Diffusion: Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials.

Q: How do I revise Diffusion: Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials. for GCSE?

Read the notes on Diffusion: Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials., then test yourself without looking. Answering questions and checking what you missed builds recall faster than re-reading.

Q: Is this Diffusion: Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials. guide aligned to the AQA specification?

Yes. This guide is linked to the Diffusion: Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials. topic in the AQA GCSE specification.

Exchange surfaces are adapted to maximise diffusion.

Study notes

From the checked teaching notes for this specification point.

The idea

Exchange surfaces are adapted to maximise diffusion. In mammals, the small intestine has villi, which are finger-like projections that increase surface area, and a thin wall with a rich blood supply to maintain a steep concentration gradient. The lungs contain alveoli, tiny air sacs with a large total surface area, thin walls and a good blood supply. Fish gills have many filaments and lamellae, giving a large surface area, and a counter-current flow of water and blood maintains a concentration gradient along the gill. Plant roots have root hair cells that increase surface area for absorbing water and mineral ions, while leaves are broad and thin with stomata and air spaces so carbon dioxide can diffuse to the cells.

What earns the marks

Identifies villi in the small intestine as projections that increase surface area, with thin walls and a rich blood supply.
Describes alveoli in the lungs as having a large total surface area, thin walls and a good blood supply.
Explains that gill filaments and lamellae increase surface area in fish and that water and blood flow in opposite directions.
States that root hair cells increase the surface area of roots for absorbing water and mineral ions.
Describes leaves as broad and thin with stomata and internal air spaces for gas exchange.
Links each adaptation to maintaining a steep concentration gradient or shortening the diffusion distance.

Common mistakes and how to put them right

Saying villi or alveoli increase volume.
Put it right: They increase surface area for exchange.
Describing fish gills as having a counter-current system without explaining that it keeps a concentration gradient along the gill.
Forgetting that leaves need stomata and air spaces, not just a broad flat shape, for carbon dioxide to reach the cells.

Exam tips

Name the structure, state the adaptation and then explain the effect on diffusion; this keeps each point complete.
Use the same framework for each organism: surface area, thickness, blood supply or concentration gradient.
For fish, mention both the large surface area of the lamellae and the opposite flow of water and blood.

Try the lesson

The start of the Diffusion: Students should be able to explain how the small intestine and lungs in mammals, gills in fish, and the roots and leaves in plants, are adapted for exchanging materials. lesson, made from checked teaching notes for this specification point.

Have a go first

Which feature of the small intestine increases the surface area for exchange?

Tip: press 1 to 4 to choose

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