Exchange surfaces

Question 1

What do exchabge surfaces depend on?

Answer 1

Its surface area to volume ratio

Question 2

In single-celled organisms, why can gases and dissolved substances diffuse directly into the cell across the cell membrane?

Answer 2

As they have a large surface area compared to their volume, so enough substances can be exchanged across the membrane to supply the volume of the cell

Question 3

Why can not enough substances diffuse from their outside surface area to supply their entire volume?

Answer 3

Multi-cellular organisms have a smaller surface area compared to their volume. This means they need some sort of exchange surface for efficient diffusion. The exchabge surface structures have to allow enough if the necessary substances to pass through

Question 4

How are exchabge surfaces adapted to maximise effectiveness?

Answer 4

1. They have a thin membrane, so substances only have a short distance to diffuse
2. They have a larger surface area so lots of a substance can diffuse at once
3. Exchange surfaces in animals have a lot of blood vessels, to get stuff into and out of the blood quickly
   4.Gas exchabge surfaces in animals are often ventilated too - air moves in and out