Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice as :
(a) If both assertion and reason are true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If the assertion is true but the reason is false.
(d) If the assertion is false but the reason is true.
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Assertion: Respiration is the breaking of the C-C bonds of complex compounds through oxidation within the cells and release of large amount of energy.
Reason: The compounds that are oxidised during respiration are called respiratory substrates.
b
Assertion: ATP acts as the energy currency of the cell.
Reason : ATP can be broken down to release energy wherever and whenever energy needs to be utilised.
(a) Cellular respiration is the mechanism of breakdown of food materials within the cell to release energy, and the trapping of this energy for synthesis of ATP. The energy released by oxidation in respiration is not used directly but is used to synthesise ATP, which is broken down whenever and wherever energy needs to be utilised. Hence, ATP acts as the energy currency of the cell. This energy trapped in ATP is utilised in various energy-requiring processes of the organisms.
Assertion: Plants have no specialised respiratory organs.
Reason: There is very little transport of gases from one plant part to another.
(a) Plants, unlike animals, have no specialised organs for gaseous exchange. Gaseous exchange in plants occurs by diffusion through stomata and lenticels. There are various reason for the absence of respiratory organs in plants. Each part of plant takes care of its own gas exchange needs. There is little transport of gases from one part to another. Plants do not have much demands for gas exchange.
Assertion: Glycolysis is also called EMP pathway.
Reason: Glycolysis is the only process of respiration in aerobic organisms.
(c) In glycolysis, also known as EMP pathway, glucose undergoes partial oxidation to form two molecules of pyruvic acid. Glycolysis occurs in the cytoplasm of the cell and is present in almost all living organisms. In anaerobic organisms, it is the only process in respiration.
Assertion: The conversion of 1,3-bishosphoglycerate (BPGA) to 3-phosphoglyceric acid (PGA) is an energy yielding step.
Reason: The energy released by conversion of BPGA to PGA is trapped by the formation of ATP.
b
Assertion: Fermentation is the incomplete oxidation of glucose into lactic acid or ethanol.
Reason: Fermentation takes place under anaerobic conditions in prokaryotes only.
(c) Fermentation is the incomplete oxidation of glucose under anaerobic conditions. In yeast (eukaryote), the pyruvic acid is converted to \(\mathrm{CO}_2\) and ethanol. Other organisms like some bacteria produce lactic acid from pyruvic acid. In animal cells like muscles, during exercise when oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase. Fermentation takes place under anaerobic conditions in many prokaryotes, eukaryotes and in germinating seeds
Assertion: Anaerobic respiration sometimes occurs in our skeletal muscles during strenous exercise.
Reason: Pyruvic acid is reduced to lactic acid by lactate dehydrogenase in the absence of oxygen.
(a) In human body, anaerobic respiration occurs in our skeletal muscles during exercise. In muscles during strenuous exercise, when oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is \(\mathrm{NADH}+\mathrm{H}^{+}\)which is reoxidised to \(\mathrm{NAD}^{+}\).
Assertion: The first step in TCA cycle is the condensation of pyruvate with oxaloacetic acid and water.
Reason: The condensation of acetyl group with oxaloacetic acid and water is catalysed by the enzyme citrate synthetase.
(d) The TCA cycle starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to yield citric acid. The reaction is catalysed by the enzyme citrate synthetase and a molecule of COA is released.
\(
\text { Acetyl } \mathrm{COA}+\mathrm{OAA}+\mathrm{H}_2 \mathrm{O} \underset{\text { synthetase }}{\stackrel{\text { Citrate }}{\longrightarrow}} \text { Citrate + CoA }
\)
Assertion: The metabolic pathway through which the electron passes from one carrier to another is called the electron transport system (ETS).
Reason: ETS is present in the inner mitochondrial membrane.
b
Assertion: Complex II and complex III of ETS are NADH dehydrogenase and cytochrome oxidase complex, respectively.
Reason: Cytochrome c acts as a mobile carrier for the transfer of electrons between complex III and IV.
(d) Complex II of ETS is succinate dehydrogenase complex and complex III of ETS is cytochrome bc, complex. Cytochrome \(c\) is a small protein attached to the outer surface of the inner mitochondrial membrane and acts as a mobile carrier for the transfer of electrons between complex III and IV.
Assertion: Oxidation of one molecule of NADH gives rise to 3 molecules of ATP and that of one molecule of \(\mathrm{FADH}_2\) produces 2 molecules of ATP.
Reason: The number of ATP molecules synthesised depends on the nature of the electron donor.
a
Assertion: In electron transport system, the electrons are passed on to oxygen resulting in the formation of \(\mathrm{H}_2 \mathrm{O}\).
Reason: Oxygen is the ultimate acceptor of electrons.
(a) Oxygen is the terminal electron acceptor of respiratory chain. In electron transport system, electrons are passed on from one carrier to another and ultimately to oxygen and at the end of this chain one molecule of water is produced as:
\(
\frac{1}{2} \mathrm{O}_2+2 \mathrm{H}^{+}+2 \mathrm{e}^{-} \longrightarrow \mathrm{H}_2 \mathrm{O}
\)
Assertion: During aerobic respiration, pyruvic acid formed as a result of glycolysis, undergoes phosphorylation reaction to form acetyl COA.
Reason: There is net gain of 36 ATP molecules during aerobic respiration of one molecule of glucose.
(d) During aerobic respiration, the final product of glycolysis, i.e., pyruvic acid is transported from the cytoplasm into mitochondria and undergoes oxidative decarboxylation reaction to form acetyl COA. Aerobic respiration is the complete oxidation of glucose into \(\mathrm{CO}_2\) and \(\mathrm{H}_2 \mathrm{O}\). There can be a net gain of 36 ATP molecules in aerobic respiration of one molecule of glucose.
Assertion: Respiratory pathway is an amphibolic pathway.
Reason: In respiration, there is breakdown of many substances (catabolism) and synthesis of many substances (anabolism) by respiratory intermediates.
a
Assertion: When carbohydrates are used as substrate and are completely oxidised, the RQ is equal to 1.
Reason: When proteins are used in respiration, the RQ is greater than 1.
(c) The respiratory quotient depends upon the type of respiratory substrate used during respiration. When carbohydrates are used as substrate and are completely oxidised, the RQ will be 1. When proteins acts as respiratory substrates the value of RQ would be about 0.9, i.e., (less than one).
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