why we yawn when we are sleepy or drowsy.

Dear Student,

Our body induce yawning to drawn in more oxygen or remove a build-up of carbon dioxide. Our brain needs oxygen to function properly and when it does not get sufficient oxygen ( a condition when we feel drowsy or sleepy), we yawn to gather a large amount of oxygen for our brain, to help it function faster and control drowsiness.

Hope this answer will help you.

Cheers!