Q60. Consider statements about aerobic respiration:
1. Glycolysis occurs in mitochondria.
2. Krebs cycle occurs in the mitochondrial matrix.
3. Oxygen is the final electron acceptor.
Which are correct?
[SSC CGL Tier I (17 September 2025, Shift 1)]
(a) Only 1 and 2
(b) Only 2 and 3
(c) Only 1 and 3
(d) All 1, 2 and 3
Answer: (B) Only 2 and 3
Explanation: Statement 1 is false because glycolysis takes place in the cytosol. The Krebs cycle operates in the mitochondrial matrix, and molecular oxygen receives electrons at the end of the respiratory chain, forming water. Therefore only statements 2 and 3 are correct.
Q59. Which structures in the upper respiratory tract help remove inhaled dust and other particles?
[SSC CHSL (29 November 2025, Shift 3)]
(a) Alveoli
(b) Bronchi
(c) Pleura
(d) Cilia
Answer: (D) Cilia
Explanation: Cilia are microscopic hair-like projections on respiratory epithelial cells. Their coordinated beating moves mucus, containing trapped dust and microorganisms, towards the throat for removal. This mucociliary clearance mechanism protects lower airways, although alveolar macrophages provide additional defence deeper in lungs.
Q58. What is the process called by which organisms take oxygen from outside and break down food to release energy?
[SSC CHSL (13 November 2025, Shift 2)]
(a) Respiration
(b) Digestion
(c) Photosynthesis
(d) Fermentation
Answer: (A) Respiration
Explanation: The question describes aerobic respiration, in which food molecules are oxidised to release chemical energy. Digestion breaks complex food into simpler substances but does not itself represent cellular energy production. Photosynthesis builds sugars, whereas fermentation proceeds without oxygen as a reactant.
Q57. In which blood cells is haemoglobin present?
[SSC CHSL (29 November 2025, Shift 1)]
(a) Red blood cells
(b) Platelets
(c) Monocytes
(d) Nerve cells
Answer: (A) Red blood cells
Explanation: Mature human red blood cells contain abundant haemoglobin for oxygen transport. Haemoglobin gives blood its characteristic red colour through iron-containing haem groups. Platelets assist clotting, monocytes are white blood cells involved in defence, and neurons transmit electrical signals.
Q56. Which medium carries carbon dioxide produced in body tissues towards the lungs?
[SSC CHSL (17 November 2025, Shift 2)]
(a) Sweat
(b) Mucus
(c) Blood
(d) Lymph only
Answer: (C) Blood
Explanation: Blood transports carbon dioxide from tissues to lungs, predominantly as bicarbonate ions in plasma and partly attached to haemoglobin or dissolved. Carbonic anhydrase in red cells rapidly assists bicarbonate formation. In lung capillaries these reactions reverse, permitting carbon dioxide exhalation.
Q55. Consider the statements:
I. Haemoglobin is the respiratory pigment of humans.
II. Haemoglobin has very low affinity for oxygen.
Which is correct?
[SSC CHSL (12 November 2025, Shift 3)]
(a) Only I
(b) Only II
(c) Both I and II
(d) Neither I nor II
Answer: (A) Only I
Explanation: Haemoglobin is the main oxygen-binding respiratory pigment in human red blood cells, so statement I is correct. It binds oxygen readily at the high oxygen partial pressure of lung capillaries and releases it more easily in oxygen-poor tissues; statement II is incorrect.
Q54. How many carbon atoms are present in a pyruvate molecule?
[UPSC CDS-I (13 April 2025)]
(a) Two
(b) Three
(c) Four
(d) Five
Answer: (B) Three
Explanation: Pyruvate is a three-carbon compound produced by glycolysis. One six-carbon glucose yields two pyruvate molecules, preserving all six original carbon atoms at this stage. Under aerobic conditions, pyruvate is further oxidised through acetyl-CoA formation and the citric acid cycle.
Q53. The amount of air breathed in and out during normal quiet respiration by human lungs is referred to as what?
[UPSC NDA-II (14 September 2025)]
(a) Vital capacity
(b) Tidal volume
(c) Inspiratory reserve volume
(d) Total lung capacity
Answer: (B) Tidal volume
Explanation: Tidal volume represents the amount of air moved with each ordinary resting breath, often estimated as roughly 500 mL in a typical adult. Vital capacity is the maximal exhalable volume after full inspiration, while total lung capacity includes residual air.
Q52. Which instrument is used to measure pulmonary volumes and capacities?
[RRB NTPC Undergraduate (20 August 2025, Shift 2)]
(a) Respirometer
(b) Sphygmomanometer
(c) Spirometer
(d) Barometer
Answer: (C) Spirometer
Explanation: A spirometer records the volume of air moving into and out of the lungs, allowing assessment of tidal volume and various capacities. A simple spirometer cannot directly measure residual volume. Sphygmomanometers measure blood pressure, while barometers measure atmospheric pressure.
Q51. Which statements about animal respiration are correct?
1. Dolphins and whales breathe through blowholes.
2. Earthworms breathe through moist skin.
[UPPSC PCS Prelims (2025)]
(a) Neither statement
(b) Only statement 1
(c) Only statement 2
(d) Both statements
Answer: (D) Both statements
Explanation: Whales and dolphins are mammals that take atmospheric air through blowholes on the head, not through gills. Earthworms rely on diffusion across a moist, vascularised skin surface. Oxygen dissolves in skin moisture before passing into underlying blood vessels.
