What is the major function of a leaf

The major function of leaf is preparing food for plant in presence of sunlight  

Explanation:

Leaf helps to lateral outgrowth of system. Leaf is very important part of the plant. Leaf consist a broad consist blade type of construction which is known as lamina.

Chlorophyll is that substance which give green color to plant and leaf. Plant lose large volume of water through the leaves the form of water. Another important use of leaves is storing the food.  

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products