Osmosis

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Osmosis
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Todays Lab

• Two experiments
• 1. Sucrose Osmosis
• 2. Osmosis in green algae
• Based on these experiments, write a complete lab
  report. Include all sections of a scientific
  paper (i.e. title, introduction, methods,
  results, discussion, and conclusion). It will be
  4-5 pgs.
• Due Monday, February 19, 2007

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Sucrose Osmosis Osmosis in a non-biological
membrane
Purpose to determine an unknown concentration of
sucrose Hypothesis (two choices)
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Sucrose Osmosis Getting Started

• Form 4 groups with 4 people in each and 1 with 3
  people
• Group 1 0.2M sucrose Group 3 0.6M
  sucrose
• Group 2 0.4M sucrose Group 4 0.8M
  sucrose
• Group 5 1.0M sucrose
• Each group will prepare 2 bags using 2 - 6
  pieces of dialysis tubing.
• Soak each piece of tubing in DI water to soften
  it. Tie knot at one end of tube with string. Fill
  tubing with 30ml of UNKNOWN Sucrose solution.
  Tie other end of each bag with a string. Attach a
  paperclip to end of one bag. This is Bag 1. The
  other is Bag 2.

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Sucrose Osmosis Continued

• d. Pat dry each bag with paper towels. Weigh
  each bag separately. Turn on balance. Open side
  door and place a weighboat on the balance. Press
  the Tare button (indicated by a T). Once zero
  is displayed, open door and place Bag 1 on the
  weighboat. Close side door. Record starting mass
  (in grams), in your notebook for Bag 1, to two
  decimal places (ex. 23.36 g). Repeat for Bag 2.
• Place both bags into your groups assigned
  sucrose solution. Record the start time. Let
  stand for 1 hour.
• After 1 hour, remove both bags from the beaker.
  Pat dry with paper towels. Re-weigh each bag,
  remembering to tare the balance with the
  weighboat on it. Record the ending mass (in
  grams) in your notebook for each bag, to two
  decimal places.
• Enter all values for both bags on the Excel
  spreadsheet as indicated.

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Osmosis in Green Algae Osmosis in a biological
membrane
Purpose to determine if two intertidal algae
are euryhaline for a large salinity
gradient Hypothesis
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Osmosis in Green Algae

• In same groups
• Group 1 0 ppt Group 2 15 ppt
  Group 3 35 ppt
• Group 4 44 ppt Group 5 65 ppt
• Each group places 1 ball of Valonia sp.
  (bubble-shaped alga) and 2-3 strands of
  Cladophora sp. (hair-like alga), in individual
  petri- dishes. Fill petri-dish with saltwater
  from the 34 ppt beaker to cover algae.
• Using a dissecting microscope, make careful,
  initial observations of each algae under the
  average ocean salinity (i.e. 34 ppt). Describe
  characteristics, including color, shape, and
  size. Draw an illustration in your notebook of
  each sample. Do not leave algae samples under
  the microscope lights for more than 10 minutes at
  a time.

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Osmosis in Green Algae

• d. Pour off the water in your sample dishes.
  Replace with your groups assigned salinity.
  Record start time. Let stand for 1 hour. Do NOT
  leave the microscope light on.
• e. After 1 hour, using a dissecting
  microscope, make careful, final observations of
  each algae. Again describe characteristics, such
  as color, shape, and size. Draw an illustration
  in your notebook of each sample.
• f. Record your qualitative observations for
  your samples on the table on the board at the
  front of the room. Copy this table with all
  initial and final observations into your
  notebook.

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Salinity
- Water is a universal solvent. (i.e. dissolves
substances) Salinity - Total amount of salt
dissolved in seawater. Salinity refers to the
number of grams of inorganic salts (i.e. NaCl)
dissolved in one kilogram (1000 g) of water.
Unit g/kg parts per thousand (ppt)
What is the average salinity of the oceans?
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Diffusion
- Movement of molecules or ions from a region
of high concentration to one of low
concentration, until they are evenly distributed.

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Diffusion
Figure 4.12
Video
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Diffusion
Diffusion across a biological membrane -
Passive transport Diffusion against a
concentration gradient from low concentration to
high concentration - Active transport
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Osmosis
Definition Diffusion of WATER molecules across
semi-permeable membranes (e.g. cell membranes)
until water concentrations are equal on both
sides of the membrane. Movement is from a
higher H2O to lower H2O
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Osmosis
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Osmosis
Why is osmosis important for life in the ocean?
Osmosis is the physical process where WATER
passes through a semi-permeable membrane that
separates 2 fluids with different SALT
concentrations. WATER is moving from an area of
Higher water and lower salt lower
water and higher salt
Video
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Osmosis Terms
Hyperosmotic solution (hypertonic) a solution
with a greater solute concentration (i.e. more
salt ions) than another
Hypoosmotic solution (hypotonic) a solution
with a lesser solute concentration (i.e. fewer
salt ions) than another
Isoosmotic solutions (isotonic) solutions of
equal solute concentrations (i.e.
same number of salt ions)
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Osmosis
Figure 4.13
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Related Terms

Euryhaline Organism that is able to withstand
large changes in salinity - no change in cell
morphology (e.g. color, shape, or
size) Stenohaline Organism that is not able to
withstand changes in salinity - changes in cell
morphology (e.g. color, shape, or size)

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Related Terms

• Osmoregulators
• Organisms that can maintain a constant internal
  salinity despite external changes in salinity.
  e.g. fish
• Osmoconformers
• Organisms that change their internal salinity
  along with the external environment. e.g.
  invertebrates

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Osmoregulators
Figure 4.14
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Writing A Scientific Paper

• Title
• Used to get readers attention concise and
  focused
• Intro
• Sets the stage for the study, and hooks reader
• Orients the reader go from general to
  specific
• Explains the importance of the study purpose
  and
• hypotheses
• Methods
• Includes info so that study can be repeated
• What measurements were made and why

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Writing A Scientific Paper

• Results
• Summarize and illustrate your findings
• Do not interpret data, just report
• Number Figures and Legends
• Discussion
• Interpret your results
• Dont over explain
• Convey confidence and authority
• Conclusion
• What would you differently and why?

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Sucrose Osmosis Data presentation
a. You will record the data in a table in Excel.
b. To calculate Absolute Weight change (g)
Final Weight (t1hr) Initial Weight (t0) c.
To calculate Weight Change Absolute Weight
Change x 100 Initial Weight
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Sucrose Osmosis Data presentation
d. Follow the instructions on the handout to
construct a graph. You will use this graph to
determine the concentration of the Unknown
Solution. Include the graph in your report.
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Sucrose Osmosis Unknown Solution concentration

• To calculate the concentration of the Unknown
  Solution, use the equation generated from the
  trendline on the graph, in the example, y
  -22.755x 16.655.
• Set y0 and solve the equation for x. The result
  will be the concentration of the Unknown
  Solution. It will be a positive number between 0
  M and 1.0M.

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Osmosis in Green Algae

• Observations