Chapter 3, Section 4Passive Transport: Diffusion and Osmosis
• Passive Transport througho diffusiono osmosis
Preview
Passive transport: the movement of certain molecules across the cell membrane without energy input from the cell.• Diffusion• Osmosis
Types of Passive Transport
P.E.O.E.(a demonstration activity)
Predict: predict what you think will happen
Explain: explain why you believe this will happen
Observe: watch the demonstration and record what happened
Explain: explain what actually happened
DEMO
Diffusion: fluid or gas molecules move from a region of high concentration to areas of low concentration (molecules spread out)• this is the result of random motion
of molecules causing them to collide and scatter• eventually the concentration of
the molecules is the same throughout the solution (dynamic equilibrium)
Diffusion
Diffusion plays an important role is moving substances across the cell membrane• small lipids (fats) and other
nonpolar substances (CO2 and O2) can easily diffuse across the cell membrane
• Example: cells consume O2, which means the O2 concentration outside the cell is always higher. O2 diffuses into the cell through the membrane
Diffusion in the Cell
P.E.O.E.(a demonstration activity)
Predict: predict what you think will happen
Explain: explain why you believe this will happen
Observe: watch the demonstration and record what happened
Explain: explain what actually happened
DEMO
Osmosis: water molecules move from areas of high concentration to areas of low concentration
Osmosis
• Solutions in which water molecules can move are said to be o Hypotonic,o Isotonic ,o or Hypertonic
Osmosis
• Hypotonico when the cell has higher concentration
of solutes than the solutiono water molecules are more concentrated
outside the cello water diffuses into the cello if too much water enters the cell, it can
burst like an overfull balloon
Osmosis
• Isotonico when the cell and solution have the
same concentration of soluteso water molecules move in and out of the
cell through the cell membrane at an equal rate (dynamic equlibrium)
o the cell does not expand or shrink
Osmosis
• Hypertonico when the solution has a higher
concentration of solutes than the cello the water concentration is higher in the
cello water moves out of the cello if too much water leaves the cell, it can
shrivel or even die
Osmosis
Osmosis
Osmosis
• Some molecules cannot easily diffuse across
a membrane
o they may be allowedto enter the cell by passing through a transport protein
o this process is called facilitated diffusion
Facilitated Diffusion
• Facilitated diffusion is still considered a form of passive transport because no energy is expended by the cell
Facilitated Diffusion