Respiration in Plants

Respiration in Plants

“Respiration in Plants” Chapter of Botany has 1% weightage in NEET Exam (2000-2021).

Here is the List of Some Important Topics:-

1. Aerobic respiration

2. Amphibolic Pathway

3. Glycolysis

4. Fermentation

Noteworthy Points of the Chapter :

1. The breaking of C-C bonds of complex coumpounds through oxidation within the cells, leading to release of considerable amount of energy is called respiration. The compounds that are oxidized during this process are known as respiratory substrates.
2. ATP acts as the energy currency of the cells.
3. Plants have no specialized organs for gaseous exchange but they have stomata and lenticles for this purpose.
4. The breakdown of glucose into pyruvic acid is called glycolysis.
5. The scheme of glycolysis was given by Embden, Meyerhof and Parnas and is often referred to as the EMP pathway.
6. Glycolysis occurs in the cytoplasm of the cell whereas citric acid cycle occurs in mitochondria.
7. In plants, glucose is derived from sucrose which is end product of photosynthesis.
8. In glycolysis, a chain of 10 reactions occur. ATP is utilised at two steps: first in the conversion of glucose to glucose 6-phosphate and second in conversion of fructose 6-phosphate to fructose 1, 6-bisphosphate.
9. ATP is synthesised during conversion of 1, 3 bisphosphoglycerate to 3 phosphoglycerate and phosphoenolpyruvate to pyruvic acid.
10. Glycolysis starts with one molecule of six-carbon compound glucose and ends with the formation of 2 molecules of 3 carbon compound, pyruvic acid. There are three major ways in which pyruvic acid is utilised in different cells.
11. In muscle cells of animals, when oxygen is inadequate, pyruvic acid is reduced to lactic acid by enzyme lactate dehydrogenase.
12. Under anaerobic condition yeast and some bacteria convert pyruvic acid to CO₂  and ethanol, catalysed by pyruvic acid decarboxylase and alcohol dehydrogenase.
13. Pyruvic acid +CoA +NAD⁺ → AcetylCoA +CO₂ + NADH + H⁺. This reaction is catalyzed by enzyme pyruvate dehydrogenase , which requires presence of Mg⁺⁺ ion.
14. Acetyl CoA enters TCA cycle, commonly called Krebs cycle.
15. During the conversion of succinyl-CoA to succinic acid in citric acid cycle, a molecule of GTP is synthesised. This is a substrate-level phosphorylation.
16. In mitochondrial matrix, 4 molecules of NADH + H⁺, 1 molecule of FADH₂ and 1 molecule of ATP is synthesized from 1 molecule of pyruvate.
17. Citric acid cycle takes place in matrix and E.T.S in inner membrane of mitochondria.
18. The metabolic pathway through which the electron passes from one carrier to another is called electron transport system (E.T.S). In ETS, electrons passes via complex I, II, III, IV and V and finally to oxygen.
19. Complex-IV of E.T.S refers to cytochrome “C” oxidase complex containing cytochromes a and a₃ and 2 copper centres.
20. Complex V of E.T.S. is ATP synthase.
21. Oxidation of one molecule of NADH through ETS gives rise to 3 molecules of ATP, while that of one molecule of FADH₂ produces 2 molecules of ATP.
22. For each ATP produced in E.T.S, 2H⁺ passes through F₀ (part of complex V) from intermembrane space to the matrix down the electrochemical gradient.
23. There can be a net gain of 36 ATP molecules during aerobic respiration of one molecule of glucose.
24. The NADH + H⁺ synthesized in glycolysis is transferred into the mitochondria and undergoes oxidative phosphorylation.
25. In fermentation there is a net gain of only 2 molecules of ATP for each molecule of glucose degraded to pyruvic acid.
26. If fatty acids were used as substrate for respiration, they would first be degraded to acetyl CoA and if glycerol, then it would be converted to PGAL and then enter the respiratory pathway.
27. Respiratory pathway is an amphibolic pathway as it involves both catabolism and anabolism.
28. The ratio of the volume of CO₂ evolved to the volume of O₂ consumed in respiration is called respiratory quotient(RQ). For carbohydrate, it is 1, for protein it is 0.9 and for fat is 0.7.