Title: Osmolarity in Plant Cells

Author: Colecia Hollie

Grade Level: 9-12

Concepts: Students will better understand the concept of osmolarity. Students will make predictions, draw tables, and graphs. Students will also be able to analyze the concepts of osmosis and relate them to the world in which they live.

Objective:  The student will be able to

1.)    investigate the behavior of osmosis in plant cells

2.)     Have a better understanding of what osmosis is.

3.)    Gather and organize data

4.)    Graph results of experiment.

TEKS:

5.1 Scientific processes. The student uses scientific methods during field and laboratory investigations. The student is expected to:

(B) collect information by observing and measuring;

(C) analyze and interpret information to construct reasonable explanations from direct and indirect evidence;

(D) communicate valid conclusions; and

(E) construct simple graphs, tables, maps, and charts using tools

5.4    Scientific processes. The student knows how to use a variety of tools and methods to conduct scientific inquiry. The student is expected to:

(B) demonstrate that repeated investigations may increase the reliability of the results.

5.3 Scientific concepts. The student knows that a system is a collection of cycles, structures, and processes that interact. The student is expected to:

(A)  describe some cycles, structures and processes that are found in a simple system; and

(B)   describe some interactions that occur in a simple system.

Materials List and Advanced Preparations:

For each group of students

Raw pumpkin

(solid) Sodium Chloride

8 200ml  beakers

test tubes and racks

graduated cylinders and volumetric flask of various sizes for making solutions

pipets and pipet pumps

deionized or distilled water

sharp knives (pairing or larger)

6’’ rulers

Cork borers in various sizes

Balances and weighing paper

Spatula

Tape and/or marking pens for labeling beakers

Paper towels or Kimwipes

Plastic wrap for sealing cut surfaces between labs

Forceps for fishing the samples out of the beakers

Osmometer and its supplies

Watch to record time

Engagement:

Does anyone in here like going to the playground?  What are some of the things that you do when you go to the playground?  Anyone like swinging?  I would like for each of you to close your eyes and imagine that you were at the playgrounds.  As you enter through the gates you see all of the things that you could be doing.  You run to the tire swing.  There are two other people who are waiting to get on the tire swing along with you.

Open your eyes, think about how the three of you would have to position yourselves on the swing in order for it to function correctly.  (Children Answer)  Why can’t all three of you sit on the same side of the tire swing?  (Weight would cause it to tip over or not function correctly.)  Who remembers what a variable is from the last lesson?  What would the variable be in this situation with the swing?

Day 1: Lecture on Osmosis approximately 35 minutes

After lecture, divide students into groups, and allow them to retrieve their materials for the experiment for the next day to expedite the experiment procedure for the following day.

Step by Step Protocol

Hint * the osmolarity of the pumpkin is less than 2%.

Solutions List:    100 mL of Deionized water (obtained from lab deionized lab faucet)

                        0.25 M Saline Solution (instructions on how to make listed below)

                           0.30 M Saline Solution (instructions on how to make listed below)

                           0.35 M Saline Solution (instruction on how to make listed below)

Instructions: For 0.25 M solution:

1.)    Put 1.4625 g of NaCl in a 200 mL beaker.

2.)    Add about 75 mL of tap water. Stir until NaCl dissolves.

3.)    Add water to make the final volume of the solution to 100 mL.

Instructions: For 0.30 M solution:

1.)     Put 1.755 g of NaCl in a 200 mL beaker.

2.)    Add about 75 mL of tap water. Stir until NaCl dissolves.

3.)    Add water to make the final volume of the solution to 100 mL.

Instructions: For 0.35 M solution:

1.)     Put 2.0475 g of NaCl in a 200 ml beaker.

2.)    Add about 75 ml of tap water. Stir until NaCl dissolves.

3.)    Add water to make the final volume of the solution to 100 ml.

Steps:  1.) Make and obtain solutions listed above and label each beaker with respective concentrations.

2.) Place each beaker into osmometer and record each osmolarity reading. This is done to make sure that the actual osmolarity readings are close to calculated osmolarities.

3.) Cut out and weigh eight pumpkin pieces to each weigh 20 grams. They should be cut in square shapes with the same dimensions and size. Record initial weights.

4.) Place two pieces in each beaker at the same time.

5.) Let pumpkin pieces stay in solution for 50 minutes.

6.) After time has expired, remove pumpkin pieces and weigh them on the scale.

7.) Record final weight readings and calculate change in mass (final mass – initial mass). Calculate average change in mass for both pieces placed in the same solution.

8.) Calculate % change in mass [(final-initial mass) / (initial)] x 100

9.) Take each solution to the osmometer and now record final osmolarity readings. Compare these to previous readings.

10.) Graph results obtained in Microsoft Excel.

*Note: Sample size if with four different beakers with eight pumpkin pieces. Two pumpkin pieces will be placed in each beaker. The one with least weight change will be closest to the concentration of the solution. This is because if the sample has the least weight change (least %weight change), there is essentially no loss of water and thus is almost in equilibrium with the solution. This will help us determine the approximate internal osmolarity of the pumpkin cells.

Explanation:

What did we notice about our predictions?

Were your predictions correct?

Who can tell me a new word that we learned today.

What do the results of this experiment tell you about osmosis?

The results of our experiment are on the board, in math class, you will soon learn how to do line graphs; therefore, we will do this one together as practice.

Evaluation: Pretend that you are an engineer for a very prestigious company. Your job is to knock down an abandoned building with as less swings as possible. Write a description of our activity and explain your results.

Elaboration:  Today we talked about osmosis.  In one sentence, briefly describe what osmosis is. For homework, collect all of your data, and then determine how you would like to represent your data (i.e. chart, diagram, graph, etc.) bring in a copy of this analysis to class and be prepared to discuss with class mates why you chose this method.

Safety: Be sure any broken glassware is correctly disposed of.

Math Connection: The students will graph the results of the science investigation using a line graph. Osmolarity vs. Change in Mass.

Inquiry based (Discovery) Learning:

Student Diversity:  The lesson can be found to be interesting to all students regardless of their background.

Name(s):________________________________________________________________

Date__________________

Class  Period:_____

Data Collection Sheet for Osmolarity Experiment

** DON’T FORGET THAT THE OSMOLARITY IS IN mOsM!!!!