Accelerated Biology Name: Diffusion and Osmosis Lab …mrswhittsweb.pbworks.com/f/diffusion+osmosis+lab.pdf · Diffusion and Osmosis Lab period: _ Date: _ Movement of molecules:

Accelerated Biology Name: __________________________

Diffusion and Osmosis Lab period: _____ Date: ______________

Movement of molecules: exploring diffusion and osmosis

Work with a partner to complete the bench work. Complete your own lab written work.

Fill in the information and data as you work through the lab.

At the end, for homework, you will be asked to analyze your data (including drawing a graph), write a conclusion and answer questions.

Turn this lab sheet with attached homework in on Nov. 18. Activity 1: Rate of Diffusion Elements and molecules, like students, cannot sit still! They are always moving, bouncing into one another, and filling the space they are put into. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration until they are evenly distributed throughout the space. In this part of the lab, you will observe the diffusion of molecules as they evenly distribute themselves (diffuse) throughout water in a container. Experiment Question: How do you think temperature will affect the rate of diffusion? Discuss your ideas with your lab partner. (hint: remember the idea of heat as a source of energy) Based on your discussion write a hypothesis that predicts how you think temperature will affect the rate of diffusion: Hypothesis: If ________________________________________________________________, then __________________________________________________________________ because ________________________________________________________________. Procedure Part A

1. Place 100 ml of water in a beaker on a piece of white paper on your lab table. Record the temperature of the water in the table on the Student Data Sheet. Leave the water undisturbed for 3 minutes to allow it to become completely still (don’t bump your table).

2. Place one drop of food coloring into the still water and start timing. 3. Record the start time in the data table. 4. Allow the food coloring to diffuse through the water until it is uniformly distributed in the

beaker. Record the time (in minutes) it takes for the food coloring to become evenly distributed.

Part B

1. Rinse out your beaker from Part A and fill it with the same amount of water as before. This time use very hot water.

2. Repeat steps 1-4 from Part A above and record your results. 3. Repeat with very cold water and record your results. 4. Analyze your results. Compare the three trials, calculate the rate of diffusion, graph your

results, answer the questions and write a conclusion.



Student Data Sheet Table 1. Rate of Diffusion Observations

Temperature (°C)

Start Time

End Time

Total Time for Diffusion

(min.)

Rate of diffusion (volume/time) mL/minute

Room temp

Hot water

Cold water

Draw a line graph of your results (be sure to LABEL your x and y axis) Graph all three results on the same graph, using different colors or line styles to indicate room temperature, cold and hot (be sure to label the lines or draw a key):



Analysis and Conclusion Use your results to help answer the following questions (you may need to do additional research on your own).

1. Describe the process of diffusion in your own words.

2. Where does the energy needed for the movement of molecules in diffusion come from?

3. Why is the rate of diffusion affected by changing water temperature?

4. What does it mean to say something diffuses to “equilibrium”? Based on your results and analysis, write a brief conclusion about how your results supported (or did not support) your hypothesis. Conclusion based on results: Challenge Question (optional extra points) Assume you have three beakers of equal volumes of water, saltwater and vegetable oil. All three liquids are at the same temperature. You drop a drop of food coloring into each beaker and record the time it takes for the food coloring to equally diffuse throughout the liquid. Predict how you think diffusion would be different in each of the three liquids AND explain why.



Activity 2: cells, osmosis and diffusion You have learned that diffusion and osmosis can occur across a cell membrane. Whether diffusion or osmosis (or both) occurs is based on the physics and chemistry of the membrane and molecules in solution. You have also learned that tonicity refers to the comparison of concentrations of two fluids separated by a membrane. If cells are in an isotonic solution, the solution has the same concentration as inside the cell. This is the optimum condition for animal cells to maintain homeostasis. A hypertonic solution has a higher solute concentration in the solution compared to inside the cell. In a hypertonic solution, a cell looses water to the solution (plasmolysis). A hypotonic solution has a lower solute concentration in the solution (outside the cell) than in the cell. Water will flow into the cell in this case to try to reach equilibrium. The cell will swell and may burst in a hypotonic solution (cytolysis). (an easy way to remember is “a hyper puppy rushes into” whatever you are discussing. For a hypertonic solution, water rushes into the solution. Get it?) Think about what kind of molecules might be found in carrot cells as you predict the results of this next experiment. Experimental Question: How will carrot cells respond in solutions of water, sugar and salt? Will the different solutions be iso-, hyper or hypotonic for the carrot cells?

Hypothesis:_____________________________________________________________________

Materials: Carrot sections, various solutions: tap water, salt, sugar Procedures:

1. Obtain 3 carrot slices and 3 small cups.

2. Measure the width of the slices and their mass (record this information in the Student Data

Table 2.

3. Place one carrot section in a cup and cover it with tap water. (be sure to label your cups)

4. Repeat with the remaining carrots and the NaCl and Sugar solutions.

5. In your data table record any changes in width and mass of the slices at 15 min., 30 min., 45

min, and at 24 hours.

6. Graph the results using a line graph with all solutions on the same graph using different

colored lines for each different solution.



Student Data Sheet – Activity 2

Table 2 width (mm) and mass (g) change in carrot slices

width (mm) of slices mass (g) of slices

Time

(min) tap water

NaCl

solution

sugar

solution tap water

NaCl

solution

sugar

solution

0 (initial)

15

30

45

24 hrs

Total

width/mass

difference



Analysis:

1. Which carrot slice gained mass? Explain what happened using the ideas of diffusion, osmosis and tonicity.

2. Which carrot slice lost mass? Explain what happened using the ideas of diffusion, osmosis and tonicity.

3. Which carrot slice did not change mass? Explain what happened using the ideas of diffusion, osmosis and tonicity.

4. Based on the results of your experiment, describe what you believe this demonstrates about the internal contents/make up of carrot cells. (what kind of molecules do you think make up most of the internal contents of carrot cells?)

Conclusion: (write your conclusion based on your hypothesis and be sure to include a discussion of tonicity.



Activity 3: Tonicity Based on your knowledge of tonicity and osmosis, you will remember that water tends to move through a membrane in the direction of higher solute concentration. You will use that knowledge to observe how animal cells respond to changes in solution concentrations of NaCl. Animal Cells

1. Using the flat side of a toothpick, gently scrape the inside of your cheek (in your mouth) to

dislodge epithelial cells. These cells easily sluff off, protecting your mouth as you chew.

2. Wipe the toothpick onto a clean microscope slide and let it dry for a moment. Drop a small

drop of methylene blue onto the sample and cover with a cover slip. (throw your toothpick in

the garbage!)

3. Using a small corner of a piece of paper towel, place it on the slide near the cover slip and let

it “soak up” any excess methylene blue.

4. With another cheek cell sample place a drop of 10% saltwater onto the cell sample and

5. drop a cover slip on the cells.

6. Wait 5 minutes and make a detailed drawing of your results.

Fresh Water = ________________ solution (isotonic, hypertonic, hypotonic) 10% saltwater = _______________ solution (isotonic, hypertonic, hypotonic) Cheek cells in fresh water Cheek cells in 10% salt solution Total magnification: _______ Total magnification: _______

Documents

Accelerated Biology Name: Diffusion and Osmosis Lab …mrswhittsweb.pbworks.com/f/diffusion+osmosis+lab.pdf · Diffusion and Osmosis Lab period: _____ Date: _____ Movement of molecules:

Accelerated Biology Name: Diffusion and Osmosis Lab …mrswhittsweb.pbworks.com/f/diffusion+osmosis+lab.pdf · Diffusion and Osmosis Lab period: _ Date: _ Movement of molecules: