UPSC Prelims 2007 Q124: Science & Technology – Biology
Which on the following is the correct sequence in order of decreasing length of the three
structural parts given below of small intestine in the human body?
- (a) Jejunum - Duodenum - Ileum
- (b) Ileum - Duodenum - Jejunum
- (c) Jejunum - Ileum - Duodenum
- (d) Ileum - Jejunum - Duodenum
Answer: (d) Ileum - Jejunum - Duodenum
Explanation
Parts of the small intestine — by length
| Part | Approx. length | Note |
|---|---|---|
| Ileum | ~3.5 m (longest) | Absorbs vitamin B12 and bile salts |
| Jejunum | ~2.5 m | Main site of nutrient absorption |
| Duodenum | ~25 cm (shortest) | C-shaped; receives bile and pancreatic juice |
Total small intestine ≈ 6-7 m — the longest part of the gut.
Decreasing order: Ileum > Jejunum > Duodenum.
Answer: (d) Ileum - Jejunum - Duodenum.
Why each option is right or wrong
- (a) Incorrect. The jejunum is not the longest, and the duodenum is the shortest — not the middle.
- (b) Incorrect. The duodenum is the shortest, so it cannot be second.
- (c) Incorrect. The ileum is longer than the jejunum.
- (d) CORRECT. Ileum (~3.5 m) > Jejunum (~2.5 m) > Duodenum (~25 cm).
Key point
Small intestine: Duodenum (25 cm, shortest) → Jejunum (2.5 m) → Ileum (3.5 m, longest).
Remember
Ileum is the longest part of the small intestine; duodenum the shortest.
Common mistakes
- Mixing up the order of position (D → J → I) with the order of length (I > J > D).
- Thinking the jejunum is longest because it is the main absorption site.
- Forgetting that duodenum means 'twelve fingers' — a hint that it is short.
Exam tip
Position: D-J-I. Length: just reverse it → I-J-D.
Sources
- NCERT Class XI — Biology, Ch 16 (Digestion and Absorption)
- NCERT Class X — Science, Ch 6 (Life Processes)