Student Exploration: Osmosis
Vocabulary: cell membrane, concentration, diffusion, dynamic equilibrium, osmosis, semipermeable membrane, solute, solvent
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
1. Suppose you were trapped on a desert island with no sources of fresh water. Should you drink water from the ocean? Explain why or why not.
2. What do you think would happen if you watered your houseplants with salt water?
A cell membrane is a thin “skin” that surrounds a cell. It is a semipermeable membrane, which means that some particles pass through the membrane easily while others cannot.
The Osmosis Gizmo™ portrays a cell (red square) in a solution of purple solute particles dissolved in green solvent particles. Press Play ([pic]) and observe.
1. Which particles can pass through the cell membrane?
2. Which particles cannot pass through the cell membrane? ___________________________
3. Click Reset ([pic]), and then click Play again. What do you notice about the size of the cell?
|Activity A: |Get the Gizmo ready: |[pic] | | |Click Reset. Set the Initial cell volume to 40%. | | |Observing osmosis |You will need a calculator for this activity. | |
Question: How do solute concentrations affect the volume of a cell?
1. Observe: Use the Solute outside slider to change the concentration of solute particles outside the cell. Click Play. In each case, focus on whether the cell gets bigger or smaller.
A. In what situation does the cell get larger? __________________________________
B. In what situation does the cell get smaller? _________________________________
2. Calculate: The concentration of a solute is the amount of solute particles in a given amount of solvent. To calculate percentage concentration, divide the number of solute particles by the total number of particles (solute + solvent), and then multiply by 100:
% concentration = (solute ÷ total particles) × 100
Select the DESCRIPTION tab. Click Reset. Set the Solute outside to 10 and check that the Initial cell volume is 40%. (Note: The cell volume is expressed as a percentage of the container size.)
A. How many solute particles are found inside the cell? ________ Outside? ________
B. How many solvent particles are found inside the cell? _______ Outside? ________
C. What is the total number of particles inside the cell? ________ Outside? ________
D. What is the % concentration of solute inside the cell? __________________
E. What is the % concentration of solute outside the cell? _________________
3. Observe: Click Play, and observe the numbers shown on the DESCRIPTION pane. How does each number change over time? Write “increases,” “decreases,” or “stays the same” (or “same”) in each space.
• Solute particles inside? ___________
• Solvent particles inside? ___________
• Solute concentration inside? _________
• Solute particles outside?...
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