What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

Define vital capacity and state its significance.

Vital capacity is the maximum volume of air a person can breathe in after a forced expiration; a higher value indicates greater respiratory capacity and is of clinical significance.

What is the site of gaseous exchange in the lungs?

The alveoli are the primary sites of exchange of gases between blood and air.

Explain the process of inspiration.

Contraction of the diaphragm and external intercostal muscles increases the thoracic and pulmonary volume, lowering intra-pulmonary pressure below atmospheric pressure so that air moves into the lungs.

How are oxygen and carbon dioxide exchanged at the alveoli?

They diffuse along partial-pressure gradients: oxygen moves from alveoli to blood and carbon dioxide from blood to alveoli, helped by the high solubility of carbon dioxide and the thin diffusion membrane.

How is oxygen transported in the blood?

About 97 per cent of oxygen is transported by red blood cells bound to haemoglobin as oxyhaemoglobin, and the rest is dissolved in plasma.

What are the major transport mechanisms for carbon dioxide?

About 70 per cent is carried as bicarbonate, 20-25 per cent as carbamino-haemoglobin and about 7 per cent dissolved in plasma.

Define oxygen dissociation curve and explain its sigmoid shape.

It is the curve relating haemoglobin saturation to partial pressure of oxygen; its sigmoid shape reflects the cooperative binding of oxygen and the effects of pCO2, pH and temperature.

What is the effect of pCO2 on oxygen transport?

High pCO2 favours dissociation of oxygen from oxyhaemoglobin (as in tissues), while low pCO2 favours its formation (as in alveoli).

How is respiration regulated?

The respiratory rhythm centre in the medulla, moderated by the pneumotaxic centre in the pons and a chemosensitive area sensitive to carbon dioxide and hydrogen ions, regulates breathing.

Name two disorders of the respiratory system.

Asthma, caused by inflammation of bronchi and bronchioles, and emphysema, in which alveolar walls are damaged, often by smoking.

Breathing and Exchange of Gases

Class 11 Biology · Biology · Chapter 14

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CBSE Class 11 · Biology

19 chapters: every table, cycle and pathway

Marks booster + cheatsheet: key concepts in 2 lines each, common traps
18 marks: Unit V, breathing to hormones
15 marks each: Units I and III
Common traps, corrected
Five kingdoms classification table
Physiological numbers, with page numbers

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CBSE Class 11 · Biology

19 chapters: every table, cycle and pathway

Marks booster + cheatsheet: key concepts in 2 lines each, common traps
18 marks: Unit V, breathing to hormones
15 marks each: Units I and III
Common traps, corrected
Five kingdoms classification table
Physiological numbers, with page numbers

Page 1 free about 8 min read, Full kit about 55 min read

₹159See the full kit

View all 44 amazing Marks Booster kits →

Summary

This chapter describes how animals, especially humans, take in oxygen and remove carbon dioxide. Mechanisms vary with habitat: lower invertebrates use diffusion, earthworms use moist skin, insects use tracheal tubes, aquatic arthropods and molluscs use gills, and terrestrial vertebrates use lungs. The human respiratory system consists of external nostrils, nasal chamber, pharynx, larynx (the sound box with the epiglottis), trachea, bronchi, bronchioles and alveoli, the thin vascularised sacs where gas exchange occurs; the lungs lie in an airtight thoracic chamber bounded by ribs, sternum and the diaphragm. Breathing has two stages: inspiration, when contraction of the diaphragm and external intercostal muscles increases thoracic and pulmonary volume and lowers intra-pulmonary pressure to draw air in, and expiration, when their relaxation reverses this. Respiratory volumes and capacities such as tidal volume, vital capacity and residual volume are measured with a spirometer. Exchange of oxygen and carbon dioxide at alveoli and tissues occurs by diffusion along partial-pressure gradients. Oxygen is carried mainly as oxyhaemoglobin and described by the sigmoid oxygen dissociation curve, while most carbon dioxide is transported as bicarbonate with the help of carbonic anhydrase. The respiratory rhythm is regulated by centres in the medulla and pons, and disorders include asthma and emphysema.

Respiratory organs in animalsHuman respiratory systemMechanism of breathingRespiratory volumes and capacitiesExchange and transport of gasesRegulation and disorders of respiration

Key terms

Alveoli

The thin, irregular-walled, vascularised bag-like structures of the lungs where gas exchange takes place.

Tidal volume

The volume of air inspired or expired during a normal respiration, about 500 mL.

Vital capacity

The maximum volume of air a person can breathe in after a forced expiration, including ERV, TV and IRV.

Oxygen dissociation curve

The sigmoid curve obtained by plotting percentage saturation of haemoglobin with oxygen against partial pressure of oxygen.

Partial pressure

The pressure contributed by an individual gas in a mixture, written pO2 for oxygen and pCO2 for carbon dioxide.

Carbonic anhydrase

The enzyme in red blood cells that catalyses the interconversion of carbon dioxide and bicarbonate.

Extra questions & answers

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The primary sites of exchange of gases in the lungs are the:

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