Cell Observation Lab Helpful Reminders about Microscope Use:

1. Making a wet mount slide: a. Obtain a very thin slice of material b. Place on a glass slide c. Put a drop of liquid on thin slice d. Carefully put cover slip on top of thin slice

2. Looking at object under microscope

a. Begin with the lowest power lens (short one). b. Place slide on stage and clip in place. c. Begin focusing with coarse adjustment knob—the big one. (Be careful so you don’t

scratch microscope lens!!!!) d. Turn to higher power lens for a closer view (adjust with fine adjustment knob).

LAB ACTIVITY: Part A: Observing Cells I. Cheek Cells

1. Make a wet-mount slide of your cheek cells using bromothymol blue. Obtain cheek cells by carefully scratching the inside of your cheek with a toothpick. (Stir liquid with toothpick) Don’t Draw Blood!!! .

2. Draw a detailed drawing of a cheek cell and label any recognizable parts. II. Elodea Cell

1. Make a wet-mount slide of an elodea leaf. (Use water) 2. Draw a detailed drawing of an elodea cell and label any recognizable parts. 3. Save the wet-mount slide for Part B of the lab activity.

III. Onion Cell

1. Obtain a very thin piece of onion skin (peeled sunburn!) Make a wet-mount slide using iodine as the liquid.

2. Draw a detailed drawing of a few onion cells IV. Potato Cell

1. Place the tissue in a drop of water on a microscope slide 2. Use a toothpick to scrape a small amount of tissue from the inside of a white potato. 3. Swirl the toothpick in the drop of water and and add a cover slip. 4. Examine the preparation on low and high power with a compound microscope. 5. Record 1-2 observations and a sketch in your notebook. 6. Remove the slide from the microscope stage and stain the potato tissue with Iodine

solution (remember the paper towel trick). 7. Reexamine the slide under the microscope.

8. Record 1-2 observations and create a detailed sketch of what you observe. V. Pond Water

1. Use one of the pond water dishes to prepare a wet mount slide and use the dissecting AND compound microscope to examine the sample for living critters.

2. Spend a few minutes looking around the slide and record 2-3 observations about what you see.

Reflection Questions:

1. What do all three of these cells have in common? Describe them. 2. What are some differences between plant and animal cells? 3. How are elodea cells different from onion and potato cells? Why the differences—think

about their jobs in the plants they come from! 4. Why don’t onion cells have chloroplasts? Explain. 5. In the stained potato cell you see many dark dots within the cells, which are called starch

grains. With this in mind describe the role these cells play for the potato plant. 6. What do you notice about the majority of pond water critters you observed? Explain.

Part B: Plasmolysis of Cells

1. Use your wet mount of the Elodea leaf from Part A or if you no longer have it prepare a new wet mount of an Elodea leaf.

2. Quickly examine the leaf under both high and low powers with the microscope and note the appearance and arrangement of the green dots (chloroplasts) in relation to the cell wall.

3. Use an eye-dropper to place one or two drops of salt water along the edge of the coverslip and use the paper towel trick you learned in the microscope lab to draw the salt water across the slide.

4. Observe the leaf again under both low and high powers with the microscope and note the appearance and arrangement of the green dots (chloroplasts) in relation to the cell wall.

5. Sketch what you observe in your notebook. You should see that the cell membrane has shrunk away from the cell wall—this is plasmolysis.

6. Add a drop of tap water to the wet mount following the same procedure in step 3. Observe the appearance of the cells. You should notice that the cell contents have returned to normal.

Reflection Questions:

1. Describe the location of the chloroplasts in a normal plant cell and a plasmolyzed plant cell (in salt water solution).

2. Describe what happened to the Elodea cells when salt water and tap water were added to the microscope slide.

3. Explain what could have happened to cause the changes that you observed.

Part C: Critical Thinking

1. In this lab you saw a human skin cells, a variety of plant cells, and single-celled critters. You may have noticed that they are all quite different shapes. Examine the 5 sets of pictures.

a. Record 1-2 observations about each picture and try to guess what types of cells you are seeing.

2. Write a paragraph explaining what you think cells do (e.g., think about the job/purpose/function of cells).