Q50. In which cellular organelle does the Krebs cycle occur?
[SSC MTS (30 October 2024, Shift 3)]
(a) Lysosome
(b) Ribosome
(c) Nucleus
(d) Mitochondria
Answer: (D) Mitochondria
Explanation: In eukaryotic cells, the citric acid or Krebs cycle occurs within the mitochondrial matrix. Its reactions oxidise acetyl groups, release carbon dioxide, and generate NADH and FADH2. These reduced carriers subsequently deliver electrons to the mitochondrial respiratory chain.
Q49. Which virus is most commonly responsible for the common cold?
[SSC MTS (4 November 2024, Shift 2)]
(a) Coronavirus
(b) Hepatitis A virus
(c) Rhinovirus
(d) Influenza virus
Answer: (C) Rhinovirus
Explanation: Rhinoviruses are major causes of common cold, typically producing a runny nose, sneezing and sore throat. Some coronaviruses also cause colds, but rhinovirus is the classic commonest answer. Influenza causes a different respiratory illness, often with more prominent fever and body aches.
Q48. At which time of day is dissolved oxygen in a pond usually lowest?
[SSC MTS (15 October 2024, Shift 1)]
(a) At dawn
(b) During afternoon
(c) At midnight
(d) In the evening
Answer: (A) At dawn
Explanation: Aquatic plants and algae photosynthesise during daylight and add oxygen to water. At night, photosynthesis stops but respiration by plants, animals and microorganisms continues to consume oxygen. Consequently, dissolved oxygen often reaches its daily minimum shortly before sunrise.
Q47. What commonly happens to dissolved oxygen in a water body when thermal pollution raises its temperature?
[SSC MTS (28 October 2024, Shift 1)]
(a) Dissolved oxygen decreases
(b) Water turbidity must become zero
(c) pH always becomes exactly neutral
(d) Dissolved oxygen increases without limit
Answer: (A) Dissolved oxygen decreases
Explanation: Warm water can hold less dissolved oxygen than cool water at similar conditions. Higher temperatures can also accelerate metabolic rates and oxygen consumption by aquatic organisms. The combined effects may stress fish and other animals that depend on dissolved oxygen for respiration.
Q46. Consider the statements:
I. Pranayama may help improve breathing efficiency and lung function.
II. During inhalation, the ribs move upwards and the diaphragm moves downwards.
Which statement(s) are correct?
[SSC CHSL (16 March 2023, Shift 3)]
(a) Both I and II
(b) Only II
(c) Neither I nor II
(d) Only I
Answer: (A) Both I and II
Explanation: Breathing exercises such as pranayama can help improve respiratory control and some measures of pulmonary function. During normal inspiration, external intercostal muscles raise the ribs while contraction of the diaphragm moves it downward, increasing thoracic volume and drawing air into lungs.
Q45. Which of the following is NOT a three-carbon compound formed or involved in glycolysis?
[SSC MTS (11 September 2023, reported shift question)]
(a) Pyruvic acid
(b) Dihydroxyacetone phosphate
(c) 2-Phosphoglycerate
(d) Fructose-6-phosphate
Answer: (D) Fructose-6-phosphate
Explanation: Fructose-6-phosphate retains six carbon atoms and appears in the early phase of glycolysis. Dihydroxyacetone phosphate and 2-phosphoglycerate are three-carbon intermediates, while pyruvate is a three-carbon final product. Glycolysis splits six-carbon sugar intermediates into two three-carbon streams.
Q44. In which blood component is the respiratory pigment haemoglobin found?
[RRB Group D (11 October 2022, Shift 2)]
(a) White blood cells
(b) Red blood cells
(c) Platelets
(d) Plasma
Answer: (B) Red blood cells
Explanation: Red blood cells are specialised for oxygen transport because their cytoplasm contains large amounts of haemoglobin. Each haemoglobin molecule has four haem groups capable of reversible oxygen binding. Blood plasma transports most carbon dioxide as bicarbonate but contains little normal free haemoglobin.
Q43. What is the air remaining in the lungs even after a forceful expiration called?
[RRB Group D (5 September 2022, Shift 2)]
(a) Residual volume
(b) Respiration volume
(c) Pulmonary volume
(d) Alveolar volume
Answer: (A) Residual volume
Explanation: Residual volume is the gas that remains in the lungs after maximum forced exhalation. It prevents complete lung collapse and allows ongoing gas exchange between breaths. It cannot be directly measured by simple spirometry because no airflow exits during its measurement.
Q42. The respiration reaction in humans is an example of which type of chemical reaction?
[RRB Group D (28 September 2022, Shift 1)]
(a) Exothermic reaction
(b) Displacement reaction
(c) Endothermic reaction
(d) Precipitation reaction
Answer: (A) Exothermic reaction
Explanation: Overall oxidation of glucose during cellular respiration releases energy, making respiration an exothermic process. Cells capture some released energy as ATP rather than releasing it all at once as heat. Displacement and precipitation describe different chemical reaction categories.
Q41. Which of the following animals generally has the fastest breathing rate?
[RRB Group D (8 September 2022, Shift 1)]
(a) Fish
(b) Human
(c) Elephant
(d) Pigeon
Answer: (A) Fish
Explanation: Fish often move water over their gills rapidly because water holds far less available oxygen per unit volume than air. Their ventilatory movements can be frequent, though rates vary greatly with species, size, temperature and activity. The examination compares typical textbook examples.
