Diffusion and Osmosis

SWBAT

• Describe how molecules move from areas of high concentration to low concentration through diffusion

• Describe how water moves from areas of low concentration of solutes to high concentrations to even the concentrations through osmosis

1. What will be the difference in how food-color dropped in cold water and hot water spreads out?

2. Why do you expect this difference to occur?

Diffusion is the spread of molecules from areas of lower concentration to higher concentration

1. Which image best depicts the hot water, which the cold?

2. What is the relationship between temperature and the speed of molecular motion?

3. If a drop of red dye was added to both, which would be pushed around and spread throughout the water faster due to molecular motion?

4. What is responsible for diffusion?

The image on the right is hot (longer arrows imply faster molecular motion). As temp. increases, so does molecular motion. Therefore, a drop of dye placed in the hot water will be pushed around more and thus spread out (diffuse) faster. The kinetic energy (random molecular motion due to heat) is responsible for the process of diffusion.

Diffusion

• Movement of molecules from areas of higher concentration to lower concentration

Diffusion

Make a prediction of what it will look like for (a) and (b)

If the dye molecules can freely pass through the membrane, predict:

How many molecules of dye to you expect on each side of the membrane after significant time has passed?

The dye diffuses down its concentration gradient: from where it is more concentrated to where it is less concentrated.

This leads to equilibrium: dye molecules still cross but at equal rates in both directions.

Diffusion

• Due to _______________ energy of molecules: ↑ temperature, ___________ rate of diffusion

• Spontaneous/___________ (requiring no energy input)

• Net movement from area of ____ [ ] to ____ [ ]

• Rate ↓ as molecular mass ____

Diffusion

• Due to kinetic energy of molecules: ↑ temperature, ↑ rate of diffusion

• Spontaneous/passive (requiring no energy input)

• Net movement from area of ↑ [ ] to ↓ [ ]

• Rate ↓ as molecular mass ↑

Osmosis is the movement of water to areas of higher solute concentration to equalize the overall concentration

• The membrane has pore sizes small enough to allow water to pass through, but larger molecules can not

Osmosis

Hypertonic: the solution with a higher solute concentration

Hypotonic: the solution with a lower solute concentration

Isotonic

1. Which side has a hypertonic solution, which a hypotonic?

2. Which side has a greater [ ] of free water?

3. What is the net direction of osmosis?

4. What will the U-tube look like during dynamic equilibrium?

Hypotonic Hypertonic

What will red blood cells look like after being exposed to distilled water?

A B C

1. Match the terms hypertonic, isotonic, and hypotonic to the diagrams A, B & C.

2. Which condition is optimal for animal cells?

3. Which condition is optimal for plant cells?

1. Which type of solution is best for our red blood cells?

2. What could happen if red blood cells are placed in pure water?

3. What type of solution is IV fluid?

H2O diffusing out H2O diffusing inEqual diffusion in and out

isotonic

Saline solution (isotonic) is best

Pure water would cause cells to burst

Cells shrink

1. Which type of solution is best for our red blood cells? Isotonic

2. What could happen if red blood cells are placed in pure water? Swell with water and burst

3. What type of solution is IV fluid? Saline is isotonic

Cell

Cell

Cell

Soln.

Soln.

Soln.

1. How many sucrose (solute) molecules are inside each cell?

2. Describe each solution (soln.) as hypertonic, hypotonic, or isotonic relative to each cell.

3. Complete the sentence: water moves from an area of _____ [solute] towards an area of _____ [solute].

4. Complete the sentence: water moves from an area of _____ [free water] towards an area of _____ [free water).

5. Make a claim with justification (see #4-5 above) for the net direction of water movement in A – C.

A

B

C

• Green circles are molecules of sucrose (sugar)• Brown is the cell, blue is the outside solutionFor each solution (hypo-, iso-, hypertonic) answer the following questions:

1. There is more free water inside/outside than inside/outside the cell.

2. Water will diffuse into/out of the cell

Reverse Osmosis

Highest to lowest sucrose molarity: E, D, C, B, A

Solution C is isotonic (same molarity as potato) because the potato neither lost nor gained mass.