BIOL 1005 Lecture Notes - Lecture 20: Semipermeable Membrane, Phagocytosis, Exocytosis

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9 Mar 2016

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Methods of moving substances across a biological membrane. Diffusion- the movement of molecules of a particular substance from areas of higher concentration to lower concentration. Increase energy speeds up the rate of diffusion by increasing the rate of movement of the molecules. Dialysis- is the movement of small molecules or ions across a membrane. Such is the case when blood is dialyzed by the kidneys to remove salts and urea. Osmosis- diffusion of water through a semi-permeable membrane from an area of greater concentration(lower osmotic pressure) to an area of lower concentration (higher osmotic pressure). Osmotic pressure- a measure of the tendency of water to move into a solution. The more solute in a solution, the greater the osmotic pressure. Also, defined as the amount of pressure which must be exerted on a solution to keep it in equilibrium (same level) when the two solutions are separated by a membrane.

Related Questions

1. predict the direction of water movement based on differences in solute concentrations. Use the terms osmotic pressure, hypotonic, isotonic, and hypertonic
2. Why do membranes have to be selectively permeable?

3. What determines whether a particular substance can diffuse (simple or facilitated) through a membrane?

4. What mechanisms drive molecules across membranes? Use the terms concentration gradient, (facilitated) diffusion and active transport.
5. Which parts of the plasma membrane proteins do you expect to be hydrophobic or hydrophilic? Justify your answer.
concise and short answers pls

1. In lecture, we described a simple osmotic pressure gradient when discussing osmosis. For question #1, describe the simple osmotic pressure gradient, in terms of osmotic pressure, that exists across the red blood cell plasma membrane when red blood cells are suspended in a severely hypotonic solution, such as a 0.2% NaCl solution. Use scientific terminology.

2. We mentioned in class that biological systems are always in a state of osmotic equilibrium due to a combination of solute diffusion in some cases and osmosis in others. In this experiment, when you add the red blood cells to a severely hypotonic solution, what substances are moving across the red blood cell plasma membrane to achieve osmotic equilibrium, Na+ and Cl- or water? Explain why based on your understanding of the permeability characteristics of biological membrane. Always use scientific language.

CAN QUESTIONS 1 AND 2 BE ANSWERED DIRECTLY AND ADEQUATLEY PLEASE.

HERE IS AN INTRO TO THE LAB EXPERIMENT

Intro:

We have known for a very long time that the mammalian red blood cell plasma membrane is very permeable to water. Even the introductory biology student understands that if you put mammalian red blood cells in water, they will rapidly swell and break open (hemolyze) due to the rapid osmosis of water into the cell. The experimental question we are asking in today's lab experiment is "Is the high water permability of mammalian red blood cell plasma membrane due solely to the lipid bilayer, or are there water channels present in the membrane?"

Experimental Design:

It has been shown by several investigators that water movement through water channels can be blocked by the known K+ channel blocker, tetraethylammonium chloride (TEAC). Brooks, Regan and Yool (2000) showed that TEAC reduces the water permeability of human water channels expressed in the plasma membranes of frog ocytes. After preincubation of the oocytes for 15 min with 100 microM TEAC, the water permeability of frog oocyte plasma membrane containing human water channels was reduced 20 to 40%. The investigators concluded that treatment of cells with TEAC can be useful in determining the presence of aquaporins in membranes.The specific objective of today's experiment is to uncover the presence of water channels in mammalian red blood cell plasma membrane by determining the effect of tetraethylammonium chloride on the water permeability of mammalian RBC plasma membrane.

1. Microscopic cells or particles suspended in water exhibit atype of movement known as

_______________________________________________________________________.

2. The yeast cells in suspension appear to jiggle back and forthbecause they are bombarded

by the ______________ energy of water molecules which are inconstant, rapid, random

motion.

3. The movement of the molecules of a gas, liquid, or solid froma region of higher

concentration of that substance to a region of lesserconcentration is termed

____________________________.

4. What are 2 factors that influence the rate of diffusion?

5. ______________ is the diffusion of a solvent across aselectively permeable membrane.

6. In ______________________, water moves out of a plant cell byosmosis causing the

protoplast to shrivel up.

7. In __________________, water moves into an animal cell byosmosis causing the cell to

swell and burst.

8. The process of ________________ can be used in treatingkidney patients to separate

urea (small molecules) from proteins (large molecules) using aselectively permeable

membrane.

9. Which type of solution (hypotonic or hypertonic) is formed inthe soil environment

around root cells when a lawn is over fertilized? Would the rootcells lose or gain water?

10. Why is it common practice to place lettuce and celery inwater before serving them?

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BIOL 1005 Lecture Notes - Lecture 20: Semipermeable Membrane, Phagocytosis, Exocytosis

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