Breathing and Exchange of Gases — Class 11 MCQs with Answers

Breathing and Exchange of Gases — important questions & MCQs with answers (Class 11 Biology)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Site of gas exchange in lungs:

   AAlveoliBBronchiCTracheaDLarynx
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   Answer: Alveoli

   Explanation: Alveoli are the thin-walled, capillary-wrapped sacs where actual gas exchange happens; bronchi and trachea only conduct air without exchanging gases with blood.

2. Q2 of 6Easy

   Breathing or pulmonary ventilation refers to:

   AGas exchange in tissuesBInhalation and exhalation of air between atmosphere and lungsCGlucose oxidationDProduction of ATP
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   Answer: Inhalation and exhalation of air between atmosphere and lungs

   Explanation: Breathing (pulmonary ventilation) is just moving air between atmosphere and lungs; using O₂ to make ATP is cellular respiration, a separate process happening inside cells.

3. Q3 of 6Medium

   Most O₂ in blood is carried by:

   APlateletsBPlasma dissolvedCWBCDHaemoglobin
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   Answer: Haemoglobin

   Explanation: About 97% of blood O₂ travels bound to haemoglobin as oxyhaemoglobin inside RBCs; only the remaining ~3% dissolves directly in plasma.

4. Q4 of 6Medium

   Tidal volume (TV) of a healthy adult human is approximately:

   A500 mLB1500 mLC3000 mLD6000 mL
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   Answer: 500 mL

   Explanation: Resting tidal volume is about 500 mL per breath at 12-16 breaths per minute — far smaller than vital capacity (~3500-4500 mL), the maximum forced exhale after deepest inhale.

5. Q5 of 6Hard

   Assertion: Insects do not need a circulatory pigment for O₂ transport. Reason: Their tracheal system delivers O₂ directly to tissues.

   ABoth true and Reason explains AssertionBBoth true but Reason does not explainCAssertion falseDBoth false
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   Answer: Both true and Reason explains Assertion

   Explanation: Both statements are true and the reason explains the assertion: insects' tracheal system delivers O₂ directly to tissues via tracheoles, so their haemolymph doesn't need a respiratory pigment like Hb.

6. Q6 of 6Hard

   Bohr effect: O₂ binding to Hb decreases when:

   AO₂ risesBpH risesCTemperature fallsDCO₂/H⁺ increases (lower pH)
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   Answer: CO₂/H⁺ increases (lower pH)

   Explanation: The Bohr effect: rising CO₂ and H⁺ (falling pH) in tissues lowers Hb's O₂ affinity, so it unloads oxygen where it's needed most — the opposite of what happens in O₂-rich lungs.

Breathing and Exchange of Gases notes: key concepts (Class 11 Biology)

Human respiration ends at the alveoli, where oxygen and carbon dioxide diffuse across a thin membrane along partial-pressure gradients. This chapter traces the conducting passages, the pressure-driven mechanics of breathing, respiratory volumes, and how blood ferries both gases between lungs and tissues.

Respiratory organs

Air travels through the nostrils, nasal chamber, pharynx, larynx, trachea, two primary bronchi and branching bronchioles ending in the alveoli of the lungs.

Conducting vs exchange zone

The passage from nostrils to terminal bronchioles conducts, warms and filters air; the alveoli form the respiratory part where actual gas exchange occurs.

Inspiration

Contraction of the diaphragm and external intercostals raises thoracic volume, dropping intra-pulmonary pressure below atmospheric so air rushes into the lungs.

Expiration

Relaxation of the diaphragm and intercostals shrinks the thorax, raising intra-pulmonary pressure above atmospheric; normal expiration is passive.

Respiratory volumes

Tidal volume (~500 mL) is normal breath air; inspiratory and expiratory reserve volumes are the extra air moved during forced breathing.

Vital capacity

Vital capacity is the maximum air exhaled after a forced inspiration (IRV + TV + ERV); residual volume (~1200 mL) always stays in the lungs.

Diffusion of gases

Gases move only by partial-pressure gradients: pO₂ is high in alveoli and low in tissues, so O₂ diffuses inward while CO₂ follows its own opposite gradient.

Transport of oxygen

About 97% of oxygen travels bound to haemoglobin as oxyhaemoglobin, each Hb binding four O₂ molecules; only about 3% dissolves in plasma.

Oxygen dissociation curve

Plotting percent Hb saturation against pO₂ gives a sigmoid curve, reflecting the cooperative binding of four O₂ molecules to haemoglobin.

Bohr effect

High CO₂, high H⁺ (low pH), high temperature and high BPG shift the curve rightward, lowering Hb affinity so more O₂ unloads in active tissues.

Transport of carbon dioxide

Roughly 70% of CO₂ is carried as bicarbonate ions, about 20–25% as carbamino-haemoglobin, and about 7% dissolved in the plasma.

Chloride shift

Carbonic anhydrase in RBCs speeds CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻; bicarbonate leaves and Cl⁻ enters the cell to maintain ionic balance.

Regulation of respiration

The respiratory rhythm centre in the medulla, aided by the pneumotaxic pons and a chemosensitive area, adjusts breathing chiefly to CO₂ and H⁺ levels.

Respiratory disorders

Asthma (bronchiole inflammation), emphysema (damaged alveolar walls, often from smoking) and occupational fibrosis like silicosis all impair gas exchange.