In the buccal cavity of human being digestion of which one of the following get started?
- (a)Protein
- (b)Fat
- (c)Carbohydrate
- (d)None of the above
Correct — C, Carbohydrate. In the buccal cavity (mouth), saliva contains the enzyme salivary amylase (ptyalin), which begins breaking down cooked starch (a carbohydrate) into maltose. So carbohydrate is the macronutrient whose digestion starts in the mouth.
- (a)Protein — Protein digestion begins in the STOMACH, where the enzyme pepsin (activated by hydrochloric acid) acts — not in the mouth.
- (b)Fat — Fat digestion mainly begins in the SMALL INTESTINE, where bile emulsifies fat and pancreatic lipase acts; the mouth has no significant role in fat digestion.
- (d)None of the above — Wrong — carbohydrate digestion clearly starts in the mouth through salivary amylase, so a definite option is correct.
Digestion of the three macronutrients begins at different points along the alimentary canal. Carbohydrate (starch) digestion starts in the mouth with salivary amylase (ptyalin); protein digestion starts in the stomach with pepsin; and fat digestion mainly starts in the small intestine with bile and pancreatic lipase. The mouth handles only carbohydrate chemically (besides mechanical chewing).
The trap is that the mouth mechanically breaks down all food, so a student may think several nutrients are being 'digested' there. But chemically, only carbohydrate is acted upon in the buccal cavity — by salivary amylase — which is why carbohydrate is the answer.
- Salivary amylase (ptyalin) in saliva begins starch (carbohydrate) digestion in the mouth.
- Protein digestion starts in the stomach with pepsin.
- Fat digestion mainly starts in the small intestine with bile and pancreatic lipase.
- The mouth also carries out mechanical (mastication) digestion, but only carbohydrate is chemically digested there.
Only carbohydrate is chemically digested in the buccal cavity, so its digestion 'starts' in the mouth.
- Assuming all foods are chemically digested in the mouth because chewing happens there
- Confusing where protein (stomach) and fat (small intestine) digestion begin
MPPSC and UPSC ask which enzyme/organ starts digestion of a nutrient, or to match enzyme to substrate — fix the chain carbohydrate → mouth (ptyalin), protein → stomach (pepsin), fat → small intestine (lipase).
Which of the following is not a digestive enzyme in the human system?
- (a) Trypsin
- (b) Gastrin
- (c) Ptyalin
- (d) Pepsin
Answer(b) Gastrin
Same digestion physiology — it turns on recognising ptyalin (salivary amylase) as a digestive enzyme, the very enzyme that starts carbohydrate digestion in the mouth (Gastrin is a hormone, not an enzyme).
Assertion (A): All the proteins in our food are digested in small intestine only. Reason (R): The protein-digesting enzymes from pancreas are released into small intestine.
- (a) Both A and R are individually true and R is the correct explanation of A
- (b) Both A and R are individually true but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer(d) A is false but R is true
Same 'where does digestion of a nutrient happen' idea — protein digestion actually begins in the stomach (not the small intestine only), the counterpart to carbohydrate digestion beginning in the mouth.
- practice — not a real PYQ
Digestion of protein in the human body begins in which organ?
- (a)Mouth
- (b)Stomach
- (c)Small intestine
- (d)Large intestine
Answer(b) Stomach — where pepsin, activated by hydrochloric acid, starts breaking down protein.
- practice — not a real PYQ
The enzyme present in human saliva that acts on starch is:
- (a)Pepsin
- (b)Trypsin
- (c)Salivary amylase (ptyalin)
- (d)Lipase
Answer(c) Salivary amylase (ptyalin) — it begins the digestion of starch in the mouth.