Page 75 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 63

CH 2 O + O 2  H 2 O + CO 2 + Energy ....... Eq. 5.1

During this reaction, a reverse redox reaction changes the CH 2 O to produce H 2 O
and CO 2 . The oxydation state of C increases from 0 in CH 2 O (reduced) to +4 in CO 2
(oxydized) and that of O decreases from 0 in O 2 (oxydized) to -2 in H 2 O(reduced).
This chemical cycle is mathematically summarized in Table 5.1.

PHOTOSYNTHESIS RESPIRATION
CO ---> CH O CH O ---> CO 2
2
2
2
(PLANTS) (ORGANISMS)

Fig. 5.1. The cycle of Carbon through photosynthesis and respiration.

Table 5.1. The chemical reactions in photosynthesis and respiration.

PHOTOSYNTHESIS
-
+
A CO 2 + 4e + 4 H  CH 2 O + H 2 O (Ox. State C: 4+  0)
-
+
D 2 H 2 O  O 2 + 4e + 4 H (Ox. State O: 2-  0)
R CO 2 + H 2 O CH 2 O + O 2
RESPIRATION
-
+
D CH 2 O + H 2 O  CO 2 + 4e + 4 H (Ox. State C: 0  4+)
A O 2 + 4e + 4 H  2 H 2 O (Ox. State O: 0  2-)
-
+
R CH 2 O + O 2  CO 2 + H 2 O
A = Electron Acceptor; D = Electron Donor, and R = Redox Reaction

Based on Fig. 5.1 and Table 5.1, it is obvious that CH 2 O or hydrocarbon is an
energy source for organisms. Hydrocarbon produced during photosynthesis is used

Abdul Kadir Salam - 2014