Answer:
The air bubbles are oxygen coming out of the leaf
Step-by-step explanation:
Though the leaf is in hot water, it is still using light to continue on the path of photosynthesis. Now, this path of photosynthesis involves letting oxygen out of the leaf. Thus, this oxygen is the one that we see as bubbles coming out of the water.
The reason for having more air bubbles at the lower surface than at the upper surface is because the leaf cells at the lower surface of the leaf possess faster photosynthetic rate in releasing
oxygen.