The Cell Membrane: Review #1
Fluid Mosaic Model
1. Explain why the present theory of cell membrane structure is called the “FLUID MOSAIC”
model?
a. the phospholipid bilayer is broken up by proteins and cholesterol giving the membrane
the look of a mosaic, and the phospholipids in the membrane are able to slide past each
other and so have a fluid motion.
2. Describe the difference between an integral protein and a peripheral protein
a. Integral proteins are found within the cell membrane often spanning from one side to
the other and have both polar and non-polar regions.
b. Peripheral proteins are attached to one side of the phospholipid bilayer.
3. What is the difference between a glycoprotein and a glycolipid?
a. Glycoprotein: a carbohydrate chain attached to a membrane protein
b. Glycolipid: a carbohydrate chain attached to a phospholipid head in the cell membrane
4. What is the collective function of all the carbohydrate chains (Glycocalyx) on the surface of the
cell membrane?
a. Cell recognition*** this is the one we talked about most
b. Adhesion
c. Protection
d. Permeability barrier
5. Use CRERC to describe the 5 major roles of membrane proteins.
a. Channel: provides passage for specific molecules from one side of the membrane to the
other in facilitated diffusion (passive)
b. Recognition: membrane proteins with carbohydrate chains attached, glycolipids, which
act as identifiers for other cells to recognize the cell.
c. Enzymatic: proteins in the membrane which are involved in enzymatic reactions within
the cell
d. Receptor: proteins in the membrane with receptors for specific molecules
e. Carrier: proteins which transfer molecules from one side of the cell membrane to the
other through a shape change.
6. What role does cholesterol play in the cell membrane?
a. Helps to stiffen up the membrane
Selectively Permeable
1. Why is the cell membrane described as being selectively permeable rather than semipermeable?
a. Semi-permeable means the membrane allows some things to pass through. Selectively
permeable refers to the cells ability to actively decide what is allowed in or out.
2. In general methods of transport across the cell membrane can be classified as being either
“passive” or as being “active”. What is the key difference between these two categories?
a. Use of energy in the form of ATP
3. List three specific types of passive transport.
a. Diffusion
b. Osmosis
c. Facilitated transport
4. Besides a concentration gradient, what else is required for Facilitated Transport?
a. Cell membrane protein, either a channel protein or a carrier protein.
5. Name at least 3 key molecules that can diffuse across the cell membrane. See Table 4.1 on p.70
a. Oxygen
b. Carbon dioxide
c. Water*** (can also be transported by facilitated diffusion through channel proteins)
Diffusion and Osmosis
1. What does the “Law of Diffusion” state?
a. Molecules will move from an area of high concentration to an area of low concentration
until equilibrium is reached.
2. Would diffusion occur more quickly in liquids or in gases, explain why?
a. Gases: the molecules are farther apart and therefore less collisions interfere with the
movement of the molecules toward areas of low concentration.
3. Give the definition for each: a) Solvent, b) Solute
a. Solvent: the liquid part of a solution in which the solute is dissolved
b. Solute: the solid which is dissolved in the solvent to form a solution
4. What is meant by a “concentration gradient”?
a. the gradual difference in the concentration of solutes in a solution between two regions
5. Many water molecules struggle to pass through the hydrophobic region of the cell membrane,
what will allow many of the molecules to slip through? –Think CRERC
a. Channel proteins
6. Define osmosis.
a. Diffusion of a water through a semipermeable membrane from an area of low solute
concentration to an area of high solute concentration.
7. How are diffusion and osmosis similar, and how are they different?
a. Similar: both obey the law of diffusion, both are passive transport
b. Different: osmosis refers to movement of water, diffusion to movement of solute.
8. Pressure caused by the concentration gradient between two different solutions is called
_________________ pressure. osmotic
9. Name the three types of solutions that cells can be placed in.
a. Hypotonic, hypertonic, isotonic
10. What will happen to an animal cell when it is placed into the following:
a.
Hypotonic solution animal cell will swell as water enters the cell (deplasmolysis or
hemolysis(red blood cells))
b. B) hypertonic solution animal cell will shrivel as water leaves the cell (plasmolysis or
crenation(red blood cells))
11. What will happen to a plant cell when it is placed into the following:\
a. Hypotonic solution plant cell will become turgid as water enters the cell. The cell will be
pressed against the cell wall.
b. B) hypertonic solution plant cell will become plasmolyzed as water leaves the cell. Cell
membrane will pull away from the cell walls and plant will wilt.
Practice Quiz Answer Key:
1.a) water … (water can diffuse through the cell membrane and is also moved across the membrane
through protein channels)
1. c)
3. c)
4. c)
5. b)
6. c)
7. d)
8. b)
9. d)
10. b)
11. a)