Photosynthesis and Entropy Generation in the Biome

So as not to exclude our floral friends from our considerations, we will contemplate the other half of the story: the generation of glucose by plant life via photosynthesis. Photosynthesis is actually comprised of two photoreactions which are used to generate the energy used by the third system (the "Calvin Cycle") to synthesize glucose. The names of the photoreactions designate the order of their "discovery"; photosystem II actually takes place before photosystem I.

  1. Photosystem I, non-cyclic electron flow path:

    2Chlorophyll + 2g(700 nm) -> 2Chlorophyll + NADPH + ATP+ H 2 O

    cyclic electron flow path:

    2Chlorophyll + 2g(700 nm) -> 2Chlorophyll + ATP+ H 2 O
  2. Photosystem II:

    H 2 O + 2g(680 nm) + 2Chlorophyll -> 2Chlorophyll + 1/2 O 2 + 2H+
  3. Calvin Cycle:

    6CO 2 + 12NADPH + 18ATP + 12H 2 O -> C 6 H 12 O 6

In summary,

12 PII + 12PI(non-cyclic) + 6PI(cyclic) + Calvin Cycle

give us

6CO 2 + 24H 2 O + 60g -> C 6 H 12 O 6 + 6O 2 + 18H 2 O.

We can of course see now how the biome functions thermodynamically. It requires a great deal of energy input in the form of sunlight, and the cumulative generation of entropy, first during the photosynthesis of glucose, and then through the respiration of glucose back into carbon dioxide and water (not to mention all of the other processes of life which go into circulating glucose through the biome) guarantees that the entropy always increases. This relentless increase in entropy, along with the conservation of energy (in terms of heat, internal energy and work) make up the two "laws" of thermodynamics.

Problems

The next chapter is about wave physics.



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1996, Kenneth R. Koehler. All Rights Reserved. This document may be freely reproduced provided that this copyright notice is included.

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