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PHSL 1010 EXAM 1-Study GuideMEMBRANE DYNAMICS
1. List and briefly describe the general functions of the cell membrane.
○ Physical isolation
○ Regulation of exchange with environment
○ Communication between cell and environment
○ Structural support
2. Do all cell membranes have the same composition? Explain.
No, The ratio of protein to lipid varies widely. Generally, the more metabolically
active a membrane is, the more proteins it contains.
3. List the three main types of lipids found in cell membranes and describe
their functional roles.
○ Cholesterol: keeps membrane flexible over wide range of temperatures
○ Phospholipids: form lipid bilayer
○ Sphingolipids: part of lipid bilayer
4. Define osmosis and explain the statement “water chases milliosmoles”
Osmosis is the movement of water from a less concentrated solution (more
water) to a more concentrated solution (less water) meaning that water goes
where the milliosmoles are the highest or to an area of higher concentration of
solutes.
5. What is osmotic equilibrium?
The equal concentration of water concentrations throughout the body.
6. What is chemical disequilibrium? How does chemical disequilibrium in the
body give rise to electrical disequilibrium? What is the result of electrical
disequilibrium?
○ Chemical disequilibrium: the uneven distribution of solutes between
ECF and ICF
○ Electrical disequilibrium: the uneven distribution of charge between the
ECF and ICF that results in the generation of electrical signals
7. Define and describe osmosis and osmotic pressure.
○ Osmosis: the movement of water across a membrane in response to a
solute concentration gradient
○ Osmotic pressure: the pressure that must be applied to oppose osmosis
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,PHSL 1010 EXAM 1-Study Guide
8. Contrast osmolarity and osmolality.
○ Osmolarity: the number of osmotically active particles per liter of solution
○ Osmolality: concentration expressed as osmoles of solutes per kg of
water. Used in clinical situations because it is easier to estimate body’ s
water content by weighing them
9. Distinguish between the terms isosmotic, hyposmotic, and hyperosmotic.
○ Isosmotic: when two solutions contain the same number of solute
particles per unit volume
○ Hyposmotic: if one solution has a lower osmolarity (contains less
particles per unit volume, is more concentrated) than a second solution
○ Hyperosmotic: if one solution has a higher osmolarity (contains more
particles per unit volume, is more concentrated) than a second solution
10. Describe and define tonicity.
Tonicity describe how a solution would affect cell volume if the cell were placed in
the solution and allowed to come to equilibrium. Depends on concentration
(osmolarity) and concentration of nonpenetrating solutes (cannot cross
membrane)
11. Compare and contrast tonicity
○ Osmolarity describes the number of solute particles dissolved in a volume
of solution.
○ Osmolarity can be used to compare any two solutions, and the
relationship is reciprocal whereas tonicity always compares a solution and
a cell.
○ Osmolarity alone does not tell you what happens to a cell placed in a
solution but tonicity tells what happens to cell volume at equilibrium when
the cell is placed in the solution.
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,PHSL 1010 EXAM 1-Study Guide
12. Why can’t osmolarity be used to predict tonicity?
The tonicity of a solution depends not only on its concentration (osmolarity) but
also on the nature of the solutes in the solution.
13. Distinguish between the terms isotonic, hypotonic, and hypertonic.
○ Hypotonic: when a cell has a higher concentration of nonpenetrating
solutes than solution→ net movement of water into cell and it swells
○ Hypertonic: when a cell has a lower concentration of nonpenetrating
solutes than solution→ net movement of water out of cell and it shrinks
○ Isotonic: when a cell has same concetration of nonpenetrating solutes in
cell and solution→ no net movement of water and does not change size
14. Contrast penetrating solutes and nonpenetrating solutes. What does it
mean when a solute is considered “functionally nonpenetrating”?
○ Penetrating solutes: solute (ions or molecules) that can enter the cell
○ Non-penetrating solutes: particles that cannot cross the cell membrane
15. What are the rules for predicting tonicity?
○ Assume that all intracellular solutes are nonpenetrating.
○ Compare osmolarities before the cell is exposed to the solution. (At
equilibrium, the cell and solution are always isosmotic.)
○ Tonicity of a solution describes the volume change of a cell at equilibrium
○ Determine tonicity by comparing nonpenetrating solute concentrations in
the cell and the solution. Net water movement is into the compartment
with the higher concentration of nonpenetrating solutes.
○ Hyposmotic solutions are always hypotonic.
16. How can a solution be isosmotic can be isotonic and hypotonic?
○ Isotonic: if all solutes in the isosmotic solution are nonpenetrating
○ Hypertonic: if there are any penetrating solutes in the isosmotic solution
17. Describe what happens to osmolarity and tonicity if there is an increase in
volume
○ Increased osmolarity: results in excretion of hypertonic urine
○ No change in osmolarity: results in excretion of isotonic urine
○ Decreased osmolarity: results in excrete dilute urine but compensation is
imperfect bc kidneys cannot excrete pure water
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, PHSL 1010 EXAM 1-Study Guide
18. Describe what happens to osmolarity and tonicity if there is an no change
in volume.
○ Increased osmolarity: results in intense thirst which prompts ingestion of
water to dilute the added solute. Kidneys help by creating highly
concentrated urine of minimal volume conserving H 2O while removing
excess NaCl
○ Decreased osmolarity: results in dehydration but no solutes are replaced
so electrolyte-containing beverages (i.e Gatorade) needed. (i.e exercise)
19. Describe what happens to osmolarity and tonicity if there is an decrease in
volume
○ Increased osmolarity: due to dehydration, diarrhea, sweating resulting in
cell shrinkage
○ No change in osmolarity: occurs with hemorrhage (blood loss) loss of
isosmotic fluid from ECF
○ Decreased osmolarity: the incomplete compensation of dehydration.
uncommon
20. What is the difference between active transport and passive transport?
Active transport uses energy where as passive transport does and solely relies
on concentration gradients.
21. Define diffusion and list seven properties of diffusion.
It is the movement of molecules from one area of higher concentration to an area
of lower concentration.
○ it is a passive process
○ molecules move from a higher concentration to lower concentration due to
concentration gradient
○ net movement of molecules occurs until concentrations come to an
equilibrium
○ it is rapid over short distances but slower in longer distances
○ directly related to temperature
○ diffusion rate is inversely related to molecular weight and size
○ can take place in an open system or across partition
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