osmosis

Document Sample

```					Northeastern Illinois University
ELED 415
Martin Enciso Jaimes

Diffusion and Osmosis

Topic: The Cell and its Environment

Concepts/Skills Focus:
As a result of this activity students will:
a. Know how to define diffusion
b. Know how to define osmosis
c. Know how osmosis is related to diffusion
d. Know how to calculate the concentration of water in liquid (percent)

Objective:
Students will demonstrate diffusion through a selectively permeable membrane.
Students will calculate the percentage of water in each of the example liquids
given in the table and write their and write the answers in the column.

Illinois State Learning Standards:

Science:
SG 11
Understand the processes of scientific inquiry and technological design to
investigate questions, conduct experiments and solve problems.

SG 12 A
Know and apply concepts that explain how living things function, adapt and
change.

SG 12 B
Know and apply concepts that describe how living things interact with each other
and with their environment.

Math:

SG 6 A
Demonstrate knowledge and use of numbers and their representations in a broad
range of theoretical and practical settings.

1
SG 6B
Investigate, represent and solve problems using number facts, operations
(addition, subtraction, multiplication, division) and their properties, algorithms
and relationships.
SG 6 C
Compute and estimate using mental mathematics, paper-and-pencil methods,
Calculators and computers.

SG 7 A
Measure and compare quantities using appropriate units, instruments and
methods.

Science and Math Processing Skills:

Science Processes                             Math Skills
a. Classifying                                a. Computation
b. Interpreting data                          b. Reading a table
c. Predicting and Inferring                   c. Percentages
d. Applying and generalizing

Time: One class period

Safety Considerations:
a. Iodine is a poison and should not be ingested.
b. Use plastic gloves when handling iodine.
c. Throw out all parts of diffusion experiment in school waste container.
d. Dispose of gloves in garbage after diffusion experiment and wash hands.

Set: Introduce students to the idea of the cell membrane as a gatekeeper by helping them
recall how a strainer or Foley Food Mill works. Ask: Why might you use a strainer or
Foley Food Mill? What do all these things have in common? Tell students that the cell
membrane acts like a filter, too, by allowing some substances, but not others to pass in
and out of the cell.

Materials:

Student worksheets
Water
Cornstarch
Iodine
Resealable bags
Plastic cups
Plastic gloves
Spoons

2
Procedure:

1.  Set
2.  Introduce hands-on diffusion activity
3.  Place students into groups of two
4.  Hand out materials
5.  Have students read over hands-on activity
6.  Do hands-on activity with students
7.  Have students put on latex gloves
8.  Have students carefully measure 100ml of water into two plastic cups (1 and
2).
9. Have students stir a tablespoon of cornstarch into one of the plastic cups (#1).
Make sure that it is stirred well.
10. Add ½ teaspoon of iodine to the second glass of water (#2). Stir the water and
iodine mixture well.
11. Carefully pour the cornstarch and water mixture from cup #1 into the
resealable bag and close it. Make sure that none of the mixture is on the
outside of the bag.
12. Place the bag carefully into the plastic cup with the iodine and water mixture
(#2). Make sure that the cornstarch mixture is below the level of the iodine
mixture in the cup.
13. Wait five minutes
14. During the five-minute wait, have the students take out the osmosis
worksheet.
15. Explain the osmosis worksheet and have the students complete it.
16. After the worksheet is complete, have the students take the bag out of the
iodine and water mixture and observe it.
17. Ask the students, "Why did the water in the bag turn purple?" (Iodine
molecules passed through the plastic into the bag and interacted with the
starch.)
18. Ask the students, "Why didn’t the iodine and water mixture in the cup turn
purple?" (The starch molecules were too big to pass through the bag).
19. This is a demonstration of diffusion through a selectively permeable
membrane.
20. Have students draw a diagram to show what happens if the concentration
outside a cell is lower than the concentration inside.

Assessment:

Students will be assessed on their verbal responses to the questions after the
hands-on activity. Students will also be assessed on their drawing of a diagram to show
what happens if the concentration outside a cell is lower than the concentration inside.
Students will also be assessed on the accuracy of their percentage calculations on the
osmosis chart.

3
Closure:

There will be a classroom discussion about what diffusion and osmosis are.
Students will discuss in groups and then share with the class answers to the questions,
what would happen if the concentration of the molecules outside the cell was lower than
the concentration inside? And, what would happen if the concentration of the molecules
outside the cell was higher than the concentration inside? Students, on the board to
visualize what happens, will draw examples.

Diffusion-Molecules in Motion
The main method by which small molecules move into and out of cells is diffusion.
Diffusion is the process by which molecules tend to move from an area of higher
concentration to an area of lower concentration.
This is a demonstration of diffusion through a selectively permeable membrane.

Procedure:

1. Work with a partner.

2. Each student should put on latex gloves.

3. With your partner, carefully measure 100ml of water into two plastic cups
labeled #1 and #2.

4. Stir a tablespoon of cornstarch into plastic cup #1. Make sure that it is stirred
well.

5. Add ½ teaspoon of iodine to the second glass of water (#2). Stir the water and
iodine mixture well.

6. Carefully pour the cornstarch and water mixture from cup #1 into the
resealable bag and close it. Make sure that none of the mixture is on the
outside of the bag.

7. Place the bag carefully into the plastic cup with the iodine and water mixture
(#2). Make sure that the cornstarch mixture is below the level of the iodine
mixture in the cup.

8. Wait five minutes

9. During the five-minute wait, take out the osmosis worksheet and complete it.

4
10. After the worksheet is complete, take the bag out of the iodine and water
mixture and observe it. What do you
observe?_______________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
11. "Why did the water in the bag turn purple?"
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
_______________________________________________________________
12. "Why didn’t the iodine and water mixture in the cup turn purple?"
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
______________________________________________________

13. Draw a diagram below to show what happens if the concentration outside a cell is
lower than the concentration inside.

Resources:

Ireland, Patrick. Cell-ebration Osmosis. 22 Aug 2000
<http://www.usd.edu/~bgoodman/Osmos.htm
Diffusion and Osmosis. Science4me.com.
<http://www.science4me.com/articles/documents/aa08_diffusion_an…>.

5

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 27 posted: 11/10/2011 language: English pages: 5