White blood cells are an important component of our immune system. One thing they do is consume and destroy bacteria by extending their plasma membrane around the bacterium and bringing it inside the cell in a vesicle. By what process do they engulf the bacterium?

Phagocytosis

Explanation:

During the process of phagocytosis, certain white blood cells called phagocytes (macrophage, neutrophil), extends their plasma membrane and draw in bacterium or other invaders into its own vacuole, digesting and destroying them.

Thereafter, the waste products containing weakened toxins are expelled from the cell through the cell membrane.

air enters through the nose, moves through the nasal cavity, the pharynx, the larynx, enters the trachea, moves through the bronchi andbronchioles till the alveoli.