Breathing and Exchange of Gases

Explanation

Sponges and other lower invertebrates have no respiratory organ at all — every cell is close enough to the surrounding water for gases to diffuse directly across the body surface. Moist cuticle is the earthworm's method, tracheal tubes are the insects', and gills belong to aquatic arthropods and molluscs.

Explanation

Each disorder is named for the structure it damages. Emphysema destroys alveolar walls so the respiratory surface shrinks. Angina pectoris is the chest pain of inadequate oxygen supply to cardiac muscle. Glomerulonephritis is inflammation of the kidney glomeruli. Tetany is the rapid muscle spasm caused by a fall in blood calcium. That gives A-II, B-III, C-IV, D-I.

Explanation

Binding of oxygen to haemoglobin is favoured by a high partial pressure of oxygen, a low partial pressure of carbon dioxide, low hydrogen ion concentration and low temperature — exactly the conditions in the alveoli. A rise in H⁺ or CO₂ shifts the dissociation curve to the right and promotes release instead, which is the Bohr effect and is what happens in the tissues.