Air Around Us

Paheli kept some water in a beaker for heating. She observed
that tiny bubbles appeared before the water started to boil.
She boiled the water for about 5 minutes and filled it in a
bottle up to the brim and kept the bottle air tight till it cooled
down to room temperature.
(a) Why did the tiny bubbles appeared?
(b) Do you think tiny bubbles will appear on heating the
water taken out from the bottle? Justify your answer.