Objective: What are the properties of the cell membrane?

Do Now: What is the function of the cell membrane?

Cell Membrane

Cell Membrane• phospholipid bilayer: two-

layer “sandwich” of phospholipids– Phosphate heads- face

outside (hydrophilic: like water)

– Lipid tails- face inside (hydrophobic: water fearing)

• Function– Membranes regulate

the transport of substances across the cell

Allow for material to move into and out of the cell

phospholipid

Protein channels

So how does material move through the membrane bilayer?

Passive transport

• Movement that does NOT require energy.

• [high] to [low]

• Movement from where there is a lot to where there is less.

Diffusion

• Moves molecules from an area of

concentration to an area of concentration.

High

Low

Diffusion does not require energy

Facilitated Diffusiontransport proteins provide a pathway for certain molecules

to pass.Ex. Sugar and water do not pass easily through the hydrophobic region so they need the proteins to help

OsmosisOsmosis: The diffusion (passive transport) of water

Do you ever feel thirsty while eating popcorn at the movies?

Cell Cell in Salt Water

What is different about the cell in salt water?

The effects of osmosis on cellsIsotonic Solution (same strength): Concentrations of solvent and solute are the same on both sides of the membrane

Hypotonic Solution: Solution with a lower solute concentration (more water)Hypertonic Solution: Solution with a higher concentration of solute

Sugar

Water

Active TransportActive transport: Movement of materials

across a cell membrane from low to high concentration using a transport protein, requires energy.

Think of active transport as walking uphill. Does walking uphill require energy?

Low

High

Transport of Large Molecules- Large molecules rely on vesicles (sacs) to get into and out of a cell. - Exocytosis: a vesicle containing protein fuses with the plasma membrane and spills its contents outside the cell

- Endocytosis: takes material into the cell within vesicles that bud inward from plasma memrane