Answer:
to exchange oxygen with carbon dioxide
Step-by-step explanation:
The structure depicted in the figure are called alveoli which are sponge like in nature. They are the primary site for the exchange of carbon di oxide and oxygen from and to the bloodstream.
Structurally they are like tiny balloons that look like a bunch of grapes as depicted in figure. They are present at the extreme end of the respiratory system after bronchioles. They are arranged in the form of groups of these small balloon like structures.These are the final sites where carbon dioxide leave and oxygen enter in our blood.
When air enters into our nose, it passes through different structures like larynx, trachea and lungs. There are many smaller structures in lungs like a maze,like bronchi, bronchioles and after bronchioles the air reaches into alveoli.
Since alveoli are extremely tiny and thin structures containing a network of capillaries embedded in them, these are the sites where gases are able to exchange. CO2 leaves and O2 enters the blood.To get inside the blood, oxygen moves through the process of diffusion into the alveolar epithelium, that is a capillary endothelium and a thin interstitial space.
Hope it help!