The respiratory system does not:
1. allow oxygen from the air to enter the blood and carbon dioxide to leave the blood and enter the air.
2. alter the pH by changing oxygen levels.
3. provide protection against some microorganisms by preventing their entry into the body and by removing them from respiratory surfaces.
4. allow for speech and sound generation.

The dorsal respiratory group of the respiratory center in the brain stem stimulates:

Condition of the body in which the tissues are starved of oxygen is called as:

Oxygenated blood through the tissues of the lungs is carried by:
1. pulmonary and bronchial veins
2. pulmonary and bronchial arteries
3. pulmonary veins and bronchial arteries
4. pulmonary arteries and bronchial veins

Air conditioning – warming, humidifying and filtering of the air, is the function performed by:

The diffusion of gases in lungs occur across the respiratory membrane. Which of the following is incorrect regarding the respiratory membrane?
1. it is the only barrier between the blood and the inhaled gases within each alveolus
2. basement membranes of alveolar type I cells and their adjacent capillaries are fused
3. oxygen cannot diffuse through the membrane and so must be actively transported
4. carbon dioxide diffuses across the membrane from the blood into the alveolar lumen

Lungs are made up of air-filled sacs, the alveoli. They do not collapse even after forceful expiration, because of
1. Residual Volume (RV)
2. Inspiratory Reserve Volume (IRV)
3. Tidal Volume (TV)
4. Expiratory Reserve Volume (ERV)

Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because
1. there is a negative pressure in the lungs
2. there is a negative intrapleural pressure pulling at the lung walls
3. there is a positive intrapleural pressure
4. pressure in the lungs is higher than the atmospheric pressure

What is true about RBCs in humans?
1. They carry about 20-25 percent of ${\mathrm{CO}}_2$
2. They transport 99.5 percent of ${\mathrm{O}}_2$
3. They transport about 80 percent oxygen only and the rest 20 percent of it is transported in a dissolved state in blood plasma
4. They do not carry ${\mathrm{CO}}_2$ at all

People living at sea level have around 5 million RBC per cubic millimeter of their blood whereas those living at an altitude of 5400 metres have around 8 million. This is because at high altitude:
1. people get pollution-free air to breathe and more oxygen is available
2. atmospheric O₂ level is less and hence more RBCs are needed to absorb the required amount of O₂ to survive
3. there is more UV radiation which enhances RBC production
4. people eat more nutritive food, therefore more RBCs are formed