The purpose of this laboratory is to examine a variety of plant cells to observe some of their characteristics
1. Make a fresh mount slide using a piece of epidermal tissue stripped from a scale of red onion (Allium). Examine the cells of this tissue. Draw two adjacent cells, labeling the cell wall, the nucleus, and the cytoplasm.
Add a few drops of hypertonic salt solution to the edge of the cover slip and draw it under the cover slip with a piece of absorbent paper. Wait for about a minute, then observe the cells again. The presence of the hypertonic solution surrounding the cells should have caused the cells to plasmolyze (plasmolysis is the shrinkage of the protoplasm of plant cells, causing it to pull away from the cell wall). Plant cells generally are connected to one another by structures called plasmodesmata which, although structurally complex, appear at low magnification to be thin strands of protoplasm passing through the cell wall to join the adjacent cells. In plasmolyzed cells these plasmodesmata should be visible as strands extending from the cell protoplasm out toward the cell wall. Draw two adjacent plasmolyzed cells, labeling the cell wall, the nucleus, the cytoplasm, and plasmodesmata.
2. Obtain a leaf from an Elodea plant, and make a wet mount slide from it. Observe and draw a cell of this leaf tissue, labeling the cell wall and the green, pigment-containing chloroplasts.
3. Use a razor blade to obtain a very thin slice of red pepper (Capsicum). Make a wet mount slide of this tissue and observe with a microscope. The red organelles present in the cells of this tissue are examples of chromoplasts. Draw a cell of this tissue, labeling the cell wall, the cytoplasm, and a chromoplast.
4. Although all plant cells share some common features, plant cells also vary widely from one tissue to another. The size and shape of plant cells can differ, as well as the thickness and chemical composition of the cell wall; the organelles present may be different; and some plant cells actually function it a. time when the cytoplasm has degraded and only the cell wall is still present. Some plant cells. contain distinctive non-protoplasmic materials, known as ergastic matter, often in the form of crystals. These crystals can occur in a variety of shapes, each with its own name.
Obtain a prepared slide of a cross-section of a Tilia stem. Scan it, focusing on the cortex and pith, looking for cells containing druses, one of the common types of plant cell crystals. Druses are compound crystals that look a little bit like ice crystals. The cells containing these, and other, crystals are called idioblasts, meaning cells easily distinguished from other cells of the same tissue. Draw an idioblast of Tilia, labeling the cell wall, and the druse.
5. A second type of crystals, called raphides, is found in the leaves of many plants, including Dieffenbachia. Raphides are long, thin, needle-like crystals which usually occur in bundles within a cell.
Removing a section of leaf tissue and grinding it lightly in a small amount of water can release the raphide-containing idioblasts from the surrounding cells, making them easy to observe. Your laboratory instructor will prepare such a slurry for you.
Using a dropper, take a small amount of water from the bottom of the Dieffenbachia slurry, place it on a slide, and cover it with a cover slip. Scan the slide to find an isolated idioblast. You make catch the raphides actually being released from the idioblast cell. Draw an idioblast and label the cell wall and the raphides.
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