UPSC Prelims 2005 Q85: Science & Technology – Biology
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
Explanation
Digestion of proteins
| Part | Verdict |
|---|---|
| A. All proteins are digested in the small intestine only | False: digestion begins in the stomach with pepsin |
| R. Pancreatic protein-digesting enzymes enter the small intestine | True — trypsin and chymotrypsin |
A is false because pepsin acts on proteins in the stomach. R is true: pancreatic juice delivers trypsin and chymotrypsin to the small intestine.
Answer: (d) A is false but R is true.
Why each option is right or wrong
- (a) Incorrect. A is false, so R cannot explain it.
- (b) Incorrect. A is false, since digestion begins in the stomach.
- (c) Incorrect. R is true, not false.
- (d) CORRECT. A is false because stomach digestion starts first, but R is true.
Key point
Stomach: pepsin; small intestine: trypsin, chymotrypsin, erepsin.
Remember
Protein digestion begins in the stomach with pepsin.
Common mistakes
- Believing digestion of protein occurs only in the intestine.
- Forgetting pepsin in the stomach.
- Mixing pancreatic and gastric enzymes.
Exam tip
Protein digestion starts in the stomach and finishes in the small intestine.
Sources
- NCERT Class XI Biology — Digestion and Absorption
- John E. Hall — Guyton and Hall Textbook of Medical Physiology (Digestion and Absorption in the Gastrointestinal Tract)