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Lecture

Bacillariophycea (DIatoms)

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Department
Biology
Course
BIOL-2152
Professor
Kent Simmons
Semester
Winter

Description
Bacillariophycea: Diatoms  Unicellular, sometimes colonial’ Free living photoautotrophs Colorless heterotrophs Plankton and periphyton in all freshwater and marine environments  25% of the earths total primary activity (1 in 4 oxygen molecules)  2 part cell walls called frustules each cell contains one or more chloroplasts  2 choroplast envelope membranes, 2 chloroplast E.R membranes attached to the nuclear  envelope 3 thylakoids to a band, central pyrenoid  fucoxanthin primary pigment,  chrysolaminarin is storage molecule silica cell wall/frustule physically strong and chemically inert protective covering  frustules cannot be attacked enzymatically  uptake of silicon does not require lots of energy  enormously flexible morphologically  but  silica is impermeable, so lots of pores  inextensible. 2 major segments which slide apart as the cells grow  escape of cells of the wall is necessary during sexual reproduction  new valves need to be secreted within the parental thecae  new valves are smaller, so the average size of a population decreases over generational time  girdle bands  connecting bands overlapping one another  essential to allow growth of the cell after cell division  valves systems of silica ribs that have grown out from a circular or elongate pattern  equipped with pores or slits for transfer  pennate or radial symmetry  motility  raphe: line running the length of the valve. Functions in motility  limited motility very important during sexual reproduction  mucilage secreted by raphe aids in movment phototaxis photosensitive region at the tip of each cell integrated into complex diurnal rythms asexual reproduction diatoms must be able to escape complete size dimunition if they are to survive achieved via sexual reproduction sexual reproduction gametic  centrate diatoms: oogamous. Male gametes flagellated  pennate diatoms: isogamous. Non flagellated  resting stages form thick, ornamented cell walls during different times in their life cycle form in the presence of a stress 
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