Bio3

7 Eukaryotic Cell Structure 

Background

Cells come in all different sizes and shapes. They are classified into two major groups based on structure. Prokaryotic cells are much smaller and do not contain any membrane-bound organelle. Eukaryotic cells are larger and contain numerous membrane-bound organelles. Prokaryotic cells will be examined in the laboratory exercise that will survey the diversity of life on earth. This laboratory exercise will focus on the structure of the two most common types of eukaryotic cells: plant and animal cells.

To appreciate the cell in action, watch 

The Inner Life of the Cell

by BioVisions at Harvard University (3 min 12 sec). This video  shows movement of organelles and substances inside your cells in real time.

Purpose

• Prepare wet mounts of plant and animal cells for microscope observation.
• Use the light microscope to compare and contrast the structure of plant vs. animal cells.

Materials (demonstrated in video)

Microscope

Microscope slides  and cover slips

Toothpick

Water (or 0.9% sodium chloride solution)

Medicine dropper

Methylene blue (or iodine) stain

Elodea plant

Cheek cells

Online: Virtual microscope with plant slide

Procedure for plant cell

1. View how to prepare a wet mount of an Elodealeaf (2 min 30 sec) OR
2. how to prepare a wet mount https://youtu.be/UWbGZMO4o_U(2 min 30 sec) 

To create a wet mount of an Elodea leaf, this general procedure was followed.

1. Put a drop of water on the center of a slide.
2. Cut an extremely small piece of an Elodea leaf and place it on the water.
3. Place a coverslip onto the slide.
4. Observe the plant cell slide under the virtual microscope by following this procedure.

   Go to the virtual microscope.
   Click Launch and then Explore
   Click the “?” in the microscope slide box
   In the slide catalogue, select “Plant Slides”.
   Inside, select “Plant Cells.” The virtual microscope loads the Plant cell slide at the center of the stage. You will see a blurry green field of view.
   Click “10X” (low power objective lens). Watch as the nosepiece moves until the low power objective lens clicks in. Use your mouse to adjust the Coarse Focusuntil the image is in focus. Fine tune it using the Fine Focus. Slowly slide the Light Adjust to the right to obtain optimum brightness. Click on the field of view to move the plant side. Draw the image of plant cells in the field of view for low power.
   Click “40X” (high power objective lens). This time, only adjust the Fine Focus & Light Adjust to obtain the clearest image with optimum light. Moving the Coarse Focus will endanger the lens & slide and make you lose your focus. 
   Draw the image in the field of view for high power.

Drawing of plant cells: label cell and observed organelles.  

Procedure for animal cell 

1. View Cheek Epithelial Cells (3 min 52 sec) to observe how to prepare a wet mount of human cheek cell and view images of the cheek cells under low & high power magnification.

To create a wet mount of cheek cells, this general procedure was followed.

1. Put a drop of methylene blue on a slide. Caution: methylene blue stains clothes and skin.
2. Gently scrape the inside of your cheek with the flat side of a toothpick.
3. Stir the end of the toothpick in the stain and then throw the toothpick away.
4. Place a coverslip onto the slide by lowering it at a 45 degree angle to prevent formation of air bubbles.
5. Draw the cheek cell images under low & high power magnification as seen in the video.

Discussion/Conclusion 

1. Stains may be used but not all organelles are seen, why?
2. Describe the shape of the plant cell. List the organelles that were visible.
3. Describe the shape of the human cell. What organelles of the cell were visible?
4. Describe visible similarities and differences between plant and animal cells.
5. What observations support the claim that plant and animal cells are eukaryotic?