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GATE 2020 BT Q.40: solution and answer

GATE 2020 · BTQ.40 · 2 marks · MCQ

Determine the correctness or otherwise of the following Assertion [a] and the Reason [r].

Assertion [a]: A zygote and its immediate descendant cells are unspecialized and are called totipotent

Reason [r]: Totipotent cells retain the capacity to differentiate into only a few cell types

  1. (A)

    Both [a] and [r] are false

  2. (B)

    Both [a] and [r] are true but [r] is not the correct reason for [a]

  3. (C)

    Both [a] and [r] are true and [r] is the correct reason for [a]

  4. (D)

    [a] is true but [r] is false

See the question in the paper
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Answer and solution

ANSWER

The correct answer is (D): Assertion [a] is true, but Reason [r] is false.

Official answer: DSource: Official answer key, GATE 2020 BT (IIT Delhi)

  1. Assertion [a]: The zygote and its immediate descendant cells (up to roughly the 8-cell stage in mammals) are unspecialized cells termed totipotent — this is the standard, textbook definition. [a] is TRUE.

  2. Reason [r]: By definition, totipotent cells retain the capacity to differentiate into ALL cell types of the organism, including extra-embryonic tissues (e.g., placenta) in addition to every embryonic cell type — not merely 'a few' cell types. (Pluripotent cells are restricted to embryonic lineages; multipotent/unipotent cells are restricted to a few or one type.)

  3. Therefore [r] as stated misdescribes totipotency and is FALSE.

  4. With [a] true and [r] false: options B and C (which require [r] true) are eliminated, and option A (both false) is eliminated since [a] is true.

  5. This leaves option (D): [a] is true but [r] is false.

KEY IDEA

Totipotency is the capacity of a cell to differentiate into every cell type of the organism — including extra-embryonic tissues like the placenta — not a limited subset; that broader capacity is what distinguishes totipotent cells from pluripotent, multipotent, or unipotent cells.

WATCH OUT FOR

Confusing totipotent with pluripotent — assuming "differentiate into a few cell types" describes totipotency, when in fact totipotent cells can form ALL cell types (embryonic and extra-embryonic), while only a limited subset (pluripotent, multipotent, unipotent) is restricted.

From the GATE 2020 BT paper. Every question of this paper · Download the full paper · All 15 Cell biology questions, with notes

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