Life Processes in Animals Part 3: MCQs (Q51–Q75)

Part 3 — Respiration: Human Respiratory System & Breathing (Questions 51–75)

51. The process of taking in oxygen and giving out carbon dioxide is called:

A. Digestion
B. Respiration (breathing and gas exchange)
C. Photosynthesis
D. Excretion
Correct answer: B. Respiration (breathing and gas exchange)

Explanations:
A) Digestion processes food — incorrect.
B) Respiration includes inhalation/exhalation and gas exchange at cells — correct.
C) Photosynthesis is in plants — incorrect.
D) Excretion is removal of waste products — incorrect.

52. The human respiratory surface where gas exchange occurs is:

A. Trachea
B. Bronchi
C. Alveoli in lungs
D. Larynx
Correct answer: C. Alveoli in lungs

Explanations:
A) Trachea conducts air but not main exchange — incorrect.
B) Bronchi are air passages — not main exchange sites — incorrect.
C) Alveoli (tiny air sacs) provide large surface area for gas exchange — correct.
D) Larynx is voice box — incorrect.

53. The main muscle involved in breathing is the:

A. Heart
B. Diaphragm
C. Liver
D. Kidney
Correct answer: B. Diaphragm

Explanations:
A) Heart pumps blood, not primary breathing muscle — incorrect.
B) Diaphragm contracts/relaxes to change thoracic volume for breathing — correct.
C) Liver not involved in breathing movements — incorrect.
D) Kidney filters blood — incorrect.

54. During inhalation (inspiration):

A. Diaphragm relaxes and moves up
B. Diaphragm contracts and moves down; ribs move up and out so chest cavity volume increases
C. Lungs collapse
D. Air leaves the lungs
Correct answer: B. Diaphragm contracts and moves down; ribs move up and out so chest cavity volume increases

Explanations:
A) Diaphragm relaxing is during exhalation — incorrect.
B) Contraction increases thoracic volume, lowering pressure, drawing air in — correct.
C) Lungs expand during inhalation — incorrect.
D) Air enters lungs during inhalation, not leaves — incorrect.

55. Which gas is taken up by red blood cells and carried to body tissues?

A. Carbon dioxide
B. Nitrogen
C. Oxygen (bound to hemoglobin)
D. Methane
Correct answer: C. Oxygen (bound to hemoglobin)

Explanations:
A) CO₂ is transported from tissues to lungs, not taken up for tissues — incorrect.
B) Nitrogen is largely inert and not used in respiration — incorrect.
C) Oxygen binds to haemoglobin in RBCs and delivered to tissues — correct.
D) Methane not involved — incorrect.

56. Carbon dioxide produced in cells is mainly transported to lungs as:

A. Dissolved CO₂ in plasma only
B. Bicarbonate ions (HCO₃⁻) formed in plasma
C. Bound only to haemoglobin as CO₂Hb
D. Converted to oxygen
Correct answer: B. Bicarbonate ions (HCO₃⁻) formed in plasma

Explanations:
A) Some CO₂ is dissolved but not main form — incorrect.
B) Majority is converted to bicarbonate ions in plasma for transport — correct.
C) Some binds to haemoglobin, but less than bicarbonate — partially true but not main — incorrect.
D) CO₂ is not converted to oxygen — incorrect.

57. Which structure prevents food from entering trachea while swallowing?

A. Epiglottis
B. Uvula
C. Bronchi
D. Larynx
Correct answer: A. Epiglottis

Explanations:
A) Epiglottis closes over trachea during swallowing — correct.
B) Uvula prevents food from entering nasal cavity, not trachea — incorrect.
C) Bronchi are airways below trachea — incorrect.
D) Larynx is voice box; epiglottis is its flap — incorrect.

58. The tiny blood vessels surrounding the alveoli are called:

A. Arterioles only
B. Capillaries
C. Bronchioles
D. Venules only
Correct answer: B. Capillaries

Explanations:
A) Arterioles are small arteries; capillaries form networks for exchange — incorrect.
B) Capillaries allow close contact between blood and alveoli for gas exchange — correct.
C) Bronchioles are small airways inside lungs — incorrect.
D) Venules carry blood away from capillary beds but capillaries are site of exchange — incorrect.

59. Which of the following statements is FALSE?

A. Breathing rate can increase during exercise.
B. Respiration at cellular level releases energy from food.
C. Lungs are able to exchange gases because alveoli have a large surface area and thin walls.
D. Bile directly digests proteins in the blood.
Correct answer: D. Bile directly digests proteins in the blood.

Explanations:
A) True — exercise increases breathing.
B) True — cellular respiration releases energy.
C) True — alveoli structure supports exchange.
D) False — bile emulsifies fats in intestine, not digest proteins in blood — correct as false.

60. Which is the correct pathway of air from outside to the alveoli?

A. Nose → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
B. Mouth → Oesophagus → Stomach → Alveoli
C. Nose → Stomach → Small intestine → Alveoli
D. Nose → Bronchioles → Trachea → Bronchi → Alveoli
Correct answer: A. Nose → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

Explanations:
A) Correct anatomical order for air passage — correct.
B) Oesophagus and stomach are digestive tract, not respiratory — incorrect.
C) Intestines are digestive — incorrect.
D) Order reversed (bronchioles before trachea) — incorrect.

61. Smoking affects respiration by:

A. Improving oxygen uptake
B. Damaging cilia, causing less filtration and leading to respiratory illness
C. Making alveoli more efficient
D. Increasing blood purification by lungs
Correct answer: B. Damaging cilia, causing less filtration and leading to respiratory illness

Explanations:
A) Smoking reduces oxygen uptake — incorrect.
B) Smoke damages cilia, causes bronchitis, emphysema, cancer — correct.
C) Alveoli efficiency decreases with smoking — incorrect.
D) Lungs don’t purify blood better with smoking — incorrect.

62. The exchange of gases between blood and body cells is called:

A. External respiration
B. Internal respiration (cellular/tissue respiration)
C. Photosynthesis
D. Pulmonary ventilation
Correct answer: B. Internal respiration (cellular/tissue respiration)

Explanations:
A) External respiration refers to alveoli-blood exchange — incorrect.
B) Internal respiration is gas exchange between blood & cells — correct.
C) Photosynthesis is plant process — incorrect.
D) Pulmonary ventilation is breathing (in/out) — incorrect.

63. Which respiratory disorder is characterized by allergic airway constriction and wheezing?

A. Tuberculosis
B. Asthma
C. Pneumonia
D. Appendicitis
Correct answer: B. Asthma

Explanations:
A) TB is infectious disease with coughing & fever — incorrect.
B) Asthma involves bronchoconstriction and wheezing — correct.
C) Pneumonia is lung infection causing inflammation — incorrect.
D) Appendicitis is abdominal inflammation — incorrect.

64. Which of the following is NOT part of the human respiratory system?

A. Trachea
B. Bronchi
C. Alveoli
D. Nephron
Correct answer: D. Nephron

Explanations:
A) Trachea is air tube — incorrect (it is part).
B) Bronchi are air passages — incorrect (they are part).
C) Alveoli are air sacs — incorrect (they are part).
D) Nephron is kidney filtration unit — correct as NOT respiratory.

65. During heavy exercise, muscles may respire anaerobically (without sufficient oxygen). A byproduct of this in human muscles is:

A. Lactic acid
B. Oxygen
C. Glucose
D. Water only
Correct answer: A. Lactic acid

Explanations:
A) Anaerobic respiration in muscles produces lactic acid causing fatigue — correct.
B) Oxygen is lacking in anaerobic conditions — incorrect.
C) Glucose is the substrate, not the byproduct — incorrect.
D) Water is produced in aerobic respiration; anaerobic produces lactic acid — incorrect.

66. Which of the following helps to trap dust particles and microbes in inhaled air?

A. Alveoli only
B. Cilia and mucus in nasal passages and trachea
C. Teeth
D. Villi
Correct answer: B. Cilia and mucus in nasal passages and trachea

Explanations:
A) Alveoli are deep lungs; filtration occurs earlier — incorrect.
B) Mucus traps particles; cilia sweep them out — correct.
C) Teeth unrelated to respiration — incorrect.
D) Villi are intestinal — incorrect.

67. Which of the following represents cellular respiration?

A. O₂ + glucose → CO₂ + H₂O + energy (ATP)
B. CO₂ + H₂O → O₂ + glucose
C. Glucose + nitrogen → proteins
D. Sunlight + water → glucose
Correct answer: A. O₂ + glucose → CO₂ + H₂O + energy (ATP)

Explanations:
A) This is aerobic cellular respiration equation — correct.
B) That’s photosynthesis direction reversed — incorrect.
C) Protein synthesis is different metabolic process — incorrect.
D) Sunlight-driven photosynthesis — not cellular respiration — incorrect.

68. Which of the following statements is correct about alveoli?

A. They are thick-walled structures for protection.
B. They have a large surface area and thin walls to facilitate gas exchange.
C. They are present in the digestive tract.
D. They secrete bile.
Correct answer: B. They have a large surface area and thin walls to facilitate gas exchange.

Explanations:
A) Alveolar walls are thin, not thick — incorrect.
B) Large surface area + thin walls + capillary network = efficient gas exchange — correct.
C) They are lung structures, not digestive — incorrect.
D) Bile secretion is liver/gall bladder function — incorrect.

69. The term tidal volume refers to:

A. The air we can force out after normal exhalation
B. The volume of air inhaled or exhaled in a normal breath at rest
C. Air left in lungs after maximal exhalation
D. Total lung capacity only in athletes
Correct answer: B. The volume of air inhaled or exhaled in a normal breath at rest

Explanations:
A) Forced vital capacity concepts are separate — incorrect.
B) Tidal volume is normal resting breath volume — correct.
C) Residual volume is left after maximal exhalation — incorrect.
D) Tidal volume applies to everyone, not just athletes — incorrect.

70. Which blood pigment carries oxygen to tissues?

A. Haemoglobin
B. Melanin
C. Insulin
D. Bile pigment
Correct answer: A. Haemoglobin

Explanations:
A) Haemoglobin in RBCs binds and transports oxygen — correct.
B) Melanin is pigment in skin — incorrect.
C) Insulin is a hormone controlling blood sugar — incorrect.
D) Bile pigment is from liver breakdown of hemoglobin — incorrect.

71. The breathing rate in humans is controlled by:

A. Voluntary actions only
B. The brain (medulla oblongata) responding to CO₂ levels in blood
C. Stomach signals only
D. The heart’s pacemaker directly
Correct answer: B. The brain (medulla oblongata) responding to CO₂ levels in blood

Explanations:
A) Breathing is partly voluntary, but mainly involuntary control — incorrect.
B) Medulla senses CO₂/pH and adjusts breathing — correct.
C) Stomach unrelated — incorrect.
D) Heart pacemaker controls heart rhythm, not breathing rate — incorrect.

72. Which of the following animals uses skin as a respiratory surface?

A. Fish only
B. Earthworms and amphibians (partly)
C. Birds only
D. Insects only
Correct answer: B. Earthworms and amphibians (partly)

Explanations:
A) Fish mainly use gills — incorrect.
B) Earthworms respire through moist skin; amphibians also use skin in addition to lungs/gills — correct.
C) Birds use lungs and air sacs — incorrect.
D) Insects use tracheal system — incorrect.

73. In which condition is breathing rate generally highest?

A. At rest while sleeping
B. During vigorous exercise
C. During deep relaxation/meditation
D. While eating slowly
Correct answer: B. During vigorous exercise

Explanations:
A) Resting breathing is slower — incorrect.
B) Exercise increases oxygen demand and CO₂ removal so breathing rate increases — correct.
C) Relaxation tends to reduce breathing rate — incorrect.
D) Eating slowly does not greatly increase breathing rate — incorrect.

74. Which part of the respiratory system is lined with ciliates and mucus-secreting cells?

A. Alveoli only
B. Trachea and bronchi
C. Heart chambers
D. Small intestine
Correct answer: B. Trachea and bronchi

Explanations:
A) Alveoli have thin epithelial layer and macrophages, not ciliated lining like trachea/bronchi — incorrect.
B) Trachea and bronchi are lined with ciliated epithelium and mucus to trap & sweep particles — correct.
C) Heart not respiratory tract — incorrect.
D) Small intestine has villi & mucus but different lining — incorrect.

75. Which of the following describes external respiration?

A. Exchange of gases between blood and body cells
B. Exchange of gases between alveoli and blood in lungs
C. Release of energy from glucose inside mitochondria
D. Breakdown of food in stomach
Correct answer: B. Exchange of gases between alveoli and blood in lungs

Explanations:
A) That is internal (tissue) respiration — incorrect.
B) External respiration is alveoli-blood gas exchange — correct.
C) Cellular respiration (inside cells) is energy release — incorrect.
D) Digestion is separate process — incorrect. (more…)