Describe how alveoli are adapted for gas exchange( 4 marks)

they give the lungs a really big surface area. they have moist, thin walls (just one cell thick) they have a lot of tiny blood vessels called capillaries.

The walls of the alveoli are only one cell thick. This makes the exchange surface very thin - shortening the diffusion distance across which gases have to move. Each alveolus is surrounded by blood capillaries which ensure a good blood supply.Adaptations of the alveoli:

Thin walls - alveolar walls are one cell thick providing gases with a short diffusion distance. Moist walls - gases dissolve in the moisture helping them to pass across the gas exchange surface. Permeable walls - allow gases to pass through.

Explanation:

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b. the carbon cycle ensures living things have a source of hydrogen

it is called the mitotic spindle