Paramecium Homeostasis: Role of Contractile Vacuoles in Water Balance, Summaries of Medicine

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K. Export, M. Gordy,

Paramecium homeostasis

Name: Date:

Student Exploration: Paramecium Homeostasis

Vocabulary: adaptation, cell mouth, cilia, concentration, contractile vacuole, food vacuole, homeostasis, hypertonic, hypotonic, macronucleus, micronucleus, oral groove, osmosis, paramecium, solute, solution, solvent

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. The images show red blood cells (RBCs) in three different solutions. A. Which image shows RBCs in normal blood plasma? _ B. Which image shows RBCs in pure water? C. Which image shows RBCs in a very salty solution?
2. What do you think is happening in images A and C? Gizmo Warm-up A paramecium is a one-celled organism that lives in ponds and other bodies of water. One of the challenges for a paramecium is to maintain a stable size and shape. On the Paramecium Homeostasis Gizmo, turn on the Show labels checkbox. Try to determine the function of each of the labeled structures.
3. Through which two structures do you think food enters the paramecium?
4. Which two structures contain DNA?
5. Which tiny structures help the paramecium to move around?
6. Which structure pumps out excess water and wastes?

B

C

A

The oval grove and cell mouth The micronucleus and the macronucleus Cilia The contractile vacuole

Activity A (continued from previous page)

4. Infer: Water moves into and out of the paramecium by a process called osmosis. Osmosis is the movement of water across a membrane from a region of lower solute concentration to a region of higher solute concentration. A. If the solute concentration in the water is low (hypotonic solution), does water move into or out of the paramecium? B. If the solute concentration in the water is high (hypertonic solution), does water move into or out of the paramecium? C. In which situation is the paramecium in danger of swelling up and bursting?
5. Experiment: The contractile vacuole is a star-shaped structure that helps the paramecium to pump out excess water. This adaptation allows the paramecium to survive in hypotonic (low solute concentration) solutions. Click Reset , and set the Water solute concentration to 1.00%. Click Play. When the contractile vacuole fills up, click Contract. Do this for a while, and then click Pause ( ). A. How does contracting the vacuole affect the volume of the paramecium? _ B. Click Play , and then click Contract many times rapidly. What happens?
6. Experiment: Click Reset. This time, try to maintain a steady volume for the paramecium. Pause the simulation after about one minute and select the TABLE tab. How many contractions per minute were required for the paramecium to maintain a relatively stable internal solute concentration and stay the same size?
7. Summarize: How does the contractile vacuole help the paramecium survive in a freshwater environment? The water will move into the paramecium The water will move out of the paramecium. The paramecium is in danger of swelling up and bursting When the vacuole is contracted, the paramecium's volume decreases. The paramecium dies of dehydration. About 24 contractions are needed per minute. In a hypertonic solution, a paramecium can maintain its volume by preventing itself from shrinking by holding in as much water as it can.

Activity B: Contractions and concentrations Get the Gizmo ready:

• Click Reset.
• Select the Paramecium controlled setting on the DESCRIPTION tab. Question: How does a paramecium respond to changing solute concentrations?

1. Form a hypothesis: How do you think the number of contractile vacuole contractions will change when the water solute concentration is reduced? Explain why you think so.
2. Gather data: Set the Water solute concentration to 2.00%. Click Play. Pause after 30 seconds. On the TABLE tab, add the total number of contractions. Record the results in the table below. Click Reset , and repeat this procedure for all of the listed concentrations. Water solute concentration Contractions in 30 seconds 2.00% 1.50% 1.00% 0.50% 0.00%
3. Analyze: What pattern do you see in your data? How does this compare to your hypothesis?
4. Predict: How many contractions would you expect in 30 seconds if the water solute concentration was 0.75%? Test your prediction with the Gizmo. Predicted contractions: Actual contractions:
5. Think and discuss: Paramecia that live in fresh water have contractile vacuoles, while those that live in salt water do not. Why do you think this is the case? When the water solution concentration is reduced, the number of vacuole contractions will increase. But when the solute concentrations rise, the number of contractions will decrease. 0 3 8 13 18 As the water solute decreases, the number of contractions increases. This goes along with my hypothesis. (^10 ) I think this is the case because paramecia that live in salt water have a hypertonic environment, meaning that the cell has a need for water so the contractile vacuole can do its job and release more water into the the cell. While paramecia that live in freshwater live in a hypotonic environment, which calls for a contractile vacuole to pump out the excess water.