Osmosis Osmosis… …is the diffusion of water molecules - PowerPoint Presentation

Slide1

Osmosis

Slide2

Osmosis…

…is the diffusion of water molecules

…happens across a semi-permeable membrane

Slide3

ONLY WATER

Water is a small but extremely important molecule that makes up most of the liquid part of the cytoplasm in living things.

Deals

ONLY

with the diffusion of

WATER

The molecules (in this case,

water

-

not

solute molecules) will tend to move from an area of

high

(water)

concentration to an area of

low

(water

)

concentration

until equilibrium is reached.

Slide4

Slide5

OSMOSIS:

FACILITATED DIFFUSION

OF WATER ACROSS A CELL MEMBRANE

Why would water molecules normally have a

hard

time getting across the cell membrane?

The inside of a cell’s lipid

bilayer

is hydrophobic (water hating)

Click me

!

Slide6

Aquaporins

Most cells have special water channel proteins

Known as –

Aquaporins

Allow H

2

O to pass right through them by facilitated diffusion.

This EXTREMELY important process is = OSMOSIS

Slide7

By knowing the concentrations of solute and solvent on the inside and outside of a cell, we can predict the direction of osmosis and the result on the cell.

Solutions on the outside of a cell can be described based on how they affect the cell

hypERtonic

hypOtonic

isotonic

Slide8

Solutions on the

outside

of a cell

(in its environment)

can be described based on how they affect the cell:

NOTE: (*tonic = solute. [High] solute means [low] water)

"HYPER" = HIGH; "HYPO" = LOW; "ISO" = equal or same.

Slide9

VISUALIZE HYPERTONIC

Cell with 2% solute, 98% solvent

Beaker with 3% solute, 97% solvent

What will happen?

a

) net movement of water

_______of

cell

b) cell will

________

c

) solution is hypertonic to the cell

BEFORE

AFTER

H

2

O

H

2

O

H

2

O

Slide10

VISUALIZE

HYPOTONIC

Cell with 2% solute, 98% solvent

Beaker with

1%

solute,

988%

solvent

What will happen?

a

) net movement of water

_______of

cell

b) cell will

________

c) solution is

hypotonic

to the cell

BEFORE

AFTER

H

2

O

H

2

O

H

2

O

Slide11

VISUALIZE ISOTONIC

Cell with 2% solute concentration, 98% solvent

Beaker = 2% solute, 98% solvent

What will happen

a

) no net movement

b) cell won’t change in size

c

) solution = isotonic to the cell

Slide12

Common mistakes when discussing hyper-, hypo-, and isotonic solutions

The solutions are named for the concentrations of the

SOLUTES

The substance that moves to balance the solute concentration is the

WATER

The solutes to not “pull” or “suck” the water across the membrane – the water simply diffuses from where it is in high concentration to low concentration

Slide13

Solute and solvent concentrations can be expressed as percentages of the entire solution.

When added together, the solute and solvent concentrations must equal 100%.

A solution with a 10 % solute concentration has a 90% solvent concentration.

Slide14

Let’s do some math!

What is the solvent concentration of a solution with a 3% concentration of solute?

What

is the solvent concentration of a solution with a 15% concentration of glucose?

What is the solute concentration of a solution with 98% solvent?

What is the solute concentration of a solution with 75% water?

Slide15

Osmotic Pressure

Driven by differences in

solute

concentration, the net movement of water into or out of a cell produces a

force

known

as

osmotic pressure

Slide16

Almost always

hypertonic…

Because cells contain a variety of solutes such as:

sugars, proteins, salts, etc.

they are almost always

hypertonic

(*the environment =

HYPOtonic

!) to fresh water; as a result, a typical cell exposed to fresh water will tend to swell up quickly from the entering water. This may in fact cause an animal cell to swell like an overinflated balloon.

Slide17

Plant cells contain a central vacuole which stores excess water - shrinking and swelling as water enters or exits the cell. Plant cells wouldn't generally burst thanks to their protective

cell walls

.

In fact, most cells in large organisms are not in contact with fresh water on a regular basis - rather, they tend to be bathed in blood or other

isotonic

fluids which have solute concentrations approximately equal to themselves.

Cells which are plump and rigid in hypotonic environments are called

turgid

; when a cell shrinks in a hypertonic environment this is called

plasmolysis

Slide18

Fill in…

Conditions

Water will…

Environment

is...

Solute

concentration in the environment is equal to that in the cell

Solute

concentration in the environment is greater than the cell

Solute

concentration in the environment is less than the cell

Move in and out in equal amounts

No net movement

Isotonic to the cell

Cell is isotonic to its environment

Move OUT of the cell

The Cell Shrinks

Hypertonic to the cell

Cell is hypotonic to its environment

Move INTO the cell

The Cell Swells

Hypotonic to the cell

Cell is hypertonic to its environment

Slide19

Some more practice!

Slide20

Show what happens to plant and animal cells subjected to isotonic, hypertonic, and hypotonic solutions in the environment:

Conditions

Plant Cell (leaf cell)

Animal cell (blood cell)

Environment

Before

After

Before

After

Solute concentration in the environment is

equal

to that in the cell:

Isotonic solution

Solute concentration in the environment is

greater

than the cell:

Hypertonic Solution

Solute concentration in the environment is

less

than the cell:

Hypotonic Solution

Slide21

Slide22

APPLY

what you have learned about osmosis…

Why do doctor’s use a

saline

solution in an IV

drip

?

Slide23

APPLY

what you have learned about osmosis…

Why

would salt kill plants

?

Slide24

APPLY

what you have learned about osmosis…

Why

do

restaurants put

out free salty snacks such as peanuts, pretzels or chips?