Biological examples of diffusion

1.  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 passivepassive process which means that no no
energyenergy is needed

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

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

4.  Concentration gradient
 Temperature
 Distance particles must travel
Faster Diffusion When...
Large concentration gradient
Higher Temperature
Short distance

5. ?
Think – Pair - Share

6. 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.
The particles
are fully
diffuse.
Draw the diagrams next to each
other and copy the captions
Has diffusion stopped completely?
Explain your answer

9. 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?

10. 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…

11. 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?

12. deoxygenated blood
(from body tissues)
oxygenated
blood (to body
tissues)
air in/out
Alveoli are the tiny air sacs at the end of the
bronchioles, in which gas exchange occurs.
alveolus
capillary
red blood cell

13. 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.

15. 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.

16. blood vessels
capillary network
Villi
small intestine

17. 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 ARE A, for maximum
absorption.
•The villi also give a GOOD BLOOD SUPPLY to absorb the nutrients.

18. A synapse is a junction between two neurones
across which electrical signals must pass.
Neurotransmitter molecules diffuse from vesicles
towards the neurotransmitter receptors, moving from
an area of high concentration to low concentration.

19. •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.

20. •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.

21. How does the placenta work?
umbilical
cord
umbilical
artery
umbilical
vein

22. Carbon dioxide diffuses
in through the stomata
 Oxygen and water diffuse
out of the stomata
carbon dioxide + water ® oxygen + glucose
 During photosynthesis, the level of
CO
2
is low inside the leaf
 This creates a big concentration
gradient so CO
2
diffuses into the cell

23. Label
the leaf