Respiration:
It is an energy liberating enzymatically controlled multistep catabolic process of stepwise breakdown of organic substances inside the living cells.
Respiratory Substrates
The organic substances which can be catabolised to liberate energy inside the living cells e.g., carbohydrates, fats and proteins.
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Type of respiration
1. Aerobic:
Takes place inside the mitochondria in the presence of molecular oxygen in most of plants and animals called aerobes. Divided into 4 phases-Glycolysis, oxidative decarboxylation, Krebs or TCA cycle and Electron Transport system.
2. Anaerobic (Fermentation):
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Involves the production of energy from the food nutrients in the absence of oxygen.
Respiratory Ratio or quotient (RQ):
The ratio of the volume of carbon dioxide released to the volume of oxygen taken in respiration in the given period of time at standard temperature and pressure.
It provides the nature of the substrate being respired by a particular tissue.
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(1) Carbohydrate RQ = 1 or unity
(2) Fats RQ = 0.7 i.e., less than one
(3) Proteins RQ = less than unity (usually 0.5 to 0.9)
(4) Fermentation RQ = ∞ or infinity
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(5) Succulents RQ = 0 or zero
(6) Maturing fatty seeds RQ = more than one
(7) Organic acids RQ = more than one
(8) Germinating fatty seeds RQ = less than one
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i. Glycolysis (splitting of sugar) results in the breakdown of glucose molecules into pyruvic acid.
ii. Completed in the cytoplasm of the living cells.
iii. Also known as Embden-Meyerhof-Parnas (EMP) pathway.
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iv. 3 steps.
1. Phosphorylation of Glucose:
Initial, 6- carbon sugar is transformed into 6-carbon sugar diphosphate. This addition of phosphate groups is called phosphorylation, it activates the sugar and preventing it from getting out of the cell.
2. Splitting of fructose-I, 6-diphosphate:
Fructose-1, 6-diphosphate is broken down into two molecules of 3-carbon sugar phosphates i.e., dihydroxy acetone
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i. Pyruvic acid releases one molecule of CO2 to produce acetaldehyde which reoxideses NADH and itself reduced to ethanol.
ii. These reaction are catalysed by pyruvic acid decarboxylase and alcohol dehydrogenase enzymes.
iii. Net yield of ATP in anaerobic respiration is of only 2 molecules of ATP that too during glycolysis is anaerobic respiration.