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NCERT Based MCQ with Explanation:
1. Which cellular process directly results in the production of ATP during respiration?
(A) Photosynthesis
(B) Glycolysis
(C) Transpiration
(D) Translation
Explanation: Glycolysis is the first step in cellular respiration where glucose is broken down into pyruvate. This process occurs in the cytoplasm and generates a small amount of ATP directly, as well as NADH, which can be used in further steps to produce more ATP.
2. Which of the following organisms can undergo fermentation?
(A) Only animals
(B) Only plants
(C) Both prokaryotes and eukaryotes
(D) Only fungi
Explanation: Fermentation is an anaerobic process that can occur in both prokaryotic and eukaryotic cells. For example, yeast (a eukaryote) performs alcoholic fermentation, while certain bacteria (prokaryotes) and muscle cells in animals perform lactic acid fermentation.
3. What is the primary purpose of the electron transport system in cellular respiration?
(A) To break down glucose
(B) To pump protons and produce ATP
(C) To store oxygen
(D) To produce glucose
Explanation: The electron transport system (ETS) is located in the inner mitochondrial membrane. It facilitates the transfer of electrons and the pumping of protons across the membrane to generate a proton gradient. This gradient is then used by ATP synthase to produce ATP.
4. Which of the following is a product of anaerobic fermentation in muscle cells?
(A) Ethanol
(B) Lactic acid
(C) Acetyl-CoA
(D) Oxygen
Explanation: During anaerobic respiration, muscle cells convert pyruvate into lactic acid to regenerate NAD+, allowing glycolysis to continue in the absence of oxygen. This process is known as lactic acid fermentation.
5. What compound is the final electron acceptor in aerobic respiration?
(A) Carbon dioxide
(B) Oxygen
(C) NAD+
(D) FADH₂
Explanation: Oxygen acts as the final electron acceptor in the electron transport chain of aerobic respiration. It combines with electrons and protons to form water, completing the process of ATP generation.
6. Which enzyme is responsible for the phosphorylation of fructose-6-phosphate in glycolysis?
(A) Phosphoglucose isomerase
(B) Phosphofructokinase
(C) Pyruvate kinase
(D) Hexokinase
Explanation: Phosphofructokinase catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate in glycolysis. This step is a rate-limiting and highly regulated step in the pathway, requiring ATP.
7. During aerobic respiration, how many molecules of carbon dioxide are released from one molecule of glucose?
(A) 1
(B) 2
(C) 4
(D) 6
Explanation: In aerobic respiration, glucose is fully oxidized to carbon dioxide and water. During this process, six molecules of CO₂ are released as by-products.
8. In which part of the cell does glycolysis occur?
(A) Nucleus
(B) Mitochondria
(C) Cytoplasm
(D) Golgi apparatus
Explanation: Glycolysis takes place in the cytoplasm of both prokaryotic and eukaryotic cells. It is the initial step of cellular respiration, breaking down glucose into pyruvate.
9. The process of converting pyruvate into lactic acid or ethanol is known as:
(A) Glycolysis
(B) The Krebs cycle
(C) Fermentation
(D) Oxidative phosphorylation
Explanation: Fermentation is an anaerobic process that converts pyruvate into either lactic acid or ethanol, depending on the organism, in order to regenerate NAD+ and allow glycolysis to continue.
10. The complete breakdown of glucose in cellular respiration produces a maximum of how many ATP molecules?
(A) 2
(B) 6
(C) 18
(D) 38
Explanation: The complete oxidation of one glucose molecule through glycolysis, the Krebs cycle, and the electron transport chain produces up to 38 ATP molecules in prokaryotic cells (often slightly less in eukaryotes due to transport costs).
11. Which molecule acts as the energy currency of the cell?
(A) Glucose
(B) NADH
(C) ATP
(D) FADH₂
Explanation: ATP (adenosine triphosphate) is considered the energy currency of the cell because it stores and transfers energy for various cellular processes. Energy is released when ATP is hydrolyzed to ADP.
12. Which pathway is exclusively anaerobic?
(A) Krebs cycle
(B) Electron transport chain
(C) Glycolysis
(D) Citric acid cycle
Explanation: Glycolysis is an anaerobic process, meaning it does not require oxygen. It can occur in the presence or absence of oxygen, making it unique among the primary pathways of cellular respiration.
13. Which process produces the most ATP during cellular respiration?
(A) Glycolysis
(B) Fermentation
(C) Electron transport chain
(D) Krebs cycle
Explanation: The electron transport chain produces the majority of ATP in cellular respiration by utilizing NADH and FADH₂ from glycolysis and the Krebs cycle to generate a proton gradient for ATP synthesis.
14. Which of the following is NOT a product of fermentation?
(A) Carbon dioxide
(B) Lactic acid
(C) Ethanol
(D) Acetyl-CoA
Explanation: Acetyl-CoA is a product of pyruvate oxidation in aerobic respiration, not fermentation. Fermentation results in products like lactic acid or ethanol and carbon dioxide.
15. In the absence of oxygen, pyruvate in yeast cells is converted into:
(A) Lactic acid
(B) Ethanol and carbon dioxide
(C) Water
(D) Acetyl-CoA
Explanation: In yeast cells, pyruvate undergoes alcoholic fermentation, resulting in the production of ethanol and carbon dioxide. This allows the cell to regenerate NAD+ for continued glycolysis.
16. The respiratory quotient (RQ) for glucose oxidation is:
(A) 0.5
(B) 0.7
(C) 0.9
(D) 1.0
Explanation: The respiratory quotient (RQ) is the ratio of CO₂ produced to O₂ consumed. For complete oxidation of glucose, equal volumes of CO₂ and O₂ are produced and consumed, so the RQ is 1.
17. The enzyme that catalyzes the first step of glycolysis is:
(A) Hexokinase
(B) ATP synthase
(C) Pyruvate dehydrogenase
(D) Lactate dehydrogenase
Explanation: Hexokinase catalyzes the phosphorylation of glucose to glucose-6-phosphate in the first step of glycolysis. This reaction is energy-dependent and uses ATP.
18. What is the function of NADH in cellular respiration?
(A) To provide oxygen
(B) To transport electrons to the electron transport chain
(C) To break down glucose
(D) To synthesize glucose
Explanation: NADH is an electron carrier molecule that transports electrons to the electron transport chain, where it is oxidized to produce ATP.
19. Where does the electron transport chain occur in eukaryotic cells?
(A) Cytoplasm
(B) Nucleus
(C) Inner mitochondrial membrane
(D) Golgi apparatus
Explanation: The electron transport chain occurs on the inner membrane of the mitochondrion, where it establishes a proton gradient necessary for ATP synthesis.
20. The enzyme complex ATP synthase is directly responsible for:
(A) Breaking down glucose
(B) Synthesizing ATP from ADP and phosphate
(C) Transporting electrons
(D) Synthesizing glucose
Explanation: ATP synthase is an enzyme complex that uses the energy from the proton gradient created by the electron transport chain to synthesize ATP from ADP and inorganic phosphate.
21. Which of the following is NOT a product of glycolysis?
(A) Pyruvate
(B) NADH
(C) ATP
(D) FADH₂
22. In which step of glycolysis is water produced?
(A) Conversion of glucose to glucose-6-phosphate
(B) Conversion of fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate
(C) Conversion of 2-phosphoglycerate to phosphoenolpyruvate
(D) Conversion of phosphoenolpyruvate to pyruvate
23. Which molecule is directly reduced in the process of lactic acid fermentation?
(A) ATP
(B) NAD+
(C) FADH₂
(D) Pyruvate
24. The overall reaction of aerobic respiration produces how many molecules of carbon dioxide per glucose molecule?
(A) 2
(B) 4
(C) 6
(D) 8
25. In which cellular organelle does oxidative phosphorylation occur?
(A) Nucleus
(B) Cytoplasm
(C) Mitochondria
(D) Endoplasmic reticulum
26. Which type of respiration occurs in the absence of oxygen?
(A) Aerobic respiration
(B) Oxidative phosphorylation
(C) Anaerobic respiration
(D) Photophosphorylation
27. Which of the following pathways is responsible for producing ethanol and carbon dioxide as by-products?
(A) Lactic acid fermentation
(B) Alcoholic fermentation
(C) Krebs cycle
(D) Glycolysis
28. What is the main purpose of the tricarboxylic acid (TCA) cycle?
(A) To produce glucose
(B) To store ATP
(C) To oxidize acetyl-CoA and produce energy carriers
(D) To synthesize amino acids
29. Which of these processes produces NAD+ as a by-product, allowing glycolysis to continue in anaerobic conditions?
(A) Electron transport chain
(B) Photosynthesis
(C) Fermentation
(D) Citric acid cycle
30. Which enzyme catalyzes the final step of glycolysis, converting phosphoenolpyruvate to pyruvate?
(A) Hexokinase
(B) Phosphofructokinase
(C) Pyruvate kinase
(D) Enolase