Pretest• What is the job of the plasma membrane?

• What is semi-permeable?

• What is the difference between active transport and passive transport?

• What is osmosis?

• What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?

• What are examples of each?

The plasma membrane maintains homeostasis for the cell

It is selectively permeable:

It controls what goes into and out of the cell

Two forms of transport across the membrane:

Passive TransportNo energy needed

• WITH the gradient (high to low)

• Examples:

– Diffusion– Osmosis

Active Transport• ENERGY used

• AGAINST the gradient

• Examples:

– Endocytosis– Exocytosis

Plasma Membrane Structure

Two key components of the membrane:

phospholipids

proteins

Crossing the Plasma Membrane: Passive Transport

Energy?Direction?Examples?

Passive Transport: Diffusion

• The phospholipids line up to form a double membrane

• Small, uncharged particles are able to pass right between the phospholipids

• This is called simple diffusion

Passive Transport: Diffusion

• There are also proteins embedded between the phospholipids.

• These proteins function as gates, allowing larger or charged molecules to get in/out of the cell

• Only molecules which are “recognized” are allowed thru these proteins

• This is facilitated diffusion

Passive transport: Diffusion

Lower Concentration

Higher Concentration

Molecules collide – pass thru membrane

Concentration gradient:

Passive Transport: Osmosis

• The movement of water• Water moves TOWARDS the molecules

• Think of it as “water wants to dissolve stuff”

• Which way will water move in each case?

Passive Transport: Osmosis

HYPERtonic ISOtonic HYPOtonic

The effect of osmosis on animal cells

Cytolysis

What do plant cells have outside of the cell membrane

that animal cells do not have?

What difference will this make with osmosis?

Effect of osmosis on plant cells

Flaccid - Turgiddue to plasmolysis - cell shrinks from cell wall

Passive transport: osmosis

Osmosis

Which way will water move?

Hypertonic or Hypotonic?

Active Transport:Which direction?

Energy Used?Examples?

Crossing the Plasma Membrane

Figure 3.8

Active transport

AGAINST the gradient

requires energy

Active Transport• Endocytosis

– Pino-

– Phago-

• Exocytosis

Figure 3.9

Ion pumps: Thru a protein, but using energy

Crossing the Plasma Membrane

Passive Transport Active Transport

Crossing the Plasma Membrane

Passive Transport

• No energy needed

• WITH the gradient

• Diffusion

• Osmosis

Active Transport

• ENERGY used

• AGAINST the gradient

• Can be through a protein

• Endocytosis

• Exocytosis

Post test• What is the job of the plasma membrane?

• What is semi-permeable?

• What is the difference between active transport and passive transport?

• What is osmosis?

• What will happen to a cell when placed in a hypertonic solution? Hypotonic solution?

• What are examples of each?