UPSC Prelims 2002 Q7: Science & Technology – Biotechnology & Genetics
With reference to the latest developments in stem - cell research, consider the following
statements:
1. The only source of human stem cells are the embryos at blastocyst stage.
2. The stem cells can be derived without causing destruction to blastocysts.
3. The stem cells can regenerate themselves in vitro virtually forever.
4. Indian research centres also created a few cell lines which can be developed into many types of
tissues.
Which of these statements are correct?
- (a) 1, 2, 3 and 4
- (b) 1, 2 and 3
- (c) 1, 2 and 4
- (d) 3 and 4
Answer: (d) 3 and 4
Explanation
Stem-cell research: statements on sources and properties
| Statement | Verdict |
|---|---|
| 1. Only source of human stem cells is the embryo at blastocyst stage | False — stem cells also come from adult tissue, cord blood and bone marrow |
| 2. Stem cells can be derived without destroying blastocysts | Developments of that time were still experimental; the official key does not accept it (modern methods such as single-blastomere biopsy and iPS cells do exist now) |
| 3. Stem cells can self-renew in vitro virtually forever | True — self-renewal is a defining property |
| 4. Indian centres created cell lines that develop into many tissues | True — Indian laboratories derived human embryonic stem cell lines |
Statement 1 is false because adult stem cells exist. Statements 3 and 4 are correct. As to statement 2, the official key counts only 3 and 4 as correct. On present-day knowledge statement 2 is also defensible, so the circulated key reflects the 2002 state of research.
Answer: (d) 3 and 4.
Why each option is right or wrong
- (a) Incorrect. Statement 1 is false because adult stem cells also exist.
- (b) Incorrect. It includes the false statement 1.
- (c) Incorrect. It includes the false statement 1 and leaves out statement 3.
- (d) CORRECT. Statements 3 and 4 are true; this matches the official key.
Key point
Stem cells have two properties: self-renewal and potency; sources include embryos, adult tissue and cord blood.
Remember
Stem cells self-renew in culture; embryos are not the only source.
Common mistakes
- Treating 'only source' statements as true; absolute words are usually false.
- Dropping statement 3, which is the defining property.
- Using today's methods to overrule the key without noting it.
Exam tip
Reject the 'only source' statement first, which leaves 3 and 4 plus possibly 2.
Sources
- Indian Council of Medical Research — Guidelines for stem cell research
- NCERT Class XII Biology — Biotechnology