Haemoglobin belongs to the class of conjugated protein.
1. The iron-containing pigment portion haem constitutes 4%.
2. The colourless protein of the histone class is called globin.
3. Each molecule of Haemoglobin contains four atoms of iron, each of which can combine with a molecule of oxygen.

(i) This disorders due to one's occupation in industries like grinding or stone breaking, construction sites, cotton industries, etc.
(ii) Dusts produced affects the respiratory tract.
(iii) Long exposure can give rise to inflammation leading to respiratory diseases like fibrosis, silicosis and asbestosis.
(iv) Inhalation of particle of silica from sand grinding and asbestos into the respiratory tract cause occupational respiratory disorders.
(v) Workers working in such industries must wear protective face masks to prevent these diseases.

Blood transports CO₂ from the tissue cells to the lungs in three ways
(i) Dissolved in plasma About 7 - 10% of CO₂ is transported in a dissolved form in the plasma.
(ii) Bound to haemoglobin About 20 - 25% of dissolved CO₂ is bound and carried in the RBCs as carbaminohaemoglobin (Hb CO₂) CO₂ + Hb Hb CO₂
(iii) As bicarbonate ions in plasma about 70% of CO₂ is transported as bicarbonate ions.

(i) It is a chronic breathlessness caused by gradual breakdown of thin walls of the alveoli.
(ii) The total surface area of gaseous exchange is minimised in alveoli (ie widening of the alveoli is called as emphysema).
(iii) Cigarette smoking is the major factor because smoke reduces the respiratory surface of the alveolar walls.

1. In haemoglobin ifthe iron component ofthe haem moieties is in the ferric state, than the normal ferrous state, it is called methaemoglobln.
2. Methaemoglobin does not bind O₂.
3. Normally RBC contains less than 1% methaemoglobin.