Reference no: EM133505651
Case Study:
Eukaryotic Cells:
In contrast to prokaryotes, eukaryotic cells have organelles and a nucleus. They may be found singly (as independent unicellular organisms), in colonies (many individual cells living together in a group), or as parts of multicellular organisms. You will be looking at three kinds of eukaryotic cells, all from multicellular organisms.
Plant cells:
Plants are autotrophic eukaryotes that conduct photosynthesis. They do so with green organelles called chloroplasts. These organelles are only visible in cells that conduct photosynthesis; parts of the "body" of the plant that do other jobs don't have visible chloroplasts. The following images are of two different plants, and from different locations on the plants. Figure 4.3a are onion cells from the bulb of the plant, and 4.3b are Elodea leaf cells.
Figure 4.3: Plant cells under a light microscope. Onion skin cells, stained. Credit: Oliver Kim, microworldarchive.org b: Elodea leaf cells, 400X magnification. Credit: scienceprofonline.com.
Examine the cells carefully. Note that the Elodea image is focusing on one layer of cells, but the cells underneath do show from behind to some degree. Are the cells in each plant all the same shape? The cell wall, nucleus, chloroplasts and cytoplasm are most obvious. The central vacuole may be visible and distinguishable in some cells. Inclusions (unidentified bits of solid material) may be visible in the cytoplasm. The cell membrane cannot be seen with the light microscope because it is so thin, but its presence and locations can be observed.
Figure 4.4: Animal cells. a: Human cheek epithelium cell, stained, 400X magnification, with bacteria (blue specks). Credit scienceprofonline.com. b: Human eosinophil, using a light microscope with DIC optics and false colored. Credit: cellsalive.com.
Animal cells:
Animals are multicellular eukaryotic heterotrophs. Different cell types can have strikingly different structure, as illustrated in Figure 4.4. Look for all the structures and organelles that you have looked for in the other eukaryotic cells - cell wall, chloroplast, nucleus, plasma membrane, cytoplasm. Since these are animal cells, they lack some organelles and structures that were present in the onion and the Elodea cells.
Animal cells:
Animals are multicellular eukaryotic heterotrophs. Different cell types can have strikingly different structure, as illustrated in Figure 4.4. Look for all the structures and organelles that you have looked for in the other eukaryotic cells - cell wall, chloroplast, nucleus, plasma membrane, cytoplasm. Since these are animal cells, they lack some organelles and structures that were present in the onion and the Elodea cells.
Questions:
Collectively, what structures did you observe in the Eukaryotic cells you examined today?
What structures did you observe in eukaryotic cells that you did NOT observe in prokaryotic cells?
What structures did you observe in the plant cells but NOT the animal cells?
List any observed structures that are universal to ALL cells.
How did the plant cells differ from each other? One organelle in particular should have been quite abundant in the Elodea cells, but absent from the onion cells. Which organelle is absent from the onion cells?
What is the function of this organelle, and why does it make sense that this organelle would not be found in the bulb of the onion?
Are there any parts of the onion plant in which you WOULD expect to find this organelle?
Notice the difference in shape between the two animal cell types. Brainstorm: why are cells in the same organism (these are both human cells) different shapes?
Find an image of a cell online. You can look at any of the sources cited in the image credits in the lab, or use Google search. Share the image with me, and include the following information:What kind of cell is it? What species?
How was the image taken? Light microscope, scanning electron microscope, or transmission electron microscope?