Enzyme ptyalin acts on starch in the

1. Analyze the question The question asks where the enzyme ptyalin acts on starch. So we need to know what ptyalin is and where it is found.

2. Explain the concept Ptyalin is another name for salivary amylase. It is secreted by the salivary glands and mixed with food in the mouth during chewing.

• Its substrate is starch (a polysaccharide).
• Its product is maltose (a disaccharide).
• It works best in a slightly alkaline to neutral medium (about pH 6.8-7).

3. Step-by-step solution

• Ptyalin = salivary amylase, so it comes from saliva.
• Saliva is released into the mouth (buccal cavity).
• Chewing mixes food with saliva, and the reaction begins there:

Starch + water → (ptyalin) → maltose

• Check the other options: • A. Oesophagus: food only passes through quickly by peristalsis. No digestive enzymes are secreted here. • B. Large intestine: it mainly absorbs water and salts. It does not digest starch. • D. Stomach: the stomach is acidic (about pH 2) because of hydrochloric acid, which stops ptyalin from working. Pepsin acts here on proteins.

4. Answer Ptyalin acts on starch in the mouth, which is option C.

5. Exam tip Remember: "Ptyalin = saliva = mouth." For the sequence of starch digestion, think Mouth → Small intestine: salivary amylase starts it, pancreatic amylase continues, and maltase finishes it to glucose.