Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Using conventional methods of diagnosis such as serum and urine analysis, early detection of a disease is possible.
Reason (R): A very low concentration of a bacterium or virus can be detected by amplification of its nucleic acid by PCR.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A) is false but (R) is true.
To treat a disease well, it has to be found early. Ordinary tests pick up a pathogen only after it has multiplied and caused symptoms. Molecular methods can find it much earlier.
Assertion (A): Using conventional methods of diagnosis such as serum and urine analysis, early detection of a disease is possible. — False. With conventional methods (serum and urine analysis), early detection is not possible. A pathogen is usually suspected only after it has produced a symptom, and by then its concentration in the body is already very high.
Reason (R): A very low concentration of a bacterium or virus can be detected by amplification of its nucleic acid by PCR. — True. PCR makes many copies of the pathogen’s nucleic acid, so even a very small amount can be detected, before symptoms appear. This is why PCR, not conventional analysis, is used for early diagnosis.
Since A is false and R is true, option (4) is the answer.
NCERT Extract:
Molecular Diagnosis – “You know that for effective treatment of a disease, early diagnosis and understanding its pathophysiology is very important. Using conventional methods of diagnosis (serum and urine analysis, etc.) early detection is not possible. … However, very low concentration of a bacteria or virus (at a time when the symptoms of the disease are not yet visible) can be detected by amplification of their nucleic acid by PCR.”