1. Diffusion
Biology

2. Learning Objectives
Examine how concentration affect how particles move: Diffusion.
Investigate passive and active transport.
Review the structure of the cell membrane and size of particles.

3. What happens to a deodorant!
If you spray some deodorant in the corner of the room. What would happen over time? Write down your claim.
Now you have 1 min to write a reason or a short explanation of your claim!
Once you are done: Read your explanation to your partner at your desk.
Revise your explanation and re-write it.

4. Fill in the blanks on your sheet as we go through the ppt Diffusion
Diffusion is the movement of molecules from an area of high concentration to an area of low concentration, until evenly spread out.

5. Why is diffusion important?
All living cells rely on diffusion to live.
They use it for:
getting raw materials for respiration (dissolved substances and gases)
removing waste products (eg. from respiration)
photosynthesis in plants (raw materials in, waste products out)
Examples…

6. Respiration- gas exchange
In breathing you exchange carbon dioxide (CO2) and oxygen (O2) between alveoli in the lungs and the blood.
This is an example of diffusion.
SEM photos of lung alveoli

7. Respiration- in cells
food + oxygen  carbon dioxide + water + energy

8. Respiration & diffusion

9. Photosynthesis & Diffusion
carbon dioxide + water  oxygen + glucose
Carbon dioxide diffuses in through the stomata
Oxygen and water diffuse out of the stomata

10. Osmosis Osmosis is a special case of diffusion.
It is the net movement of water across a selectively permeable membrane from a high concentration to a low concentration.
Selectively permeable membrane ???
The cell membrane has very small holes in it. Small molecules can pass through, but larger ones cant.
We say it is selectively permeable.

11. Water concentration gradient
In osmosis water moves both ways to balance up the concentrations. The overall (net) movement is to the area of low water concentration.
Water molecule
Solute molecule
Key:
High Water Concentration,
few molecules of solute.
Dilute solution
Water movement
SQA LO: Hypertonic, isotonic, hypotonic
Low Water Concentration, many molecules of solute.
Concentrated solution

12. Osmosis in action
Have a look at:

13. Now try your osmosis problems on your worksheet

14. Now let´s investigate how size affects movement of particle across a membrane!
Problem: Would Starch or Iodine diffuse across a membrane?
Hypothesis: Formulate an hypothesis.
Experiment: Carry out an experiment.
Results: Collect Data.
Write a Lab Report: Follow the format provided.

15. TITLE: a brief, concise yet descriptive title
I will normally give this to you (because I am nice  )
This lesson we will be investigating..
Effect of size on the movement of particles across the cell membrane.

16. BACKGROUND: Include any preliminary observations or background information about the subject
What do YOU remember about osmosis in cells?
Can you include a diagram?
Have you used all your relevant key words?

17. Which variable might affect…
Generate Ideas
Change
What will be our evidence?
Measure/observe
Hazards and risks

18. HYPOTHESIS: What do you think will happen and why?
If a selectively permeable bag containing starch solution is placed in a beaker containing drops of iodine solution then the color inside the bag will change to blue black because iodine molecules will diffuse into the bag as they are smaller than starch molecules.

19. MATERIALS: a list of what you need to carry out the experiment
Can you list all the equipment required for this experiment?
You WILL be given;
Iodine solution, Starch solution, Dialysis tubing
Beaker with water.

20. VARIABLES: both IV and DV need to be clearly identified
Independent Variable(IV):
This is the thing YOU are changing in your experiment
Dependant Variable (DV):
This is the thing YOU are measuring in your experiment

21. How will you make this experiment a fair test?
An investigation or experiment where only the independent variable has been allowed to affect the dependent variable.
This means only changing one variable and keeping everything else the same.
This way you know that ONLY the variable YOU changed could cause a change in the results
What do you need to keep the same in your experiment?

22. Things you need to think about!
What volume of solution will you add to each test tube?
How long will each piece of potato be? How will you measure this?
How long will you leave it for?

23. Method Obtain a dialysis tubing.
Open the tubing and tie a knot on one end.
Pour 10 mL of Starch solution and then then tie a knot.
Pour 100 mL of water into a beaker.
Put mL of Iodine.
Place the dialysis tubing into the Iodine solution in the beaker.
Leave the experiment to run for 30 min
Record your results.
Write a formal report using the template provided.

24. CONCLUSION: accept/reject your hypothesis using data from your results.
What happened and why?
Is this what I thought would happen?
What evidence have I got that supports my findings?
Has this proved or disproved a some of my scientific understanding?