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2014S_BIO153H5S_Lab2_Prokaryotes & Protists(1).pdf

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Christoph Richter

Week 2 Prokaryotes and protistsObjectivesBe able to describethe difference between Grampositive and Gramnegative bacteriathe range of morphologies types of locomotion lifestyles and modes of reproduction in a sample of protistsBe able to identifythe major differences between prokaryotic and eukaryotic cellsthe different bacteria and protists presented in labFigure 21 Phylogeny of prokaryotes and eukaryotes Dashed lines indicate groups that are classified as prokaryotes Bolded names indicate groups with representatives that are examined in detail in this labOverviewProkaryotes and protists are by far the most abundant organisms on the planet They are indispensable to life on earth They produce more than half of Earths atmospheric oxygen and the bacteria among them are responsible for putting nitrogen into a form plants can use They are present in numbers so immense that the weight or biomass of all prokaryotes and protists on Earth exceeds the biomass of all larger life forms Much of the diversity exhibited by these organisms lies in the array of their metabolic pathways as opposed to any structural differences Today we will focus on the basic characteristics of bacteria and protists that are used as distinguishing characteristics and examine some representative genera from the two groupsPROKARYOTESProkaryotes are microscopic singlecelled organisms They differ from eukaryotes in that they do not have a membranebound nucleus pro from the Greek word for before and karyon from the Greek word for kernel in reference to the nucleus eu means good well or true Instead of having chromosomal DNA their genetic material is arranged in a circular loop called a plasmid and they reproduce asexually through a simple cellsplitting process called binary fission Prokaryotic cells are very small roughly the size of an animal mitochondrion about 12 m in BIO153 2014 Lab 2 diameter and 10 m long There are two major domains among the prokaryotes Archaea and EubacteriaDomain ArchaeaOrganisms in the domain Archaea look similar to bacteria but differ significantly at the biochemical and genetic levels Archaea live in extremely anaerobic environments and have been called extremophiles Different archaeans have been classified as thermophiles live in environments with temperatures of 60100C or more halophiles live in extremely salty conditions acidophiles live in acidic environments and methanogens methane producers Given these environmental preferences you will not find it surprising that we wont have specimens of this unusual group in lab for you to examineDomain EubacteriaEubacteria commonly called bacteria are the most abundant forms of life They occur in soil water in our food and in our bodies They perform many important ecological roles They serve as decomposers agents of fermentation nutrient recyclers and aid in our digestionBacteria are generally quite small and have simple shapes although there are some bacteria notably the cyanobacteria with more complex morphologies Bacteria have traditionally been identified and classified on the basis of their biochemistry and the conditions under which they grow Molecular biology has made it possible to classify bacteria on the basis of similarities among DNA sequences and this has revolutionized bacterial systematics However simple classifications are still possible using cell morphology and organizations of aggregates of cells For this lab we will focus only on the basic morphology of bacteria concepts behind the Gramstaining technique for identifying bacteria and the basic features of cyanobacteriaActivity 21 Bacterial morphologyOne way bacteria are classified is by their shape For example rodshaped cells are termedbacilli sing bacillus spherical cells are termed cocci sing coccus spiralshaped cells are termed spirilli sing spirillum The genus or species name may also reflect the nature of the groupings in which they occur Diplo means that the bacterial cells occur in pairs strepto means they form chains staphylo means the cells form bunches like grapes Used together a spherical bacterium that occurs in pairs would be called DiplococciMaterials compound microscopeprepared slide of three bacterial types spiral spherical and rodshapedsupplementary image of bacterial cell typesProcedure1 Examine the prepared slide of bacteria under 40X objectives Sketch and label the three shapes of bacteria you see all three are on the same slideuse the coaxial stage controls to see them all
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