Cell Biology
Prokaryotic and eukaryotic cells
Observation of cells and organelles
In this lab you will be looking at an example of a Prokaryotic cell (Bacillus cereus) and a some examples of Eukaryotic cells from each of the four kingdoms.
Names and uses for dyes:
Iodine: stains violet/ purple upon contact: Shows the presence of starch Crystal violet: binds cell wall with starch components
Methylene blue: Binds DNA
Janus Green B: used in histology and to stain mitochondria (changes color depending on amount oxygen)
Malachite green: used to stain bacteria
Methods
Prokaryotic Cells
Prepare a wet mount of bacterial culture
1. Take a culture tube containing bacteria and re-suspend the cells by rolling the tube between your palms. The solution should look turbid.
2. Transfer a small drop (the smaller the better) of the culture to the center of a clean microscopic slide.
3. Observe your sample under the lowest objective, then increase the magnification of your observations.
4. Place this slide in a 10% bleach container.
Eukaryotic Cells Kingdom: Protista
Prepare a sample of Euglena for observation
1. Transfer a small drop (the smaller the better) from the container of Euglena to the center of a clean microscopic slide.
2. Observe the slide under the lowest objective, then increase the magnification of your observations.
3. Label any structures you recognize.
4. Wash and dry your slide and use it for the next procedure.
Kingdom: Fungi
Prepare a yeast sample for observation.
1. Transfer a small drop (the smaller the better) from the beaker containing the yeast culture to the center of a clean microscopic slide.
2. Observe your sample under the lowest objective, then increase the magnification of your observations.
3. Wash and dry your slide and use it for the next procedure.
Kingdom: Plantae Prepare a slice of potato or carrot tissue for light microscopy. BE CAREFUL NOT TO CUT YOURSELF.
1. Obtain a small piece of potato or carrot and use a razor blade to shave off as thin a slice as
possible. (i.e. you want to get the white, starchy part of the potato, not the potato skin.) The slice should be only one or two cells thick, and should appear transparent.
2. Place the tissue slice in the center of your microscope slide, add a drop of water from a dropper bottle, and then place a cover slip over the preparation.
3. Observe the preparation on the microscope. Remember to start with the lower objective and view the thinnest edge of your preparation. Draw the cell; be sure to note the magnification of the image you sketch. Explore the settings of your microscope to determine if you can visualize cell structure better.
4. Add a drop of iodine to the potato section on your slide. Place a drop of a given solution at one edge of the cover slip. Touch a lab wipe to the opposite side of the cover slip; the lab wipe will absorb the water by capillary action and draw the solution over the tissue slice. DO NOT OVERSTAIN.
5. Observe the preparation again and sketch each sample.
6. Wash and dry your slide and use it for the next procedure.
Prepare an onion slice for light microscopy
1. Obtain a small piece of onion using a sharp blade/ knife. Remove the fleshy “leaves” from a section and snap the leaf to produce a piece of membranerous tissue. Remove a small piece of tissue and spread smoothly in a drop of water on a slide. Lower a cover slip gently on top of your sample to avoid trapping air bubbles.
2. Follow the same procedure for the carrot or potato to observe or stain your onion cells.
Prepare a wet mount of Elodea cells for microscopy
This aquatic plant is useful for observing the typical features of plant cell, which include the cell wall, chloroplasts, nucleus, streaming cytoplasm and the central vacuole. This leaf is only two cells thick; you may be able to find differences between the top and bottom surfaces.
1. Cut one leaf from the Elodea plant. Place the leaf in the center of the slide, add a drop of water and place a cover slip over the mount.
2. Observe the Elodea leaf at various magnifications. Scan the preparation and look for streaming cytoplasm, which may be more active at the tip of the leaf.
3. Sketch a typical Elodea cell, including the cell wall, chloroplasts, nucleus, and the central vacuole in your sketch.
4. Wash, and dry the slide and place it on the cart.
Kingdom: Anamalia
Prepare a slide of human cheek cells
Our colorless human cheek cells are transparent and difficult to see, so you will be adding stain to these cells before viewing them.
1. Obtain a clean slide and coverslip and a sterile toothpick.
2. Make a stained wet mount of a human cheek cell: place a drop of methylene blue on a clean microscope slide. Pick up some of your cheek cells by gently scraping the inside of your cheek with the side of a sterile toothpick. Transfer the cells to the drop of stain and place a coverslip on top. (I will show you how to slowly lower a coverslip to prevent air bubbles from entering your slide).
3. Draw and label a FEW REPRESENTATIVE cheek cells at low AND high powers. (The cells are too small to see with the scanning objective; remember that you should use this objective only to orient yourself. Label any visible cellular structures.
The egg as semi-permeable membrane (Demonstration only)
In this demonstration an eggshell filled with distilled water will be floated in a solution of starch and glucose. The eggshell represents a semi-permeable membrane. The egg will float in the solution for a time and then we will test to see if the solution in the eggshell has changed or not.
1. What do you think will happen in this experiment. Write down your hypothesis stating what you think will be the final solution in the eggshell.
2. Record the results of the experiment. How did it compare with your hypothesis?
3. Record your thoughts about what happened in this experiment.
Cell biology lab sheet
Prokaryotic and eukaryotic cells
Names: _______________________
Always, choose a few, ideal examples and draw them accurately – don’t draw thousands of cells that all look alike!
Prokaryotic Cells
Record your observations of the bacterial culture.
Eukaryotic Cells Kingdom: Protista
Kingdom: Fungi
Record your observations of the yeast sample.
Kingdom: Plantae
Record your observations of the potato or carrot tissue
Record your observations of an onion.
Record your observations of Elodea cells.
Kingdom: Anamalia
Record your observations of human cheek cells.
The egg as semi-permeable membrane Hypothesis:
Results:
Conclusions:
