1. MOVEMENT INTO AND OUT OF CELLS

2. Smells and liquids spreading out
Why can you smell cooked food from a distance?
Why does the colour of concentrated fruit drink change when it is added to water?
Why can you smell perfume or aftershave when someone walks past you?

3. Smells and liquids spreading out
Smelling cooked food or perfume and diluting juice in water all involve things moving around and spreading out.
These processes are all examples of diffusion.
Diffusion involves the movement of molecules.
What type of molecules are moving in these examples?

4. Moving molecules ice (solid) water (liquid) water vapour (gas)
The molecules in every substance are always moving.
In which state are molecules able to spread out?
ice (solid)
water (liquid)
water vapour (gas)
Diffusion involves the movement of gas and dissolved molecules. Why don’t solid molecules diffuse?

5. Diffusion and changing concentrations
When smelling body spray where is the smell strongest and where is the smell weakest?
Diffusion means the smell
spreads out and gets weaker
further away from the source.
Smell is strongest
at source.
How does the concentration of smell molecules change during diffusion?
Smell molecules move from an area of high concentration to an area of lower concentration. This is called a concentration gradient.

6. Changing concentrations
Diffusion can be represented on a simple diagram.
Where will the molecules be after diffusion?
before diffusion
after diffusion
What has happened to the concentration of the molecules?
Diffusion is the movement of gas or dissolved molecules from higher to lower concentration.
Molecules diffuse down a concentration gradient.
What does this mean?

7. Diffusion animation 1

8. Diffusion animation 2

9. Diffusion animation 3

10. Why is diffusion so important?
Diffusion explains why you can smell smelly smells and what happens when you dilute a concentrated fruit drink.
More importantly, diffusion is an essential process that is going on inside your body right now and keeping you alive!
Diffusion occurs in the organ systems that control your breathing, circulation, digestion and other life processes.

11. Diffusion and life processes
Diffusion is the movement of gas or dissolved molecules.
What gas and dissolved
molecules do body cells need?
Your body’s survival depends
on oxygen and dissolved food
molecules getting into your cells.
How do these vital substances cross boundaries within the body to get to where they are needed?
Oxygen and dissolved food molecules
must diffuse into and out of the blood
for transportation around the body.
Where does diffusion take place within the body?

12. Diffusion in and out of cells
Oxygen and dissolved food molecules are transported to the body’s cells in the bloodstream.
How does the concentration of these useful substances in the blood compare with the concentration inside the cells?
The concentration of
oxygen and dissolved
food molecules
is higher in the blood
arriving at the cells
than inside the cells.

13. Diffusion in and out of cells
How do oxygen and dissolved food molecules pass
from the blood into the cells?
Oxygen and dissolved food molecules diffuse into the body cells, moving from higher to lower concentration.
The concentration of
oxygen and dissolved
food molecules
is higher in the blood
arriving at the cells
than inside the cells.
diffusion
What process involving these useful substances takes place inside the cell?

14. Diffusion in and out of cells
The cells use the food and oxygen for respiration.
Carbon dioxide is the waste product of respiration and will poison a cell if it is not removed. How is it removed?
diffusion
Carbon dioxide molecules diffuse from the cells into the bloodstream, moving from higher to lower concentration.
How is this waste carbon dioxide removed from the body?

15. What is active transport?
Movement of substances in and out of cells by diffusion involves molecules moving down a concentration gradient from high to low concentration.
high concentration
diffusion
active transport
low concentration
Sometimes substances move into cells from low to high concentration. This is called active transport.
Active transport needs energy to make it happen.
How do molecules move along the concentration gradient during active transport?

16. Active transport and plants
Plants need mineral elements from the soil for healthy growth. Minerals enter a plant though its roots.
The concentration of minerals in the soil is lower than that inside a root hair cell, so how do minerals enter the root cell?
root hair
cell
mineral
element
soil

17. Active transport and plants
Minerals enter a root cell by active transport.
The plant uses energy to move minerals up the concentration gradient from the soil into its root cells.
Why is it important for plants to use energy in this way?
active transport
root hair
cell
mineral
element
soil

18. What is osmosis? Osmosis is a special type of diffusion.
Diffusion involves gas or dissolved molecules, but osmosis only involves the movement of water molecules.
water
molecule
Osmosis occurs across a semipermeable membrane which has tiny holes in it.
These holes are small enough for water molecules to pass through but larger molecules cannot pass through.

19. What happens during osmosis?
Osmosis is a type of diffusion, so what do you think happens to water molecules during this process?
osmosis
water
molecule
semipermeable membrane
Osmosis is the movement of water molecules from a region of high water concentration to a region of low water concentration across a semipermeable membrane.

20. Osmosis experiment A bag made from a semipermeable membrane is tied
to a glass tube and filled with a strong sugar solution.
This bag is placed in a weak sugar solution.
strong sugar
solution
weak sugar
solution
What happens to the water molecules in the weak solution?
What happens to the liquid inside the semipermeable bag?

21. Osmosis experiment
The volume of liquid in the semipermeable bag increases. The liquid rises up the glass tube and then stops.
Why does this happen?
strong sugar
solution
weak sugar
solution
Water molecules diffuse across the membrane from the weak sugar solution into the strong sugar solution.
This continues until the concentration is the same on both sides of the membrane.

22. Osmosis animation 1

23. Osmosis animation 2

24. Experiment to demonstrate diffusion

25. Experiment to investigate osmosis