Q.(A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A) : The zygote gives rise to heart-shaped embryo and subsequently proembryo in most angiosperms. Reason (R) : The zygote is present at the micropylar end of the embryo sac and develops into an embryo.

Concept: Embryo development sequence in angiosperms

The zygote in angiosperms undergoes a defined developmental sequence. After fertilization, the zygote divides to form the proembryo first—a small, undifferentiated mass of cells. The proembryo then differentiates through globular and heart-shaped stages before maturing into the complete embryo.

Assertion (A) is false because it reverses the correct order: the zygote produces the proembryo first, which then develops through the heart-shaped stage, not the other way around. …

The question tests your understanding of embryo development in angiosperms, specifically the sequence of stages from zygote to mature embryo. This is a classic area where the order of events matters critically.

In angiosperm embryology, the zygote undergoes a precise developmental program. The reason statement gives us the starting point: the zygote sits at the micropylar end of the embryo sac (the end where the pollen tube entered) and will indeed develop into the embryo. That much is accurate.

The assertion, however, claims a specific sequence: zygote → heart-shaped embryo → proembryo. This is where we need to recall the actual developmental timeline.

The correct embryonic sequence

1. Zygote formation and first divisions

   After fertilization, the zygote undergoes its first mitotic division to produce two cells: a smaller apical cell (toward the micropyle) and a larger basal cell. The apical cell will form most of the embryo proper, while the basal cell contributes to the suspensor.

2. Proembryo stage

   Through further divisions, a small cluster of undifferentiated cells forms—this is the proembryo. It's an early, globular mass without distinct organ primordia. This stage comes early in development, not late.

3. Globular embryo

   The proembryo develops into a more organized globular embryo, still roughly spherical but with emerging polarity.

4. Heart-shaped embryo

   In dicots, the embryo then transitions to a heart-shaped stage as the two cotyledons begin to bulge out, creating the characteristic bilateral symmetry. This is a later stage, well after the proembryo.

5. Mature embryo

   Further development leads to torpedo and finally mature embryo stages. …