Q80. Which of the following properties of alveoli is/are helpful in gaseous exchange during respiration in human beings?
I. Very thin epithelial lining.
II. Elastic fibres in the alveolar wall.
III. Many surrounding blood capillaries.
Select the correct answer.
[UPSC NDA-II (13 September 2026)]
(a) I and II only
(b) I and III only
(c) III only
(d) I, II and III
Answer: (D) I, II and III
Explanation: The alveolar epithelial layer is extremely thin, reducing diffusion distance. Numerous surrounding capillaries maintain concentration gradients for oxygen and carbon dioxide. Elastic fibres permit stretching and recoil during ventilation. Together these three characteristics support efficient lung gas exchange.
Q79. In which of the following parts of organisms does gaseous exchange during respiration NOT take place?
[UPSC NDA-II (13 September 2026)]
(a) Skin of earthworms
(b) Alveoli of humans
(c) Gills of Pila
(d) Bronchi of humans
Answer: (D) Bronchi of humans
Explanation: Earthworms exchange gases across moist skin, aquatic snails such as Pila use gills, and human alveoli exchange oxygen and carbon dioxide with blood. Bronchi mainly conduct air towards the respiratory region; their walls are not the principal gas-exchange surface.
Q78. Which one of the following respiratory volumes of the human lung is the lowest?
[UPSC NDA (2026, GAT)]
(a) Tidal volume
(b) Residual volume
(c) Inspiratory reserve volume
(d) Expiratory reserve volume
Answer: (A) Tidal volume
Explanation: Tidal volume is the air moved during quiet breathing, generally about 500 mL in an average adult. Residual volume remains after forced expiration and is typically over a litre. Inspiratory and expiratory reserve volumes also generally exceed resting tidal volume.
Q77. Which valve guards the opening between the right ventricle and the pulmonary artery?
[UPSC NDA (2026, GAT)]
(a) Semilunar valve
(b) Bicuspid valve
(c) Mitral valve
(d) Tricuspid valve
Answer: (A) Semilunar valve
Explanation: The pulmonary semilunar valve stands at the exit of the right ventricle into the pulmonary trunk. It prevents blood flowing backward during ventricular relaxation. The tricuspid valve lies between the right atrium and ventricle; the mitral valve is on the left.
Q76. What is the process called in which organisms take in oxygen and use it to break down food to release energy for cellular activities?
[RRB Group D (6 August 2026, Shift 1)]
(a) Photosynthesis
(b) Transpiration
(c) Respiration
(d) Fermentation
Answer: (C) Respiration
Explanation: Cellular respiration releases usable energy from organic nutrients such as glucose and conserves part of it as ATP. In aerobic respiration, oxygen participates as the final electron acceptor. Photosynthesis makes carbohydrates, while transpiration is water loss from plant surfaces.
Q75. Which process releases energy in plants through the breakdown of glucose?
[RRB Group D (3 August 2026, Shift 1)]
(a) Excretion
(b) Respiration
(c) Transpiration
(d) Photosynthesis
Answer: (B) Respiration
Explanation: Plants perform cellular respiration continuously in living cells, using carbohydrate molecules to generate ATP. Photosynthesis stores light energy in glucose and normally requires light, whereas respiration can occur day and night. The two processes have distinct purposes and reactions.
Q74. Which respiratory process occurs without oxygen and releases relatively little energy?
[RRB Group D (10 August 2026, Shift 1)]
(a) Transpiration
(b) Aerobic respiration
(c) Anaerobic respiration
(d) Photosynthesis
Answer: (C) Anaerobic respiration
Explanation: Anaerobic energy pathways do not require molecular oxygen. Fermentation follows glycolysis and regenerates NAD+, allowing limited ATP formation: typically two ATP per glucose from glycolysis. Aerobic respiration supports much greater ATP production through electron transport and oxidative phosphorylation.
Q73. Compared with anaerobic respiration, the energy released during aerobic respiration is generally ______.
[RRB Group D (20 August 2026, Shift 3)]
(a) Slower
(b) Less
(c) Greater
(d) Equal
Answer: (C) Greater
Explanation: With oxygen available, cells can oxidise glucose more completely to carbon dioxide and water. The electron transport chain powers synthesis of considerably more ATP than glycolysis followed by fermentation. Actual ATP yield depends on the organism and cellular conditions.
Q72. Which cell organelle is the major site of aerobic respiration in eukaryotic cells?
[RRB Group D (9 August 2026, Shift 2)]
(a) Ribosome
(b) Mitochondria
(c) Nucleus
(d) Endoplasmic reticulum
Answer: (B) Mitochondria
Explanation: Mitochondria contain the enzymes of the citric acid cycle in their matrix and the electron transport complexes in their inner membrane. Glycolysis occurs separately in the cytosol. This division explains why mitochondria are described as the main ATP-producing organelles.
Q71. Which of the following processes does NOT consume atmospheric oxygen?
[RRB Group D (5 August 2026, Shift 2)]
(a) Photosynthesis by green plants
(b) Respiration by animals
(c) Combustion of fuels
(d) Respiration by plants
Answer: (A) Photosynthesis by green plants
Explanation: Oxygenic photosynthesis uses carbon dioxide and water, captures light energy, and produces oxygen rather than consuming it as a reactant. By contrast, aerobic respiration in plants and animals consumes oxygen. Combustion also ordinarily requires an oxidising agent such as atmospheric oxygen.