2122958480

2122958480 - Evolution of Life Time-Frame Bill. Yr. Ago...

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1 Photosynthesis: energy transduction Lecture 12 Chp. 6 Evolution of Life Time-Frame Bill. Yr. Ago Time Events 4.5 BYA Origin of the earth 3.5-3.3 BYA Fossils resembling prokaryotes 2.8-2.5 BYA Biomarkers & cyanob. fossils 2.2-1.9 BYA Oxygen level rise 1.9-1.6 BYA Respiration level oxygen 1.5 BYA Cytoskeleton ancestral form? 1.2 BYA Eukaryote: Red algal fossil 0.6 BYA Land plant invasion, crown taxa Brown algae, dinoflag. fossils O 2 CO 2 (Modified after Green 2003) Gas composition of Air: 78 % - Nitrogen (N 2 ) 21 % - Oxygen (O 2 ) 0.033 % - Carbon dioxide (CO 2 ) Rest is Argon etc. Photoautotrophes: Nature's gift to all heterotrophs • Gain electrons from splitting of water by using unlimited supply of energy from sunlight. • Inorganic carbon (CO 2 ) is extracted from atmosphere and converted to food. • Energy derived from photosynthesis is used to fix inorganic nitrogen (N= N di-nitrogen) and used for amino acid and protein synthesis. •O 2 is released from H 2 O oxidation.
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2 Photosynthesis the most important reaction on earth: Chemical expression 6CO 2 + 12 H 2 O C 6 H 12 O 6 + 6 O 2 + 6 H 2 O • When light is absorbed by a pigment molecule, the energy is transferred to an electron (Photexcitation). • The excited electron is transferred through a series of pigments and electron acceptors. • With each exergonic electron transfer, some energy is lost. Other energy is used to drive H + out of the stroma and across the thylakoid membrane. Origin of Choloroplast: endosymbiosys of Eukaryote and Cyanobacterium Hypothesis – one time N N Eukaryote Host Cyanobacterium Chloroplast envelope has 2 membranes * + Gained: (a) Chl a – primary light absorber in photosynthesis, (b) complete Photosystem I, & Photosystem II, (c) water splitting complex by which e - are gained, (d) O 2 evolution capability, (e) photophosphorylation capability (f) protein, carbohydrate, fatty acid synthesis capability Anabolic (photosynthesis) vs. Catabolic (aerobic respiration) Plant & animal Oxygenic plants utilize the visible spectrum (400 – 700 nm)
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3 For light energy captured from sunlight it has to be absorbed
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2122958480 - Evolution of Life Time-Frame Bill. Yr. Ago...

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