1. Hemoglobin uses quaternary as its protein structure. (quaternary structure)
2. Iron is important in the structure of haeonglobin because it’s the iron atom that binds oxygen as the blood travels between the lungs and the tissues.
3 and 4( i’m not sure about this one but i hope this will help))
The inner surface of the alveolus is lined by a special type of alveolar cell called a pneumocyte
Type I pneumocytes are very thin in order to mediate gas exchange with the bloodstream (via diffusion)
Type II pneumocytes secrete a pulmonary surfactant in order to reduce the surface tension within the alveoli
Alveolar air spaces are surrounded by a dense network of capillaries, which transport respiratory gases to and from the lungs
The capillaries are located close to the pneumocytes and are composed of a very thin, single-layer endothelium
The capillaries transport oxygen within red blood cells, while white blood cells may extravasate into the lung tissue.
i hope this will help u since it took some time but goodluck!!! :)