CDS (I) 2020 General Knowledge · Question 19 of 120

Correct — D, Amylase. Digestion begins in the mouth, before food has gone anywhere else. Saliva from the salivary glands contains salivary amylase, which starts breaking starch down into simpler sugars while the tongue mixes the food. Anything secreted further along the canal necessarily meets the food later — pepsin waits in the stomach and trypsin further on in the small intestine. So the first enzyme to mix with food in the digestive tract is amylase, and the reason is anatomical order rather than any property of the enzyme itself.

• (a)Trypsin — A protein-digesting enzyme of the pancreatic juice, which enters the small intestine. It meets food only after the mouth and the stomach have finished with it.
• (b)Cellulose — Cellulose is not an enzyme at all — it is the carbohydrate that makes up plant cell walls, and humans have no enzyme to digest it. The enzyme with the matching name is cellulase, which we do not produce.
• (c)Pepsin — The protein-digesting enzyme released by the gastric glands in the stomach wall, working in the acidic medium hydrochloric acid provides. It is second in line, not first.

Enzymes act in the order the food passes them. Saliva brings amylase in the mouth, which acts on starch. The stomach adds hydrochloric acid, pepsin and mucus, and pepsin acts on protein in an acidic medium. In the small intestine bile emulsifies fat and turns the medium alkaline, while pancreatic juice supplies trypsin for protein, amylase for remaining starch and lipase for fat. Intestinal juice completes the job, and the products are absorbed through the villi.

The question is testing sequence, and it plants one option that does not belong to the category at all. Cellulose is a substrate, not an enzyme, and spotting that removes it immediately — a useful habit whenever a list mixes similar-sounding names. Of the three real enzymes, the ordering follows the anatomy from mouth to stomach to small intestine, so amylase, pepsin, trypsin. One nuance worth carrying: amylase is secreted twice, once by the salivary glands and again by the pancreas, so the same enzyme opens the process and returns to finish the starch that survived the stomach's acid.

• Saliva contains salivary amylase, which breaks starch down into simple sugar in the mouth.
• Gastric glands in the stomach wall release hydrochloric acid, pepsin and mucus.
• Pepsin needs the acidic medium created by hydrochloric acid; trypsin works in the alkaline medium of the small intestine.
• Cellulose is a plant-cell-wall carbohydrate, not an enzyme, and humans cannot digest it.
• Pancreatic juice supplies trypsin, pancreatic amylase and lipase to the small intestine.

• Picking pepsin because the stomach feels like where digestion 'really' begins.
• Reading cellulose as an enzyme; the enzyme name would be cellulase, and humans do not make it.
• Forgetting that amylase appears twice, in saliva and again in pancreatic juice.

As the first or last enzyme to act, as an enzyme-to-site match, or through the optimum pH of pepsin against trypsin.

• practice — not a real PYQ

  The protein-digesting enzyme secreted by the gastric glands of the stomach is

  • (a)amylase
  • (b)pepsin
  • (c)trypsin
  • (d)lipase

  Answer(b) pepsin — released with hydrochloric acid and mucus, and active only in an acidic medium.

• practice — not a real PYQ

  Salivary amylase acts on which one of the following components of food?

  • (a)Proteins
  • (b)Fats
  • (c)Starch
  • (d)Vitamins

  Answer(c) Starch — it breaks the complex carbohydrate down into simple sugar while the food is still in the mouth.