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Diffusion and Osmosis

- A “Moving” Topic -

Another Potato Demo...1) Send two group members to obtain:

- Two Beakers- Dry-Erase Marker- Triple Beam Balance

Another Potato Demo...1) Send two group members to obtain:

- Two Beakers- Dry-Erase Marker- Triple Beam Balance

2) Get two slices of potatothat are approximatelythe same size.

Another Potato Demo...3) Using the balance, determine the mass of

each potato slice. Record in your table.

4) Using the dry-erase marker, label one beaker “water” and the other one “sugar solution.”

5) Using the beaker, measure 100mL of water for each beaker.

Another Potato Demo...6) Put a piece of paper on the balance. Measure

out 30 grams of sugar and then add it to the “sugar solution” beaker. Mix.

7) Place one potato slice in each beaker.

8) Wait.

Passive Transport• Cells maintain stable internal conditions by

controlling what enters and leaves the cell.



What word do we use to describe “maintaining stable internal conditions?”

(think 7 characteristics of life)



Homeostasis!



• Some substances can cross the cell membrane without the cell having to use any energy.

• This is known as passive transport.

Homeostasis!

Passive Transport• There are three types of passive transport:

1) Diffusion

2) Osmosis

3) Facilitated Diffusion

Diffusion• Diffusion is the simplest type of passive

transport.


transport.

• Diffusion – the movement of molecules from an area of high concentration to an area of low concentration.


transport.


• Concentration –


transport.


• Concentration – the amount of a substance present.

(Smelly) Example of Diffusion

• Mr. Mathis sprays some cologne in the room.

• Eventually, everyone in the room will be able to smell it.


• Mr. Mathis sprays some cologne in the room.

• Eventually, everyone in the room will be able to smell it.

Why?


• After the initial spray, there is a high concentration of the cologne in one spot.

• The smell diffuses across the room, moving to areas where the concentration is low.

Another Example of Diffusion

• If you place a cube of sugar into a beaker of water, the concentration of sugar is highest at the bottom of the beaker.

Another Example of Diffusion

• If you place a cube of sugar into a beaker of water, the concentration of sugar is highest at the bottom of the beaker.

• As the cube dissolves, the sugar molecules diffuse through the solution, moving toward the top of the beaker, where the concentration is lowest.

Diffusion• Diffusion occurs because molecules are in

constant motion.

• Molecules tend to move from areas of high concentration to areas of low concentration.

Diffusion• In the absence of other influences, diffusion

will eventually lead to equilibrium.

• At equilibrium, the concentration of molecules is the same throughout the space that the molecules occupy.

Diffusion and the Cell Membrane

• Cell membranes allow some molecules (but not others) to pass through.


• If a molecule can diffuse through the cell membrane, it will diffuse until it reaches equilibrium.

• Diffusion across the cell membrane is called simple diffusion.


• Simple diffusion of molecules across the cell membrane depends on the size, charge and polarity of the molecule.

Diffusion and the Cell Membrane• For example:

– The cell membrane is made of phospholipids.– Oxygen and carbon dioxide are capable of

dissolving in lipids, so can easily diffuse through the membrane.

Diffusion and the Cell Membrane• For example:

– Small molecules that can not dissolve in lipids may pass into the cell via pores in the membrane.

Back to the Potato Lab1) Remove the potato slices from the water

solutions.

2) Pat them dry with paper towels and then measure the mass of each one on the triple beam balance.

3) Using the formula below, determine the percent change in mass and record in your table.

Percent Change in Mass:

____(final mass – initial mass)___initial mass

Exit-Slip1) Diffusion is the movement of molecules

from an area of ____ concentration to ____ concentration.a) High ; Lowb) Medium ; Highc) Low ; Highd) High ; Medium

2) Diffusion is a type of _____ ______, because it requires no energy input from the cell.

a) active transportb) molecular transportc) effective transportd) passive transport

3) Assuming the pink dotscan pass through the cell membrane, in whatdirection will they move?a) Out of the Cellb) Remain Constantc) Into the Cell

4) The dots will move until they reach a state of ...a) Equalityb) Equilibriumc) Homeostasisd) Concentration

Bell-RingerTrue or False

1) Diffusion is the movement of molecules from an area of low concentration to an area of high concentration.

2) Cells use diffusion in order to move important molecules, such as oxygen, in and out of themselves.

3) Cells must use ATP in order to power diffusion.

Bell-RingerTrue or False

4) In the picture to the right,the dots will diffuse intothe cell.

5) The cell pictured below is at equilibrium.

Osmosis • Osmosis is the movement of water from

an area of high concentration to an area of low concentration.

• In other words, osmosis is the diffusion of water.

The Direction of Movement • The direction of osmosis depends on the

concentration of molecules dissolved in water.

• We use three important terms to describe solutions: – Hypotonic– Hypertonic– Isotonic

Hypotonic• A solution is hypotonic when the

concentration of molecules outside the cell is lower than the concentration of molecules inside the cell.

Hypotonic• To determine how water will move, we

must first determine the concentration of the water.

• Assume that each solution is made up only of water and the molecule dissolved in it.

Hypotonic• To determine the concentration of water,

subtract the concentration of the molecules dissolved in it from 100%



What is the concentration of water inside the cell?



100% - 5% =95% Water



What is the concentration of water outside the cell?



100% - 1% =99% Water



How will the water move?



Into the Cell!

Hypotonic• When a solution is hypotonic to the cell,

water will diffuse from outside the cell into the cell.

• This will cause the cell to swell.

Hypertonic• A solution is hypertonic when the

concentration of molecules outside the cell is higher than the concentration of molecules inside the cell.

Hypertonic


Hypertonic

100% - 7% = 93% Water

Hypertonic


Hypertonic

100% - 10% = 90% Water

Hypertonic


Hypertonic

Out of the cell!

Hypertonic• When a solution is hypertonic to the cell,

water will diffuse from inside the cell out into the solution.

• This will cause the cell to shrivel.

Isotonic• A solution is isotonic when the

concentration of molecules outside the cell is the same as the concentration of molecules inside the cell.

Isotonic


Isotonic

100% - 10% = 90% Water

Isotonic


Isotonic

100% - 10% = 90% Water

Isotonic


Isotonic

In and out of the cell at equal rates

Isotonic• When a solution is isotonic to the cell,

water will move both in and out of the cell at the same rate.

• The cell will show no change.

-Tonic Pictures• Pick an object and sketch it in three

different environments: Isotonic, Hypotonic and Hypertonic

• Be sure to show how would these three environments change this object.

Exit SlipMatch the words on the left to the

corresponding picture on the right.

1) Hypotonic

2) Hypertonic

3) Isotonic

A

B

C

Bell-Ringer1) What is the concentration of water outside the

cell?

2) What is the concentration of water inside the cell?

3) How will the water move?

4) The solution is ______tonic

Observing Osmosis

Observing Osmosis...1) Send one group member to obtain:

- A Glass Slide and Cover - Small piece of Red Onion

2) Tear off a thin slice of the red onion skin. Place the skin and a drop of water on the slide. Cover with the cover slip.

Observing Osmosis...3) Observe the onion cells at 4x, 10x and

40x magnification. Sketch the cells.

4) After everyone in the group has sketched the cells, remove the cover slip and use a paper towel to dry off the onion and slide.

5) Place two drops of salt water (front desk) on the onion skin and re-cover.

6) Repeat step #3.

7) Answer questions.

Exit-Slip1) Osmosis is, specifically, the diffusion of...

a) Ionsb) Lipidsc) Moleculesd) Water

2) The cells to the rightare mostly likely foundin a ______ solution.a) Hypertonicb) Hypotonicc) Isotonic

3) In the example to the right, water will move...a) Out of the cell

b) Into the cellc) In and Out of the cell at the same rate

4) After the water moves, the cell will look like which picture below?

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Documents

concentration of sugar

area of high concentration

area of low concentration

beaker water

beaker of water

sugar solution beaker

sugar molecules

types of passive transport