings transported substances close to cells, leaving only a short final distance for diffusion.

When explaining the need for a transport system, link a low surface area to volume ratio to insufficient exchange and long diffusion distances. A transport system does not remove the need for diffusion.

When explaining why a large organism needs a transport system, link its smaller surface area : volume ratio to the needs of cells deep inside it.

Link each problem to its solution: a small surface area:volume ratio limits exchange at the exterior, while a long diffusion distance makes diffusion to internal cells too slow. Exchange surfaces and transport systems solve these related problems.

A large multicellular organism needs specialised exchange surfaces to take in or release enough material, and a transport system to carry substances between those surfaces and cells throughout the body. In animals, oxygen can enter at a gas-exchange surface and then be carried in the blood to cells that are too deep for direct exchange with the surroundings. Carbon dioxide can be carried back for removal.

A system that moves substances between exchange surfaces and cells throughout a multicellular organism.

A transport system moves substances rapidly between the exchange surface and the rest of the organism. It delivers incoming substances to cells and carries substances away from cells for removal or further exchange. This movement also helps maintain concentration gradients at exchange surfaces.

A group of vessels that carries substances between different parts of a multicellular organism.

In a large multicellular organism, many cells are far from the outside, so transport systems carry substances between different parts of the body.

A system that moves substances around a multicellular organism, reducing the distance they must travel by diffusion.

Transport system

Definition

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AQA GCSE Biology · 8461

Edexcel GCSE Biology · 1BI0

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OCR GCSE Biology A · J247

OCR GCSE Biology B · J257