• Diffusion: Movement of molecules from an area of high to
low concentration
• Movement continues until equilibrium is reached
– Equilibrium: molecules spread evenly
• This is how many molecules move within cells
Diffusion (contd)
Where is the
higher CARBON
DIOXIDE
concentration?
Where is the
higher oxygen
concentration?
• Passive transport: No energy (ATP) required to
move molecules
• Which molecule will enter and which will exit
this cell?
– Oxygen will enter, CO2 will exit
The woman inhales a breath of oxygen
The
oxygen
spreads
into the
womans
lungs
The
oxygen
fills the air
sacs
(alveoli)
located in
her lungs
Where is the HIGH
oxygen
concentration?
Where is the LOW
oxygen
concentration?
Due to
diffusion, the
oxygen will
spread from
the area of
high to the
area of low
concentration
The heart pumps this oxygenrich blood around your body
Cell X needs oxygen just like all cells. But cell X is not in direct contact
with the blood and oxygen. So how does cell X get oxygen?
Where is the HIGH oxygen concentration?
Cell X (and all other cells) gets oxygen through the process of diffusion!
The reverse process is true w/ carbon dioxide. Over time, CO2
waste builds up in cells. Too much is fatal. It must be removed.
Where is the HIGH carbon dioxide concentration?
CO2 diffuses from the cells (high concentration) and into the blood
stream (low concentration)
The heart pumps the CO2 rich blood back to the lungs.
Where is the HIGH
carbon dioxide
concentration?
CO2 diffuses into the
air sacs (alveoli)
The
diaphragm
muscle
pushes the
CO2 out of
the lungs
CO2 is expelled from the woman…the process repeats with every
breath!
Osmosis
• Defined: Diffusion of
water from an area of
high to low
concentration
• High H2O concentration
– Less solutes
– Ex: Distilled water
• Low H2O concentration
– More solutes
– Ex: Salt water
• Dots represent dissolved particles (not water
molecules)
Group Explanation
A cell has been placed into a mystery solution and
appears to have shrunken/shriveled.
1) What can you conclude about the water concentration inside the
cells compared to outside?
2) What can you conclude about the solute concentration inside the
cells compared to outside?
3) Which type of solution is the cell placed in?
4) Using your explanation of osmosis, explain why the cell appears
to have shrunken.
A cell has been placed into a mystery solution and
appears to have shrunken.
1) What can you conclude about the water concentration inside the cells
compared to outside?
This means there was a greater water concentration inside the cell and it lost
water.
2) What can you conclude about the solute concentration inside the cells
compared to outside?
Because the water concentration was high (see question 1), there must have
been a low amount of solutes inside the cell.
3) Which type of solution is the cell placed in?
hypertonic
4) Using your explanation of osmosis, explain why the cell appears to have
shrunken.
The cell shrunk because it lost water. There was a greater water concentration
inside the cell so therefore water diffused out of the cell.
Facilitated
Diffusion
• Defined: Larger molecules enter/exit with the help
of protein channels in the plasma membrane
• No energy is required (passive)
• Q: Why are the molecules moving from left to right
and not from right to left?
• A: Left side has the higher concentration
Kobe Kuiz
1) In which direction does diffusion occur?
2) Across which part of the cell does diffusion mostly
occur?
3) Which molecule of energy is not required during
passive transport?
4) True or False: More solutes creates less concentrated
water.
5) Which solution is involved in osmosis?
6) Examine the picture. If the dots are solutes, where is
the high solute concentration?
7) Examine the picture. If the dots are water molecules,
where is the low water concentration?
8) Examine the picture. If the dots are water molecules,
which way will osmosis occur?
9) Examine the picture. If the dots are solute molecules,
which way will osmosis occur?
Kobe Kuiz Answers
1)
2)
3)
4)
5)
6)
7)
8)
9)
In which direction does diffusion occur?
 From a high to low concentration
Across which part of the cell does diffusion mostly occur?
 Cell membrane
Which molecule of energy is not required during passive transport?
 ATP
True or False: More solutes creates less concentrated water.
 True
Which solution is involved in osmosis?
 water
Examine the picture. If the dots are solutes, where is the high solute
concentration?
 Left side
Examine the picture. If the dots are water molecules, where is the low water
concentration?
 Right side
Examine the picture. If the dots are water molecules, which way will osmosis
occur?
 From left t(high concentration) to right (low concentration)
Examine the picture. If the dots are solute molecules, which way will osmosis
occur?
 From right (high water concentration) to left (low water concentration)