Revision Notes on Respiration in Plants
Significance of respiration:
Respiration plays a significant role in the life of plants. The important ones are given below:
(i) It releases energy, which is consumed in various metabolic processes necessary for life of plant.
(ii) Energy produced can be regulated according to requirement of all activities.
(iii) It converts in soluble foods into soluble form.
(iv) Intermediate products of cell respiration can be used in different metabolic pathways
Differences between Photosynthesis and Respiration
|
Photosynthesis |
Respiration |
|
Occurs only in chlorophyll containing cells of plants. |
Occurs in all plant and animal cells. |
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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. |
CO2 and H2O are products. |
|
Synthesizes foods. |
Oxidizeds foods. |
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CO2 and H2O are raw materials. |
O2 and food molecules are raw materials. |
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Photosynthesis is an endothermal process. |
Respiration is an exothermal process. |
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Stores energy. |
Releases energy. |
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It includes the process of hydrolysis, carboxylation etc. |
It includes the process of the dehydrolysis, decarboxylation, etc. |
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Results in an increase in weight. |
Results in a decrease in weight. |
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It is an anabolic process. |
It is a catabolic process. |
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Require cytochrome. |
Also require cytochrome. |
Differences between cell respiration and combustion
|
S.No. |
Characters |
Cell respiration |
Combustion |
|
(i) |
Nature of process |
Biochemical and stepped process. |
Physico-chemical and spontaneous process. |
|
(ii) |
Site of occurrence |
Inside the cells. |
Non-cellular. |
|
(iii) |
Control |
Biological control. |
Uncontrolled. |
|
(iv) |
Energy release |
Energy released in steps. |
Large amount of energy is released at a time. |
|
(v) |
Temperature |
Remain within limits. |
Rises very high. |
|
(vi) |
Light |
No light is produced. |
Light may be produced. |
|
(vii) |
Enzymes |
Controlled by enzymes. |
Not controlled by enzymes. |
|
(viii) |
Intermediates |
A number of intermediates are produced. |
No intermediate is produced. |
Glycolysis Cycle
Enzymes of glycolysis and their co-factors
|
S. No. |
Enzyme |
Coenzyme (s) and cofactor |
Activator (s) |
Inhibitor (s) |
Kind of reaction catalyzed |
|
(i) |
Hexokinase |
Mg2+ |
ATP4-, Pi |
Glucose 6-phopshate |
Phosphoryl transfer |
|
(ii) |
Phosphogluco-isomerase |
Mg2- |
- |
2-dioxyglucose 6-phosphate |
Isomerization |
|
(iii) |
Phosphofructo-kinase |
Mg2+ |
Fructose 2, 6-diphosphate, AMP, ADP, cAMP, K+ |
ATP 4-, citrate |
Phosphoryl transfer |
|
(iv) |
Aldolase |
Zn2+ ( in microbes) |
- |
Chelating agents |
Aldol cleavage |
|
(v) |
Phosphotriose isomerase |
Mg2+ |
- |
- |
Isomerization |
|
(vi) |
Glyceraldehyde 3-phosphate dehydrogenase |
NAD |
- |
Iodoacetate |
Phosphorylation coupled to oxidation |
|
(vii) |
Phosphoglycerate kinase |
Mg2+ |
- |
- |
Phosphoryl transfer |
|
(viii) |
Phosphoglycerate mutase |
Mg2+ 2,3-diphos phoglycerate |
- |
- |
Phosphoryl shift |
|
(ix) |
Enolase |
Mg2+ , Mn2+, Zn2+, Cd2+ |
- |
Fluoride+ phosphate |
Dehydration |
|
(x) |
Pyruvate kinase |
Mg2+, K+ |
- |
Acetyl CoA, analine, Ca2+ |
Phosphoryl transfer |
Total input and output materials in glycolysis
|
Total Inputs |
Total Outputs |
|
1 molecule of glucose (6 C) |
2 molecules of pyruvate (2×3 C) |
|
2 ATP |
4 ATP |
|
4 ADP |
2 ADP |
|
2 × NAD + |
2× NADH + 2H+ |
|
2 Pi |
2×H2O |
Kreb’s Cycle
Enzymes of Kreb's cycle
|
Step |
Enzyme |
(Location in mitochondria) |
Coenzyme(s) and cofactor (s) |
Inhibitor(s) |
Type of reaction catalyzed |
|
(a) |
Citrate synthetase |
Matrix space |
CoA |
Monofluoro-acetyl- CoA |
Condensation |
|
(b) |
Aconitase |
Inner membrane |
Fe2+ |
Fluoroacetate |
Isomerization |
|
(c) |
Isocitrate dehydrogenase |
Matrix space |
NAD+, NADP+, Mg2+, Mn2+ |
ATP |
Oxidative decarboxylation |
|
(d) |
alpha-ketoglutarate dehydrogenase complex |
Matrix space |
TPP,LA,FAD,CoA, NAD+ |
Arsenite,Succinyl-CoA, NADH |
Oxidative decarboxylation |
|
(e) |
Succinyl-CoA synthetase |
Matrix space |
CoA |
- |
Substrate level phosphorylation |
|
(f) |
Succinate dehydrogenase |
Inner membrane |
FAD |
Melonate, Oxaloacetate |
Oxidation |
|
(g) |
Fumarase |
Matrix space |
None |
- |
Hydration |
|
(h) |
Malate dehydrogenase |
Matrix space |
NAD+ |
NADH |
Oxidation |
Products formed during aerobic respiration by Glycolysis and Kreb’s cycle
Total formation of ATP
|
ATP formation in Glycolysis |
|||||
|
Steps |
Product of reactions |
In terms of ATP |
|||
|
ATP formation by substrate phosphorylation |
1, 3-diphosphoglyceric acid (2 moles) ® 3 phosphoglyceric acid (2 moles) Phosphoenolpyruvic acid (2 moles) ® Pyruvic acid (2 moles) |
2 ATP 2 ATP |
2 ATP 2 ATP |
||
|
Total |
4 ATP |
||||
|
ATP formation by oxidative phosphorylation or ETC |
1, 3 - disphosphoglyceraldehyde (2 moles) 1, 3 – diphosphoglyceric acid (2 moles) |
2 NADH2 |
6 ATP |
||
|
Total ATP formed |
4 + 6 ATP = |
10 ATP |
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ATP consumed in Glycolysis |
Glucose (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 |
||
|
Total |
2 ATP |
||||
|
Net gain of ATP = total ATP formed – Total ATP consumed |
10 ATP – 2ATP |
8 ATP |
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ATP formation in Kreb’s cycle |
|||||
|
ATP formation by substrate phosphorylation |
Succinyl CoA (2 mols) ® Succinic acid (2 mols) |
2 GTP |
2 ATP |
||
|
Total |
2 ATP |
||||
|
ATP formation by oxidative phosphorylation or ETC |
Pyruvic 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 NADH2 |
6 ATP
6 ATP
6 ATP
4 ATP
6 ATP |
||
|
Total |
28 ATP |
||||
|
Net gain in Kreb’s cycle (substrate phosphorylation + oxidative phosphorylation) |
2ATP + 28 ATP |
30 ATP |
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|
Net gain of ATP in glycolysis and Kreb’s cycle |
Net gain of ATP in glycolysis + Net gain of ATP in Kreb’s cycle |
8 ATP + 30 ATP |
38 ATP |
||
|
Over all ATP production by oxidative phosphorylation or ETC |
ATP formed by oxidative phosphorylation in glycolysis + ATP formed by oxidative phosphorylation or ETC. |
6 ATP + 28 ATP |
34 ATP |
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Difference between Aerobic, Anaerobic Respiration and Fermentation
|
Aerobic Respiration |
Anaerobic Respiration |
Fermentation |
|
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. |