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Cellular Transport

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Getting stuff into and out of cells! What was diffusion again? ... at it another way: there's more stuff dissolved in the water outside the cell than inside it. ... – PowerPoint PPT presentation

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Title: 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?
2
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
7
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.

10
Title Diffusion of substances through a
semi-permeable membrane
11
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.
12
Question Can simple sugars (such as glucose)
and/or complex sugars (such as starch) cross the
membrane?
13
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
14
Materials Dialysis tubing String Dilute
iodine solution Benedicts solution Liquid
starch Corn syrup Water Glass
bowls Test tubes and rack Droppers
15
Hypothesis I think that . . . because . . .
16
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

19
DataStarch test
Summary of results
20
DataGlucose test
Summary of results
21
Conclusion
22
  • 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.

23
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.
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