13 - Principles of Eukaryotic Diversity Eukaryotic...

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1 Eukaryotic Diversity II 1. Friday – Endosymbiosis HW due 2. Friday - GAE involves a computer simulation of diffusion 3. One laptop per group of 3 or two laptops per group of 4 or 5 with downloaded app. Wolfram CDF Player , plus diffusion simulation from course website. “Enable dynamic” button 4. Fully charged laptop, watch/timer, calculator Principles of Eukaryotic Diversity Eukaryotes evolved as complex assemblages of several organisms Endosymbiosis – the uptake of another organism and its evolution into an organelle. (Focus of Friday’s discussion) Eukaryotes acquired aerobic respiration and oxygenic photosynthesis from bacterial endosymbionts. Prokaryotes – lateral gene transfer Eukaryotes – endosymbiosis (with internal LGT) Unifying features include: nucleus, sexual life cycle, endomembrane system, and complex cytoskeleton. Eukaryotes originated the sexual stages, i.e., syngamy and meiosis, in life cycles. Eukaryotes manifest more organellar, cellular, and multicellular diversity than prokaryotes. Eukaryotes can be divided into three artificial groups: basal, “heterotrophic” and “photosynthetic” groups. Independent origins of eukaryotic multicellularity - > 20 origins Basal “Photosynthetic” “Heterotrophic” unicellular flagellate Basal flagellated eukaryotes Likely origin of multicellularity in some lineages Group discussion - Why are unicellular organisms constrained in their ability to develop large sizes? Thiomargarita Valonia Thiomargarita - the largest known unicellular prokaryote (0.75 mm in diameter). It grows buried in sulfide-rich ocean sediments. Valonia - a very large unicellular eukaryote (5 cm in diameter) in the green algae. It grows in protective sites on coral reefs.
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2 Group discussion - Why are unicellular organisms constrained in their ability to develop large sizes? Thiomargarita Valonia What are the convergent design strategies operating in the evolution of multicellular eukaryotes? Colony - a loose association of “independent” cells Volvox - (multicellular?) Volvox - up to 60,000 Chlamydomonas -like cells limited cell specialization but some organization specialized cells are capable of regenerating the organism cells can not live as independent unicells Chlamydomonas - (unicellular) Gonium - (small colony) Pandorina - (large colony) F. Fig. 28-13 Design strategies of multicellular eukaryotes Colony - a loose association of “independent” cells Choanoflagellates - closest living relatives of the animal lineage adult cells as individual cells or a colony attached to substrate phagocytosis of prokaryotes and food particles individual cells undergo asexual reproduction Sponges - multicellular sessile animals composed of several cell types totipotency - an individual cell can often regenerate the entire organism separated cells can reform the sponge Sponges Choanoflagellates Choanoflagellates and sponges Feeding cells (or choanocytes) of sponges are virtually identical to choanoflagellates F. Fig. 31.11
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This note was uploaded on 04/05/2012 for the course BSCI 207 taught by Professor Higgins during the Spring '08 term at Maryland.

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13 - Principles of Eukaryotic Diversity Eukaryotic...

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