Protozoa and Algae - Lecture notes 16 PDF

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Protozoa and AlgaeAdditional Notes Date Links Week Week 8Protozoa Means ‘first animals' Single cell eukaryotes Lack a rigid cell wall, are generally motile and inhabit ‘wet’environments (although may also form a resting stage - cysts or spores - with thick cell wall). Are heterotrophs Some species a...

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Protozoa and Algae

Week 8 Protozoa Means ‘first animals' Single cell eukaryotes Lack a rigid cell wall, are generally motile and inhabit ‘wet’environments (although may also form a resting stage - cysts or spores with thick cell wall). Are heterotrophs Some species are parasites of animals or plants. Algae Essentially, protozoa that have a plastid. Those algae in which the plastid is a chloroplast are phototrophs Collectively, the protozoa and algae are referred to as protists Examples of protozoa and algae on our world Malaria: caused by Plasmodium falciparum, P. vivax, etc.. P. infestans: the cause of potato blight Phytophthora palmivora – affects cocoa pods Red tides: caused by dinoflagellates appear in warm, nutrient rich environments fish and shellfish take up the toxins produced by these which can lead to paralytic neurotoxin poisoning when these fish/shellfish are consumed when these blooms die away they strip the oxygen which can lead to the killing of fish chalk deposits such as The White Cliffs of Dover - made from a single cell alga Emiliania huxleyi covers itself in plates of calcium carbonate

this protist can take CO2 and convert it either into sugars (organic) or into calcium carbonate (inorganic) these are very important in carbon cycling in oceans as they can capture a huge amount of CO2 to lock away as chalk - which is then brought to the bottom of the ocean there is a concern with the drop in pH in oceans as the CaCO3 will be dissolved, releasing CO2 The evolution of the eukaryotes Eukaryotes are believed to have evolved from the prokaryotic Archaea, through a process of internal membrane formation (to create nucleus, ER, etc), cell enlargement and serial endosymbiosis (mitochondria and plastids). this process is shown on the right can also see this internal membrane formation in modern day bacteria as shown below e.g. cyanobacteria with their thylakoid membranes

4 main groups of protozoa  alveolates  euglenoids  oomycetes  sarcodina 1 - Alveolates as the name suggests, cell possesses alveoli

these are sac like membrane structures filled with fluid that lie underneath the cell membrane The three main phyla of alveolates are:  Ciliates (e.g. Paramecium) some or all of the cell surface is covered with cilia that beat to propel them, to either move through the water or to draw in food/particles Free-living ciliates feed mainly on bacteria, algae or even other ciliates Some ciliates harbour symbiotic algae or retain functional chloroplasts from prey Ciliates in soils form cysts in order to survive long periods of drying  Sporozoans (e.g. Plasmodium, Cryptosporidium) Haploid parasitic protozoa Have complex life cycle usually involving growth stage within host cell. A major sub-group of the phylum Sporozoa are the apicomplexans – have distinctive structure at apical end of sporozoite (involved in host cell invasion)  Dinoflagellates [see last lecture] 2 - Euglenoids Flagellated protozoa including:  Euglena Many species of the genus possess chloroplasts, but are also capable of heterotrophic growth. In some species the chloroplast is easily lost (= ‘bleaching’).  Trypanosomes flagellated pathogens of plants and animals life cycle involves insect host like plasmodium, possessing a kinetoplast (this being a specialised DNA containing structure in the mitochondrion)  Leishmania 3 - Oomycetes Filamentous protozoa that may be free-living or parasitic Many grow as ‘fungal-like’ hyphae and appear as rusts or mildews. Originally considered to be fungi, now clear that they are related to the Chromista (golden algae). 4. Sarcodina Rhizopoda) these are the largest group of protozoa cointaning 12000 extant species this group comprises the amoeba - unicellular protozoa that use pseudopodia for locomotion and feeding (phagocytosis) these amoeba move in response to chemical gradients

move through assembly/disassembly of the actin that comprises the cytoskeleton Most species free-living, although some important parasites Example 1 Entamoeba histolytica major human pathogen E. histolytica has two stages in life cycle: a) Motile amoeba (trophozoite); b) cyst Ingested cysts are resistant to stomach acid and hatch to form amoebae (its previous stage in its life cycle) in colon. New cysts form and pass through the bowel Normally no symptoms, but in some individuals amoebae become invasive and attack organs, resulting in localised infection (amoebic dysentery) or systemic infection of many organs including the brain...