QUIZ:Which organelle:1.Makes proteins2.Packages and ships proteins3.Makes ATP from carbohydrates4.Define amphipathic.5.Labels:A.B.C.D.E.

A B

ED

C

Membrane Transport

Passive: osmosis, diffusionActive: endocytosis, exocytosis

Concentration gradient drives the NET movement of molecules

Molecules move randomly and continuously. Impacts change their direction.

High Low

Permeability

Osmosis

Movement of water across a membrane from high concentration to low concentration

The greater (steeper) the concentration gradient, the faster the rate of diffusion.

Another rule of thumb:

InsideCell

OutsideCell

Con

cent

ratio

n of

sol

utes Cell A will diffuse faster

Cell A

Cell B

Effect of temperature on diffusion

Cell B will diffuse faster

Cell A

Cell B

Cell A Cell B

Tem

pera

ture

°C 22°

38°

Active Transport

© Brooks/Cole - Thomson Learning

Sodium-potassium Pump

© Brooks/Cole - Thomson Learning

3 factors that affect movement of molecules across membranes

• Effect of ConcentrationEffect of Concentration: the greater the concentration difference across the membrane, the faster the rate of diffusion (agar blocks)

• Effect of TemperatureEffect of Temperature: the higher the temperature, the faster the rate of diffusion due to increased energy of solute molecules (agar blocks)

• Effect of Pore SizeEffect of Pore Size: only solutes small enough to pass through the pores of a membrane are able to diffuse (dialysis: iodine moved in, glucose moved out, starch remained in)

Objective 3: Recognize the role of water potential in regulating the movement of water across membranes and note factors that affect water potential.

Objective 4: Describe the tonicity of biological solutions

Water potential: the potential energy of a volume of water; expressed as a pressure

Definitions

Osmosis - the diffusion of water

across membranes

Which way will the water go?

Definitions

• Solute - the substance dissolved in a liquid (e.g., sugar, salt)

• Solvent - the liquid in which the solute is dissolved (e.g., water)

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this p icture.

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

“Free” water molecules can pass through membrane.

These solute molecules are too big to pass through membrane.

Higher water potential Lower water potential

• Hypotonic - solution that contains FEWER solute particles than another solution

• Hypertonic - solution that contains MORE solute particles than another solution

Obj. 4: Tonicity of solutions

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Rule of Thumb• The net movement of WATERWATER is from hypotonichypotonic conditions to hypertonichypertonic conditions.

• If two systems are equal in the number of dissolved particles, they are said to be isotonicisotonic and no net change in volumes will occur.

Hypotonic Hypertonic

Notes on Diffusion and Osmosis

• Both solutes and solvents (water) can diffuse across a membrane and the concentration difference will eventually equalize • We are interested in the period of time before the system equalizes (becomes isotonic), to observe which direction diffusion is occurring• Always pay attention to both solutes and solvents in a question - both may be important!

Objective 5: Recognize the role of the cell wall and of the vacuole in producing turgor pressure to maintain the shape of the plant cell.

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Distilled water

Salt water

HIGH turgor pressure

LOW turgor pressure

Cell and cell wall do not change size.Vacuole swells and shrinks.

The pressure that develops between the cell wall and vacuole is called TURGOR pressure.

Plant cells ONLY

Egg inDistilled water

Egg inSugar water

H2O

H2O

Distilled water

H2O

Sugar water

H2O

Water is hypOtonicEgg is hypERtonic

Water is hypERtonicEgg is hypOtonic

Water moves from hypotonichypotonic conditions to hypertonichypertonic conditions.

Discussion questions

Many hospital patients receive intravenous liquids to replace body fluids. These liquids are generally complex solutions of salts and sugars. If all the patient needs is fluid, why doesn’t the physician simply inject pure water?

Why can’t we drink salt water?

Dialysis tubing is a model for a cell membrane.

Iodine solution

Starch & glucose

Dialysis tubing is a model for a cell membrane.

Iodine solution

Starch & glucose

Iodine + starch=blue

IodineGlucose

Cells have a selectively permeable membrane

Predict the effects of temperature and concentration gradients on diffusion rates

Concentration gradients

5% 0.5%

Started with 0%, diffused 5%Started with 0%, diffused 0.5%

5 - 0 = 5 0.5 - 0 = 0.5

Much greater concentration gradient

Sodium hydroxide solution

Agar Blocks