chapter 3, section 4

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