OsmosisOsmosis

Today’s Lab:Today’s Lab:A. Two experiments:

1. Sucrose Osmosis

2. Osmosis in green algae

B. 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.

C. Due Monday, February 19, 2007

Sucrose Osmosis – Osmosis in a non-biological membranePurpose: to determine an unknown concentration of

sucrose

Hypothesis (two choices):

Sucrose Osmosis: Getting Starteda. 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

b. Each group will prepare 2 bags using: 2 - 6” pieces of dialysis tubing.

c. 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.

Sucrose Osmosis: Continuedd. 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.

e. Place both bags into your group’s assigned sucrose solution. Record the start time. Let stand for 1 hour.

f. 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.

g. Enter all values for both bags on the Excel spreadsheet as indicated.

Osmosis in Green Algae –Osmosis in a biological membranePurpose:

to determine if two intertidal algae are euryhaline for a large salinity gradient

Hypothesis:

Osmosis in Green Algaea. In same groups:

Group 1 – 0 ppt Group 2 – 15 ppt Group 3 – 35 ppt Group 4 – 44 ppt Group 5 – 65 ppt

b. 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.

c. 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.

Osmosis in Green Algae

d. Pour off the water in your sample dishes. Replace with your group’s 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.

- 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?

Salinity

- Movement of molecules or ions from a region of

high concentration to one of low concentration,

until they are evenly distributed.

e.g. an open bottle of perfume in a room.

Diffusion

Figure 4.12

Diffusion

Video

Diffusion across a biological membrane:

- Passive transport

Diffusion against a concentration gradient; from low concentration to high concentration:

- Active transport

Diffusion

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]

Osmosis

Osmosis

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]

Why is osmosis important for life in the ocean?

Osmosis

Video

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)

Osmosis Terms:

Hyp

oosm

otic

Hyperosmotic

Hypoosmotic

Hyperosmotic

Isoosmotic

Osmosis

Figure 4.13

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)

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

Osmoregulators

Figure 4.14

Writing A Scientific Paper Title:

Used to get readers attention – concise and focused

Intro:Sets the stage for the study, and hooks readerOrients the reader – go from general to specificExplains the importance of the study – purpose and

hypotheses

Methods:Includes info so that study can be repeatedWhat measurements were made and why

Writing A Scientific Paper Results:

Summarize and illustrate your findingsDo not interpret data, just reportNumber Figures and Legends

Discussion:Interpret your resultsDon’t over explainConvey confidence and authority

Conclusion:What would you differently and why?

Sucrose Osmosis: Data presentationa. You will record the data in a table in Excel.

[Sucrose] Bag #

Initial Weight (t=0)

g

Final Weight

(t=1hr) g

Abs. Weight change

g% Weight change

0.2M 12

0.4M 12

0.6M 12

0.8M 12

1.0M 12

b. To calculate Absolute Weight change (g):

Final Weight (t=1hr) – Initial Weight (t=0)

c. To calculate % Weight Change:Absolute Weight Change x 100

Initial Weight

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.

y = -22.755x + 16.655

R2 = 0.9381

-10

-5

0

5

10

15

20

0.0 0.2 0.4 0.6 0.8 1.0 1.2

Sucrose Concentration (M)

% W

eig

ht

Ch

ang

e

Sucrose Osmosis: Unknown Solution concentratione. 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.

f. Set y=0 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.

Osmosis in Green Algae

Observations