BIOL 2011L Lecture Notes - Lecture 3: Osmotic Pressure, Colligative Properties, Lipid Bilayer

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23 Nov 2017

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Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. It may also be used to describe a physical process in which any solvent moves across a semipermeable membrane (permeable to the solvent, but not the solute) separating two solutions of different concentrations. Osmotic pressure is defined as the external pressure required to be applied so that there is no net movement of solvent across the membrane. Osmotic pressure is a colligative property, meaning that the osmotic pressure depends on the molar concentration of the solute but not on its identity. Osmosis is a vital process in biological systems, as biological membranes are semipermeable. Permeability depends on solubility, charge, or chemistry, as well as solute size.

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.

Question 1

Plasma membranes are selectively permeable. This means that

	A.	glucose cannot enter the cell.
	B.	the plasma membrane allows some substances to enter or leave a cell more easily than others.
	C.	plasma membranes must be very thick.

Question 2

Oxygen molecules O₂ crosse a plasma membrane by

	A.	passive transport
	B.	osmosis
	C.	active transport

Question 3

Facilitated diffusion across a biological membrane requires ________ and moves a substance ________ its concentration gradient.

		A. energy and channel proteins; against (up)
		B. transport proteins that make channels ; down
		C. energy ; down

Question 4

When two aqueous solutions that differ in solute concentration are placed on either side of a semipermeable membrane and osmosis is allowed to take place, the water will

		A. move to the side with lower water concentration
	B.	move to the side with higher water concentration
	C.	move to the side with lower solute concentration

Question 5

Kinetic energy differs from chemical energy in that

	A.	chemical energy is a particular form of kinetic energy.
	B.	kinetic energy is the energy of a moving object, whereas chemical energy is the potential energy of molecules.
	C.	kinetic energy is stored energy that has the potential to do work, and chemical energy is the energy of movement.

Question 6

When a cell uses chemical energy to perform work, it uses the energy released from a(n) ________ reaction to drive a(n) ________ reaction.

	A.	exergonic; endergonic
	B.	endergonic; exergonic
	C.	spontaneous; exergonic

Question 7

When an enzyme catalyzes a reaction

		A. it raises the activation energy of the reaction.
		B. it lowers the activation energy of the reaction.
		C. it is used once and discarded.

Question 8

Which of the following statements regarding enzyme function is false?

		A. An enzyme's function depends on its three-dimensional shape.
		B. Enzymes are very specific for their substrates.
		C. Enzymes are used up when they catalyze a chemical reaction so must be synthesized for each new chemical reaction

BIOL 2011L Lecture Notes - Lecture 3: Osmotic Pressure, Colligative Properties, Lipid Bilayer

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