Q70. Which gas is essential for aerobic respiration in animals?
[RRB Group D (4 August 2026, Shift 3)]
(a) Hydrogen
(b) Oxygen
(c) Carbon dioxide
(d) Nitrogen
Answer: (B) Oxygen
Explanation: Oxygen acts as the terminal electron acceptor in mitochondrial electron transport, combining with electrons and hydrogen ions to form water. Without adequate oxygen, oxidative phosphorylation slows or stops. Cells may temporarily rely more heavily on glycolysis to obtain limited ATP.
Q69. If oxygen supply to muscles becomes inadequate during strenuous activity, what may happen to pyruvate?
[RRB Group D (10 August 2026, Shift 3)]
(a) It becomes ethanol and carbon dioxide
(b) It is fully oxidised aerobically to carbon dioxide and water
(c) It is converted into lactic acid by an anaerobic pathway
(d) It changes directly into ATP without by-products
Answer: (C) It is converted into lactic acid by an anaerobic pathway
Explanation: When oxygen delivery cannot meet muscle energy demand, glycolytic pyruvate can be reduced to lactate. This regenerates NAD+ needed to sustain glycolysis. Human muscle cells do not normally convert pyruvate into ethanol, a product associated with yeast fermentation.
Q68. Which human organ is most directly affected by inhaling tobacco smoke?
[RRB Group D (14 August 2026, Shift 1)]
(a) Pancreas
(b) Brain
(c) Intestine
(d) Lungs
Answer: (D) Lungs
Explanation: Inhaled smoke first enters the respiratory passages and lungs, exposing airway cells and alveoli to particulates and toxic chemicals. Persistent exposure increases the risk of chronic obstructive pulmonary disease, lung cancer and impaired gas exchange, although smoking damages other organs too.
Q67. Why does carbon monoxide from tobacco smoke impair the transport of oxygen in blood?
[RRB Group D (21 August 2026, Shift 1)]
(a) It destroys every red blood cell immediately
(b) It binds strongly to haemoglobin, reducing oxygen carriage
(c) It increases oxygen binding to platelets
(d) It converts oxygen into nitrogen
Answer: (B) It binds strongly to haemoglobin, reducing oxygen carriage
Explanation: Carbon monoxide binds haemoglobin with far greater affinity than oxygen, forming carboxyhaemoglobin. This occupies oxygen-binding sites and hinders oxygen delivery to tissues. Carbon monoxide can additionally make haemoglobin release its remaining oxygen less readily, worsening cellular oxygen deprivation.
Q66. Which tiny balloon-like structures are present at the ends of the smallest air passages in human lungs?
[RRB Group D (11 August 2026, Shift 2)]
(a) Bronchi
(b) Villi
(c) Bronchioles
(d) Alveoli
Answer: (D) Alveoli
Explanation: Alveoli are minute air sacs grouped around alveolar ducts. Their extensive surface area, very thin walls and adjacent capillaries allow rapid diffusion of oxygen into blood and carbon dioxide out of blood. Villi are absorptive projections of the small intestine.
Q65. Which three-carbon molecule is formed during the initial breakdown of glucose in respiration?
[RRB Group D (18 August 2026, Shift 3)]
(a) Fructose-6-phosphate
(b) Acetyl coenzyme A
(c) Pyruvate
(d) Glucose-6-phosphate
Answer: (C) Pyruvate
Explanation: Glycolysis converts one six-carbon glucose molecule into two three-carbon pyruvate molecules in the cytosol. The pathway produces a net gain of two ATP and reduces NAD+ to NADH. Pyruvate then enters aerobic oxidation or anaerobic fermentation pathways.
Q64. Which statement about respiration is INCORRECT?
[RRB Group D (6 August 2026, Shift 3)]
(a) Yeast can produce ethanol and carbon dioxide
(b) Yeast produces water as the principal end-product of alcoholic fermentation
(c) The first stage of glucose breakdown occurs in cytoplasm
(d) Anaerobic respiration can occur without oxygen
Answer: (B) Yeast produces water as the principal end-product of alcoholic fermentation
Explanation: Alcoholic fermentation in yeast chiefly yields ethanol and carbon dioxide from pyruvate, while regenerating NAD+ for glycolysis. Water is not the defining major product of this pathway. Glycolysis occurs in cytoplasm and does not itself require molecular oxygen.
Q63. What happens to gases as blood passes through capillaries around pulmonary alveoli?
[RRB Group D (9 August 2026, Shift 3)]
(a) Both oxygen and carbon dioxide enter blood from alveoli
(b) Carbon dioxide enters blood and oxygen enters alveoli
(c) No exchange occurs
(d) Oxygen enters blood while carbon dioxide enters alveoli
Answer: (D) Oxygen enters blood while carbon dioxide enters alveoli
Explanation: Oxygen diffuses from alveolar air across the respiratory membrane into capillary blood because of partial-pressure differences. Carbon dioxide diffuses in the opposite direction and is exhaled. Effective exchange also depends on adequate alveolar ventilation and pulmonary blood flow.
Q62. Which of the following does NOT normally occur during inhalation?
[RRB Group D (12 August 2026, Shift 2)]
(a) Blood releases oxygen to the alveolar air
(b) Air enters the lungs
(c) The thoracic cavity expands
(d) The diaphragm moves downward and becomes flatter
Answer: (A) Blood releases oxygen to the alveolar air
Explanation: During inspiration, diaphragm contraction enlarges the thoracic cavity and lowers intrapulmonary pressure, drawing air into lungs. At the alveoli, oxygen normally enters pulmonary blood from inhaled air rather than being released by blood into that air.
Q61. Which pigment of human blood carries oxygen?
[RRB Group D (4 August 2026, Shift 3)]
(a) Myosin
(b) Haemoglobin
(c) Insulin
(d) Chlorophyll
Answer: (B) Haemoglobin
Explanation: Haemoglobin is an iron-containing protein concentrated inside red blood cells. Its haem groups reversibly bind oxygen in the lungs and release it at tissues. Myosin is a muscle protein, insulin is a pancreatic hormone, and chlorophyll is a photosynthetic pigment.
