Question

what will happen if a human being starts taking air with mouth instead of nose

Answer 1

They may get breathing problems as a lot of dust particles also enter in our mouth along with air. Because there are no receptors present like in nose which protects us from dust particles.

Answer 2

if you breath through your mouth the dust particles would enter your body which can make you ill . if you breath through your nose than the dust particles are trapped between the hair present in your nose thus making a clean air to enter in your body