Diffusion and facilitated diffusion

Overview

Term diffusion, state of a system once diffusion has reached equilibrium and term facilitated diffusion.

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 the term diffusion.

   Model answer

   Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.

2. 2

   Why is diffusion described as a passive process?

   Model answer

   It results from the random kinetic movement of the particles themselves, so the cell expends no energy on it.

3. 3

   What is the state of a system once diffusion has reached equilibrium?

   Model answer

   The particles are evenly distributed, and although they continue to move at random there is no further net movement in either direction.

4. 4

   State two substances that enter or leave a respiring cell by simple diffusion.

   Model answer

   Oxygen diffuses into the cell and carbon dioxide diffuses out of it.

5. 5

   How does a steeper concentration gradient affect the rate of diffusion?

   Model answer

   A steeper gradient increases the rate, because the difference in the number of particles moving each way is greater.

6. 6

   How does a rise in temperature affect the rate of diffusion?

   Model answer

   The particles gain kinetic energy and move faster, so the rate of diffusion increases.

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