Free Respiration MCQs with Answers

• A. trachea, alveoli, bronchi, bronchioles
• B. bronchi, trachea, bronchioles, alveoli
• C. trachea, bronchi, bronchioles, alveoli
• D. bronchioles, bronchi, trachea, alveoli

Explanation: Air passes down the single trachea, which divides into two bronchi, one to each lung, and these branch repeatedly into ever finer…

• A. epiglottis
• B. uvula
• C. soft palate
• D. glottis

Explanation: The epiglottis is a flap of cartilage that folds back over the opening of the larynx as the larynx rises during swallowing, so the bolus…

• A. complete rings would restrict the flow of air
• B. cartilage is too expensive for the body to make
• C. the gap allows nerves to reach the lung
• D. the incomplete side lies against the oesophagus and lets it expand during swallowing

Explanation: The cartilage keeps the airway permanently open so it cannot collapse when pressure falls during inspiration, while the soft muscular gap…

• A. Their supporting rings of cartilage
• B. Their walls, one cell thick, giving an enormous surface area with a dense capillary network
• C. The cilia lining their inner surface
• D. The mucus that coats them

Explanation: Around 300 million alveoli give a surface of roughly 70 square metres, and a wall a single cell thick lying against an equally thin…

• A. contracts and flattens, increasing the volume of the thorax
• B. relaxes and domes upwards, increasing the volume of the thorax
• C. contracts and domes upwards, decreasing the volume of the thorax
• D. does not move at all

Explanation: A flattening diaphragm and the external intercostals swinging the ribs up and out together enlarge the thoracic cavity, so the pressure…

• A. no air actually leaves the lungs
• B. the internal intercostal muscles contract forcefully
• C. it results from the elastic recoil of the lungs and relaxation of the inspiratory muscles
• D. the diaphragm contracts to push air out

Explanation: When the diaphragm and external intercostals simply relax, the stretched elastic tissue of the lungs recoils and the thoracic volume falls…

• A. vital capacity
• B. tidal volume
• C. residual volume
• D. total lung capacity

Explanation: The tidal volume of an adult at rest is about 500 cm3, of which roughly 150 cm3 stays in the airways as dead space and never reaches the…

• A. the air left in the lungs after the deepest possible expiration
• B. the volume of one quiet breath
• C. the volume of air in the dead space
• D. the maximum volume of air that can be expelled after the deepest possible inspiration

Explanation: Vital capacity is the sum of the tidal volume and the inspiratory and expiratory reserve volumes, so it measures the usable range of the…

• A. hydrogen carbonate ions dissolved in the plasma
• B. carbaminohaemoglobin
• C. carbon dioxide dissolved in the plasma
• D. carbon monoxide

Explanation: About seventy per cent of carbon dioxide enters the red cells, where carbonic anhydrase converts it with water into carbonic acid, which…

• A. one molecule of oxygen
• B. four molecules of oxygen
• C. two molecules of oxygen
• D. an unlimited number of oxygen molecules

Explanation: Haemoglobin has four polypeptide chains, each with an iron containing haem group that binds one oxygen molecule, giving a maximum of four.

• A. the chloride shift
• B. the countercurrent effect
• C. the Bohr effect
• D. the induced fit effect

Explanation: Carbon dioxide lowers the pH of the blood, which alters the shape of haemoglobin and reduces its affinity for oxygen, shifting the…

• A. oxygen in the alveoli
• B. glucose in the blood
• C. nitrogen in the blood
• D. carbon dioxide in the blood, monitored by the medulla oblongata

Explanation: Chemoreceptors in the medulla and in the great arteries respond to the fall in pH that a rise in carbon dioxide produces, and the…

• A. binds haemoglobin far more strongly than oxygen does and does not readily let go
• B. dissolves the walls of the alveoli
• C. destroys the red blood cells immediately
• D. prevents the diaphragm from contracting

Explanation: Carbon monoxide has roughly two hundred times the affinity of oxygen for haemoglobin and forms stable carboxyhaemoglobin, so those binding…

• A. out of the red cell as oxygen enters
• B. into the red cell to balance the hydrogen carbonate ions leaving it
• C. from the plasma into the alveolar air
• D. into the plasma from the kidney tubules

Explanation: As hydrogen carbonate ions formed inside the red cell diffuse out into the plasma, the cell would be left with a net positive charge, so…

• A. tidal volume
• B. inspiratory reserve volume
• C. residual volume
• D. vital capacity

Explanation: About 1,200 cm3 cannot be expelled, and this residual volume keeps the alveoli partly inflated so they do not collapse and stick shut, and…

• A. tar
• B. carbon monoxide
• C. benzene
• D. nicotine

Explanation: Nicotine reaches the brain within seconds and acts on receptors there to give the reward that makes smoking so hard to give up, while also…

• A. the carcinogenic chemicals in tar
• B. the heat of the smoke
• C. nicotine acting on the brain
• D. the loss of surfactant from the alveoli

Explanation: Tar contains carcinogens such as benzopyrene that mutate the genes controlling cell division in the bronchial epithelium, and years of…

• A. the trachea is blocked by mucus
• B. the walls between alveoli break down, reducing the surface area for gas exchange
• C. the diaphragm is paralysed
• D. the blood contains too few white cells

Explanation: Smoke attracts phagocytes that release elastase, which digests the elastic tissue, so alveoli merge into large air spaces with much less…

• A. the alveoli fill with blood
• B. the ribs lose their cartilage
• C. smoke paralyses the cilia and stimulates extra mucus, which then collects in the airways
• D. the vocal cords are permanently inflamed

Explanation: Cilia that normally sweep the mucus escalator upwards are stopped by the smoke, while the irritation makes goblet cells secrete more…

• A. the smoke changes chemically once it leaves the smoker's lungs
• B. non smokers absorb nicotine through the skin
• C. it affects only people who are already ill
• D. sidestream smoke contains the same tar, nicotine and carbon monoxide, which bystanders inhale

Explanation: Smoke drifting from the burning tip is unfiltered and carries the same carcinogens, so people sharing the room inhale them and their risk…