Instructions

For Part 1 and 2, access the PhET: Diffusion simulation by using the interactive below or clicking on this link: https://phet.colorado.edu/sims/html/diffusion/latest/diffusion_all.html 

Continue reading the instructions below, and answer the questions. 

Part 1: What is diffusion?

1. Familiarise yourself with what is on your screen. Find: 

1. • • the container (white box)

     • impremeable barrier (green line)

     • particles  (blue and red spheres) and how to add particles

     • ways to visualise number of particles, centre of mass, flow rate.

2. Add several blue particles to the left side of the container. 

3. Watch what happens to the particles for 20-30 seconds.
   Question 1: Describe how the particles move. Use words like: random, collisions, spreading out.

4. Add the semi-permeable membrane by clicking "Remove Divider"

5. Keep watching until the particles appear evenly spread.
   Question 2: What happens to the distribution of particles over time?
   Question 3: Write your own definition of 'diffusion' based on what you observed.
   Hint: Think 'from high concentration to low concentration'
   Question 4: Think about where you see diffusion in every day life. For example, the smell of perfume spreading across a room, food colouring in water or smoke spreading through the air. Choose ONE example, and explain how diffusion is happening. Describe:
   - Where is the higher concentration?
   - Where is the lower concentration?
   - How do the particles move?

Instructions continued

For Part 3, access the PhET: Membrane Transport simulation by using the interactive below or clicking on this link: https://phet.colorado.edu/sims/html/membrane-transport/latest/membrane-transport_all.html 

Continue reading the instructions below, and answer the questions. 

Part 3: How do molecules diffuse into cells? 

1. Make sure you click on the Simple Diffusion tab. 

2. Familiarise yourself with what is on your screen. Find: 

1. • • the semi-permeable cell membrane (two layers of circles with two "tails")

     • extracellular side (outside, blue) and intracellular side (inside, yellow) of the cell membrane

     • choice of solute molecules, and buttons to increase or decrease their concentration

     • panel to view the solute concentrations across the membrane for each solute

2. Take turns adding each solute to ONE side of the membrane only.

3. Watch what happens to the particles for 20-30 seconds.
   Question 9: Describe what happens to the distribution of each particle, over time.
   Question 10: Does increasing the concentration of one solute affect the rate of diffusion of another solute? For example, does increasing the concentration of glucose molecules affect the rate of diffusion of sodium ions?
   Question 11: Write your own definition of 'semi-permeable' based on what you observed.

Part 4: Summary Questions

Complete these sentences:

Question 12: Diffusion is the movement of particles from ____________ to ____________ concentration.

Question 13: Two factors that affect the rate of diffusion are _________________ and _____________ _____________.

Question 14: A semi-permeable membrane lets _____________ molecules pass through but blocks ____________ ones.