Cellular Transport

1
Bellringer Have you seen those commercials for
Washington Mutual? Theyve got all these old
bankers stuck behind ropes. What do you think
the bankers would do if the ropes were removed?
Remember when we were studying water? Which
property of water would the bankers be mimicking?
Is it 1) Water is polar, 2) Water resists
temperature change, 3) Water expands when it
freezes, or 4) Water diffuses?
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Cellular Transport

• Getting stuff into and out of cells!

3
What was diffusion again?

• In science talk Diffusion is the net, random
  movement of particles from an area of higher
  concentration to an area of lower concentration.
• In everyday talk Things move away from where
  theyre crowded until everything is spaced out
  more or less evenly. When particles are spread
  out evenly, they are in dynamic equilibrium
  (still moving, but staying spread out).

4

• Water is important to life, so diffusion gets a
  special name when its water thats doing the
  diffusing. Osmosis is the diffusion of water.
• And where does the movement of water matter most
  to life? Across the cell membrane of course!

5
Recall the diffusion problems we solved last week
. . .
Semi-permeable membrane
Kool-aid
Water
If the Kool-aid and water can both cross the
semi-permeable membrane, which way do they each
move?
6
Water and cells
Cells are usually floating around in an aqueous
solution, so the concentration of water inside
the cell versus the concentration of water
outside the cell determines which way the water
moves.
Outside the cell 100 water
Cell 75 water
Water moves into the cell
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The cell can find itself in three different
environments
25 water
conc. of stuff outside conc. of stuff inside
The concentration of water inside the cell might
be greater than the concentration outside the
cell. (Looking at it another way theres more
stuff dissolved in the water outside the cell
than inside it.)
75 water
Hypertonic surroundings
conc. of stuff outside conc. of stuff inside
75 water
The concentration of water inside the cell might
be equal to the concentration outside the cell.
(Looking at it another way theres the same
amount of stuff dissolved in the water outside
the cell as inside it.)
75 water
Isotonic surroundings
conc. of stuff outside 100 water
The concentration of water inside the cell might
be less than the concentration outside the cell.
(Looking at it another way theres less stuff
dissolved in the water outside the cell than
inside it.)
75 water
Hypotonic surroundings
8
What happens to cells in these different
environments?

• Turn to page 197 in your textbook and look at the
  pictures of blood cells and plant cells in
  hyper-, iso-, and hypotonic solutions. Were
  going to add these sketches to your notes, with a
  description in words under each picture
  explaining which way the water moves and what
  happens to the cell as a result. Well do the
  first one together. Your homework is to finish
  adding these sketches to your notes. I will
  check that your drawings and descriptions are
  completed at the beginning of next class.

9
And now for the lab . . .

• Your lab report should include the following
  headings
• Title
• Purpose
• Question
• Background
• Materials
• Hypothesis
• Procedure
• Data
• Conclusion
• Analysis questions
• Lets go through them one-by-one.

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Title Diffusion of substances through a
semi-permeable membrane
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Purpose The purpose of this lab is to revisit
and refine our skill of testing for
carbohydrates. We will also be increasing our
understanding of the structure and function of
the cell membrane. We will explore the
importance of diffusion to cells.
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Question Can simple sugars (such as glucose)
and/or complex sugars (such as starch) cross the
membrane?
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Background Cells need certain substances to
work. Glucose is used by some cells as a source
of ______ . The structure of glucose is as
followsStarch is made by some cells to store
______ . The structure of starch is as follows
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Materials Dialysis tubing String Dilute
iodine solution Benedicts solution Liquid
starch Corn syrup Water Glass
bowls Test tubes and rack Droppers
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Hypothesis I think that . . . because . . .
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Procedure Dialysis tubing was already partially
filled with starch and corn syrup, and the ends
were tied with string. In order to test whether
the starch and/or glucose crossed the membrane,
we must test the surrounding water for the
presence of there carbohydrates.
17
Test for starch

• Use a dropper to remove some of the water
  surrounding the starch tube
• Put of few drops of this water in a test tube
• Add a couple drops of dilute iodine
• Record in your data table whether there was a
  color change

18
Test for glucose

• Use a dropper to remove some of the water
  surrounding the corn syrup tube
• Put of few drops of this water in a test tube
• Add a couple drops of Benedicts solution
• Heat the test tube in a hot water bath for 1
  minute
• Record in your data table whether there was a
  color change

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DataStarch test
Summary of results
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DataGlucose test
Summary of results
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Conclusion
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• Analysis questions
• Did starch pass through the dialysis tubing (our
  model for a cell membrane)? Give evidence to
  support your answer.
• Did glucose (corn syrup) pass through the
  dialysis tubing? Give evidence to support your
  answer.
• Do cell membranes permit all, none, or some
  substances to pass through? Give evidence to
  support your answer.
• When the starch tubes are first put in the water,
  where is the concentration of starch molecules
  higher, inside or outside the dialysis membrane?
  From the point of view of the starch tube, is it
  in a hyper-, iso-, or hypotonic solution?
• When the glucose tubes are first put in the
  water, where is the concentration of glucose
  higher, inside or outside the dialysis membrane?
  From the point of view of the glucose tube, is it
  in a hyper-, iso-, or hypotonic solution?
• Did the starch and sugar molecules move from an
  area of higher to lower concentration, or from
  lower to higher concentration? Give evidence to
  support your answer.
• Does this experiment illustrate diffusion? Give
  evidence to support your answer.
• In an experiment similar to the one you just
  performed, a student put a mixture of IKI and
  water inside the dialysis membrane. She then
  placed the membrane in a beaker containing a
  mixture of starch and water. After 10 minutes the
  starch mixture turned blue/black. Explain what
  might have happened.
• Starch molecules are large complex carbohydrates.
  Simple sugars like glucose are small carbohydrate
  molecules. What do you think may be one of the
  factors that determines whether molecules can
  pass through a cell membrane? Give evidence to
  support your idea.

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Exit slip
If I only filled each of the dialysis tubes
half-full of starch or glucose, why the tubes
were bloated (completely filled with liquid) by
the end of the period? Write your thoughts on
the slip of paper provided. Make sure your name
is on it as well.