Tag: zoology

Passive or simple diffusion is the movement of solutes (gas or ions) from an area of high concentration to an area of low concentration. Gases diffuse across the systemic capillary membrane and the cell membranes of the target tissue. Carbon dioxide diffuses from systemic tissues to lungs, and oxygen diffuses from lungs to systemic tissues

So, the correct answer is 'Simple diffusion'

Successive opening and closing of mouth and external nostrils do not take place during pulmonary respiration.

The mechanism of pulmonary respiration: It includes breathing movement, exchange of gases, in lungs, transport of gases by blood and exchange of gases by tissue. 

The medulla oblongata (with the inspiratory centre and expiratory centre) and pons varolli (with pneumotoxic centre) are the breathing centre that regulates the breathing mechanism. Inspiratory centre stimulates inspiratory muscle (diaphragm) to control the rhythm of respiration. Expiratory centre remains inactive during normal breathing but it controls both expiration and inspiration during exercise. Pneumotoxic centre controls the switch off point of the breathing sending signal to inspiratory centre. The medulla’s control centre detects low pH of tissue fluid during formation of more carbonic acids, the centre increases the rate of breathing to eleiminate the excess CO2. The concentration of O2 has little effect on breathing centers. However, when O2 level is severely depressed, O2 sensors in the aorta and carotid arteries send signals to breathing control center to increase the breathing rate.