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Chapter 5 -- Protozoan Groups

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Joshua Burton

on 13 February 2013

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Transcript of Chapter 5 -- Protozoan Groups

Excystment – the process of escaping or emerging from a cyst. A return of favorable conditions may initiate excystment for protozoa in which the cysts are in their quiescent stage. Encystment and Excystment Encystment – process of cyst formation. Stimulating factors may be as a result of adverse environmental change such as food deficiency, change in pH, low oxygen concentration, and dehydration. Encystment and Excystment Protozoa successfully thrive in harsh conditions such as heat, cold and dryness. Their ability to form cysts contributes greatly to their adaptive capabilities.

A cyst is a resilient, quiescent stage of an organism, having a protective external covering, and a complete shutdown of metabolic activity. Encystment and Excystment Some sexual phenomena in protozoa do not involve syngamy – fertilization of an individual gamete by another gamete.

Examples include:
Autogamy – gametic nuclei fuse within the parent organism to restore the diploid number
Conjugation – temporary union of protozoa as they exchange gametic nuclei or chromatin material. Reproduction Sexual Processes – Protozoa reproduce asexually but there are some elements of sexual reproduction that can be observed among them.

These features include a reduction in the chromosome number (diploid to haploid), the development of gametes, or gamete nuclei, and the fusion of gamete nuclei. Reproduction Schizogony (Multiple fission) – several nuclear divisions precede division of the cytoplasm so that numerous progeny are produced simultaneously.

Formation of spores by multiple fission is referred to as sporogony. Reproduction Asexual Reproduction – protozoa produce genetically identical individuals by the process of fission.

Binary fission – produces progeny that are identical in size and shape.

Budding – produces progeny that are considerably smaller than the parent cell. Reproduction Osmoregulation refers to the maintenance of appropriate concentrations of salt and water within the cell.

Contractile vacuoles are responsible for osmoregulation in protozoa. They are located in the ectoplasm and act as pumps to remove excess water from the cytoplasm. Excretion and Osmoregulation Heterotrophs are further categorized into:

Phagotrophs (Holozoic feeders) – ingest visible particles of food.

Osmotrophs (Saprozoic feeders) – ingest food in a soluble form. Nutrition and Digestion Protozoa can be categorized as autotrophic and heterotrophic.

Autotrophic nutrition is characterized by the ability to use inorganic substances to synthesize complex organic compounds.

Heterotrophic nutrition describes the dependence on other organisms for the acquisition of organic molecules. Nutrition and Digestion Pseudopodia exist in several forms:
Lobopodia – blunt extensions of the cell body containing central granular endoplasm (sol/fluid), and a peripheral nongranular layer called ectoplasm (gel/semisolid).
Filipodia – thin branching extensions that contain only ectoplasm.
Reticulopodia – pseudopodia that repeatedly branch and rejoin to form a network like mesh.
Axopodia – long thin pseudopodia supported by axial rods of microtubules in a spiral or geometric array. Pseudopodia The actions of cilia and flagella are somewhat different, but there is no sharp morphological distinction between them.

Cilia are typically present in large numbers and are relatively short. They propel water parallel to their surface of attachment.

Flagella are longer and less numerous. They propel water parallel to their own main axis. Cilia and Flagella (Undulipodia) Extrusomes – membrane-bound organelles that are used to expel something from the cell.

Locomotor Organelles – cilia and flagella facilitate protozoan movement. Ciliary movement generates water currents that may aid the ingestion of food, respiration, reproduction, excretion, and osmoregulation. Form and Function Mitochondria – perform aerobic metabolism for energy acquisition.

Golgi Apparatus – part of the secretory system of the endoplasmic reticulum. The Golgi bodies are also called dictyosomes.

Plastids – contain photosynthetic pigments. Form and Function Nucleolus – multiple nucleoli may be present in some protozoa. They contain ribosomal RNA and may be specialized portions of certain chromosomes carrying multiple copies of the genes that encode ribosomal RNA. Form and Function Protozoa are functionally complete organisms with particular micro-anatomical structures.

The Nucleus – membrane-bound structure whose interior communicates with the cytoplasm by small pores. The genetic material is stored on chromosomes within the nucleus. Some ciliates have a large macronucleus and several micronuclei. Form and Function Ciliates – have numerous cilia covering the cell membrane. Cilia are the hair-like vibratile structures used for moving particles along the cell surface, or for locomotion. Protozoan Body Types Protozoa are highly adaptive and can be found wherever life exists. They can be sessile or free-swimming and usually thrive in moist habitats.

Protozoa have many symbiotic interactions with plants and animals. Parasitic protozoa are the cause of many diseases in humans and domestic animals. Protozoa Unicellular eukaryotic organisms are collectively referred to as protista or protozoa. All their life activities occur within a single plasma membrane.

The name was initially meant to describe two animal-like features: a motile stage in the life cycle, and the absence of a cell wall. Protozoa Amebas – have irregular shapes caused by flowing protoplasm inside the cell membrane. They may be testate (shelled) or naked. Protozoan Body Types Unicellular Eukaryotes Protozoan Groups Phagocytosis is the process by which holozoic feeders ingest their food. There is an infolding of the plasma membrane around the food particle which becomes contained within a vesicle called the phagosome. Nutrition and Digestion A pseudopodium is a temporary protrusion of cytoplasm that functions in locomotion, and the ingestion of food. They are the chief means of locomotion for ameboid cells. Pseudopodia Flagellates – have one or more flagella; the whip-like organelle of locomotion. Protozoan Body Types The phylogeny of eukaryotes is important to biologists and has important practical goals.
Treatments effective against particular pathogens may work on related organisms.

Adaptive Diversification – Protozoa are highly adaptive. Amebas range from bottom-dwelling, naked species to planktonic forms with tests. Some have photosynthetic capabilities and many are symbiotic species. Phylogeny and Adaptive Diversification Members of this clade are characterized by a combination of flattened mitochondrial cristae and one posterior flagellum on flagellated cells.

Opisthokonta contains animals and fungi, microsporidians and choanoflagellates. Opisthokonta Amoebozoans include naked and testate amebas, as well as those with flagellated stages in the life cycle.

They typically have branched tubular mitochondrial cristae.

Acanthamoeba castellani is an amoebozoan that kills cells of the human cornea. It is spread through contact lenses that are not properly disinfected. Amoebozoa This clade consists of glaucophytes, red algae, green algae, bryophytes and vascular plants.

The group is photosynthetic, having chloroplasts derived from the primary endosymbiotic event with a cyanobacterium. Plantae Centrohelids are amebas with flattened mitochondrial cristae.

Most live in freshwater, but some reside in brackish or marine environments.

Their axopodial structure is distinctive, with a triangular or hexagonal arrangement of microtubules in the axoneme. Centrohelida Radiolarians are also marine forms that mostly live in plankton. They have siliceous skeletons and perforated central capsules to allow cytoplasmic continuity between the inner and outer cytoplasm.

They are among the oldest known protozoa . Radiolaria Foraminiferans are mostly marine forms that secrete complex tests of calcium carbonate.
Test – a shell or hardened outer covering

Slender pseudopodia extend through openings in the test, then run together to form a protoplasmic net in which they trap their prey Foraminifera Cercozoans do not share a common body plan as there are flagellated and ameboid members. Cercozoa Toxoplasma (a coccidian) is a common parasite in the intestines of cats. In humans, the parasite poses a threat to AIDS patients and pregnant women.

About 2% of all mental retardation cases in the US occur as a result of congenital toxoplasmosis. Humans can be become infected by eating raw/undercooked meats, or ingesting oocysts from cat feces. Apicomplexa Plasmodium (a coccidian) is the sporozoan parasite that causes malaria. It is transmitted by the female Anopheles mosquito, and can also be contracted congenitally.

Malaria is one of the most serious diseases in the world, accounted for an estimated 700,000 – 2 million deaths per annum. Apicomplexa Apicomplexan parasites are classified as coccidians, and gregarines.

Coccidians – infect both vetebrates and invertebrates

Gregarines – reside mainly in the digestive tract, and body cavity of some invertebrates. Apicomplexa All members of this phylum are endoparasitic. They reside inside of a host organism.

Many apicomplexans lack cilia and flagella.

They are characterized by a particular combination of organelles that are referred to as the apical complex.

The apical complex includes rhoptries and micronemes the aid in penetrating the host cell. Apicomplexa “Red Tide” describes the phenomenon where the prolific reproduction of dinoflagellates causes the water to turn red, from the pigments in their chromatophores.

The toxins produced by the bloom of dinoflagellates may be highly poisonous to humans, fish, and other forms of marine life. Dinoflagellata Some dinoflagellates such as zooxanthellae have mutualistic associations with some sea anemones, horny and stony corals, and clams. Only those stony corals with symbiotic zooanthellae can form coral reefs.

Dinoflagellates can also be harmful to other organisms when they produce a “red tide” Dinoflagellata Many are photoautotrophic, with chromatophores that contain chlorophylls a and c. Some species are among the most important primary producers in marine environments.

Dinoflagellates usually have two flagella, one borne longitudinally and the other equatorially. Dinoflagellata Ciliates always have multiple nuclei. At least one macronucleus and one micronucleus, but varying to many of either type.

Macronuclei seemingly have developmental, synthetic and metabolic functions, while micronuclei participate in sexual reproduction. Ciliophora This grouping constitutes the ciliates. They are the most structurally complex and diversely specialized of all protozoa.

Most ciliates are holozoic feeders, and posses a cytostome (mouth).

Most ciliates have contractile vacuoles. Ciliophora Alveolata is a general grouping of Ciliophora, Dinoflagellata and Apicomplexa. The members of this clade are characterized by the presence of alveoli.

Alveoli are membrane-bound sacs that lie beneath the plasma membrane, giving structural support, and may produces pellicles or thecal plates. Alveolata Brown algae, yellow algae, and diatoms are stramenopiles. They are generally plant-like forms that collect energy with plastids, although there are some animal-like forms.

Opalinids, a group of animal parasites, and plant pathogens such as slime nets and oomycetes are members of this clade. Stramenopiles Members of this clade have tubular mitochondrial cristae. They may have flagella, but are considered heterokonts because their flagellates have two different flagella.

Both flagella are inserted at the cell anterior, instead of the posterior. One is short and smooth, the other long and hairy. Stramenopiles Parabasalids such as Trichomonas vaginalis are known to infect the urogenital tract of humans, causing nongonococcal urethritis and vaginitis. Parabasalids Members of this phyla are characterized by an axostyle --- a stiffening rod of microtubules that extends longitudinally through the cell body.

Their Golgi apparatus has a modified region called a parabasal body, which functions as part of the secretory system in the endoplasmic reticulum. Parabasalids Naegleria fowleri has been identified as the cause of primary amebic meningoencephalitis. The ameba are transmitted through the nasal passages when inhaled from contaminated water.

They migrate along the olfactory nerves to the brain, where they destroy tissue. Heterolobosea Heteroloboseans are naked amebas whose pseudopodia form in an abrupt manner. Their life cycle includes both amebic and flagellated stages.

Most feed on bacteria and are generally harmless to humans. Heterolobosea Euglenozoa are divided into to subgroups:

Euglenids – have chloroplasts surrounded by a double membrane, containing chlorophyll b.

Kinetoplastans – parasitic to plants and animals. Have a kinetoplast which is a specialized mitochondrial form with nets of circular DNA. Euglenozoa Monophyletic group characterized by the persistence of the nucleoli during mitosis, and the presence of discoid mitochondrial cristae.

Euglenozoa have a series of longitudinal microtubules just beneath the plasma membrane that help to stiffen the membrane into a pellicle --- a thin, translucent envelope that protozoa use as a covering. Euglenozoa Protozoa are classified by their recognizable features, such as branching pseudopodia.

Taxonomic classifications identify the morphological features that assist in distinguishing species. Protozoan Taxa Protozoa in these taxa do not have mitochondria.

Giardia are representative of the diplomonads, and are also a common intestinal parasite. They are transmitted by contaminated food, water and fecal matter. Their infections may cause a discomforting diarrhea and the malabsorption of nutrients. Retortamonads and the Diplomonads Species of Trypanosoma are known to cause African sleeping sickness in humans, as well as African trypanosomiasis and Chagas disease.
The protozoan parasite is transmitted by biting bugs and affects macrophages and muscle cells. Euglenozoa Unicellular Eukaryotes Protozoan Groups
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