UPSC Prelims 2001 Q138: Science & Technology – Biology
Match List I with List II
and select the correct answer using the codes given below the Lists:
List I (Substance)
I. Ptyalin
II. Pepsin
III. Renin
IV. Oxytocin
List II (Physiological role)
A) Converts angiotensinogen in blood into angiotensin
B) Digests starch
C) Digests proteins
D) Hydrolyses fats
E) Induces contraction of smooth muscles
- (a) I - B, II - C, III - A, IV - E
- (b) I - C, II - D, III - B, IV - E
- (c) I - B, II - C, III - E, IV - A
- (d) I - C, II - A, III - B, IV - D
Answer: (a) I - B, II - C, III - A, IV - E
Explanation
Matching substances with their physiological roles
| Substance (List I) | Role (List II) |
|---|---|
| I. Ptyalin (salivary amylase) | B. Digests starch |
| II. Pepsin | C. Digests proteins (in the stomach) |
| III. Renin | A. Converts angiotensinogen into angiotensin (from the kidney) |
| IV. Oxytocin | E. Induces contraction of smooth muscles (uterus in childbirth) |
Ptyalin in saliva begins starch digestion, pepsin digests proteins in the stomach, renin from the kidney starts the angiotensin system that raises blood pressure, and oxytocin makes smooth muscle contract. Item D (fat digestion) belongs to lipase.
Answer: (a) I - B, II - C, III - A, IV - E.
Why each option is right or wrong
- (a) CORRECT. Ptyalin–starch, pepsin–protein, renin–angiotensin, oxytocin–contraction.
- (b) Incorrect. Ptyalin digests starch, not proteins.
- (c) Incorrect. Renin and oxytocin are swapped.
- (d) Incorrect. Ptyalin digests starch, and oxytocin does not digest fats.
Key point
Renin (kidney, blood pressure) is different from rennin (stomach of infants, milk curdling).
Remember
Ptyalin starch; pepsin protein; renin angiotensin; oxytocin contraction.
Common mistakes
- Confusing renin with rennin.
- Giving fat digestion to an enzyme other than lipase.
- Mixing up ptyalin (starch) and pepsin (protein).
Exam tip
Match digestive enzymes by where they work: mouth starch, stomach protein, intestine fat.
Sources
- NCERT Class XI — Biology, chapters 'Digestion and Absorption', 'Excretory Products and their Elimination' and 'Chemical Coordination and Integration'
- Guyton and Hall — Textbook of Medical Physiology, chapter on the renin-angiotensin system