Zoology MCQs for NEET — Practice Questions with Answers

The NCERT text defines it as: 'This process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing, commonly known as respiration.'

The context mentions: '...insects have a network of tubes (tracheal tubes) to transport atmospheric air within the body.'

The NCERT states: 'As the solubility of CO2 is 20-25 times higher than that of O2, the amount of CO2 that can diffuse through the diffusion membrane per unit difference in partial pressure is much higher compared to that of O2.'

The NCERT text describes the thoracic chamber as formed 'dorsally by the vertebral column, ventrally by the sternum, laterally by the ribs and on the lower side by the dome-shaped diaphragm.'

The NCERT lists five steps of respiration: (i) Breathing or pulmonary ventilation (ii) Diffusion of gases (O2 and CO2) across alveolar membrane (iii) Transport of gases by the blood (iv) Diffusion of O2 and CO2 between blood and tissues (v) Utilisation of O2 by the cells for catabolic reactions. Production of hemoglobin is a physiological process, not a direct step in gas exchange and cellular respiration itself.

The NCERT states: 'On an average, a healthy human breathes 12-16 times/minute.'

According to the NCERT text, 'Inspiration can occur if the pressure within the lungs (intra-pulmonary pressure) is less than the atmospheric pressure... This is achieved by the contraction of diaphragm which increases the volume of thoracic chamber in antero-posterior axis. The contraction of external inter-costal muscles lifts up the ribs and the sternum causing an increase in the volume of the thoracic chamber in the dorso-ventral axis. The overall increase in the thoracic volume causes a similar increase in pulmonary volume. An increase in pulmonary volume decreases the intra-pulmonary pressure to less than the atmospheric pressure which forces the air from outside to move into the lungs, i.e., inspiration (Figure 14.2a).'

The NCERT states, 'The volume of air involved in breathing movements can be estimated by using a spirometer which helps in clinical assessment of pulmonary functions.' While many volumes are defined, Residual Volume (RV) and consequently capacities that include RV (like TLC and FRC) cannot be measured directly by a spirometer, as some air always remains in the lungs. Inspiratory Reserve Volume (IRV) is a measurable change in volume during forced inspiration.

The NCERT states, 'Relaxation of the diaphragm and the inter-costal muscles returns the diaphragm and sternum to their normal positions and reduce the thoracic volume and thereby the pulmonary volume. This leads to an increase in intra-pulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs, i.e., expiration (Figure 14.2b).' Thus, the increase in intra-pulmonary pressure above atmospheric pressure is the primary driver.

The NCERT states, 'The conducting part transports the atmospheric air to the alveoli, clears it from foreign particles, humidifies and also brings the air to body temperature. Exchange part is the site of actual diffusion of O2 and CO2 between blood and atmospheric air.' Thus, the conducting part does not serve as the site of gas diffusion.