Life Processes in Animals Part 4: MCQs (Q76–Q100)

Part 4 — Modes of Respiration in Animals & Applied Questions (Questions 76–100)

76. Fish primarily breathe using:

A. Lungs
B. Gills
C. Tracheae
D. Skin only
Correct answer: B. Gills

Explanations:
A) Lungs are for terrestrial vertebrates — incorrect.
B) Gills extract dissolved oxygen from water — correct.
C) Tracheal system is in insects — incorrect.
D) Some exchange across skin occurs but primary organ is gills — incorrect.

77. Insects breathe through a network of tubes called:

A. Gills
B. Tracheal system with spiracles
C. Alveoli
D. Lungs with alveoli
Correct answer: B. Tracheal system with spiracles

Explanations:
A) Gills are aquatic organ — incorrect.
B) Insects use tracheae that open via spiracles for direct gas diffusion — correct.
C) Alveoli are mammalian lungs — incorrect.
D) Insects lack lungs — incorrect.

78. Amphibians (like frogs) use which of the following for respiration?

A. Lungs only
B. Skin and lungs both (cutaneous and pulmonary respiration)
C. Gills only as adults
D. Tracheae only
Correct answer: B. Skin and lungs both (cutaneous and pulmonary respiration)

Explanations:
A) Adults use lungs but skin also important — incomplete/incorrect.
B) Frogs respire through skin (especially in water) and lungs on land — correct.
C) Larval amphibians (tadpoles) may have gills; adults usually use lungs and skin — incorrect.
D) Tracheae are insect structures — incorrect.

79. Birds have efficient respiration partly because:

A. They have alveoli like mammals only
B. They possess air sacs that allow unidirectional flow of air through lungs
C. They breathe only through skin
D. They use gills
Correct answer: B. They possess air sacs that allow unidirectional flow of air through lungs

Explanations:
A) Birds have a different system (air sacs & parabronchi) not simple alveoli — incorrect.
B) Air sacs produce a more continuous and efficient airflow enabling high oxygen extraction — correct.
C) Birds don’t respire via skin — incorrect.
D) Gills are aquatic organs — incorrect.

80. Which animal can hold breath for long periods by having large oxygen stores and slowing metabolism?

A. Whale (marine mammals)
B. Earthworm
C. Ant
D. Sparrow
Correct answer: A. Whale (marine mammals)

Explanations:
A) Marine mammals store oxygen in blood/muscles (myoglobin) and manage diving — correct.
B) Earthworms respire through skin and need oxygen constantly — incorrect.
C) Ants are small and don’t hold breath like diving mammals — incorrect.
D) Sparrows are birds that do not hold breath underwater — incorrect.

81. Which of these statements about gills is CORRECT?

A. Gills have large surface area and thin membranes to extract dissolved oxygen.
B. Gills pump oxygen into air.
C. Gills are used for chewing food in fishes.
D. Gills store bile for digestion.
Correct answer: A. Gills have large surface area and thin membranes to extract dissolved oxygen.

Explanations:
A) True — gills are structured for efficient gas exchange in water — correct.
B) Gills extract O₂ from water; they don’t pump it into air — incorrect.
C) Gills are respiratory, not digestive — incorrect.
D) Bile storage is gall bladder function — incorrect.

82. Which statement is TRUE for cellular respiration?

A. It occurs only in plants.
B. It occurs in mitochondria and releases ATP energy.
C. It produces oxygen as end product.
D. It occurs in the nucleus only.
Correct answer: B. It occurs in mitochondria and releases ATP energy.

Explanations:
A) Occurs in nearly all living cells (plants & animals) — incorrect.
B) Mitochondria are site of aerobic respiration producing ATP — correct.
C) Oxygen is a reactant in aerobic respiration, not a product — incorrect.
D) Nucleus is site of genetic material, not main respiration — incorrect.

83. A snorkel allows a swimmer to breathe when face is submerged by providing:

A. Direct oxygen to blood stream via skin
B. Air passage to the atmosphere while keeping face under water
C. Increased pressure to lungs
D. More haemoglobin in blood
Correct answer: B. Air passage to the atmosphere while keeping face under water

Explanations:
A) Skin does not absorb atmospheric O₂ significantly — incorrect.
B) Snorkel is a tube that reaches above water allowing breathing — correct.
C) Snorkel does not increase pressure to lungs; it just provides airway — incorrect.
D) Haemoglobin levels remain unchanged — incorrect.

84. Which of the following is an adaptation of aquatic animals for respiration?

A. Lungs only
B. Presence of gills, thin membranes and large surface area for gas exchange in water
C. Thick skin to prevent water loss
D. Wings for flying
Correct answer: B. Presence of gills, thin membranes and large surface area for gas exchange in water

Explanations:
A) Some aquatic animals have lungs (e.g., whales), but gills are common adaptation — incomplete/incorrect.
B) Gills and thin membranes provide efficient O₂ extraction from water — correct.
C) Thick skin prevents water loss in terrestrial animals; aquatic animals need permeable surfaces — incorrect.
D) Wings are for flight, unrelated to respiration — incorrect.

85. Which structure in an insect allows direct transport of oxygen to cells?

A. Lungs
B. Tracheoles (end branches of tracheal tubes)
C. Alveoli
D. Gills
Correct answer: B. Tracheoles (end branches of tracheal tubes)

Explanations:
A) Insects lack lungs — incorrect.
B) Tracheoles reach body cells and allow direct diffusion of gases — correct.
C) Alveoli are mammalian lung structures — incorrect.
D) Gills are aquatic structures — incorrect.

86. Why do alveoli have a rich blood supply?

A. To digest food there
B. For efficient exchange of oxygen and carbon dioxide between air and blood
C. To produce haemoglobin
D. To filtrate blood like kidneys
Correct answer: B. For efficient exchange of oxygen and carbon dioxide between air and blood

Explanations:
A) Alveoli are respiratory surfaces, not digestive — incorrect.
B) Dense capillary network ensures rapid gas exchange — correct.
C) Haemoglobin is produced in bone marrow/erythrocytes, not alveoli — incorrect.
D) Filtration occurs in kidneys — incorrect.

87. Which of the following animals uses both lungs and skin for respiration?

A. Earthworm only
B. Frog (amphibian)
C. Fish only
D. Insect only
Correct answer: B. Frog (amphibian)

Explanations:
A) Earthworms primarily use skin, not lungs — incorrect.
B) Frogs breathe through lungs on land and skin (cutaneous) in water — correct.
C) Fish use gills — incorrect.
D) Insects use tracheae — incorrect.

88. The major difference between breathing and cellular respiration is:

A. There is no difference — they’re same.
B. Breathing is physical movement of air; cellular respiration is biochemical process releasing energy inside cells.
C. Breathing happens in mitochondria only.
D. Cellular respiration occurs only when breathing stops.
Correct answer: B. Breathing is physical movement of air; cellular respiration is biochemical process releasing energy inside cells.

Explanations:
A) They are distinct processes — incorrect.
B) Clear difference: ventilation vs oxidation of glucose — correct.
C) Breathing is an organ-level action, not in mitochondria — incorrect.
D) Cellular respiration continues as long as cells have substrates & oxygen — incorrect.

89. Which of the following is an immediate effect of smoking on lungs?

A. Increased ciliary action and better cleaning
B. Damage to cilia, leading to accumulation of dust and mucus
C. Instant increase in alveolar surface area
D. Decrease in carbon dioxide production by body
Correct answer: B. Damage to cilia, leading to accumulation of dust and mucus

Explanations:
A) Smoking reduces ciliary function — incorrect.
B) Cilia are damaged leading to infection risk and mucus accumulation — correct.
C) Alveolar surface area decreases with emphysema — incorrect.
D) CO₂ production depends on metabolism; smoking doesn’t decrease it immediately — incorrect.

90. During exhalation (expiration) at rest:

A. The diaphragm contracts and moves down
B. The diaphragm relaxes and moves up; chest cavity volume decreases causing air to flow out
C. The chest cavity volume increases hugely
D. Air rushes in due to lower outside pressure
Correct answer: B. The diaphragm relaxes and moves up; chest cavity volume decreases causing air to flow out

Explanations:
A) Diaphragm contraction is for inhalation — incorrect.
B) Relaxation reduces thoracic volume, increases pressure, pushing air out — correct.
C) Chest cavity decreases, not increases — incorrect.
D) Air flows out because internal pressure becomes higher than outside — incorrect.

91. Which of the following best explains why alveoli are moist?

A. Moisture helps dissolve gases, enabling diffusion of O₂ and CO₂ across membranes
B. Moisture stops gas exchange
C. Moisture is only for taste
D. Moisture causes alveoli to stick together permanently
Correct answer: A. Moisture helps dissolve gases, enabling diffusion of O₂ and CO₂ across membranes

Explanations:
A) Gases dissolve in the thin fluid layer before diffusing; moisture aids exchange — correct.
B) Moisture is essential, not inhibitory (excess can be pathological) — incorrect.
C) Taste is unrelated — incorrect.
D) Surface tension can cause collapse but surfactant prevents sticking; permanent sticking is abnormal — incorrect.

92. Which organism performs internal respiration in specialized alveoli-like structures called book lungs?

A. Mammals
B. Spiders (arthropods) — book lungs in some arachnids
C. Fish
D. Birds
Correct answer: B. Spiders (arthropods) — book lungs in some arachnids

Explanations:
A) Mammals have alveoli, not book lungs — incorrect.
B) Many spiders have book lungs for gas exchange — correct.
C) Fish have gills — incorrect.
D) Birds have parabronchi & air sacs — incorrect.

93. The process of breathing in (inspiration) is aided by contraction of which muscle?

A. Cardiac muscle
B. Diaphragm and external intercostal muscles
C. Leg muscles
D. Muscles of small intestine
Correct answer: B. Diaphragm and external intercostal muscles

Explanations:
A) Cardiac muscle pumps blood — not primary for inhalation — incorrect.
B) Diaphragm contraction and raising of ribs by external intercostals expand thoracic cavity — correct.
C) Leg muscles not involved — incorrect.
D) Intestinal muscles move food, not air — incorrect.

94. Which is the correct reason why oxygen diffuses from alveoli into blood?

A. Oxygen moves from a region of low concentration to high concentration
B. Oxygen moves from higher partial pressure in alveoli to lower partial pressure in blood (diffusion down partial pressure gradient)
C. Oxygen is actively transported using ATP across alveolar wall
D. Oxygen is pumped by the heart into blood
Correct answer: B. Oxygen moves from higher partial pressure in alveoli to lower partial pressure in blood (diffusion down partial pressure gradient)

Explanations:
A) Diffusion goes high → low concentration, not low → high — incorrect.
B) Partial pressure gradient drives passive diffusion of O₂ into blood — correct.
C) Oxygen diffusion is passive, not ATP-driven — incorrect.
D) Heart pumps blood but does not pump oxygen molecules across alveolar membrane — incorrect.

95. Which of these is a structural adaptation in birds for efficient respiration required for flight?

A. Reduced surface area in lungs
B. Air sacs and lightweight bones aiding continuous airflow and lower body weight
C. Multiple stomachs for digestion
D. Thick heavy bones
Correct answer: B. Air sacs and lightweight bones aiding continuous airflow and lower body weight

Explanations:
A) Birds require large effective respiratory efficiency, not reduced area — incorrect.
B) Air sacs provide efficient oxygenation; hollow bones reduce weight — correct.
C) Multiple stomachs are digestive adaptations in some animals, not respiratory — incorrect.
D) Heavy bones would hinder flight — incorrect.

96. The primary respiratory pigment in human blood is:

A. Carotene
B. Haemoglobin
C. Chlorophyll
D. Keratin
Correct answer: B. Haemoglobin

Explanations:
A) Carotene is plant pigment — incorrect.
B) Haemoglobin binds oxygen in RBCs — correct.
C) Chlorophyll is plant photosynthetic pigment — incorrect.
D) Keratin is structural protein in skin/hair — incorrect.

97. In which way does the breathing rate change with altitude (high mountains) initially?

A. Decreases immediately because less oxygen available
B. Increases (hyperventilation) to take in more air because partial pressure of O₂ is lower
C. Remains unchanged forever
D. Stops completely
Correct answer: B. Increases (hyperventilation) to take in more air because partial pressure of O₂ is lower

Explanations:
A) Body responds by increasing breathing rather than decreasing — incorrect.
B) Reduced O₂ partial pressure leads to faster breathing to compensate — correct.
C) Body adapts over time but initial change is increase — incorrect.
D) Breathing doesn’t stop — incorrect.

98. Which of these shows correct pairing (animal — respiration organ)?

A. Fish — Lungs
B. Insect — Gills
C. Earthworm — Skin
D. Human — Gills
Correct answer: C. Earthworm — Skin

Explanations:
A) Fish usually have gills, not lungs — incorrect.
B) Insects use tracheal system, not gills (some aquatic insects have gill-like structures) — incorrect.
C) Earthworms respire through moist skin — correct.
D) Humans have lungs, not gills — incorrect.

99. A person hyperventilates (breathes rapidly) and then holds breath. What happens to carbon dioxide (CO₂) level in blood immediately after hyperventilation?

A. CO₂ rises sharply
B. CO₂ falls (because more CO₂ was exhaled)
C. CO₂ converts to oxygen
D. CO₂ is unchanged
Correct answer: B. CO₂ falls (because more CO₂ was exhaled)

Explanations:
A) Hyperventilation expels CO₂ so levels drop, not rise — incorrect.
B) Rapid breathing removes CO₂ faster, reducing blood CO₂ — correct.
C) CO₂ is not converted into oxygen — incorrect.
D) It changes (decreases) — incorrect.

100. Which of the following statements is TRUE?

A. All respiration in animals is aerobic.
B. Anaerobic respiration does not release any energy.
C. Some organisms and tissues can perform anaerobic respiration producing less energy and different end-products (e.g., lactic acid in muscles, ethanol in microbes).
D. Cellular respiration does not involve oxygen at all.
Correct answer: C. Some organisms and tissues can perform anaerobic respiration producing less energy and different end-products (e.g., lactic acid in muscles, ethanol in microbes).

Explanations:
A) Not all respiration is aerobic (anaerobic exists) — incorrect.
B) Anaerobic respiration releases energy but less than aerobic — incorrect.
C) Correct: anaerobic pathways yield less ATP and produce lactic acid or ethanol depending on organism — correct.
D) Aerobic cellular respiration requires oxygen — incorrect. (more…)