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 Assertion is true but Reason is false.
(d) If both Assertion and Reason are false.
Q.1. Assertion : Stomata are absent in submerged hydrophytes.
Reason : Respiration occurs by means of air chambers in submerged plants. [AIIMS 1997]
AnswerAnswer: (b) Stomata are absent since gaseous exchange takes place through diffusion in submerged plants.
Q.2. Assertion : Glycolysis is the first step of respiration in which glucose completely breaks into CO2 and H2O.
Reason : In this process, there is net gain of twenty four molecules of ATP. [AIIMS 2009]
AnswerAnswer: (d) Glycolysis is the process of breakdown of glucose or similar hexose sugar into two molecules of pyruvic acid through a series of enzyme mediated reactions, releasing energy (ATP) and reducing power (NADH2). It is the first step of respiration, which occurs inside the cytoplasm and is independent of O2. In glycolysis, two molecules of ATP are consumed during double phosphorylation of glucose to form fructose 1, 6 diphosphate. Four molecules of ATP are produced in the conversion of 1, 3-diphosphoglycerate to 3-phosphoglycerate and phosphenol pyruvate to pyruvate whereas, two molecules of NADH2 are formed during oxidation of glyceraldehyde 3-phosphate to 1,3-diphosphoglycerate. Since, each NADH is equivalent to 3 ATP, so net gain in glycolysis is 8 ATP.
Q.3. Assertion : Glycolysis occurs in cytoplasm.
Reason : Enzymes for glycolysis are found in cytoplasm. It is common in aerobic/anaerobic respiration.
AnswerAnswer: (a) Glycolysis occurs in cytoplasm as all necessary enzymes are found in it. This process is common in aerobic/anaerobic respiration. In this process, one glucose molecule is converted into 2 moles of pyruvic acid.
Q.4. Assertion : Substrate level phosphorylation is present in glycolysis.
Reason : Substrate level phosphorylation causes synthesis of ATP.
AnswerAnswer: (b) One of the two phosphates of diphosphoglycerate is linked by high energy bond. It can synthesize ATP and form 3- phosphoglycerate. The enzyme is phosphoglycerate kinase. The direct synthesis of ATP from metabolites is called substrate level phosphorylation. During formation of phosphoenol pyruvate the phosphate radical pick up energy. It helps in the production of ATP by substrate level phosphorylation.
Q.5. Assertion: Fructose-1, 6 diphosphate is converted into glyceraldehyde-3-phosphate and dihydroxy-acetone-3-phosphate.
Reason: In the presence of enzyme aldolase, conversion of fructose-1,6 diphosphate into 3-phosphoglyceraldehyde and dihydroxyacetone-3-phosphate is facilitated.
Q.6. Assertion: Plants do not have specialised respiratory organs.
Reason: There is very little transport of gases from one plant part to another.
AnswerAnswer: (a) Unlike animals, plants 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 needs of gaseous exchange. There is little transport of gases from one part to another. Plants do not require much for gas exchange. All plant parts respire at rates far lower than animals. To take care of their own needs of gases during photosynthesis, leaves are well adapted. Moreover, leaves also utilise oxygen released during photosynthesis. In plants, cells are closely packed and located quite close to the surface of the plant.
Q.7. Assertion: The process of glycolysis is also known as EMP pathway.
Reason: It is the only process of respiration in aerobic organisms.
AnswerAnswer: (c) Glycolysis is also known as EMP pathway, as it was discovered by three German scientists-Gustav Embden, Otto Meyerhof and J. Parnas in 1930. In glycolysis, partial oxidation of glucose takes place that form two molecules of pyruvic acid. It occurs in the cytoplasm of the cell and is present in almost all living organisms. Aerobic respiration consists of different processes i.e., (i) glycolysis, (ii) oxidative decarboxylation of pyruvic acid, (iii) Krebs’ cycle and (iv) terminal oxidation and oxidative phosphorylation.
Q.8. Assertion: This conversion of 1,3-biphosphoglycerate (BPGA) to 3- phosphoglyceric acid (PGA) is an energy yielding step.
Reason: By the formation of ATP, this energy is trapped.
Q.9. Assertion: The incomplete oxidation of glucose into lactic acid or ethanol is fermentation.
Reason: In only prokaryotes, it takes place under anaerobic condition.
AnswerAnswer: (c) Fermentation is the incomplete oxidation of glucose under anaerobic conditions. In yeast the pyruvic acid is converted to CO2 and ethanol. Other organisms like some bacteria produce lactic acid from pyruvic acid. In animal cells also, like muscles during exercise when oxygen is inadequate for cellular respiration, pyruvic acid is reduced to lactic acid in the presence of lactate dehydrogenase. Under anaerobic conditions fermentation takes place in many prokaryotes, unicellular eukaryotes and in germinating seeds.
Q.10. Assertion : Banking industry makes use of yeasts such as Saccharomyces cerevisiae.
Reason : Carbon dioxide produced during fermentation causes bread dough to rise by thermal expansion.
AnswerAnswer: (a) Baker’s yeast (Saccharomyces cerevisiae) is added to flour during kneading. Yeast secretes enzymes like amylase (changes some starch to maltose), maltase (maltose to glucose) and zymase (glucose to ethyl alcohol and carbon dioxide). The dough swells up or leavens. Leavened dough is baked and both alcohol and carbon dioxide evaporate, the bread becomes soft and porous.
Q.11. Assertion: During strenuous exercise, anaerobic respiration sometimes occurs in our skeletal muscles.
Reason: Pyruvic acid is reduced to lactic acid in the presence of lactate dehydrogenase and in the absence of oxygen.
AnswerAnswer: (a) In human body anaerobic respiration occurs in our skeletal muscles during strenous exercise. When oxygen is inadequate for cellular respiration pyruvic acid is reduced to lactic acid by lactate dehydrogenase. The reducing agent is NADH = H+ which is reoxidised to NAD+.
Q.12. Assertion : In alcoholic fermentation, the hexose molecule is converted into glucose and fructose.
Reason : Alcoholic fermentation is anaerobic respiration brought about by enzyme zymase.
AnswerAnswer: (a) Alcoholic fermentation is the respiration in absence of O2. In this process, hexose molecule is changed to ethyl alcohol and CO2. In presence of zymase enzyme. In this less amount of energy is released as compared to aerobic respiration.
Q.13. Assertion : Under aerobic conditions, pyruvate gives rise to lactate.
Reason : Under anaerobic condition, pyruvate gives rise to acetyl CoA.
AnswerAnswer: (d) Under aerobic conditions, the products are pyruvate and coenzyme NADH. Pyruvate directly enters the mitochondrial matrix and is converted into acetyl-CoA. Under anaerobic conditions, pyruvate is used as a hydrogen acceptor and converted into lactate. In anaerobic conditions, pyruvate remains in the cytosol.
Q.14. Assertion: Both in aerobic and anaerobic conditions terminal oxidation occurs.
Reason: Terminal oxidation stops at terminal step of respiration.
AnswerAnswer: (d) Terminal oxidation is the name of oxidation found in aerobic respiration that occurs towards the end of catabolic process and involves the passage of both electrons and protons of reduced coenzymes to oxygen.
Q.15. Assertion: The breaking of the C- C bonds of complex compound through oxidation within the cells and release of large amount of energy is respiration.
Reason: During respiration, the compounds that are oxidised are called respiratory substrates.
AnswerAnswer: (b) Respiration is an energy releasing enzymatically controlled process that involves a step-wise oxidative breakdown of food substances inside living cells. Food reaches every cell of an organism for respiration to take place. During cellular respiration, the oxidation of food substances takes place. This process occurs in cytoplasm and mitochondria. During oxidation, chemical bonds (e.g., C – C bonds) are broken that releases energy and forms a number of biochemical intermediates. This energy is used in the synthesis of ATP. Those organic substances which are oxidised during respiration to liberate energy inside the living cells are respiratory substrate. The common respiratory substrates are carbohydrates, proteins, fats and organic acids. the most common respiratory substrate is glucose.
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