Chapter 6Photosynthesis And The Chloroplast

Chapter - The Earth's Earliest Life Forms I.& environment A.()inprimevalseas B.Suc

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Chapter 6 Photosynthesis And The Chloroplast The Earth's Earliest Life Forms I. Early life got raw materials & energy from simple organic molecules dissolved in aqueous environment A. These molecules formed abiotically (via nonbiological chemical reactions) in primeval seas B. Such organisms (like us) depending on an external source of organic compounds are heterotrophs C. The number of heterotrophs on primitive Earth was probably severely restricted initially because the spontaneous production of organic molecules occurs very slowly D. Evolution of life on Earth got a tremendous boost when organisms appeared that employed a new metabolic strategy 1. Unlike their predecessors, they could make their own organic nutrients from the simplest types of inorganic molecules (carbon dioxide [CO 2 2 S]) 2. Such organisms that can survive on CO 2 as their principal carbon source are autotrophs II. Life as autotroph requires much energy since it takes a large input of energy to manufacture complex molecules from CO 2 : 2 types of autotrophs evolved that can be distinguished by their energy source A. Chemoautotrophs - use chemical energy stored in inorganic molecules (ammonia, H 2 S, nitrites) to convert CO 2 to organic compounds; all are prokaryotes 1. Their relative contribution to the formation of biomass on Earth is small B. Photoautotrophs – Sun's radiant energy is used; most Earth biomass made by photosynthesis (PS) 1. They include higher plants, eukaryotic algae, some flagellated protists & members of 5 groups of prokaryotes (heliobacteria, cyanobacteria, purple sulfur, green nonsulfur & green sulfur bacteria) 2. They capture the energy that fuels the activities of nearly every organism on Earth 3. All of these organisms carry out photosynthesis, a process in which energy from sunlight is transformed into chemical energy that is stored in carbohydrates & other organic molecules III. In photosynthesis, sunlight energy is converted to chemical energy that is stored in A. Relatively low energy electrons are removed from a donor compound & converted to high energy electrons by energy from light absorption B. High energy electrons reduce carbon skeletons to make reduced biomolecules, like starches & oils IV. Earliest photosynthetic organisms (photoautotrophs) may have dominated Earth for 2 billion 2 S as electron source via this reaction: CO 2 + 2H 2 S + light <—> (CH 2 O) + H 2 O + 2S A. Many bacteria still do, but H 2 S is not abundant or widespread, so these organisms are restricted in their importance & distribution (limited to habitats like sulfur springs & deep sea vents) B. ~2.7 billion years ago, a new photosynthetic prokaryote arose; used the much more abundant H 2 O (water) instead as a source of electrons
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1. 2 ; molecular oxygen) of much consequence via following reaction: CO 2 + 2H
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This note was uploaded on 09/10/2008 for the course BIO 201 taught by Professor Janicke during the Spring '08 term at SUNY Buffalo.

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Chapter - The Earth's Earliest Life Forms I.& environment A.()inprimevalseas B.Suc

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