Lesson 2.2 Osmosis and Diffusion Name Date Period Key Terms Solute Hypertonic Hypotonic Isotonic Diffusion 1. Your teacher opens a container of food in the classroom that has been in the refrigerator since last school year. Describe how the smell moves through the classroom. 2. Why is it dangerous to drink seawater? 3. Two identical carrots are placed into two different solutions. One solution is concentrated corn syrup A. The other is pure distilled water. The carrot placed in the corn syrup (A) shrivels up. The carrot placed in the distilled water (B) swells up. Explain these results. Use diagrams to aid in your explanation. Explore You will now investigate what happens to cells when exposed to solutions containing different concentrations of a solute. A solute is a dissolved material, like salt.
A high concentration of a solute makes a solution hypertonic relative to the concentration of solutes in a cell. A low concentration of a solute makes a solution hypotonic relative to the concentration of solutes in a cell. A concentration of a solute that is the same as the concentration of solute inside of the cell is isotonic. Fluids move or diffuse in response to solute concentration gradients. Fluids move toward areas where they are LEAST concentrated. Fluids continue to diffuse until they reach equilibrium (even distribution of particles). This investigation will help you to discover how fluids will move in responses to differences in solute concentration. 4. What do you predict will happen to cells placed into a hypertonic solution? Support your prediction. 5. What do you predict will happen to cells placed into a hypotonic solution? Support your prediction. 6. What do you predict will happen to cells placed into an isotonic solution? Support your prediction. Procedure a. Take a small piece of elodea leaf using forceps (tweezers). b. Lay the sheet of cells flat on the surface of a clean glass slide, and then add one drop of tap water. c. Using a pin, lower a thin glass cover slip or cover glass onto the slide. Make sure there are no air bubbles. d. Make sure the lowest power objective lens (the shortest lens if there are several present) is in line with the optical tube, and the microscope light is turned on. Then place the prepared slide onto the stage of the microscope. e. Looking from the side (NOT through the eyepiece), lower the tube using the coarse focus knob until the end of the objective lens is just above the cover glass. Do this carefully so as not to crack the cover glass (and possibly damage the objective lens). f. Now look through the eyepiece and turn ONLY the smaller, fine focusing knob to move the optical tube upwards until you can see the cells on the elodea. They should look something like lizard skin. Draw what you observe in Figure 1.a g. Swap the objective lens for a higher powered one so that you can see the cells at greater magnification. You should be able to make out the nucleus, cell walls and green colored chloroplasts. Draw what you observe in Figure 1.b. h. Swap this objective lens for an even higherpowered one and draw what you observe in Figure 1.c. i. Complete steps A H using concentrated salt solution. Diagram what you observe in Figures 2.a 2.c. j. Complete steps A H using distilled water. Diagram what you observe in Figures 3.a 3.c.
Elodea Isotonic Solution Figure 1.a Low Power Objective 40x Figure 1.b Medium Power Objective 100x Figure 1.c High Power Objective 400x Elodea Hypertonic Solution Figure 2.a Low Power Objective 40x Figure 2.b Medium Power Objective 100x Figure 2.c High Power Objective 400x Elodea Hypotonic Solution Figure 3.a Low Power Objective 40x Figure 3.b Medium Power Objective 100x Figure 3.c High Power Objective 400x 7. What happened to the interior of the cell when you observed the elodea cells in an isotonic solution? 8. What happened to the interior of the cell when you observed the elodea cells in a hypertonic solution? 9. Why do you think this occurred? 10. What happened to the interior of the cell when you observed the elodea cells in a hypotonic solution? 11. Why do you think this occurred? 12. Do you think these elodea cells are in an isotonic, hypertonic or hypotonic solution? Support your answer. (Note: the rectangles are cell walls and the circular pieces are the organelles enclosed in a plasma membrane).
13. The elodea cells outside of the box are in an isotonic solution. Do you think the cells inside the box are in an isotonic, hypertonic or hypotonic solution? Support your answer. Explain 14. Compare your prediction to the observed results. Was your initial thinking supported or has your thinking changed? Explain your answer. 15. Refer back to the glass of water with the shark in it in the engage. What would happen to the cells in your body if you drink salt water? Explain your answer in your own words. Complete the questions on the following page.
Osmosis Problem Solving This cell Is placed in this solution What will happen? Why? 1. 6. This cell Is placed in a solution and after a short time looks like this What kind of solution was it placed in? How do you know? 2. 7. 3. 8. 4. 9. 5. 10.