Download Cell Specialization Lab

Cell Specialization Lab
Introduction:
In this lab, you will have the opportunity to prepare samples and view four different types of cells. You
will view an animal squamous cell by taking a sample from your cheek. You will also view a underground leaf
cell by looking at an onion. You can view a typical plant cell by looking at the leaf of a water plant called
Elodea. The last cell you will see is a “stinging” cell, called an idioblast that comes from the plant
Dieffenbachia picta.
You are responsible for preparing, observing, and illustrating all four cell types but the order in which
you observe does not matter. Each illustration should be done in your science notebook. Trace a petri dish to
make a circle; this circle represents the field of view under the microscope. Each drawing needs a title (what
is it?), total magnification (e.g. 400x), appropriate detail, color, and labeled cell parts (e.g. chloroplast,
cell membrane).
Instructions for Animal Cell:
1. Obtain a slide, cover slip. Clean both the slide and the cover slip.
2. Put one small drop of water on the slide.
3. Using a clean toothpick, gently scrape the toothpick inside your mouth along the
cheek wall.
4. Smear the toothpick across the slide where the water drop is.
5. Add one drop of methylene blue.
6. Carefully drop the cover slip over your sample and gently press on one corner of it.
7. Carefully wick away the excess moisture (teacher will show you how to wick).
8. Find one or more good-looking cells (they look like little fried eggs). Observe under medium and high
powers. Make a detailed drawing of one or more cells under high power. Label the cell parts (cell membrane,
cytoplasm, and nucleus) in your drawings that you can see. If you see additional parts label them.
9. Appropriately dispose of your tooth pick and wicking materials.
10. Clean and dry both slide and cover slip.
Instructions for Elodea:
1. Clean and dry the slide and cover slip.
2. Get a small leaf of the Elodea plant.
3. Put a drop of water on your slide and set the leaf on it.
4. Use a cover slip to help flatten the leaf; push gently on the corner of the slip to try to remove any air bubbles.
5. Observe the outer edge of the leaf. Describe record in your journal any evidence you see that some cells are
specialized (different from other elodea cells).
6. Move the slide back to cells that represent the typical plant cell. View under medium and high power. After
several minutes under the light, make quality observations and draw several cells under high power. Label the
parts of the cell in your drawing that you can see.
7. After several minutes under the light, make quality observations of cells throughout the leaf. You should be
able to see the “cytoplasmic streaming”—the movement of chloroplasts around the cell – in at least one of the
cells on the leaf. Label the parts of the cell in your drawings that you can see and describe what the chloroplasts
are doing.
8. Appropriately discard your leaf sample, clean and dry your slide and cover slip thoroughly.
Instructions for Onion Cell:
1. Clean and dry your slide and cover slip.
2. Obtain a very thin section of onion from your teacher. Peel a single outer purple layer of the section given to
you and place it on the slide so that it is flat.
3. Place one drop of water on the onion.
4. Place the cover slip over the sample and press lightly on one corner to remove the air bubbles.
5. Find some cells that are colorful and observe them on both medium and high powers. Make quality
observations and draw several cells under medium or high power.
6. Label all of the cell parts in each drawing that you can see.
7. While you are watching on medium or high power, add several drops of salt water to the side of your cover
slip and wick it through by using a piece of paper towel on the opposite side of the cover slip.
8. Wait several minutes, record your observations and draw what you now see. Label that part(s) that you could
not see before.
9. Add several drops of distilled H2O to the slide. Wait several minutes. Record you observations in a final
drawing.
10. Appropriately discard the sample, clean and dry both cover slip and slide
thoroughly.
Instructions for Idioblasts:
Readings: Idioblasts that Shoot (Original source: The Remarkable Shooting Idioblast, Carolina Tips).
The ejection of sharp, needle-like crystals from specialized spindle-shaped cells of the plant
Dieffenbachia picta is a phenomenon that is neat to watch. People are fascinated when they see these distinctive
cells, called idioblasts; shoot out needle after needle--like a microscopic blow gun. Each idioblast (see Fig. A)
contains a large bundle of double pointed, sharp, needle-like crystals called raphids. Forceful ejection of the
raphids can sometimes be seen under a microscope.
A
B
The raphids are made of calcium oxalate, which is actually a non-living piece of material that exists
inside this cell. It has been speculated that these raphids help the plant to use excess oxalate. The raphids are
formed in a special vacuole within the cells. It is also speculated that the raphids may be an evolutionary
adaptation to help the plant survive. Any animal that tries to eat the stem or leaves of the Dieffenbachia will not
enjoy the experience.
Dieffenbachia is also known as Dumb Cane, because it has been widely known for centuries that when a
human tries to eat the plant, the mouth and throat will become paralyzed, thus causing the person not to be able
to speak (being dumb) and even not being able to eat for a full day or more. For many years it was thought that
the calcium oxalate was the paralyzing agent in the plant, but in 1972, it was found that the plant tissue actually
contains a venomous enzyme similar to snakes and scorpions. The raphids allow the venom to enter the mouth
and throat tissue, and the venom travels down small grooves on the opposite side of the raphids and enter the
cells of the throat. Scanning electron micrographs suggest that the raphids are also barbed, which would prevent
them from dislodging.
When crushed plant tissue is placed in a drop of water on a glass slide and put under a microscope, some
idioblasts will be seen firing and others will be still (see Fig. B). It was not known why this was so, until it was
observed under a scanning microscope with a color video monitor. The camera showed that cells that were not
firing had smooth round tips, while the firing tips were broken and jagged. The number of raphids fired is
proportional to the amount of damage done to the tip. It seems to be the water pressure, called turgor pressure
inside of the idioblast that forces out the raphids. When the pressure is high, they fire. How this works is that the
raphids are surrounded by a jelly-like substance that puts pressure on them. As the turgor, or water pressure
increases in the idioblast due to something literally “putting the squeeze” on the outside (i.e. a “bite”), the
raphids are literally squirted out the end. The more the pressure, the more they “squirt,” or fire. Once the last of
the raphids is ejected, the idioblast literally spills its guts if the pressure remains.
Instructions for Dieffenbachia idioblasts:
1. Obtain a mortar and pestle and a small chunk (less than 1 square inch) of the plant.
2. Put 15 drops of water in the mortar and add the piece of plant.
3. Crush and mix the plant for 2-3 minutes.
4. Let the pestle rest on the mortar (at a slight angle) for 2 minutes.
5. With a dropper, put 1-2 drops of mixture from the bottom of the mortar on a slide with a cover slip.
6. Examine under low power until you find an idioblast, and work up to medium & high power.
7. If most of our idioblasts are unbroken, mash the stuff in the mortar some more and prepare a new slide.
8. Record quality observations and draw what you see out of each slide set, labeling the parts.
9. Carefully clean, wash, rinse, and dry the mortar, pestle, slide, and cover slip.
10. Find out if your teacher has any other slides for you to look at. Follow the directions given for those slides.
11. When you are finished with all four cells, put the microscope to “bed” in the proper manner.
Questions for the lab (answer IQIA in your science notebook):
1. Describe the differences between the Elodea and the onion.
2. Hypothesize/explain why there are these differences (as described in #1), even though they are both
plant cells.
3. Describe the differences between typical plant and animal cells.
4. The cheek cells you observed were flattened and more irregularly shaped; they weren’t round like
most “models” show animal cells. Hypothesize why cells that form the lining of your mouth might be
flattened.
5. Describe the differences between the idioblast cells and normal plant cells. What is it about idioblasts
that make them so special?
6. Summarize the firing mechanism of the raphids (See the reading section above).
7. When observing the Elodea, you should have noticed that the chloroplasts were moving around the
inside of the cell. This is called cytoplasmic streaming. Hypothesize why the cell circulates its cytoplasm
(hint: it is tied to the job of the chloroplast).
8. Hypothesize why there is a difference in the cell structures between plants and animals and explain
why those differences are important for the way the different organisms live.
9. If homeostasis is disrupted, can it be corrected? Use evidence from the lab to support your answer.
10. Explain how each of these four cell types are an example of cell specialization. What physical features
are related to the cell’s function?