Theory question 108
Respiration(a) (i) Briefly explain the term respiration.
(ii) Name the two types of respiration and write a balanced equation to summarize each of them.
(b) Outline the mechanisms involved in: (i) inhalation; (ii) exhalation in human beings.
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(a)(i) Respiration is the breaking down of food (mainly glucose) in living cells to release energy, with carbon(IV) oxide and water (or alcohol/lactic acid) as by-products.
(ii) Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (2898 kJ).
Anaerobic respiration: in yeast C6H12O6 → 2C2H5OH + 2CO2 + energy (210 kJ); in muscle C6H12O6 → 2C3H6O3 (lactic acid) + energy.
(b)(i) Inhalation: external intercostal muscles contract, pulling the ribs upwards and outwards; diaphragm muscles contract and the diaphragm flattens; the volume of the thorax increases and pressure in the lungs falls below atmospheric pressure; air rushes in through the nose and trachea into the lungs.
(ii) Exhalation: external intercostal muscles relax (internal ones contract) and the ribs move down and inwards; diaphragm relaxes and domes upwards; volume of the thorax decreases and pressure in the lungs rises; air is forced out.
Link volume change to pressure change.