Download Passive transport

The Cell Membrane and
Passive Transport
The Cell Membrane
•
made of two phospholipid layers
• The cell membrane has two major functions.
1. forms a boundary between inside and outside of the cell
2. controls passage of materials
cell membrane
inside cell
outside cell
AKA: Fluid mosaic model
• There are other molecules imbedded
•
All provide a specific function
cell membrane
carbohydrate
chain
cholesterol
protein
protein channel
protein
The membrane is “selectively permeable”
• Only some molecules can pass
3.4 Diffusion and Osmosis
KEY CONCEPT Materials move across membranes
because of concentration differences.
3.4 Diffusion and Osmosis
Passive transport does not require energy input from a
cell.
• Molecules can move across the cell membrane
through passive transport.
• There are two types of
passive transport.
• diffusion
• osmosis
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
3.4 Diffusion and Osmosis
• There are three types of solutions in osmosis.
• isotonic
•
hypertonic
•
hypotonic
Group Explanation
A cell has been placed into a mystery solution
and appears to have shrunken.
1)
2)
3)
4)
Which type of solution is the cell placed in?
What can you conclude about the water concentration
inside the cells compared to outside?
What can you conclude about the solute concentration
inside the cells compared to outside?
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.
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.
1)
3.4 Diffusion and Osmosis
Some molecules can only diffuse through transport
proteins.
• Some molecules cannot easily diffuse across the cell
membrane.
• Facilitated diffusion is
diffusion through transport
proteins.