Study Guide Chapter 3.3-3.4
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by Kathy Egbert
| 24 Questions
Chapter 3.3 Key Concept: The cell membrane is a barrier that separates a cell from the external environment
Vocabulary words for this section that you need to know:

  • cell membrane
  • selective permeability
  • phospholipid
  • receptor
  • Fluid Mosaic Model
Much of this section is a review from Chapter 2 when we studied lipids as a carbon molecule. The first part of the section should be review for you.
Cell membrane has two major functions: 1) forms a boundary between the inside and outside of the cell; and 2) controls passage of materials in and out of the cell
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5
The cell membrane is made of a phospholipid bilayer. Label its three parts: 1) charged phosphate group or head, 2) glycerol, and 3) the two fatty acid chains or tails. Mark the end that is polar (likes water) and the end that is nonpolar (doesn't like water). This is all review from Chapter 2.
There are other molecules embedded in the membrane. The Fluid Mosaic Model describes the arrangement of these molecules and the fluidity of the membrane (meaning that these molecules move around in the membrane - they are not stationary).
Fluid Mosaic Model - abt 2 1/2 mins
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List the function of each of the main three molecules that are found in the cell membrane.
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Some molecules can cross the membrane while others cannot. What term describes this property: ________________ __________________(type the name of the term on the figure below)
Receptors detect a signal from a molecule and perform an action in response. There are two types of receptors: 1) intracellular and 2) membrane.
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Figure A above is the Intracellular Receptor that is located inside the cell and it is able to bind to a molecule to cross the membrane Figure B above is the Membrane Receptor that is located in the membrane and the molecule binds to it, causing a change of shape that transmits the molecule across the membrane
True
False
Chapter Section 3.4 Key Concept: Materials move across membranes because of a concentration gradient (i.e., a difference in concentrations)
Vocabulary words that you need to be familiar with are:

  • passive transport
  • facilitated diffusion
  • diffusion
  • osmosis
  • concentration gradient
  • hypotonic
  • hypertonic
  • isotonic
  • plasmolysis
  • tonicity

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A concentration gradient means there is a difference in the concentration of a substance in one location compared to another location.
True
False
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Describe what is meant by a molecule moving down a concentration gradient.
A A molecule moves from where there is a low concentration of a substance to a location where there is a higher concentration of the same substance
B A molecule moves from where there is a higher concentration of a substance to a location where there is a lower concentration of the same substance.
Diffusion (A) and Osmosis (B) are both forms of Passive Transport - this means that no energy is required to cause the movement. They both have movement from a higher concentration to a lower concentration. The difference is that diffusion is the movement of substances, and osmosis is the movement of water.
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The higher the concentration of dissolved particles in a solution, means that the concentration of water molecules in that solution is _______________.
A higher
B lower
Facilitated Diffusion uses a transport protein to move molecules from a higher concentration to a lower concentration across a cell membrane. It doesn't require energy.
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Facilitated diffusion differs from simple diffusion because it requires a transport protein to move it across the membrane.
True
False
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In facilitated diffusion, do molecules move down a concentration gradient or against a concentration gradient?
A down a concentration gradient from higher to lower
B against a concentration gradient from lower to higher
Let's practice with some problems to solidify your understanding of diffusion and osmosis.
Remember: With diffusion, solutes move from an area of high concentration to an area of lower concentration.

Remember: With osmosis wherever more solutes are, water follows! Or, water also goes from an area of high amount of water to an area of lower amount of water.

You will put your answers in the multiple choice questions that follow. Your choices will be "move to inside", "move to outside", "no movement", and "equal movement",
DIFFUSIONOSMOSIS
Does the SOLUTE move inside or outside the cell?Does WATER move inside or outside the cell?Intracellular fluid (inside the cell) Extracellular fluid (outside of the cell)
125% salt10% salt
3410% salt10% salt
563% glucose1% glucose
782% protein1% protein
9109% salt9% salt
111213% water25% water
131459% water45% water
151690% water92% water
171874% glucose87% glucose
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Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition.​ 5% salt inside the cell​ 10% salt outside the cell. The answer to #1 and #2 in the Table is (remember column 1 will be diffusion of solutes; and column 2 will be osmosis of water):
A to inside; to outside
B to outside; to inside
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Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​10% salt inside​ 10% salt outside. The answer to #3 and #4 in the Table is:
A to inside; to outside
B to inside; to outside
C equal movement; no movement
D no movement; no movement
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Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​3% glucose inside​ 1% glucose outside. The answer to #5 and #6 in the Table is:
A to inside; to outside
B to outside; to inside
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1
Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​2% protein inside​ 1% protein outside. The answer to #7 and #8 in the Table is:
A to inside; to outside
B to outside; to inside
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1
Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​9% salt inside cell​ 9% salt outside cell. The answer to #9 and #10 in the Table is:
A to inside; to outside
B to outside; to inside
C equal movement; no movement
D no movement; no movement
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Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​13% water inside cell​ 25% water outside cell. The answer to #11 and #12 in the Table is:
A to inside; to outside
B to outside; to inside
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Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​59% water inside cell ​45% water outside cell. The answer to #13 and #14 in the Table is:
A to inside; to outside
B to outside; to inside
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Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​90% water inside cell​ 92% water outside cell. The answer to #15 and #16 in the Table is:
A to inside; to outside
B to outside; to inside
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1
Use the Table above with the cell conditions in Columns 3 and 4 to determine movement of solutes and water for each condition. ​74% glucose inside cell​ 87% glucose outside cell. The answer to #17 and #18 in the Table is:
A to inside; to outside
B to outside; to inside
Try some scenarios of conditions that affect the rate of diffusion. Each diagram shows substances at different concentrations separated by a cell membrane. The green squares represent glucose.
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Refer to figure above
A Figure "i" has a faster diffusion rate than "ii", because the thicker membrane in "ii" will slow diffusion
B Figure "ii" has a faster diffusion rate than "i", because the thinner membrane in "i" will slow diffusion
C Figures "i" and "ii" will have the same diffusion rate. The thickness of the membrane doesn't affect the rate of diffusion.
Another scenario of conditions that affect the rate of diffusion. Each diagram shows substances at different concentrations separated by a cell membrane. The green squares represent glucose.
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Use Figure above
A Figure "i" will have a faster diffusion rate than "ii", because there are fewer solutes that have to pass through the cell membrane
B Figure "ii" will have a faster diffusion rate than "i", because there is a greater gradient between the concentrations on the two sides of the membrane
C Figure "i" and "ii" will have the same rate of diffusion because the difference in concentrations across the membrane doesn't affect the rate of diffusion
Last scenario of conditions that affect the rate of diffusion. Each diagram shows substances at different concentrations separated by a cell membrane. The green squares represent glucose.
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Use Figure above
A Figure "i" will have a faster diffusion rate than Figure "ii" because the cooler temperature slows down the movement of glucose molecules
B Figure "ii" will have a faster diffusion rate than Figure "i" because the warmer temperature makes the molecules move around more and faster
C The rate of diffusion will be the same in Figure "i" and "ii" because temperature doesn't affect the movement of molecules
The experiments below show visking osmometers, which are used to measure osmosis. Visking tubes are partially permeable. The experiments have different solutions in each. They were left for a day. The water level at the start of the day is shown. Go t
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Experiment A. There was no change in the level of water in the visking tube or beaker after a 24 hour period, because the glucose concentrations inside and outside the visking tubing were the same.
True
False
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Experiment B. Water moved out of the visking tube into the beaker, so the water level in the beaker rose higher and the water level in the glass tubing went down.
True
False
One last concept to learn about diffusion and osmosis. There are three types of solutions cells can be placed in 1) isotonic, 2) hypertonic, and 3) hypotonic and cells react differently in each.
Watch the video on Tonicity to see how the solutions affect cells.
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You become so dehydrated on a hot summer day that you go into shock and are taken to an emergency room at a hospital. They start you on an IV of saline solution to get you rehydrated. Why can't they give you an IV with just water in it?
A Plain water is isotonic with your blood, so it would cause your blood cells to swell and burst.
B Plan water is hypertonic compared to your blood, so it would cause your blood cells to shrink and shrivel up and die.
C Plain water is hypotonic compared to your blood, so it would cause your blood cells to swell and burst.
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