A baby frog breathes through gills, while an adult frog breathes through lungs and moist skin. Why is it so?

Look at this rose plant. It is kept outside and is watered regularly. 

Leaf 1: Coated with Vaseline on its underside.

Leaf 2: Half covered with a strip of black paper. 

1. Analyse and predict what would happen to leaf 1 after a few days?

2. Evaluate which part of leaf 2 will show positive result when tested for starch. Explain why?