In the given diagram of the oxygen dissociation curve, under normal physiological conditions, the partial pressure of oxygen at the tissue level is represented by:
   
1. A
2. B
3. C
4. D

Assertion: Gas exchange with water as the respiratory medium is much more demanding than breathing air.
Reason: Air contains much more O2 than water at the same ${\mathrm{PO}}_2$.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false

Assertion: In nasal cavity, mucus which lies superficial to the microscopic cilia filters inspired air.
Reason: The cilia of the respiratory epithelium move the secreted mucus and particulate matter towards the external nostrils.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false

Assertion: The terminal bronchiole is the most distal segment of the conducting zone.
Reason: They are the narrowest airways of the lungs.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false

Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R): 

In the light of the above statements choose the correct answer from the options given below:

Assertion: Not all the air in each breath is available for the exchange of oxygen and carbon dioxide.
Reason: Dead space is the volume of air which is inhaled that does not take part in the gas exchange

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false

Assertion: A person who is born and lives at sea level will develop a slightly smaller lung capacity than a person who spends their life at a high altitude.
Reason: The partial pressure of oxygen is lower at higher altitude which, as a result means that oxygen less readily diffuses into the bloodstream.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Residual volume cannot be measured directly by spirometery.
Reason: The tidal volume, vital capacity, inspiratory capacity and expiratory reserve volume can be measured directly with a spirometer and are the basic elements of a ventilatory pulmonary function test.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Infant respiratory distress syndrome[hyaline membrane disease] is the leading cause of death of preterm infants.
Reason: The lungs of infants with respiratory distress syndrome are developmentally deficient in a material called surfactant.

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false.

Assertion: Exposure to small concentrations of CO hinder the ability of Hb to deliver oxygen to the body.
Reason: Carboxyhemoglobin [HbCO] forms more readily than does oxyhemoglobin (${\mathrm{HbO}}_2$).

1. Both assertion and reason are true and the reason is the correct explanation of the assertion.
2. Both assertion and reason are true but the reason is not the correct explanation of the assertion.
3. Assertion is true but reason is false.
4. Both assertion and reason are false