Q20. In human blood, oxygen is chiefly bound to which component?
[WBCS Preliminary Examination (2020)]
(a) Red blood cells
(b) White blood cells
(c) Vitamin B12
(d) Vitamin E
Answer: (A) Red blood cells
Explanation: Most oxygen in arterial blood is reversibly attached to haemoglobin within red blood cells. A smaller amount travels physically dissolved in plasma. The haemoglobin-oxygen interaction allows a much higher oxygen-carrying capacity than dissolved oxygen alone could provide.
Q19. Which among the following fermentation processes is aerobic?
[RPSC Second Grade Teacher (18 February 2019)]
(a) Lactic acid fermentation
(b) Glycolysis
(c) Alcoholic fermentation
(d) Acetic acid fermentation
Answer: (D) Acetic acid fermentation
Explanation: Industrial acetic acid fermentation by acetic acid bacteria requires oxygen to oxidise ethanol into acetic acid. Despite the traditional word fermentation, the conversion is aerobic. Alcoholic and lactic fermentation regenerate NAD+ without using oxygen as the terminal electron acceptor.
Q18. ATP is produced in aerobic respiration through which phosphorylation mechanisms?
[RPSC Second Grade Teacher (18 February 2019)]
(a) Oxidative phosphorylation only
(b) Both oxidative and substrate-level phosphorylation
(c) Substrate-level phosphorylation only
(d) Oxidative and photophosphorylation
Answer: (B) Both oxidative and substrate-level phosphorylation
Explanation: Glycolysis and the citric acid cycle generate small amounts of ATP or GTP by substrate-level phosphorylation. The majority of ATP in aerobic eukaryotic respiration normally arises through oxidative phosphorylation, where the respiratory electron transport chain establishes a proton gradient.
Q17. Which set correctly describes major products of the tricarboxylic acid cycle?
[RPSC Second Grade Teacher (4 July 2019)]
(a) Carbon dioxide and water only
(b) Carbon dioxide and NADH only
(c) NADH and FADH2 only
(d) Carbon dioxide, NADH and FADH2
Answer: (D) Carbon dioxide, NADH and FADH2
Explanation: Each turn of the citric acid cycle releases two carbon dioxide molecules and generates reduced electron carriers, including NADH and FADH2. It also produces one GTP or ATP equivalent. These carriers supply electrons for the later oxidative phosphorylation stage.
Q16. Complete the analogy: Heart : Circulation :: Lungs : ______.
[SSC CHSL (8 July 2019)]
(a) Ribs
(b) Oxygen
(c) Excretion
(d) Respiration
Answer: (D) Respiration
Explanation: The heart pumps blood through pulmonary and systemic circuits, making it central to circulation. The lungs ventilate and exchange respiratory gases, replenishing blood oxygen and eliminating carbon dioxide. The analogy matches each organ to its primary associated physiological system or function.
Q15. Which substance has traditionally been associated with muscle fatigue after intense exercise?
[WBCS Preliminary Examination (2018)]
(a) Carbon dioxide
(b) Creatinine
(c) Lactic acid
(d) Ethyl alcohol
Answer: (C) Lactic acid
Explanation: This traditional exam answer is lactic acid, referring to elevated lactate during vigorous glycolysis. Current exercise science distinguishes lactate production from the complex causes of fatigue and muscle cramping. Lactate also serves as a useful fuel and metabolic intermediate.
Q14. About how much oxygen can 100 mL of normal human blood carry?
[WBCS Preliminary Examination (2018)]
(a) 40 mL
(b) 10 mL
(c) 20 mL
(d) 30 mL
Answer: (C) 20 mL
Explanation: Normal whole blood typically carries roughly 20 mL oxygen per 100 mL when haemoglobin is nearly fully saturated. This follows from around 15 grams of haemoglobin per decilitre and an oxygen capacity of about 1.34 mL per gram.
Q13. What is the main respiratory organ of a whale?
[WBCS Preliminary Examination (2018)]
(a) Integument
(b) Gills
(c) Lungs
(d) Trachea alone
Answer: (C) Lungs
Explanation: Whales are mammals, not fish, and breathe atmospheric air using lungs. They surface periodically to inhale and exhale through blowholes. Their specialised diving physiology permits prolonged breath-holding, but they cannot extract dissolved oxygen from seawater using gills.
Q12. Alveoli are tiny balloon-like structures found in which organ?
[SSC CHSL (10 March 2018)]
(a) Lungs
(b) Kidneys
(c) Liver
(d) Heart
Answer: (A) Lungs
Explanation: Alveoli are terminal pulmonary air sacs where oxygen crosses into blood and carbon dioxide leaves it. They are lined by thin epithelial cells and closely surrounded by capillaries. Surfactant helps prevent alveolar collapse by reducing surface tension within the sacs.
Q11. In human muscle cells, pyruvate may be converted into lactic acid when which substance is insufficient?
[SSC CHSL (6 March 2018)]
(a) Water
(b) Oxygen
(c) Carbon dioxide
(d) Nitrogen
Answer: (B) Oxygen
Explanation: When oxygen availability or oxidative capacity is inadequate relative to metabolic demand, cells may reduce pyruvate to lactate. This reaction regenerates NAD+ and allows glycolysis to continue producing a small amount of ATP without depending directly on oxygen.
