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• Diffusion: Movement of molecules from an area
of high to low concentration
• Movement continues until equilibrium is reached
• Equilibrium: same amount of molecules on the
outside of a cell as the inside
Diffusion (contd)
• Passive transport: No energy required to move
molecules
• If more molecules outside the cell… they move
inside
• If more molecules inside the cell…they move
outside
• Will O2 move into this cell or out of this cell?
Diffusion (contd)
Where is the high
Oxygen concentration?
Where is the high CARBON
DIOXIDE concentration?
• Passive transport: No energy (ATP) required to
move molecules
• If more molecules outside the cell… they move
inside (and vise versa)
Where is the HIGH
oxygen
concentration?
Where is the LOW
oxygen
concentration?
Where is the HIGH oxygen concentration?
Where is the LOW oxygen concentration?
Cell X gets oxygen through the process of diffusion!
The reverse process is true w/ carbon dioxide.
Where is the HIGH carbon dioxide concentration?
Where is the HIGH
carbon dioxide
concentration?
Osmosis
• Defined: Diffusion of
water from an area of
high to low
concentration
• High H20 concentration
if: less particles
dissolved in the water
• Low H20 concentration
if: more particles
dissolved in the water
• Dots represent dissolved particles (not water
molecules)
Group Explanation
A cell has been placed into a mystery solution and
appears to have shrunken.
1) Which type of solution is the cell placed in?
2) What can you conclude about the water concentration inside
the cells compared to outside?
3) What can you conclude about the solute concentration inside
the cells compared to outside?
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) Which type of solution is the cell placed in?
hypertonic
2) What can you conclude about the water concentration inside the cells
compared to outside?
If the cell shrunk it lost water. This means the cell had a greater water
concentration.
3) What can you conclude about the solute concentration inside the cells
compared to outside?
The solute concentration inside the cell is low. I know this because the cell has
a high water concentration. The fewer solutes, the higher the water
concentration.
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 exiting this cell and not
entering?
• A: There are more molecules inside than out
Active Transport
• Defined: Molecules move from a LOW to a HIGH
concentration
• ATP energy opens/closes protein channel
– ATP = Adenosine Triphosphate
• Acts like a pump
Contractile vacuole of a Paramecium
Water being pumped out of this
cell to prevent bursting
Endocytosis
• Endocytosis: Process in which the plasma membrane
takes in substances (2 types)
– 1) Phagocytosis: when a cell engulfs a solid particle
– 2) Pinocytosis: when a cell engulfs a liquid particle
• Unfortunately, viruses can also enter our cells this way
Endocytosis & the lysosome
Exocytosis
• Defined: Process when substances are expelled from
the cell
• Proteins, nutrients, and waste exit by exocytosis
• Vesicle carry & release objects through the plasma
membrane
Quick Review
• Diffusion is the movement
of particles from high to
low concentrations
• Some methods of
movement don’t require
energy (Passive
Transport)
• Some methods of
movement require energy
(Active transport)
• Farts smell because of
diffusion