A hidden, folded surface

The idea

Respiratory organs of land animals have a large surface area in contact with air; being fine and delicate, this surface lies within the body, with passages bringing air to it and a mechanism to move air in and out.

A delicate surface

The part of the body where oxygen enters the blood has to be very thin so that gases can pass across it.

Where in the body of a land animal would you expect such a thin surface to be?

• Inside the body
• On the outside, in the open
• On the feet

Build the organ

Press Next step to add one feature at a time.

Four features

Land animals take oxygen from the atmosphere. The organ that does this has a surface with a large area in contact with the air. This surface is very fine and delicate, so it is usually placed inside the body. Passages bring the air to it, and a mechanism moves air in and out.

Respiratory organs of land animals have a large surface area in contact with air; being fine and delicate, this surface lies within the body, with passages bringing air to it and a mechanism to move air in and out.

Notes

Land animals' respiratory organs have a large surface in contact with air, inside the body (it is fine and delicate), with passages for air and a mechanism to move air in and out.

Check yourself

Why is the respiratory surface usually placed inside the body?

What is the purpose of the passages leading to the respiratory surface?

The surface across which oxygen and carbon dioxide are exchanged is ...

Besides a large surface and passages, what else do respiratory organs of land animals have?

• It must stay away from the oxygen-rich air. The surface has to be in contact with the oxygen-rich atmosphere, which is why passages bring air to it.
• It is thick and needs more space. The surface is very fine and delicate, not thick.
• It is fine and delicate, so this protects it — correct. Yes!
• They take air to the surface inside the body — correct. Yes!
• They protect the delicate surface from the air. The surface is protected by being placed within the body; the passages bring air to it.
• They make the surface smaller. The surface has a large area in contact with the air.
• thick and tough. The book says this surface is very fine and delicate.
• very fine and delicate — correct. Yes!
• small in area. The structure increases the surface area in contact with the oxygen-rich atmosphere.
• A mechanism that keeps air from reaching the surface. Air has to reach the surface, since oxygen is absorbed there.
• A thick wall that blocks gas exchange. Exchange of oxygen and carbon dioxide takes place across the surface.
• A mechanism for moving air in and out — correct. Yes!