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The upcoming discussion will update you about the difference between photorespiration and dark respiration.
Difference # Photorespiration:
1.It is dependent on light.
2.It occurs only is green tissues of C3-plants and very little in C4 plants.
3.It is obligatorily coupled to and completely dependent on the Calvin cycle (C3-cycle).
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4.It is accomplished in cytoplasm, chloroplasts, peroxisomes and mitochondria and involves glycolate pathway (C2-cycle).
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5.It consumes O2 at 3 places (reactions nos., i, ii, and iv) and releases Co2 only at one place (reaction no. iv).
6.It involves oxidation both by transfer of electrons to O2 and incorporation of an oxy¬gen atom derived from molecular O2.
7.One molecule of NH, is released per molecule of Co2 released.
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8.Neither reduced co-enzymes nor ATPs are generated. There is no net conservation of energy. On the contrary, an input of energy is required to drive the C2-cycle.
9.It is markedly influenced by the conc. of C02 and 02 in excess of 2-3%. Competition between CO2 and O2 is evident.
Difference # Dark Respiration:
1.It is independent of light.
2.It occurs in all living tissues of aerobic organisms.
3.It is not obligatorily coupled to C3-cycle. Dark respiration and C3-cycle are both spatially and temporally separated.
4.It is accomplished in cytoplasm and mitochondria only and involves glycolysis, TCA (Krebs’ Cycle) and terminal oxidation.
5.O2 is consumed only in terminal oxidation (through cytochrome oxidase) while CO2 is released at several places.
6.Terminal oxidation involves transfer of electrons to O2 and the formation of water.
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7.No ammonia is produced.
8.Reduced coenzymes and ATPs are formed. Dark respiration involve both substrate level and oxidative phosphorylation. Although ATPs are required in initial steps, but there is net gains of ATPs in the overall process. About 40% of the energy available from the oxidation of glucose is conserved in the form of ATPs.
9.It is not markedly influenced by the concentrations of CO2 or O2 . The competition between CO2 and O2 is not evident.
