Diffusion, Osmosis and Biological Membranes

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Transcript Diffusion, Osmosis and Biological Membranes

Diffusion, Osmosis and Biological
Lab 4
Phospholipid Bilayer
Phospholipid Bilayer
Triglycerides (Neutral Fat)
•Fats are synthesized from 2 components:
1. Fatty acid: long chain C and H atoms ending in a COOH group
2. Glycerol: a three C molecule; note, glycerol is an alcohol
•Glycerol forms a backbone to which 3 fatty acids are attached via a dehydration
fat molecule
•Provides long term energy storage, insulation
Mechanisms by which substances move into and
out of the cell
• Diffusion
– Mode by which small, uncharged molecules enter of leave a cell
• Osmosis
– Diffusion of water
• Dialysis
– Diffusion of dissolved solute
• Endocytosis
– Ingestion of large molecules into a cell
– 2 types: Phagocytosis: Cell eating
Pinocytosis: Cell drinking
• Membrane Carrier Proteins
– Transport liquid insoluble material (ions, glucose, amino acids) by 3
• Facilitated Diffusion: A carrier protein in the membrane combines with a
substance moving across the membrane down its [gradient]
• Protein Channels: Passage of nonlipid soluble molecules
• Active Transport: Transfers molecules DOWN OR AGAINST [gradient] with
use of ENERGY!!
Why so many mechanisms to gets things into
and out of the cell?
Because the membrane is selectively
permeable. It allows easy entry of some
molecules and more difficult entry of others,
possibly preventing entry at all!
- Molecules move from area of [highest] to areas of [lower], DOWN the
concentration gradient
- Molecules eventually reach equilibrium
Factors that affect diffusion
-Temperature is an increase in molecular speed (kinetic
-Therefore, will higher temperature increase or decrease
the rate of diffusion?
Molecular Weight
-Larger molecules will have more ‘drag’ across the
membrane thus producing a slower rate of diffusion
-Test using HCl (36.461) and NH4OH (35.050)
Lab A: Molecular Motion - Diffusion
Use a coverslip with water on it to observe the diffusion of carmine dye.
Lab B: Effects of Temperature on
Use 2 test tubes with water and a crystal of potassium permanganate. Observe
the diffusion when one test tube has cold water and the other has warm water.
Lab C: Effects of Molecular Weight on
Use hydrochloric acid (HCl) and ammonium hydroxide (NH4OH) to observe the
rate of molecular weight on diffusion.
HCl: Molecular weight = 36
Na4OH: Molecular weight = 35
Lab D: Membrane Permeability
Use dialysis tubing to observe permeability of molecules. Dialysis tubing acts as a
molecular sieve through which molecules SMALLER then the holes in the tubing
membrane pass.
We will be testing permeability of starch and glucose solutions and deciphering
which solution is permeable (due to its smaller size) using Benedict’s Reagent.
Lab E: Osmosis
Use potato cylinders to test the direction of water movement. Osmosis will be
determined by the [solute] of a salt solution as compared to that of the [solute] of
the potato
Lab F: Plasmolysis
Observe plasmolysis in the plant cell Elodea. Plant cells have a rigid outer cell wall.
View the difference between normal and salt-treated Elodea cells.