ParameciumHomeostasisSE

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Howard Community College *

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101

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Biology

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Jan 9, 2024

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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 B. Which image shows RBCs in pure water? C C. Which image shows RBCs in a very salty solution? A 2. What do you think is happening in images A and C? In image A, the red blood cells are hypertonic and in Image C the red blood cells are hypotonic. This is due to the flow of water in and out of the cells. 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. 1. Through which two structures do you think food enters the paramecium? I think food enters the paramecium through the oral groove and cell mouth 2. Which two structures contain DNA? Micronucleus and macronueclous contain DNA. 3. Which tiny structures help the paramecium to move around? Cillia aids in the movement of the parmecium 4. Which structure pumps out excess water and wastes? the Contractile vacuole pumps out excess water and waste. Reproduction for educational use only. Public sharing or posting prohibited. © 2020 ExploreLearning™ All rights reserved

Activity A: Maintaining a water balance Get the Gizmo ready : ● Select the User controlled setting. ● Check that the Water solute concentration is 1.00%. Introduction: Every organism needs to maintain stable internal conditions—a process known as homeostasis —in order to survive. A paramecium maintains homeostasis by responding to variations in the concentration of salt in the water in which it lives. (The concentration of a solution is equal to the amount of solute that is dissolved in a given amount of solvent .) Question: How do changing solute concentrations affect a paramecium? 1. Predict : In the Paramecium Homeostasis Gizmo, the solute is salt and the solvent is water. A. Look at the top left of the Gizmo. What is the water solute concentration? 1.00% A solute concentration of 1.00% means that for every 1 gram of water there is 0.01 grams of solute (salt). B. What is the concentration of solutes inside the paramecium? 1.80% The water solution outside the paramecium is said to be hypotonic because it has a lower solute concentration than the solution inside the paramecium. C. Based on the internal and external solute concentrations, do you think the paramecium will swell up or shrink in this solution? Explain your reasoning. Based on the solute concentrations, both in and outside the cell, I think that the paramecium will swell up in this solution. Hypotonic solutions cause swelling as there is greater amounts of water entering the cell. 2. Observe : Click Play ( ), and observe the size of the paramecium. A. What do you notice? The paramecium increases in size B. What happens after about 16 seconds? The paramecium bursts at 16 seconds 3. Observe : Click Reset ( ). Set the Water solute concentration to 2.00%. (This is a hypertonic solution because it has a higher solute concentration than the solution inside the paramecium.) Click Play . What happens to the volume of the paramecium now? The volume of the paramecium when the water solute concentration is at 2.00% decreases .

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? water flows into the paramecium B. If the solute concentration in the water is high (hypertonic solution), does water move into or out of the paramecium? water flows out the paramecium 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? When the vacoule contracts, the volume of the paramecium decreases. B. Click Play , and then click Contract many times rapidly. What happens? The paramecium dies of dehydration. 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? 24 contractions per minute were required for the paramecium to remain stable. 7. Summarize : How does the contractile vacuole help the paramecium survive in a freshwater environment? In a hypertonic solution, the contractile vacoule removes excess water to prevent the paramecium from swelling or bursting. 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?

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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. An increase in vacoule contractions will decrease the water solute concentration. 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% 0 1.50% 3 1.00% 8 0.50% 13 0.00% 18 3. Analyze : What pattern do you see in your data? How does this compare to your hypothesis? As the water solute decreased, the contractions increased. This supported my thesis. 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: 10 Actual contractions: 11 5. Think and discuss : Paramecia that live in freshwater have contractile vacuoles, while those that live in salt water do not. Why do you think this is the case? Contractile vacoules remove excess water to prevent bursting of the cells. This is ideal for paramecia that live in freshwater as they are exposed to a hypotonic environment where water flows into the cell. On the other hand, salt-water parameica do not need these contractile vacoules as they are in hyertonic envornments, were they are pushing water out of their cells.

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