UPSC Prelims 2002 · General Studies
Question 7: Science and Technology
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?
AnswerThe answer is (d).
Statement 1 is false: besides blastocyst (embryonic) stem cells, stem cells are also found in adult tissue such as bone marrow and in umbilical cord blood. Statement 3 is true: embryonic stem cells in culture keep dividing and renewing themselves almost without limit. Statement 4 is true: Indian laboratories reported human embryonic stem cell lines around 2001-02 that can develop into many tissue types. Since 1 is false, only option (d) fits; statement 2 is read as false for the time of the question.
- 1. Adult tissues and cord blood also yield stem cells, so blastocysts are not the only source.
- 2. Deriving embryonic stem cells then meant destroying the blastocyst; the key does not accept this one.
- 3. Embryonic stem cells self-renew in culture almost without limit.
- 4. Indian centres reported stem cell lines able to form many tissue types.
How you could have got this
- If you were sure statement 1 is not correct, (a), (b) and (c) go: each of them includes 1.
What you needed to know: Adult tissues and cord blood also yield stem cells, so blastocysts are not the only source.
The red flag in statement 1 is “only”. In UPSC’s papers, statements with “only” were true 27% of the time (82 statements). A hint, not a rule.
Only (d) is left. You didn’t need statements 2, 3 or 4.
This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Includes statement 1, which is false because adult and cord-blood stem cells exist.
- (b) Includes statement 1, which is false.
- (c) Includes statement 1, which is false.
- (d) Right: only statements 3 and 4 are accepted.
Worth knowing: Statement 2 is arguable, since adult and cord-blood stem cells are obtained without destroying a blastocyst, but (d) is the only option consistent with statement 1 being false.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2002, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.