As usual, I have assembled some passages from some of the abstracts submitted by students in the 1996 class, as an example. The foundation of this abstract was one submitted by Karen Lemons, a gem of clarity and brevity. I added to this various contributions from others, especially Melanie Shadish who included some nicely crafted details. However, the abstracts submitted this time were very well done...congratulations to all! All contributions shown here have been edited. Note: since 1996, I have omitted lab exercises on organisms other than plants!

[A study of the cell boundary of a Forsythia stem, the cell membrane and chloroplasts of a Mnium leaf, the nucleus and mitochondria of Rhoeo discolor leaf epidermis, and cyclosis in the plasmodium of Physarum(Patricia Tellekamp)]

Karen Lemons with Jeffrey Holt

51 Beacon Road, Windham, Phone #

[In this exercise, several experiments were performed on different organelles of various plant species to test hypotheses concerning different aspects of plant cell physiology (Melanie Shadish)]. A freshly mounted section of Forsythia stem exhibited xylem that was greenish in color. The wood cell boundaries treated with the stain, Phloroglucinol HCl, turned purple probably due to a chemical reaction with the lignin in the wood. [Lignin is known is known to have a chemical structure that would cause this reaction (Melanie Shadish)]. [Further testing with a different dye that interacts with lignin would assist in verifying that lignin is present in the cell wall (Jeff Holt)]. A Mnium leaf was wet mounted to test whether its cells were alive, and therefore had a functional cell membrane capable of excluding sodium and chloride ions but not water. One wet mount was made in distilled water and another was made in 6% sodium chloride. [Because of the cell wall resisting turgor pressure in the distilled water, the cells did not enlarge or burst (Patricia Tellekamp)]. The cytoplasm shrunk and separated from the cell wall in the presence of sodium chloride. This response is known as plasmolysis, which ultimately results from a loss of turgor pressure when a cell is in a severely hyptertonic solution. We concluded that the cells were alive because the cell membrane was functional; it was able to exclude salt ions, but not water. Another experiment was designed to determine the function of the chloroplasts in cells of the Mnium leaf. In the presence of iodine, the chloroplasts displayed purple/black spots. These spots were starch grains; a storage form of a photosynthetic product (carbohydrate), indicating that chloroplasts function in photosynthesis. [We observed the plant-specific organelle, the vacuole, by observing a wet mount of Rhoeo discolor leaf lower epidermis which has a large vacuole containing a purple pigment. We hypothesized that, since mitochondria were not seen at all, plant cells lack mitochondria. (Melanie Shadish)]. To determine the presence of mitochondria in plant cells, methylene blue was used [since it is known to change to a dark blue color in the presence of electrons and hydrogen ions. The respiration pathway includes enzymes which liberate electrons and hydrogen ions (Amy Lusk)]. Small structures [presumably mitochondria (Chuck Goddard)] could be seen. [Our final experiment was to determine if cytoplasmic streaming in plant cells could operate like the mechanism based on electrical action potential, calcium ions, and ATP causing the actin and myosin of vertebrate muscle cells to slide past one another. The hypothesis was tested using the slime mold, Physarum (Melanie Shadish)]. An action potential created by brief contact with wires connected to a 1.5 volt battery was applied to the plasmodium undergoing cyclosis on an agar surface. [Microscopic observation showed nuclei moving through the cytoplasmic channels at a slow rate with regular reversals in direction of flow. When the action potential was applied, cyclosis became more rapid. When a drop of 10-4 M Ca+2 was applied to the plasmodium, cyclosis seemed to have ceased. A drop of 10 M Ca+2 was applied, cyclosis was very slow. However a drop of EGTA restored the rate of cyclosis.(Melanie Shadish)] [It is important that cells both produce sufficient ATP and release sufficient Ca+2 to increase cyclosis. Adding excess calcium probably depletes ATP supplies, slowing cyclosis. The EGTA chelating agent probably sequesters excess free-calcium thus restoring ATP driven cyclosis (Ross Koning)]. [If calcium and electricity are applied to the cell for too long or too rapidly, all of the ATP in the cell is used up quickly and cyclosis stops (Tracy Gervais)]. [This series of experiments served to acclimate students to the use of microscopes, chemicals, and give experience with dose responses to visualize processes that are not commonly familiar (Damon Crooks)].


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