1. Protozoa are microscopic, unicellular organisms that lack chlorophyll, are motile during at least one stage in their development, and reproduce most often by binary fission.
Classification of Protozoa (Figure 12.7)
1. In classification schemes based on rRNA, protozoa are not a single group of organisms.
2. Protozoa have traditionally been put into groups based on their mode of locomotion. (Table 12.2)
3. Sarcomastigophora include the Mastigophora, the flagellated protozoa, and Sarcodina, which move by means of pseudopodia.
4. Ciliophora move by means of cilia.
5. Apicomplexa, also referred to as the sporozoa, include Plasmodium sp., the cause of malaria.
6. Microsporidia, an intracellular protozoa, causes disease in immunocompromised individuals.
1. Most protozoa are free-living and are found in marine and fresh water as well as terrestrial environments.
2. They are important decomposers in many ecosystems and are a key part of the food chain.
Structure of Protozoa
1. Protozoa lack a cell wall, but most maintain a definite shape using the material lying just beneath the plasma membrane.
2. Life cycles are often complex and include more than one habitat. (Figure 12.9)
3. Protozoa feed by either phagocytosis or pinocytosis.
Protozoan Reproduction (Figure 12.10)
1. Reproduction is often by binary fission; some reproduce by multiple fissions or schizogony.
Protozoa and Human Disease (Table 12.2)
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