Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].
Assertion [a]: It is possible to regenerate a whole plant from a single plant cell.
Reason [r]: It is easier to introduce transgenes in to plants than animals.
Both [a] and [r] are true and [r] is the correct reason for [a]
Both [a] and [r] are true but [r] is not the correct reason for [a]
Both [a] and [r] are false
[a] is true but [r] is false
ANSWER
Option (B): both [a] and [r] are true, but [r] is not the correct reason for [a].
Official answer: BSource: Official answer key, GATE 2019 BT (IIT Madras)
Test the assertion first. Plant cells are totipotent: a single cell, or a protoplast, grown on a medium with a suitable auxin to cytokinin balance forms callus and then shoots and roots, giving a whole plant. So [a] is true.
Test the reason. Plant cells take up foreign DNA readily, for example through Agrobacterium tumefaciens (Ti plasmid) or the gene gun, and a transformed cell can be grown into a complete transgenic plant. Animal transgenesis needs embryo microinjection or embryonic stem cells, and the change must reach the germline. So [r] is a fair general statement and is true.
Now ask whether [r] explains [a]. The assertion is about totipotency, a developmental property of plant cells. It holds whether or not any transgene is introduced, and the ease of gene transfer says nothing about why a single cell can regenerate.
The link actually runs the other way. Totipotency is one reason transgenes are easier to use in plants, because a transformed single cell can be regenerated into a whole plant. So [r] does not account for [a].
Option (A) fails because [r] is not the explanation for [a]. Option (C) fails because both statements are true. Option (D) fails because [r] is true. Option (B) is correct.
KEY IDEA
In an assertion-reason question, check each statement on its own, then ask whether the reason explains the assertion. Totipotency is a property of plant cells. The ease of transgene transfer is a consequence of it, not the cause.
WATCH OUT FOR
Choosing (A) because both statements are true and both concern plant biotechnology. The reason does not explain the assertion, and if anything the explanation runs from [a] to [r].
From the GATE 2019 BT paper. Every question of this paper · Download the full paper · All 8 Plant tissue culture questions, with notes
