Do Now 10/27/2011EXTRA CREDIT DO NOW: 

The cells of plant seeds store oils in the form of droplets enclosed by membranes. These membranes are very different from the cell membrane even though they are made of the same phospholipids.

Draw a simple model for a membrane around an oil droplet, and briefly explain why this arrangement is more stable than bilayer.

hydrophobic

hydrophilic

Since the oil is hydrophobic, this membrane has only ONE LAYER. Polar head groups on the outside, hydrophobic tails in the oil

A Quick Demonstration…

How is this picture of outer space similar to the demonstration?

Diffusion!

HotWater

ColdWater

Passive Transport

• Passive transport is the movement of molecules from areas of high concentration to areas of lower concentration. It happens spontaneously (spontaneous = requires no addition of energy)

It’s the same for stardust and molecules!

• Diffusion: The movement of particles from an area of high concentration to lower concentration.

• It’s caused by the random motion of atoms (aka thermal energy)

• When the concentration of particles becomes equal in all parts of the environment, that’s called equilibrium.

Equilibrium

• When the concentration of solute is equal throughout a solution.

Dynamic Equilibrium

• Dynamic equilibrium refers to a state where the overall conditions don’t change, but individual parts keep moving

• Example: 5 molecules move in, 5 molecules move out, still at equilibrium.

Diffusion: A type of passive transport

• Passive transport is the movement of matter into or out of a cell WITHOUT the use of energy by the cell.

• Diffusion across the cell membrane is how small molecules get into and out of cells.

Concentration Gradient

• A concentration gradient is a difference in concentration across a space.

• Going “down” the concentration gradient means moving from an area of high concentration to low

High Concentration Low Concentration

“down” the gradient

How your cells get O2 and get rid of CO2

Diffusion: why flatworms are flat !

• Since they have no respiratory system, planarians like this have a flattened body plan to allow for fast diffusion of oxygen and carbon dioxide to all their cells.

Do Now 11/16

• Which of the following molecules do you think could NOT pass through the cell membrane by diffusion?A. Na+

B. O2

C. CO2

D. C6H12O6

E. CN-

Only SMALL molecules can fit through the cell

membrane without transport

proteins

Osmosis: The diffusion of water across a semi-permeable

membrane

Things always move from

areas of higher concentration to

lower concentration spontaneously

(passively)

Effects of Osmosis can be serious for a cell!

Isotonic

No net change

Hypertonic

Water outOf cell

Hypotonic

Water into cell

Hypo Hypo Hippo

How cells cope

Osmosis & Plants

Plant Cells & Osmosis

Plasmolysis

Hypotonic environmentCauses turgor pressure.Plant is healthy.

Hypertonic environmentCauses wilting.Plant is unhealthy.

Plasmolysis

One Last Time

Facilitated Diffusion

• Facilitated diffusion is like regular diffusion in that substances are moving from high concentration to low without the use of cell energy.

• The difference is the solute molecules can’t get through the membrane alone, and travel through proteins instead.

MembraneProteins

Solutes too bigOr too polarTo diffuse normally

Facilitated Diffusion

Wrap Up / Key Ideas• Diffusion: The movement of solute molecules down a

concentration gradient. Small molecules (e.g. H2O, O2, CO2) cross the cell membrane via diffusion

• Osmosis: The diffusion of water across a semi-permeable membrane.

• Facilitated Diffusion: The diffusion of large and/or polar molecules across the cell membrane through proteins.

• Passive Transport: Movement of material into or out of a cell without the use of energy by the cell.

• Concentration gradient: A difference in solute concentration across a space.

DO Now 11/17

• Reverse osmosis is a process used to desalinate salt water to make it drinkable. – How might this process work? Sketch a design that

uses a semi-permeable membrane to purify water.– Is this process passive or active? How do you

know?

You Need Energy to Go Up a Concentration Gradient!

Salt water at high pressure

Selective membrane prevents large solutes and ions from passing through.

They become MORE concentrated

Fresh water out

Passive TransportDefinition:

The process of substances passing through the cell membrane WITHOUT ANY INPUT OF ENERGY BY THE CELL.

Definition:

Solute molecules move from an area of high concentra-tion to an area of low conc. Powered by the random motion of molecules.

Definition:

Cell uses carrier proteins in membrane to allow the diffusion of molecules that can’t pass through membrane alone.

Definition:

Diffusion of water from an area of high H2O conc. (low solute conc.) to low (high solute conc.)

Key Term:

Isotonic:Solute conc. = Inside & out.No net H2O

change.

Type 1Type 2 Type 3

Required for

And

DIFFUSION

OSMOSIS FACILITATEDDIFFUSION

EquilibriumHypertonic:Solute conc. Bigroutside. H2O out

Hypotonic:Solute conc. Lower outside.H2O in. Hypo-Hippo

Ions (charged

molecules)

LargeMolecules

Read All About it!

• Section 5-1 “Diffusion” pp. 95-96

• SR #1, p. 100.