Lecture_26_soma - The glories of multicellularity...

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1 Requirements for Multicellularity Lecture 26 Bis2A Or the multicellular covenant The glories of multicellularity Why are there multicellular organisms? What do they do in the biosphere? What adaptations make multicellularity possible? Multicellular organisms are a small minority among Eukaryotes Multicellularity in land plants Light (energy for photosynthesis) CO 2 (carbon for photosynthesis) Water and nutrients (N, P, K, etc.) What can a plant do that a cyanobacteria cannot? -Chloroplasts evolved from the cyanos What are the advantages of multicellularity for a photosynthesizing organism? What are the disadvantages? Multicellularity in animals Sensory system (looking for food) Central nervous system (identifying food) Locomotory system (getting the food) Through gut (eating the food)
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2 Metabolic lifestyles of multicellular organisms Prokaryotes Animals, plants, and fungi Photosynthesis + + Methanogens (H 2 eaters) + Sulfur reducers + Nitrifiers (NH 4 + )+ Iron bacteria (Fe 2+ => Fe 3+ Carboxido bacteria (CO => CO 2 Phosphite bacteria (PO 3 3- => PO 4 3- Other chemoautotrophs + Aerobic heterotrophs + + Anaerobic heterotrophs + Eukaryotes evolved as heterotrophs (predators in the ecological sense) Photosynthesis (in plants) and anaerobic heterotrophy (in some protists) evolved secondarily through symbiosis with prokaryotes (chloroplasts and hydrogenosomes) Multicellular organisms need prokaryotes and protists Oxygen! Aerobic heterotrophs (animals) need oxygen - made by cyanobacteria Nitrogen Neither plants nor animals can absorb nitrogen from atmosphere Digestion of complex organics Termite Spirochete Protist Trichonympha , a flagellate protist Wood particles Multicellular organisms create new ecological niches for prokaryotes and protists Many bacteria and most protists are heterotrophs Many bacterial and protist heterotrophs are parasites Others are animal and plant symbionts / mutualists For example, the human gut has ~ 1.5 kg of bacteria; the number of bacteria in our guts is greater than the number of cells in our body, their collective genome is much larger than ours, and their metabolic output is about the same as of the human liver. Bacterial gut fauna is essential to our health! Some bacteria have become obligate symbionts of animals or plants Aphid Buchnera Multicellularity as an ecological adaptation Multicellular organisms are only a small fraction of biodiversity on Earth Multicellularity evolved independently several times in Eukaryotes Multicellular organisms have only a small sub-set of metabolic lifestyles (food sources) compared to prokaryotes Multicellularity is an ecological adaptation that allows increased consumption of resources by a single individual Plants are large-scale photosynthetics Animals are top-of-the-food-chain predators Fungi are consummate decomposers of anything organic Multicellular organisms depend of prokaryotes and single-cell eukaryotes for survival, but also create new ecological niches for them
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Lecture_26_soma - The glories of multicellularity...

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