Paramecium Homeostasis Gizmos Paramecium Homeostasis Student Version CBD by 7akgJz52


									Name: ____________________________________________ Date ______________ Period: ______

                                              Paramecium Homeostasis
                                          Gizmos at:
                          In order to survive, all living things must be able to react to changes in their environment. For
                          example, humans react to hot weather by sweating and to cold weather by shivering.
                          Homeostasis is the process of maintaining internal stability in response to external changes.

                        For single-celled protists like the paramecium, one of the most significant challenges is to adapt
                        to the concentration of solutes such as salt, calcium, and phosphorus in the water
around them. When the concentration of solutes in the water is greater than that within the cell, water will move out
of the cell by osmosis, causing the paramecium to dehydrate.

An even greater problem occurs when the concentration of solutes in the water is lower than that within the cell. In this
case, water will move into the cell by osmosis, causing it to swell up and even burst! The paramecium has evolved a
unique mechanism to deal with this problem --the contractile vacuole.

Observing Paramecium Behavior

In this activity, you will observe how a paramecium responds to a variety of water solute concentrations.

1. Observe the paramecium in the SIMULATION pane of the Gizmotm. On the DESCRIPTION pane, check the Show
labels checkbox.

1. What is the name for the tiny, hair-like structures that allow the paramecium to move? ___________

2. Where do you think the food enters the paramecium? _________________________________

          Where is the food stored after it is eaten? _______________________________

3. In what two structures is the DNA found in the paramecium? ___________________________________________

4. The purpose of the contractile vacuole is to expel excess water from the cell, preventing the        cell from swelling
up. Locate this structure and sketch it here:

                                                                          (Note: A paramecium has two
                                                                          contractile vacuoles, but for
                                                                          simplicity only one is shown here.)

    2. With the Water solute concentration set to 1.00%, click Play (       ). Observe the paramecium and the
    Paramecium solute concentration for 1 minute.

1. Describe what you see. How does the contractile vacuole change before and during a contraction?

    2. Select the TABLE tab. The number of contractions is recorded for each ten-second interval. How
       many total contractions occur in one minute? _____________

3. Select the GRAPH tab. What do you notice about the paramecium solute concentration?
How does this relate to the definition of homeostasis? _________________________________________

    4. Based on the behavior of the paramecium, what do you think is the ideal solute concentration in the paramecium?

3. Click Reset (      ), and select the DESCRIPTION tab. Set the Water solute concentration to 1.60%. (To quickly set
a slider to a certain value, type the number to the right of the slider and click Enter.)

1. The concentration of solute is higher in the paramecium (1.80%) than in the water (1.60%). Which direction will water
tend to move, into or out of the paramecium? ___________________ (Remember that water moves in an attempt to
equalize solute concentrations.) Will this movement of water tend to make the paramecium expand or shrink?

2. In this example of homeostasis, the paramecium tries to maintain its size. Will it be advantageous for the paramecium
to expel water to do this? _____________ Based on this, predict whether or not you expect to see the contractile
vacuole contracting after you start the simulation. Explain your thinking.

3. Click Play, and then select the TABLE tab. After 60 seconds, click Pause (   ). Was your prediction correct?
_____________ If not, how were the results different?

4. Observe the GRAPH. You should notice that the solute concentration
 in the paramecium goes down for about ten seconds, and then quickly
jumps back up. When its solute concentration jumps quickly like that,
what must be happening to the volume of water inside the paramecium?
    What do you think the contractile vacuole had to do with this?
5. In general, what does a contraction look like on the graph?
6. Did the paramecium's contractile vacuole contract more often in the second experiment (water solute
concentration = 1.60%) or in the first experiment (water solute concentration = 1.00%)?

4. Experiment with a variety of other water solute concentrations. For each experiment, record the water solute
concentration and the number of contractions in one minute on Table 4. If you run more than five experiments, create
an additional table at the end of this worksheet.

                                                           Table 4

          Experiment                 Water Solute Concentration            Contractions per minute
1. Graph your data from Table 4 on Grid 4.1. (Be sure to label the X – independent variable and Y axis – dependent
variable) What is the relationship between the water solute concentration and the number
of paramecium contractions?
Claim: ____________________________________________________________________________________________

                                                     Grid 4.1

    2. Is this relationship linear? (In other words, do the data points form a straight line?) ___________

    3. When is the number of contractions greatest? _________________________________________

        When is it least? __________________________________________________

    4. Did you ever observe zero contractions? ____________ Explain why or why not. ___________

Controlling Paramecium Behavior
By selecting the User controlled option, you can control the contractile vacuole. Can you keep the paramecium
1. On the DESCRIPTION pane select User controlled. Set the Water solute concentration to 1.00%
  and click Play. After 10 seconds, click Pause.
        1. What happens to the concentration of solutes within the paramecium? ___________________
           Why do you think this is? _______________________________________________________

        2. What happens to the size of the paramecium? ___________________________
           What do you think might happen if this trend continues? ______________________________

        3. To test your hypothesis, click Play and wait a few more seconds. What happened to the
           paramecium? __________________________________________

        4. What is the importance of the contractile vacuole and homeostasis?
2. Click Reset, and set the Water solute concentration to 2.00%.
 1. What do you think will happen to the volume of the paramecium in this case? Write down your hypothesis.
 2. Click Play. What do you observe? Explain this finding. __________________________________

3. Click Reset, choose a new solute concentration, and click Play. To pump water
    out of the paramecium, click the Contract button.
 1. What happens to the paramecium if the contractile vacuole doesn't contract
    enough? __________________________
 2. What happens if there are too many contractions? ________________________
 3. How would decreasing the water solute concentration affect the number of contractions
needed for survival? _____________________________________________________________________________
Check your answer using the Gizmo.
 4. How would increasing the water solute concentration affect the number of needed contractions?
Check your answer using the Gizmo.
5. What water solute concentration levels require the paramecium to make no contractions at all?
Explain why this is so in a scientific format (Claim, Evidence, Reasoning).

Write a conclusion for this activity. How does a paramecium respond to changes in water
solute concentration? Use the term "homeostasis" in your explanation. Be sure you write your answer in complete
sentences in a scientific format using claim, evidence, & reasoning.

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