Concept:Ptyalin is a digestive enzyme present in saliva that begins the breakdown of starch.
Explanation:Ptyalin is secreted by the salivary glands into the mouth.
It acts on cooked or raw starch and converts it into maltose.
This makes the mouth the first site of starch digestion.
The oesophagus only transports food to the stomach; no starch digestion occurs there.
The stomach mainly secretes pepsin and renin for protein digestion, not ptyalin.
The large intestine is not a site for starch digestion.
Therefore, the correct site where ptyalin acts on starch is the mouth.
Answer:C. mouth