Features of efficient exchange surfaces

Overview

Recall questions on large surface area, a short diffusion distance, a moist surface and a maintained concentration gradient, how the leaf and the alveolus each achieve them, and why gases must dissolve before they can cross a membrane.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Name the three general features shared by efficient exchange surfaces.

   Model answer

   They have a large surface area, a thin separating surface and a steep concentration gradient maintained across them.

2. 2

   Why does a thin separating surface speed up exchange?

   Model answer

   It shortens the distance that molecules must diffuse, so the same gradient drives a faster rate of movement.

3. 3

   How is a concentration gradient across an exchange surface maintained in a living organism?

   Model answer

   Substances are continually removed on one side and continually delivered to the other, usually by a flow of blood or air, so the difference in concentration is never allowed to disappear.

4. 4

   Give two ways in which the surface area of an exchange surface can be increased.

   Model answer

   The surface can be folded or infolded, and it can be extended into projections such as villi, microvilli or hairs.

5. 5

   How is the leaf mesophyll adapted as an exchange surface?

   Model answer

   The loosely packed spongy mesophyll cells present a very large moist surface to the internal air spaces of the leaf.

6. 6

   Explain how a root hair increases the surface area available for absorption.

   Model answer

   The root hair is a long narrow extension of an epidermal cell that projects into the soil, greatly increasing the area in contact with the soil solution.

Other ways to work this

The same content, four other ways.

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Six ways to work the same material.