The amount of air breathed in and out during a normal respiration by human lungs is referred to as
- (a)Vital capacity
- (b)Tidal volume
- (c)Inspiratory volume
- (d)Total lung capacity
Correct — B, Tidal volume. Tidal volume is the amount of air a person breathes in, or breathes out, in a single normal, effortless breath — about 500 millilitres in a resting adult. Because the question specifies 'normal respiration' (quiet breathing, not a deep forced breath), the quantity being described is exactly the tidal volume.
- (a)Vital capacity — Vital capacity is the maximum air you can exhale after breathing in as deeply as possible — a large forced volume (around 4-5 litres), not the small amount moved in ordinary quiet breathing.
- (c)Inspiratory volume — The related term, inspiratory reserve volume, is the extra air you can draw in beyond a normal breath. It measures the reserve on top of tidal volume, not the normal breath itself.
- (d)Total lung capacity — Total lung capacity is the entire volume the lungs can hold when filled to the maximum (about 6 litres). It is the sum of all lung volumes, far larger than one quiet breath.
Lung function is described using standard respiratory volumes. Tidal volume is the air exchanged in one normal breath (about 500 mL). Adding the reserves you can inhale and exhale by force gives the vital capacity, and adding the air that always remains in the lungs (residual volume) to that gives the total lung capacity.
The question hinges on the phrase 'normal respiration'. That single word rules out the forced or maximal measures — vital capacity and total lung capacity are about deep, forced breathing, while tidal volume is defined precisely as the quiet, everyday breath. Knowing that 'tidal' refers to the gentle in-and-out of ordinary breathing pins the answer.
- Tidal volume is the air moved in or out in one normal breath, about 500 mL in a resting adult.
- Vital capacity is the maximum air exhaled after the deepest possible inhalation (about 4-5 litres).
- Total lung capacity is the greatest volume the lungs can hold, about 6 litres.
- Residual volume is the air that stays in the lungs even after full exhalation and cannot be breathed out.
'Normal respiration' points to the everyday quiet breath, which is the tidal volume - option (b).
- Vital capacity and total lung capacity involve deep or forced breathing — do not pick them for a 'normal' or 'quiet' breath.
- Tidal volume is a single breath, whereas capacities are sums of several volumes; keep 'volume' and 'capacity' distinct.
Asked to define or identify a respiratory volume from a description, or to pick which term matches quiet versus forced breathing.
Oxygen transportation in a human body takes place through I. Blood II. Lungs III. Tissue. The correct sequence of transportation is
- (a) I, II, III
- (b) III, I, II
- (c) II, I, III
- (d) I, III, II
Answer(c) II, I, III — oxygen passes from the lungs into the blood and is then delivered to the tissues.
Both questions probe the human respiratory pathway — Q134 on the volume of a normal breath, this one on how the air's oxygen then moves from lungs to blood to tissue.
- practice — not a real PYQ
The approximate tidal volume of air in a healthy resting adult human is
- (a)50 mL
- (b)500 mL
- (c)1500 mL
- (d)4500 mL
Answer(b) 500 mL — a normal quiet breath moves about half a litre of air in or out.
- practice — not a real PYQ
The maximum volume of air a person can breathe out after the deepest possible inhalation is called
- (a)Tidal volume
- (b)Residual volume
- (c)Vital capacity
- (d)Dead space volume
Answer(c) Vital capacity — it is the largest volume exhaled after a maximum inhalation.