1. What is the best way to float a thin metal pin on water? How come it works, although the pin is much more dense / heavier than the water?

2. When are water drops larger – with or without soap? Why?

Journal 1 07.13.09

Try it out:Observing water:1) Drop on wax and on glass.2) Floating a metal pin.3) Pepper on water, with soap.4) Ice on liquid water.

For each trial, describe what happened. Explain why.

Consider the two beakers with grapes and soda: Green grapes – peeled off Purple grapes – not peeled. A.Describe what you see in words

and a drawing. B. Try to explain why this

happens.C. Suggest a way to confirm your

explanation.

J

Journal1 07.13.09

Membrane structure

Membrane StructureIntroduction

Use Power notes handout

Properties of Water H2O

Water Molecules are Polar:

•Electrons spend more time around the O than the H.

•The “O” side is more negative and “H” side more positive.

•The + and – sides attract one another Water is Sticky!

Water Molecules are Polar: Notes

Animation of water behaviorAnimation: Closeups on WATER

-

+

Polar Solute

Non-Polar

Polar substances – Mix well with water(Sugar, Salt, Water colors…)

Notes

Non-polar substances – Do not mix well with water(Oils, waxes, Fats)

The same can be saidIn other terms..

WATER: Observations1. Capillary climbing2. Glass versus Wax3. Paper chromatography4. Drops on Penny5. Pepper on water and… soap!6. Phooo on wet towel! 7. Oil and water?!For each – describe what you see..

Water behavior Polarity-based Explanation

Observe the two bottles. 1.Describe the behavior of the

solvents (the liquids) and the solutes (materials that mix into the liquids).

2. Explain this behavior in terms of the hydrophobic – hydrophilic nature of the substances.

Hydrophilic – “loves” water

Hydrophobic – “hates” water(or rather – hated by water)

Totally hydrophobic: Oil

Half hydrophobic, half hydrophilic:

phospholipids

Membrane structureNotes

Solvent: Fluid Substance that is present in large amount (water, oil)Solute: Substance that is in small amount and mixed into the solvent. (food coloring, paint, sugar..)Solution: Solute mixed into solventConcentration: Amount of solute in unit volume of solvent.

Power notes: Membrane Structure

Membrane Fluidity Animation Stolaf

http://www.stolaf.edu/people/giannini/flashanimat/lipids/membrane%20fluidity.swf

Formation of a bilayer (Click on Left Menu to choose)

Membrane Structure (with cutting through a sphere..)

Purpose of biological membranes:* Constitute the border line of the cell and defines regions within the cell.

* Membranes control what passes through, into and out of the cell.

tails

Phospholipids arrange themselves in a lipid bilayer:

Water

Water

Hydro-phobic

Hydrophilic

Hydrophilic

Membrane Structure (with cutting through a sphere..)

Fluid Mosaic Model for membrane Structure:

•Flexibility: The phospholipids in each layer can move from side to side, behaving like a fluid.

• Mosaic: Many proteins and other molecules are embedded in the bilayer.

Membrane Fluidity Animation Stolaf

Membrane molecules that are not phospholipids:

Proteins: Aid cell identification and movement across the membrane.

Cholesterol: A small and rigid lipid. Solidifies the membrane.

Carbohydrates: for cell identification.

BUBBLE LAB

1) Soap bubbles – why / how do they form?

2) What are similarities between a membrane and a soap bubble?

Soap Bubbles explained

water

soap

Lipid bilayer, soap bubble:1) Draw, label – polar and

apolar areas.

2) What are similarities and differneces between a bilayer membrane and a soap bubble?

Soap Bubbles explained

Membrane, Soap Bubble: Compare: How Similar? How different?

water

soap

Biological membranes are

semi-permeablePass easily:

-Small molecules-Non-charged particles

-WATER!

Pass only with help: -Large particles

- Ions ?

Notes

UnchargedPolar

Charged(“super-polar”)

+ -

Large(proteins)

Non-polar (lipids)

Pass freely:

H2O IonsNa+ Cl-

Need help to pass:

Phospholipid in 3D

Triglyceride 3D

Saturated and non-Saturated Fatty Acids

Membrane Fluidity Animation Stolaf