Onion+cell+Lab

__**Problem:**__ What will happen when cells are exposed to hypertonic and hypotonic solutions?

__**Materials:**__ Forceps Piece of onion Scalpel Glass slides Dropper pipette Coverslips Iodine solution Paper towels Microscope Concentrated salt solution Distilled water

__**Procedure:**__ 1. Put on safety goggles. Using forceps, peel a thin layer from the inner surface of a piece of onion. 2. Use a scapel or razor blade to cut a small piece out of the layer you removed. The layer should be transparent and very thin. 3. Place the piece of onion in the center of a glass slide. Add a drop of distilled water to the piece of onion, and cover it with a coverslip. 4. Put a drop of iodine solution at the end of the coverslip. (caution: iodine can stain skin and clothing; be careful not to spill it on yourself) 5. Hold a piece of paper towel near the opposite edge of the coverslip, as shown in the diagram on page 195 of your textbook. 6. Draw the iodine under the coverslip, where it will stain the onion cells. 7. Examine the slide under the low-power objective of the microscope 8. Sketch one cell, and label any structures you recognize. 9. Count the # of cells that fit across the field of view. 10. Remove the slide from the microscope and set it aside. 11. Prepare another wet mount slide of an onion skin 12. Place a drop of concentrated salt solution on the edge of the coverslip. 13. Draw the salt solution under the coverslip, where it will come in contact with the onion cells. 14. Sketch one cell, and label any structures. 15. Remove the slide from the stage. 16. Place a drop of distilled water on the edge of the coverslip 17. Draw the distilled water under the coverslip, where it will come in contact with the onion cells. 18. Sketch one cell, and label any structures.


 * Log onto the Quia For a prelab quiz.**

1. Form a hypothesis for this lab. 2. What are the safety considerations for this lab? (list #s from safety contract) 3. Look at the materials list, which item is a hypotonic solution? 4. Which item is a hypertonic solution? 5. What is the independent variable? 6. What is the dependent variable?

1. What structures did you see in the onion cells? 2. Describe the changes you observed in the onion cells when exposed to the hypertonic solution. 3. Describe the changes you observed in the onion cells when exposed to the hypotonic solution. 4. What process accounts for the changes you saw? 5. What part of the cell is involved in the process you observed? 6. Why didn’t the onion cells burst in the distilled water? 7. What might happen if you repeated the experiment with animal cells? 8. Evaluate your hypothesis. 9. Write a conclusion.
 * Review the Post lab questions:**