1. How can a shark find injured prey so quickly?
Diffusion & Life
B2 Additional

2. Learning Objectives To describe DIFFUSION
To explain what affects the RATE of DIFFUSION
To link diffusion with EXAMPLES in BIOLOGY
Respiration
Digestion
Placenta
Leaf Cells
Nerve Impulses

3. Diffusion
Starter:
Explain in terms of particles how the smell of the perfume gets from one side of the class to the other

4. When you have just sprayed perfume, the concentration of perfume particles in that area is very high.
Diffusion is the movement of the ‘smelly’ particles, through particles of air, to an area where they are at a LOWER concentration.

5. Maybe you can smell your dinner cooking when you get home
Maybe you can smell your dinner cooking when you get home... This is due to diffusion.

6. Moving molecules
In which states are molecules able to diffuse?
gas (e.g. steam)
liquid (e.g. water)
solid (e.g. ice)
Molecules in liquids and gases are constantly moving and bumping into each other. This means that they tend to spread out.

7. Diffusion
The net movement of particles from an area of high concentration to an area of low concentration
Due to the random movement of particles
A passive process which means that no energy is needed

8. What effect might the gradient have on speed of diffusion?
LOW concentration
HIGH concentration
A difference in concentration between 2 areas is called a CONCENTRATION GRADIENT.
What effect might the gradient have on speed of diffusion?

9. Rate of Diffusion Steep concentration gradient
Draw both sets of diagrams, write how the rate of diffusion changes when the concentration gradient changes
Rate of Diffusion
Fast
Steep concentration gradient
Slow
Shallow concentration gradient 9

10. Factors Affecting Diffusion
Concentration gradient
Temperature
Distance particles must travel
Faster Diffusion When...
Large concentration gradient
Higher Temperature
Short distance

11. When will diffusion stop?
Think – Pair - Share ?

12. Has diffusion stopped completely?
Draw the diagrams next to each other and copy the captions
The particles are fully diffuse.
The particles are separate when first put together.
They slowly start to mix due to their random motion.
The particles are now nearly fully diffuse.
Has diffusion stopped completely?
Explain your answer 12

13. Diffusion in action: one gas
Teacher notes
This activity could be used as a starter exercise to work on diffusion.

14. Diffusion in action: two gases
Teacher notes
This activity could be used as a starter exercise to work on diffusion.

15. What substances are we talking about?
Biological diffusion
Dissolved substances have to pass through the partially permeable cell membrane to get into or out of a cell. Diffusion is one of the processes that allows this to happen..
What substances are we talking about?

16. 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)
Plants use of photosynthesis (raw materials in, waste products out)
Examples…

17. 1. Diffusion and breathing
Oxygen in inhaled air diffuses through the lungs and into the bloodstream. The oxygen is then transported throughout the body.
Carbon dioxide is the waste gas produced by respiration. Carbon dioxide diffuses from body tissues into the bloodstream and is exhaled via the lungs.
Where does gas exchange take place in the lungs?

18. Cross-section through an alveolus
Alveoli are the tiny air sacs at the end of the bronchioles, in which gas exchange occurs.
air in/out
deoxygenated blood (from body tissues)
alveolus
capillary
Teacher notes
Alveoli = plural; alveolus = singular
oxygenated blood (to body tissues)
red blood cell

19. How are alveoli adapted?
Alveoli have several adaptations that help to make gas exchange very efficient:
They are very thin – only one cell thick.
They are covered by a network of fine capillaries, enabling gases to pass almost directly between the lungs and bloodstream.
They are moist, encouraging gas molecules to easily dissolve.
They have a large combined surface area, allowing large amounts of gases to be exchanged with each breath.

20. Respiration & diffusion

21. 2. Diffusion and digestion
Digestion breaks down large food molecules into smaller molecules such as glucose, amino acids and fatty acids that can be easily absorbed.
Small food molecules are usually absorbed in the small intestine, diffusing across the intestine wall and into the bloodstream.

22. How is the small intestine adapted?
capillary network
Villi
small intestine
blood vessels

23. Diffusion in Digestion
The small intestine has these things called villi. The best way of explaining them, is that they look like millions of little sausages.
The villi INCREASE THE OVERALL SURFACE AREA of the small intestine, thus increasing the volume of substances which can be absorbed by diffusion.
The villi have a very GOOD BLOOD SUPPLY as each contains a capillary, which leads to the main blood supply, so when substances diffuse, they can go straight to the bloodstream.
Attached to each villi are thousands and thousands of MICROVILLI. These are exactly the same as the villi, except a lot smaller.
Again, the purpose of these is to further increase the surface area. Like before, as well, this increasing the volume of substances which can be absorbed.
So, the main points to remember are:
The villi and microvilli result in a LARGE SURFACE AREA, for maximum absorption.
The villi also give a GOOD BLOOD SUPPLY to absorb the nutrients.

24. 3. Diffusion and nerves impulses
A synapse is a junction between two neurones across which electrical signals must pass.
synaptic cleft
neurotransmitter
neurotransmitter receptor
nerve impulse
Neurotransmitter molecules diffuse from vesicles towards the neurotransmitter receptors, moving from an area of high concentration to low concentration.

25. 4. Diffusion and the placenta
The placenta is an organ that develops in the uterus during pregnancy.
The umbilical cord connects the placenta to the foetus.
It enables nutrients and oxygen to pass from the mother to the foetus by diffusion, and waste substances to diffuse from the foetus back to the mother.

26. Diffusion and the placenta
The placenta can stop certain molecules and bacteria from diffusing through
It is unable to stop many harmful substances such as alcohol, chemicals and some types of virus from diffusing through, reaching the foetus.

27. Diffusion and the placenta
How does the placenta work?
blood to mother
low in O2/nutrients,
high in CO2/waste
umbilical cord
umbilical artery
placental villi increase surface area for diffusion
blood from mother
high in O2/nutrients
low in CO2/waste
umbilical vein

28. Photosynthesis & Diffusion
carbon dioxide + water  oxygen + glucose
Carbon dioxide diffuses in through the stomata
Oxygen and water diffuse out of the stomata
During photosynthesis, the level of CO2 is low inside the leaf
This creates a big concentration gradient so CO2 diffuses into the cell

29. Diffusion and the leaf
Label the leaf