LAB: Observing Plant and Animal Cells



Observing Cells

Background Information:

One of the first scientists to look at cells under a microscope was an English scientist by the name of Robert Hooke. He viewed and described the appearance of cork under the microscope and decided to name the tiny box-like structures that he observed “cells” because they looked like the small chambers where monks lived.

By the early part of the 19th century, it was accepted that all living things are composed of cells. Cells come in a variety of shapes and sizes, and cells perform different functions. Although cells may appear outwardly different, they resemble each other because they share common structures. In this lab you will look at two types of cells, a human cheek cell and an onion cell and see how they are similar and how they are different.

Prelab:

1. What is the purpose of the iodine and methylene blue in this lab?

2. What shape do you think the plant cells will be?

3. What organelles do you think you will be able to see in this lab?

4. What will the toothpick be used for?

5. Why is it important to get a thin layer of onion?

Materials:

Microscope

Dropper

2 clean slides

2 cover slips

Toothpick

Cheek cells

Onion cells

Bacteria Slide

Letter “e”

Chloroplast Slide

Mitochondria Slide

Iodine

Methylene blue

Paper towel

Letter “e” Procedure:

1. Get a clean slide. Place a drop of water on the slide. Place one of the letter e’s on the drop of water and then Place a cover-slip on the slide, slowly lowering it over the sample to avoid creating air bubbles.

2. Place the slide on the stage and view the slide under the low power.

3. Observe the letter “e” under 4x, 10x, and 40x. Sketch what you see at 4x and 40x power in the data section of your notebook. (Total of 2 cell pictures)

Bacteria Cell Procedure:

1. Go to the microscope set up with the bacteria sample.

2. Starting at low power, slowly bring the slide into focus.

3. Observe the bacteria at 4x, 10x, and 40x. Sketch what you see at each 10x and 40x in the data section of your notebook. (2 cell pictures)

Mitochondria Procedure:

1. Go to the microscope set up with the mitochondria sample.

2. Starting at low power, slowly bring the slide into focus.

3. Observe the mitochondria at 4x, 10x, and 40x. Sketch what you see at 40x in the data section of your notebook. (1 cell picture)

Chloroplast Procedure:

1. Go to the microscope set up with the mitochondria sample.

2. Starting at low power, slowly bring the slide into focus.

3. Observe the mitochondria at 4x, 10x, and 40x. Sketch what you see at 40x in the data section of your notebook. (1 cell picture)

Onion Cell Procedure:

1. Set up your microscope.

2. Get a clean slide. Place a drop of water on the slide. Using one of the cut sections of onions at your station, remove the single layer of epidermal cells from the onion (the thinner the better) Place the layer of tissue on a slide and then add a small drop of iodine to the slide. Place a cover-slip on the slide, slowly lowering it over the sample to avoid creating air bubbles.

3. Place the slide on the stage and view the slide under the low power.

4. Observe the cells under 4x, 10x, and 40x. Sketch what you see at each power in the data section in your lab notebook. (Total of 3 cell pictures)

5. Once finished learn the slide and cover slips and leave them to dry

Cheek Cell Procedure:

1. Put a drop of methylene blue on a slide. Caution: methylene blue will stain clothes and skin.

2. Gently scrape the inside of your cheek with the flat side of a toothpick. Scrape lightly.

3. Stir the end of the toothpick into the stain and throw the toothpick away.

4. Place a cover-slip onto the slide

6. Place the slide on the microscope. Use the Scanning/Low power/ 4x objective to focus, look at the stained slide under the microscope. You probably will not see the cells at this power. Sketch what you see in the data section of your lab notebook and place the magnification next to the drawing.

7. Switch to 10x power. Cells should be visible, but they will be small and look like blobs. Solid dark objects are probably not cellular. Sketch what you see in the data section in your lab notebook.

8. Once you think you have located a cell, switch to a high power (40x) and refocus using the fine focus. Sketch what you seen in the data section of your lab notebook.

9. Once finished learn the slide and cover slips and leave them to dry. (Total of 3 cell pictures)

Data:

Onion Cells:

Scanning (4x)

[pic]

Low (10x)

[pic]

High (40x)[pic]

Cheek Cells:

Scanning (4x)

[pic]

Low (10x)

[pic]

High (40x)

[pic]

The light microscope used in this lab is not powerful enough to view other organelles in the cheek cell. Fill out the table below to show what we could and could not see through our microscope.

Onion Cells

|What organelles could be seen? |What organelles could not be seen? |

| | |

Cheek Cells

|What organelles could be seen? |What organelles could not be seen? |

| | |

Post lab Questions:

Answer the following questions in complete sentences

1. What purpose did the letter “e” slide serve in regards to microscope use?

2. What type of cell did the cheek cell represent? What about the onion cell?

3. How does the shape of the onion cells differ from that of the cheek cells?

4. Which cells seem to be arranged in a more regular pattern?

5. What structures were you able to see in both types of cells?

6. Both plant cells and animal cells contain mitochondrion and yet there were not visible in the cells you viewed in this lab. Does this mean that these organelles are not found in cheek and onion cells? Why or why not? Explain your reasoning.

7. In class and in your reading you learned that one difference between plant and animal cells is that plant cells contain chloroplasts. Were any chloroplasts visible in the onion cells? Why or why not? Explain your reasoning.

Conclusion:

Recall/Restate: Identify the purpose of the experiment?

Explain: Why did you do this lab? What were you trying to find out? Briefly explain the procedure that you followed.

Results: State the results of the experiment.

Uncertainty: Describe any uncertainties that exist, if any. What errors happened that you could not control? What were some uncontrolled variables that may have affected the results? Explain any errors that you came across that could be fixed for the next time it is conducted.

New: Write at least two (2) new things you learned or discovered or had questions from the experiment. Include the appropriate SCIENTIFIC VOCABULARY in your explanation. Describe how you could take this experiment further.

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