Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
AP Biology N. Cunningham Evolution Note packet The Origin of Life (a.k.a.The Heterotroph Hypothesis) A. The question arises, how have the first forms of life ever evolved? According to scientific theory, the following steps have been hypothesized that supports the view that the first form of life was a primitive, heterotrophic cell that subsequently led to more complex forms of life. 1. The earth and its atmosphere formed. Primordial gases? Gases came from molten interior of the planet. Consisted of CO, CO2, H2, N2, H2O (steam), S, HCl What gas was missing from the primitive atmosphere? OXYGEN! 2. The primordial seas formed. As the earth cooled, gases condensed to form the first seas. 3. Complex molecules were synthesized. a. Organic “soup” formed Organic molecules (have carbon with hydrogen) were formed from the inorganic molecules. b. Energy sources? UV, lightning, radioactivity, energy from volcanoes, heat were abundant c. What kinds of molecules formed? Monomers like amino acids that would later serve as building blocks for the synthesis of larger polymers. d. Oparin and Haldane independently theorized that organic molecules could only form in the absence of oxygen. Why? Oxygen is a very reactive molecule. Had it been present, oxygen would have prevented other molecules from forming by replacing them with most reactants in chemical reactions. e. Stanley Miller’s experiment? He tested the theories of Oparin and Haldane by simulating primordial conditions in the lab. He applied electric sparks to simple gases (but no oxygen) in a flask. After 1 week, the water contained various organic molecules like amino acids. 4. Polymers and self-replicating molecules were synthesized. Monomers combined to form polymers by dehydration synthesis. 5. Organic molecules were concentrated and isolated into protobionts (precursors of cells) Protobionts were able to carry out chemical reactions within a border across which materials could be exchanged. 6. PRIMITIVE HETEROTROPHIC PROKARYOTES FORMED!!! The first cells formed that were able to consume organics molecules. Food source? Organic molecules like proteins, lipids, glucose from the sea Reproduction? Asexual (binary fission) Type of respiration? Anaerobic 7. Primitive autotrophic prokaryotes formed. First organisms to make their own food! Who were these autotrophs – at first? 1st chemosynthesis- autotrophic bacteria that make food via hydrogen sulfide from underwater volcanic gases Next- photosynthetic bacteria (cyanobacteria) use light for food production (cyclic photophosphoylation) Eventually – eukaryotic photosynthetic organisms – eventually non-cyclic photophosphorylations Type of autotrophic nutrition? First chemosynthesis – in prokaryotes Then photosynthesis – cyclic photophosphorylation Finally photosynthesis –non cyclic photophosphorylation How did this change the world? Oxygen was released into the atmosphere! 8. Oxygen and the ozone layer formed Ozone (03) formed as a protective layer against UV- allowed for terrestrial existence. Presence of oxygen allowed for aerobic respiration to evolve (more energy production meant organisms could get larger) 9. Eukaryotes formed (endosymbiotic theory) Mitochondria and chloroplasts – once prokaryotes- took up residence inside of other cells to become first eukaryotic cells This brought about changes in… Respiration Aerobic More energy means larger organisms can evolve as well. Reproduction Sexual (more diversity means greater chance for survival) http://www.pbs.org/wgbh/nova/evol ution/where-did-we-comefrom.html