Transcript Diffusion - Thomas A. Stewart Secondary School

Diffusion
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What is diffusion?
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Diffusion and concentration
Why can the student smell the sock from a distance?
The sock can be smelt because sweat and other
molecules are moving away from it and spreading out in
the air. This is called diffusion.
Where is the smell strongest?
The smell is strongest at the sock. The smell becomes
weaker further away from the sock.
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Moving molecules
In which states are molecules able to diffuse?
solid (e.g. ice)
liquid (e.g. water)
gas (e.g. steam)
Molecules in liquids and gases are constantly moving and
bumping into each other. This means that they tend to
spread out. By contrast, solids cannot diffuse.
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Diffusion in action: one gas
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Diffusion in action: two gases
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Changing concentrations
During diffusion molecules move from an area of high
concentration to an area of low concentration. They are
said to move down a concentration gradient.
Diffusion is a passive
process which means that
no energy is needed.
high
low
concentration concentration
Molecules diffuse until they
are evenly spaced apart
and equilibrium is reached.
The rate of diffusion depends on several factors, such as
the distance the particles have to travel and the difference
in concentration.
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Diffusion: true or false?
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Why is diffusion important to life?
Diffusion is the main way in which substances move
over short distances in organisms. What substances
need to move?
Oxygen, food and waste products are some of the
substances that move by diffusion.
In animals, how do these vital substances get to where
they are needed?
The substances are
transported in the
bloodstream, from
where they can diffuse
in and out of cells.
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Diffusion and breathing
Breathing involves the exchange of gases in the lungs; a
process that occurs by diffusion. What happens when
you breathe in?
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?
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Structures of the respiratory system
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Cross-section through an alveolus
Alveoli are the tiny air sacs at the end of the bronchioles,
in which gas exchange occurs.
deoxygenated blood
(from body tissues)
air in/out
alveolus
capillary
red blood cell
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oxygenated blood
(to body tissues)
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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.
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What happens in the alveoli?
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Diffusion and digestion
Carbohydrates, proteins and fats are made up of large
molecules that cannot be readily absorbed by the body.
Digestion breaks down large food molecules into smaller
molecules such as glucose, amino acids and fatty acids
that can be easily absorbed.
In which part of the digestive system is most food absorbed?
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Diffusion and the small intestine
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Diffusion and the placenta
The placenta is an organ that develops in the uterus of
female mammals during pregnancy. The umbilical cord
connects the placenta to the fetus.
The placenta enables
nutrients and oxygen to
pass from the mother to the
fetus by diffusion, and waste
substances to diffuse from
the fetus back to the mother.
The placenta can filter out certain molecules and bacteria, but
is unable to stop many harmful substances such as alcohol,
chemicals and some types of virus from reaching the fetus.
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Diffusion and the placenta
How does the placenta work?
umbilical
cord
umbilical
artery
umbilical
vein
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blood to mother
low in O2/nutrients,
high in CO2/waste
placental villi
increase surface
area for diffusion
blood from mother
high in O2/nutrients,
low in CO2/waste
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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.
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Diffusion in plants
Plants use carbon dioxide and produce oxygen during
photosynthesis. These gases move in and out of the plant
by diffusion.
When the concentration of
carbon dioxide inside the
plant is low, it will diffuse in
from the air, through pores in
the leaves into the plant cells.
If the concentration of
oxygen is high inside the
plant, it will diffuse from the
plant cells through the pores
and into the air.
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Glossary
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Anagrams
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Which process?
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Multiple-choice quiz
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