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Eukaryotic Organelles and Prokaryotic Symbionts

Eukaryotic Organelles and Prokaryotic Symbionts - its long...

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Eukaryotic Organelles and Prokaryotic Symbionts Since ciliates (an many freshwater protozoans) are hypotonic , removal of water crossing the cell membrane by osmosis is a significant problem. One commonly employed mechanism is a contractile vacuole, shown in Figure 8. Water is collected into the central ring of the vacuole and actively transported from the cell. .
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Food is taken into the cell by an oral groove (or gullet, as shown in Figure 9), where small particles of the food are phagocytosed into food vacuoles. Often this can be accomplished in the laboratory period by using yeast stained with congo red dye, allowing students to see food vacuoles forming. The food vacuoles travel through the cytoplasm and are digested, with the molecules eventually passing into the cytoplasm, and wastes being expelled from the cell by exocytosis .
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Ciliates travel along a spiral path, as shown in Figure 10., with the cell rotating along
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Unformatted text preview: its long axis and the direction of travel resembling a sine wave. During asexual reproduction, ciliates divide by transverse binary fission, as shown in Figure 11. You may recall that bacteria have a somewhat similar type of binary fission, although no nuclei occur in bacteria. Ciliates possess two types of nuclei---a large macronucleus and one or more small micronuclei. The macronucleus controls the normal metabolism of the cell. The micronucleus are involved in sexual reproduction in a process known as conjugation that is shown in Figure 12. The macronucleus disintegrates and the micronucleus undergoes meiosis. Two ciliates then exchange a haploid micronucleus.The micronuclei give rise to a new macronucleus containing certain housekeeping genes....
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