Early Life, Page 4: [Previous Page] [Next Page] [Syllabus] Textbook pages 71 - 79

Biochemical Pathways (Part Deux-The Autotrophs)

Photosynthesis
The process by which plants and some bacteria (remember cyanobacteria and stromatolites?) use the energy from sunlight to produce organic molecules. Sunlight energy absorbed by the chlorophyll splits H₂O, with the H⁺ reducing the CO₂ to sugar, and the O₂ given off as a gas. The shorthand equation is:
6H₂O + 6CO₂ --Light--> C₆H₁₂O₆ + 6O₂

This is the REVERSE of oxidation, shown previously. The earliest photosynthetic micro-organisms used hydrogen sulfide, not water in their reactions (called anoxygenic photosynthesis) :

Sulfur bacteria: 12H₂S + 6CO₂ --Light--> C₆H₁₂O₆ + 12S + 6H₂O

Chemosynthesis
Some autotrophic microorganisms can live in the dark and obtain energy by oxidizing inorganic chemicals. The shorthand equation is:

6CO₂ + 6H₂O + Reduced chemical (e.g. H₂S, Fe²⁺) ---> C₆H₁₂O₆ + Oxidized chemical (e.g. S, Fe³⁺)
Examples of this include many of the microbes living at the deep sea vents.


So, what do you suppose is a Phototroph? How about a Chemotroph? Does any one know what is a Lithotroph? (inorganic chem rxns) How about an Organotroph? (organic chemical rxns) Lots of "trophs"!