Aim: How did life on earth begin? How is life able to exist today????? I. Heterotroph Hypothesis A. Autotroph - An organism capable of synthesizing its own food from inorganic substances, using light or chemical energy. Green plants, algae, and certain bacteria are autotrophs. 1. Carry out photosynthesis 6CO2 + 12H2O + sunlight ---> 6O 2 + C6 H12O 6 + 6H2 O or... carbon dioxide + water + sunlight ---> oxygen + carbohydrate + water

B. Heterotroph - An organism that cannot synthesize its own food and is dependent upon complex organic substances for nutrition. Animals are heterotrophs. 1. Carry out respiration 1 glucose + 6 oxygen = 6 carbon dioxide + 6 water + energy C6H12O6 + 6O2  6CO2 + 6H2O + energyCO2H2Oenergy

respiration - process by which an organism exchanges gases with its environment.

C = Carbon H = Hydrogen O = Oxygen N = Nitrogen C 6 H 12 O 6 = Glucose Subscript indicates how many molecules of the particular element are present. CO 2 = Carbon Dioxide H 2 O = Water O 2 = Oxygen

6CO H 2 O + sunlight 6O 2 + C 6 H 12 O 6 + 6H 2 O Reactants Yields Products C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O + energyCO 2H 2 Oenergy Photosynthesis Respiration

C. Early Earth Atmosphere 1. The early Earth atmosphere contained mostly hydrogen, water, ammonia, and methane. 2. Stanley Miller and Harold Urey recreated early Earth. a. They filled a flask with hydrogen, methane, ammonia and water to represent the atmosphere. b. They passed electric sparks through the mixture to simulate lightning. c. The result: several amino acids (building blocks of proteins) began to accumulate.

Over time, the molecules became more complex and began to collaborate to run metabolic processes. Eventually, the first cells came into being. These cells were heterotrophs, which could not produce their own food and instead fed on the organic material from the primordial soup.

Heterotroph cells Anaerobic cells – do not need oxygen to create energy Release CO 2 into atmosphere Photosynthetic autotrophs Release oxygen into atmosphere Aerobic heterotrophs (anaerobic organisms die)