Question

(i) Why is respiratory pigment needed in multicellular organisms with large body size?
(ii) Give reasons for the following:
(a) Rings of cartilage are present in the throat.
(b) Lungs always contain a residual volume of air.
(c) The diaphragm flattens and ribs are lifted up when we breathe in.
(d) Walls of alveoli contain an extensive network of blood vessels.

Answer 1

(i). For multicellular organisms of substantial size, efficient oxygen transport necessitates respiratory pigments, such as hemoglobin, because:
• The oxygen demands of these organisms cannot be met by simple diffusion alone.
• Respiratory pigments facilitate oxygen binding and transport throughout the organism's entirety.

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(ii). (a) The throat contains cartilage rings.
Explanation: These cartilaginous rings in the trachea maintain an open airway, preventing its collapse during respiration.
(b) Lungs retain a reserve volume of air.
Explanation: This residual air prevents lung collapse and ensures uninterrupted gas exchange throughout the breathing cycle.
(c) The diaphragm flattens and ribs elevate during inhalation.
Explanation: During inhalation:
• Diaphragmatic contraction and flattening expand the thoracic cavity.
• Rib elevation and outward movement decrease intra-pulmonary pressure, drawing air inward.
(d) Alveolar walls are richly supplied with blood vessels.
Explanation: This extensive vascularization of the alveoli optimizes the exchange of oxygen and carbon dioxide between the pulmonary system and the bloodstream.