Question

Like in animals, in plants also, the embryo develops in a phased manner that happens in sequential order. Below is a list of various stages of embryogenesis in a model dicot plant (Capsella bursa-pastoris). Arrange them sequentially in the proper order of development.
(A) Globular stage
(B) Torpedo stage
(C) Heart stage
(D) Pro-embryo stage

• A. (D), (A), (C), (B).
• B. (D), (B), (C), (A).
• C. (B), (A), (D), (C).
• D. (C), (B), (D), (A).

Hint:

To remember the stages of dicot embryogenesis, think of their physical shapes progressing from simple to complex:
Pro-embryo (D) $\rightarrow$ Round Ball (Globular, A) $\rightarrow$ Heart-shaped (C) $\rightarrow$ Elongated (Torpedo, B).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Dicot embryogenesis is the process by which a single-celled zygote undergoes mitotic divisions to develop into a mature, structured embryo.
*Capsella bursa-pastoris* (shepherd's purse) is the classic model plant used to study the distinct developmental phases of dicot embryogenesis.

Step 2: Detailed Explanation:
Let us arrange the developmental stages of dicot embryogenesis in their correct chronological sequence:
-
Step 1: (D) Pro-embryo stage:
The zygote divides transversely into an apical cell and a basal cell.
Subsequent divisions form a multicellular suspensor and a small group of cells at the apex called the pro-embryo.
- (A) Globular stage:
As cell divisions continue, the pro-embryo becomes a spherical, symmetric ball of cells called the globular stage.
At this stage, the basic tissue layers (protoderm, ground meristem, procambium) begin to differentiate.
-
Step 2: (C) Heart stage:
Due to rapid localized cell divisions on two opposite sides of the globular embryo, two lobes arise.
These lobes are the precursors of the two cotyledons, giving the embryo a distinct, bilateral heart-shaped appearance.
-
Step 3: (B) Torpedo stage:
The cotyledons and the hypocotyl-radicle axis elongate significantly, turning the heart-shaped structure into an elongated, cylindrical shape resembling a torpedo.
This is followed by the mature embryo stage, where the cotyledons curve inside the seed coat.
Therefore, the correct chronological sequence of development is: (D) $\rightarrow$ (A) $\rightarrow$ (C) $\rightarrow$ (B).

Step 3: Final Answer:
The correct chronological sequence of embryonic development is (D), (A), (C), (B).