In the lungs of smokers, a process called metaplasia occurs where the normal lining cells of the lungs are replaced by squamous metaplastic cells (many layer of squamous epithelial cells). functionally, why is this an undesirable body reaction to tobacco smoke?

This an undesirable body reaction to tobacco smoke because the renewed squamous cells cannot discharge and do not have cilia, it hinders lung function.

Squamous cells are thin, flat cells that look like fish scales, and are found in the tissue that forms the surface of the skin, the lining of the hollow organs of the body, and the lining of the respiratory and digestive tracts. Most cancers of the anus, cervix, head and neck, and vagina are squamous cell carcinomas.

I am hoping that this answer has satisfied your query and it will be able to help you in your endeavor, and if you would like, feel free to ask another question.

the cell cycle is the final answer! : )

thinking it would be physical characteristics