The many cellular activities of protozoa, clearly visible at the light microscopic level, exhibit a degree of order and organization that indicate a high level of coordination. Motility, feeding, contractile vacuolar activity, and cytoplasmic streaming are among some of the well-documented activities that have been observed by light microscopy. These activities and other physiological responses are becoming increasingly understood at the molecular level. Much of this gain can be attributed to combined evidence from electron microscopy and biochemistry that clarifies structural-functional relationships at the subcellular level. Our knowledge of the molecular basis for cellular mechanics, including motility, responses to environmental stimuli, and coordination of physiological events, is one of the newest and most rapidly developing fields in cellular biology. In spite of many recent strides in understanding the molecular basis for cellular functions, our knowledge is only scanty and much remains to be discovered (eg, Sleigh 1984a, b; Bereiter-Hahn et al 1987). Considerable progress has been made, however, in explaining the many varied activities of protozoa from the perspective of general cellular biological theory. And, protozoa have proven to be very useful tools in examining some of the basic cytomechanical properties of eukaryotic cells. The clearly identifiable motile organelles of some protozoa, including cilia and flagella, and the relative ease of isolating cells and observing cytoplasmic activity as in ameboid movement, have provided additional tools to the cell biologist in verifying observations obtained with other cell types.
KeywordsFrontal Zone Cytoplasmic Streaming Power Stroke Flagellar Motion Phototactic Response
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