Transport Across Membranes: Diffusion, Osmosis and Water Potential

Overview

Recall questions on Diffusion, Osmosis and Water Potential.

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

   Define diffusion.

   Model answer

   Diffusion is the net movement of molecules or ions from a region of higher concentration to a region of lower concentration, down a concentration gradient, as a result of their random motion.

2. 2

   State five factors that affect the rate of diffusion.

   Model answer

   The steepness of the concentration gradient, the temperature, the surface area available, the distance to be travelled, and the size and lipid solubility of the diffusing molecules.

3. 3

   Why can a large multicellular animal not rely on diffusion alone to supply its cells with oxygen?

   Model answer

   As an organism gets larger its surface area to volume ratio falls and its diffusion distances increase, so diffusion becomes far too slow to meet demand and a transport system is needed.

4. 4

   Define osmosis.

   Model answer

   Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane.

5. 5

   What is meant by water potential?

   Model answer

   Water potential is a measure of the tendency of water molecules to move from one place to another, given by the pressure the water molecules exert.

6. 6

   What symbol and unit are used for water potential?

   Model answer

   Water potential is given the symbol Ψ and is measured in kilopascals (kPa).

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