Protozoa Structure and Function

Structure of Protozoa

• Pellicle serves as a rigid outer layer in some protozoa, maintaining shape.
• Cytoplasm differentiates into ectoplasm (outer) and endoplasm (inner), significant in species with pseudopodia, especially amebas.
• Contractile vacuoles assist in osmoregulation, present in protozoa like Naegleria and Balantidium.
• Subpellicular microtubules aid slow movement in Apicomplexa, which lack external organelles for locomotion.
• Distinctive undulating membranes found in trichomonads and trypanosomes contribute to movement and feeding.
• Organelles present include Golgi apparatus, mitochondria, lysosomes, food vacuoles, and conoids in Apicomplexa.

Nutrition

• Protozoa are holozoic, requiring organic materials for nutrition, which can be particulate or in solution.
• Amebas utilize phagocytosis for food ingestion, digesting in food vacuoles and egesting waste.
• Some protozoa possess a permanent cytosome or micropore for feeding.
• Pinocytosis involves fluid absorption through temporary openings in the cell membrane that form food vacuoles.
• Types of nutrition:
  • Autotrophic: Uses light energy for photosynthesis.
  • Heterotrophic: Ingests organic material.
  • Mixotrophic: Combines autotrophic and heterotrophic methods depending on light availability.

Reproduction

• Reproduction can be asexual (binary fission) or sexual.
• Binary fission involves organelle duplication and division into two organisms.
• Some protozoa, like Testacea, have a protective shell and move via pseudopodia.

Testacea and Foraminifera

• Testacea have a siliceous or chitinoid shell, sometimes reinforced with sand grains.
• Foraminifera, found in all oceans, have calcium carbonate tests with slender pseudopodia for prey capture and digestion.

Phylum Mastigophora

• Zooflagellates are unicellular and may be free-living or parasitic, with one or two flagella for movement and feeding.
• Reproduction primarily occurs by binary fission; cyst formation is observed in some species.

Subphyla and Species

• Phytomastigina (Class Euglenoidina): Includes Euglena, found in freshwater with flagella and a red eyespot for light orientation. Autotrophic by day, becomes saprozoic in the dark.
• Volvocaceae (Class Volvocaceae): Volvox is a colonial freshwater flagellate with cellulose cell walls and flagella.
• Opalinea (Class Opalinea): Parasitic, found in amphibian digestive systems; characterized by a large body with cilia.

Phylum Sporozoa

• Comprised of endoparasitic protozoans lacking locomotor structures and possessing tough coverings and a single nucleus.
• Reproduction includes asexual (multiple fission) and sexual stages involving anisogamy.
• Classes:
  • Gregarinina: Parasites of invertebrates, low economic significance.
  • Coccidiomorpha: Intracellular parasites with significant medical and veterinary importance.

Coccidiida Life Cycle

• Eimeria: causes coccidiosis, with symptoms such as severe diarrhea in domestic animals.
• Life cycle involves asexual reproduction (schizogony) in host intestinal cells and sexual reproduction (gametogony) leading to oocyst formation.
• Infection occurs via sporulated oocysts ingested by new hosts.

Malaria and Piroplasmosis

• Malaria, caused by Plasmodium species, leads to significant morbidity and mortality worldwide.
• Piroplasmosis affects Equidae, transmitted mainly by ticks, characterized by bloodborne infections.

Phylum Microsporidia

• Microsporidia are obligate intracellular parasites that infect a wide range of hosts, including those with strong immune systems.
• Notable species include Nosema bombycis (affects silkworms) and Nosema apis (affects honey bees, causing nosemosis).

Conclusion

• Protozoa exhibit varied structures, complex nutritional strategies, and multifaceted reproductive strategies, making them significant both ecologically and medically.