All Free Biology MCQs with Answers
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19844 questions · page 700 of 1985
6991. The cell organelles involved, in some cases, with extra-cellular digestion are _ .
- A. Golgi complex
- B. Lysosomes
- C. Peroxisomes
- D. Glyoxysomes
Explanation: Lysosomes function as the digestive system of the cell, serving both to degrade material taken up from outside the cell and to digest obsolete components of the cell itself.
Correct answer: Lysosomes6992. In lactic acid fermentation, pyruvic acid converts into lactic acid by accepting electrons from:
- A. NAD+
- B. NADP+
- C. NADH
- D. NADPH
Explanation: Lactic Acid Fermentation: In this anaerobic process, pyruvic acid is reduced to lactic acid. This is coupled with the oxidation of NADH to NAD+, which is crucial because it regenerates NAD+ needed for glycolysis to continue. The electron acceptor in this process is pyruvic acid, which receives electrons from NADH, not NAD+.
Correct answer: NADH6993. Given is the first step of Krebs cycle.Acetyl Co-A + Oxaloacetate → XThe product X is:
- A. Citrate
- B. Malate
- C. Fumarate
- D. Succinate
Explanation: The Krebs cycle, also known as the citric acid cycle, begins with the condensation of Acetyl Co-A and Oxaloacetate to form citrate. This reaction is catalyzed by the enzyme citrate synthase. Citrate is the first product of the Krebs cycle, and it is crucial for the subsequent steps in energy production.
Correct answer: Citrate6994. Oxygen is required in aerobic respiration for:
- A. The reduction of hydrogen carriers
- B. The oxidation of glyceraldehyde 3-phosphate
- C. Accepting electrons at the end of the electron transport chain
- D. Maintaining an oxygen concentration gradient in mitochondria
Explanation: The correct answer is Option C: accepting electrons at the end of the electron transport chain. Oxygen's primary role in aerobic respiration is to accept electrons at the end of the electron transport chain, allowing the chain to continue and produce ATP efficiently. This process occurs in the mitochondria, where oxygen combines with electrons and protons to form water.
Correct answer: Accepting electrons at the end of the electron transport chain6995. The given diagram shows some of the reactions that occur in the preparatory phase of glycolysis.The conversion that takes place at step 1 and 3 is:
- A. ATP→ADP
- B. ADP→ATP
- C. NAD+→NADH
- D. NADH→NAD+
Explanation: During the preparatory phase of glycolysis, 2 molecules of ATP are invested to convert glucose to Glucose-6-phosphate and fructose-6-phosphate to fructose-1,6-bisphosphate. So option A is correct.
Correct answer: ATP→ADP6996. The equation that summarises the conversion of glucose into lactic acid during anaerobicrespiration is:
- A. C6H12O6 → 2 C3H6O3
- B. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
- C. C6H12O6 → 2 C2H5OH + 2 CO2
- D. C6H12O6 → 6 CO2 + 6 H2O
Explanation: The correct equation for the conversion of glucose into lactic acid during anaerobic respiration is C6H12O6 → 2 C3H6O3. This accurately reflects the process in which one molecule of glucose is converted into two molecules of lactic acid under anaerobic conditions, commonly occurring in muscle cells during intense exercise when oxygen is limited.
Correct answer: C6H12O6 → 2 C3H6O36997. The given diagram summarizes the reactions of anaerobic respiration.Based on the given summary, adenosine triphosphate (ATP) molecules would have been released during the:
- A. Breakdown of pyruvic acid into ethanol
- B. Formation of pyruvic acid from glucose
- C. Breakdown of pyruvic acid into lactic acid
- D. Release of carbon dioxide gas from pyruvic acid
Explanation: The correct answer is the formation of pyruvic acid from glucose. This step is known as glycolysis, which is the initial stage of both aerobic and anaerobic respiration. During glycolysis, glucose is broken down into two molecules of pyruvate, and ATP is produced. In anaerobic conditions, pyruvate can be further converted into either ethanol or lactic acid, but these subsequent steps do not produce ATP. Therefore, the only stage in anaerobic respiration where ATP is generated is during the formation of pyruvic acid from glucose.
Correct answer: Formation of pyruvic acid from glucose6998. In cellular respiration, the molecules of nicotinamide adenine dinucleotide (NADH) and Flavin adenine dinucleotide (FADH) are produced during:
- A. Glycolysis
- B. Krebs cycle
- C. Pyruvate oxidation
- D. Electron transport chain
Explanation: The correct answer is the Krebs cycle.During cellular respiration, NADH and FADH2 are primarily produced in the Krebs cycle.
Correct answer: Krebs cycle6999. The given diagram summarises the reactions of anaerobic respiration:
- A. A.
- B. B.
- C. C.
- D. D.
Explanation: The correct answer is the formation of pyruvic acid from glucose. This step is known as glycolysis, which is the initial stage of both aerobic and anaerobic respiration. During glycolysis, glucose is broken down into two molecules of pyruvate, and ATP is produced. In anaerobic conditions, pyruvate can be further converted into either ethanol or lactic acid, but these subsequent steps do not produce ATP. Therefore, the only stage in anaerobic respiration where ATP is generated is during the formation of pyruvic acid from glucose.
Correct answer: B.7000. β-oxidation occurs in
- A. Nucleus
- B. Cytoplasm
- C. Mitochondria
- D. Chloroplast
Explanation: β-Oxidation is a process that occurs in the mitochondria.It involves the breakdown of fatty acids into acetyl-CoA, which enters the citric acid cycle to produce energy.The correct answer is C (Mitochondria). β-Oxidation is a mitochondrial process where fatty acids are broken down to generate energy in the form of ATP.
Correct answer: Mitochondria