Transcript Document
PROTOZOA An introduction • • • • • • • Protozoan / Protozoa Protozoology “First animal” Eukaryotic protists. Generally, single-celled. Size: Between 5 & 250 μm in dia More than 65,000 described species across 7 phyla. Size-wise… • Leishmania donovani – Cause of the human disease kala azar – 1 - 4 μm • Amoeba proteus measures 600 μm • Certain ciliates reach 2 mm • A protective envelope extinct members of Foraminiferida measure upto 15 cm in dia. OCCURENCE • Moist habitats - Sea, Soil & in freshwater • Even in polar regions & at high altitudes • Under dry conditions, forms a cyst – Eg.: Naeglaria, an amoeba. • Parasitic protozoa – Eg.: Malarial parasite, Plasmodium ECOLOGY • Free-living forms • Symbiotic protozoa – Eg.: in the termite gut, beneficial to host • Parasitic protozoa – Cause disease. FREE-LIVING PROTOZOA Factors which influence their distribution and population • • • • • Moisture Temperature Light Nutrient availability Other physical & chemical conditions. • LIGHT – Bear chromatophores – Carry out photosynthesis; requires sunlight – Few protozoa avoid light. • pH – Optimum pH range of 6 – 8 for maximum metabolic activity. – Yet, extremities: 3.2 to 8.7 • NUTRIENTS: – Some protozoa thrive in water rich in oxygen but low in organic matter (mountain springs, brooks, or ponds) – Water rich in minerals – Water where there is active oxidation & degradation of organic matter (the majority of freshwater protozoa, such as the ciliates). – Water with little oxygen – Salt & freshwater. • Anaerobic protozoa – Spp of Metopus, Saprodinium & Epalxis • Aerobic protozoa – Bodo, Paramecium, Aspidisca, and Vorticella. • Temperature – Optimum temperature between 16 and 25°C – Max. between 36 and 40°C – Rarely, 30 to 56°C of hot springs SYMBIOTIC PROTOZOA • Commensalism – Host is neither injured nor benefited, but commensal is benefited – Ectocommensalism • Protozoa attach themselves to a host’s body. – Endocommensalism • Protozoa, inside the host’s body. • Mutualism – Beneficial to both – Eg.: Flagellates in the termite gut digest woody material eaten by termite to a glycogenous substance which can be used by the host cells PARASITIC PROTOZOA • Parasite lives at the expense of the other. • Host may develop pathological conditions. • Parasite feeds on host cells, cell fragments, cytoplasm and even nuclei. • Eg.: Sporozoa • Hyperparasitism – Parasitic protozoa that parasitize other protozoan In the food chain…. • In marine waters – Zooplankton: Protozoa that feed on the photosynthetic phytoplankton – Light energy Phytoplankton Zooplankton Carnivores • Dead bodies of producers & consumers Decomposition by fungi & bacteria Ingestion of bacteria by protozoa. (Saprophytic) PROTOZOAN MORPHOLOGY INTRA-CELLULAR ORGANELLES • Protein fibrils - Fibrillar bundles, myonemes & microtubules: For contractility • Cytoplasm: – Ectoplasm (gel-like) & Endoplasm (voluminous & fluid) • Membrane-bound systems in endoplasm • Endoplasmic reticulum • Ribosomes • Golgi complexes • Mitochrondria • Kinetosomes or blepharoplasts: Intracytoplasmic basal bodies of cilia or flagella. • Food vacuoles • Contractile vacuoles, and • Nuclei • In the ciliates, two dissimilar nuclei – One large Macronucleus controls the metabolic activities and regeneration processes – One small Micronucleus for reproductive activity. • Cell membrane (plasmalemma) – Physical protection – Exchange of substances (semipermeable) – Site of perception of chemical and mechanical stimuli – Establishment of contact with other cells (cell sensitivity to external factors). • PELLICLE – Combinations of membranes – Eg.: in Euglena, Paramecium • A diffuse layer of mucopolysaccharides over the plasmalemma • For Pinocytosis: Uptake of fluids and soluble nutrients through small invaginations in the cell membrane that subsequently form intracellular vesicles • THECAE, SHELLS, TESTS, LORICAE Feeding Structures • • • • • • Pseudopodial engulfment of amoebas Tentacular feeding tubes of suctorians Cytostome of many ciliates Oral groove Peristome Cytopharynx: – A region, nutrients pass through & get enclosed in a food vacuole. LOCOMOTOR ORGANELLES • Pseudopodium – Temporary projection of part of the cytoplasm when pellicle is absent – Eg.: Amoebas (Sarcodina) – For capturing food substances. • Flagellum – An extremely fine filamentous extension of the cell – Varies from 1 to 8; Usually, 1 or 2 – 2 parts: an elastic filament called an axoneme and the contractile cytoplasmic sheath that surrounds the axoneme. • Cilia – Locomotor function – Also aid in the ingestion of food – Fine & short threadlike extensions from the cell – Uniform or different in lengths REPRODUCTION • Asexual reproduction • Sexual reproduction • Both asexual and sexual processes – Some parasitic protozoa • Asexual reproduction – Cell division • Binary fission • Multiple fission – Budding: A variation of unequal cell division. BINARY FISSION • • • • • In amoebas Pseudopodia are withdrawn Nucleus divides Organism elongates Constricts in the center to form 2 daughter cells. MULTIPLE FISSION • Formation of multiple nuclei within the mother cell • Corresponding number of daughter cells • Occurs commonly in the foraminifera, the radiolaria, and the heliozoa. • In the sporozoa, malarial parasite Plasmodium – Schizogony BUDDING • Formation of a new organism by the protrusion of part of another • New cell is genetically identical to the primary one (a clone). • Exogenous budding: – Involves formation and separation of the bud toward the outside. • Endogenous budding – In many suctorian species – Formed inside the mother cell SEXUAL REPRODUCTION • Sexual fusion of two gametes (syngamy or gametogamy) • Conjugation: – A temporary union of two individual cells for purpose of exchanging nuclear material – found exclusively in ciliates – After exchange of nuclei, the conjugants separate – Each of them gives rise to its respective progeny by fission or budding. • When they are unlike in morphology (as well as physiology), they are anisogametes and can be either microgametes or ma crogametes. That is, they are like the spermatozoa and the ova of metazoa, respectively. Thus microgametes are motile, relatively small, and usually numerous in comparison to macrogametes. Anisogametes are common among the sporozoa. For example, in Plasm odium vivax (a sporozoan that causes a type of malaria), anisogamy results in the formation of ookinetes or motile zygotes which give rise to a large number of sporozoites (long, slender bodies with an oval nucleus and firm cuticle, capable of producing new infection). REGENERATION • Capacity to regenerate lost parts from simple forms to those with highly complex structures. • The collar functions as a food catching device.