Notes on Respiration in Plants

Significance of respiration:

Respiration plays a significant role in the life of plants. The important ones are given below:

  1. It releases energy, which is consumed in various metabolic processes necessary for life of plant.
  2. Energy produced can be regulated according to requirement of all activities.
  3. It converts in soluble foods into soluble form.
  4. Intermediate products of cell respiration can be used in different metabolic pathways

Differences between Photosynthesis and Respiration

PhotosynthesisRespiration
Occurs only in chlorophyll containing cells of plants.Occurs in all plant and animal cells.
Takes place only in the presence of light.Takes place continually both in light and in the dark.
During photosynthesis, radiant energy is converted into potential energy.During respiration, potential energy is converted into kinetic energy.
Sugars, water and oxygen  are products.CO and H2O are products.
Synthesizes foods.Oxidizeds foods.
CO2 and H2O are raw materials.O2 and food molecules are raw materials.
Photosynthesis is an endothermal process.Respiration is an exothermal process.
Stores energy.Releases energy.
It includes the process of hydrolysis, carboxylation etc.It includes the process of the dehydrolysis, decarboxylation, etc.
Results in an increase in weight.Results in a decrease in weight.
It is an anabolic process.It is a catabolic process.
Require cytochrome.Also require cytochrome.

Differences between cell respiration and combustion

CharactersCell respirationCombustion
Nature of processBiochemical and stepped process.Physico-chemical and spontaneous process.
Site of occurrenceInside the cells.Non-cellular.
ControlBiological control.Uncontrolled.
Energy releaseEnergy released in steps.Large amount of energy is released at a time.
TemperatureRemain within limits.Rises very high.
LightNo light is produced.Light may be produced.
EnzymesControlled by enzymes.Not controlled by enzymes.
IntermediatesA number of intermediates are produced.No intermediate is produced.

Glycolysis Cycle

201472 153949498 6360 glycolysis cycle

Enzymes of glycolysis and their co-factors

EnzymeCoenzyme (s) and cofactorActivator (s)Inhibitor (s)Kind of reaction catalyzed
HexokinaseMg2+ATP4-, PiGlucose 6-phopshatePhosphoryl transfer
Phosphogluco-isomeraseMg2-2-dioxyglucose6-phosphateIsomerization
Phosphofructo-kinaseMg2+Fructose 2, 6-diphosphate, AMP, ADP, cAMP, K+ATP 4-, citratePhosphoryl transfer
AldolaseZn2+( in microbes)Chelating agentsAldol cleavage
Phosphotriose isomeraseMg2+Isomerization
Glyceraldehyde3-phosphate dehydrogenaseNADIodoacetatePhosphorylation coupled to oxidation
Phosphoglycerate kinaseMg2+Phosphoryl transfer
Phosphoglycerate mutaseMg2+  2,3-diphos phoglyceratePhosphoryl shift
EnolaseMg2+ , Mn2+, Zn2+, Cd2+Fluoride+ phosphateDehydration
Pyruvate kinaseMg2+, K+Acetyl CoA, analine, Ca2+Phosphoryl transfer

Total input and output materials in glycolysis

Total InputsTotal Outputs
1 molecule  of glucose (6 C)2 molecules of pyruvate (2×3 C)
2 ATP4 ATP
4 ADP2 ADP
2 × NAD +2× NADH + 2H+
2 PiH2O

Kreb’s Cycle

201472 154057830 2717 reductive tca cycle

Enzymes of Kreb’s cycle

Enzyme(Location in mitochondria)Coenzyme(s) and cofactor (s)Inhibitor(s)Type of reaction catalyzed
Citrate synthetaseMatrix space CoAMonofluoro-acetyl- CoACondensation
AconitaseInner membraneFe2+FluoroacetateIsomerization
Isocitrate dehydrogenaseMatrix spaceNAD+, NADP+, Mg2+, Mn2+ATPOxidative decarboxylation
alpha-ketoglutarate dehydrogenase complexMatrix spaceTPP,LA,FAD,CoA,NAD+Arsenite,Succinyl-CoA, NADHOxidative decarboxylation
Succinyl-CoA synthetaseMatrix spaceCoASubstrate levelphosphorylation
Succinate dehydrogenaseInner membraneFADMelonate, OxaloacetateOxidation
FumaraseMatrix spaceNoneHydration
Malate dehydrogenaseMatrix spaceNAD+NADHOxidation

Products formed during aerobic respiration by Glycolysis and Kreb’s cycle

Total formation of ATP         

 ATP formation in GlycolysisStepsProduct of reactionsIn terms of ATP
ATP formation by substrate phosphorylation1, 3-diphosphoglyceric acid (2 moles) ® 3 phosphoglyceric acid (2 moles)Phosphoenolpyruvic acid (2 moles) ®Pyruvic acid (2 moles)2 ATP2 ATP2 ATP2 ATP
  Total4 ATP
ATP formation by oxidative phosphorylation or ETC1, 3 – disphosphoglyceraldehyde (2 moles)1, 3 – diphosphoglyceric acid (2 moles)2 NADH26 ATP
 Total ATP formed4 + 6 ATP =10 ATP
ATP consumed in GlycolysisGlucose (1 mole) ® Glucose 6 phosphate (1 mole)Fructose 6 phosphate (1 mole) ®Fructose 1, 6-diphosphate (1 mole)– 1 ATP– 1 ATP– 1 ATP – 1 ATP
  Total2 ATP
 Net gain of ATP = total ATP formed – Total ATP consumed10 ATP – 2ATP8 ATP
ATP formation in Kreb’s cycle
ATP formation by substrate phosphorylationSuccinyl CoA (2 mols) ®Succinic acid (2 mols)2 GTP2 ATP
  Total2 ATP
ATP formation by oxidative phosphorylation or ETCPyruvic acid (2 mols) ®Acetyl CoA (2 mols)Isocitric acid (2 mols) ® Oxalosuccinic acid (2 mols)a-Ketoglutaric acid (2 mols) ® Succinyl CoA (2 mols)Succinic acid (2 mols) ® Fumaric acid (2 mols)Malic acid (2 mols) ® Oxaloacetic acid (2 mols)2 NADH2 2 NADH2 2 NADH2 2 FADH2 2 NADH26 ATP 6 ATP 6 ATP 4 ATP 6 ATP
  Total28 ATP
 Net gain in Kreb’s cycle (substrate phosphorylation + oxidative phosphorylation)2ATP + 28 ATP30 ATP
Net gain of ATP in glycolysis and Kreb’s cycleNet gain of ATP in glycolysis + Net gain of ATP in Kreb’s cycle8 ATP + 30 ATP38 ATP
Over all ATP production by oxidative phosphorylation or ETCATP formed by oxidative phosphorylation in glycolysis + ATP formed by oxidative phosphorylation or ETC.6 ATP + 28 ATP34 ATP

Difference between Aerobic, Anaerobic Respiration and Fermentation

Aerobic RespirationAnaerobic RespirationFermentation
Molecular oxygen is the ultimate electron acceptor for biological oxidation. The ETS serves to transfer electrons from oxidisable donor to molecular oxygen. The early enzymatic steps involve dehydrogenation whereas the final steps are mediated by a group of enzyme called cytochromes. Ultimately the electrons are transferred to oxygen which is reduced to water. During aerobic respiration ATP is generated by coupled reaction The ultimate electron acceptor is an inorganic compound other than oxygen. The compounds accepting the hydrogen (electrons) are nitrates, sulphates, carbonates or CO2. Anaerobic respiration produces ATP through phosphorylation reaction involving electron transfer systems. (mechanism not known)The final electron acceptors are organic compounds. Both electron donors (oxidizable substrate) and electron acceptors (oxidizing agent) are organic compounds and usually both substrates arise from same organic molecules during metabolism. Thus part of the nutrient molecule is oxidised and part reduced and the metabolism results in intramolecular electron rearrangement. ATP is generated by substrate level phosphorylation. This reaction differs from oxidative phosphorylation because oxygen itself is not required for ATP generation.    

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