1. Movement In and Out of Cells
Contents
Movement In and Out of Cells
What is diffusion?
Diffusion and life processes
Active transport
Osmosis
Experiments: diffusion and osmosis
Multiple-choice quiz

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. Movement In and Out of Cells
Contents
Movement In and Out of Cells
What is diffusion?
Diffusion and life processes
Active transport
Osmosis
Experiments: diffusion and osmosis
Multiple-choice quiz

11. 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.

12. 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?

13. Diffusion and breathing
Breathing involves the exchange of gases in the lungs, a process which occurs by diffusion.
What is the vital gas that
you breathe in?
oxygen
What is the waste gas that
you breathe out?
carbon dioxide
The lungs have a huge surface area to maximize the exchange of oxygen and carbon dioxide with each breath.
Where in the lungs does gas exchange take place?

14. Diffusion and breathing
Gas exchange takes place in the alveoli, the tiny air sacs at the end of the bronchioles.
What are these blood vessels around each alveolus called?

15. Diffusion and breathing – oxygen
Inhaling increases the concentration of oxygen molecules in an alveolus.
At this point, how does this compare with the concentration of oxygen in deoxygenated blood in the capillary?
deoxygenated blood
from the body
When you inhale,
the concentration
of oxygen inside
each alveolus is
higher than in
deoxygenated
blood.
oxygen
into alveoli
oxygenated blood
to the body

16. Diffusion and breathing – oxygen
How is the concentration of oxygen in the blood increased?
Oxygen molecules diffuse across the lining of the alveolus
into the blood in the capillary, moving from higher to lower concentration.
diffusion
deoxygenated blood
from the body
When you inhale,
the concentration
of oxygen inside
each alveolus is
higher than in
deoxygenated
blood.
oxygen
into alveoli
oxygenated blood
to the body

17. Diffusion and breathing – carbon dioxide
Deoxygenated blood from the body is low in oxygen
but has high levels of carbon dioxide.
How does this compare with concentration of carbon dioxide
in the alveolus?
deoxygenated blood
from the body
The concentration
of carbon dioxide
in deoxygenated
blood is higher
than in
deoxygenated
blood.
oxygenated blood
to the body

18. Diffusion and breathing – carbon dioxide
How is the concentration of carbon dioxide in the blood reduced?
Carbon dioxide molecules diffuse from the blood in the capillary into the alveolus, moving from higher to lower concentration.
diffusion
deoxygenated blood
from the body
The concentration
of carbon dioxide
in deoxygenated
blood is higher
than in
deoxygenated
blood.
carbon dioxide
out of alveoli
oxygenated blood
to the body

19. Gas exchange animation

20. Diffusion and digestion
Carbohydrates, proteins and fat are made up of large molecules that cannot be used directly by the body.
Digestion breaks large food molecules into smaller molecules that can be used by the body.
Dissolved food molecules
then need to be transported
from the small intestine into
the bloodstream.
Where in the small intestine does this diffusion take place?

21. Inside the small intestine

22. Cross-section of a villus
Each villus separates the digested food in the small intestine from a network of capillaries.

23. Diffusion from the small intestine
Each villus has a surface layer that is one cell thick.
How does the concentration of dissolved food molecules in the small intestine compare with the blood entering a villus?
inside the
small intestine
The concentration of
dissolved food molecules
is higher in the small
intestine than in the
blood entering the villus.
blood entering
villus
blood leaving
villus
wall of small
intestine

24. Diffusion from the small intestine
How is the concentration of dissolved food molecules in the blood increased?
Dissolved food molecules diffuse from the small intestine into the blood, moving from higher to lower concentration.
inside the
small intestine
The concentration of
dissolved food molecules
is higher in the small
intestine than in the
blood entering the villus.
diffusion
blood entering
villus
blood leaving
villus
wall of small
intestine

25. 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.

26. 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?

27. 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?

28. Movement In and Out of Cells
Contents
Movement In and Out of Cells
What is diffusion?
Diffusion and life processes
Active transport
Osmosis
Experiments: diffusion and osmosis
Multiple-choice quiz

29. 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?

30. 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

31. 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

32. Movement In and Out of Cells
Contents
Movement In and Out of Cells
What is diffusion?
Diffusion and life processes
Active transport
Osmosis
Experiments: diffusion and osmosis
Multiple-choice quiz

33. 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.

34. 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.

35. 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?

36. 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.

37. Osmosis animation 1

38. Osmosis animation 2

39. Movement In and Out of Cells
Contents
Movement In and Out of Cells
What is diffusion?
Diffusion and life processes
Active transport
Osmosis
Experiments: diffusion and osmosis
Multiple-choice quiz

40. Experiment to demonstrate diffusion

41. Experiment to investigate osmosis

42. Movement In and Out of Cells
Contents
Movement In and Out of Cells
What is diffusion?
Diffusion and life processes
Active transport
Osmosis
Experiments: diffusion and osmosis
Multiple-choice quiz

43. Multiple-choice quiz