Parts of respiratory system are: Nostrils, nasal cavity, pharynx, trachea, lungs, bronchus, bronchioles, alveoli and diaphragm.

2.  Where are lungs located?

Lungs are located in the thoracic cavity, which is separated, by abdominal cavity by a muscular partition called diaphragm.

3.  What is the function of nasal cavity?

- In the nasal cavity, the air is warmed, moistened.
- The dust particles are entrapped in the mucous and by the fine hair present on the inner lining of nose. 
- The nasal cavity is separated from oral cavity by a bony palate, so we can breathe in air even when we eat.

4.  Why we cannot breathe while swallowing the food? 

The nasal cavity is separated from oral cavity by a bony palate, so we can breathe in air even while we eat. But at the time of swallowing, the food is in the pharynx region. The pharynx leads into trachea or windpipe through a slit called glottis.  
While swallowing food, glottis is covered by a small cartilaginous flap of skin called epiglottis.  This results in closure of trachea. 
This prevents entry of food in trachea. Closure of trachea stops breathing while swallowing. 

5.  Why the trachea does not collapse when there is not much air present in it?

Trachea does not collapse when there is not much air in it, as it is supported by rings of cartilage.  

6.  Name the region in lungs where actual gas exchange takes place.

 Alveoli.

7.   Explain the mechanism of breathing in human beings.  

Breathing has two events: Taking in of air (inhalation) and taking out of air (exhalation). Inhalation occurs when

- diaphragm and muscles attached to ribs contract
- chest cavity expands
- rib cage move upwards and outwards
- volume inside chest cavity increases
- air pressure decreases inside and air from outside rushes into lungs through nostrils, trachea and bronchi.
- alveolar sacs get filled with oxygen rich air (air moves in)
- exchange of gases takes place through the thin walls of alveoli and blood capillaries.

Exhalation occurs when
- carbon dioxide absorbed by blood from the tissues is carried to the alveoli of lungs for exhalation
- diaphragm and rib muscles relax
- chest cavity comes back to its original size
- rib cage comes back to its original size
- volume inside chest cavity decreases
- air pressure increases inside and air from inside rushes out through alveoli, bronchi, trachea and nostrils.
- Carbon dioxide is subsequently pushed out of lungs.

8.  Differentiate between the process of inhalation and exhalation.