Transport of gases depend on partial pressure of gases and also on Boyle's law. This means Pressure is inversely proportional to Volume when temperature remains constant. Thus gases transport from high pressure to low pressure. Oxygen is inhaled into the lungs from the atmosphere and thus partial pressure of oxygen is more in atmosphere and less in alveoli. Tidal volume is amount of air inhaled or exhaled in one breath and is 500ml out of which 350 ml is anatomic dead space. Trachea is made up of 16-20 shaped c shaped cartilaginous rings. Humans have two pairs of vocal cords: True and False and only true pair helps in production of sound.