Pre Fertilisation: Structures & Events - NEET Biology Class 12 Free MCQ

Starting from the innermost part, the correct sequence of parts in an ovule is  Embryosac,  nucellus, integument. This sequence can be seen in following

A diagrammatic view of an ovule
Topic in NCERT: The Megasporangium (Ovule)
Line in NCERT: "Integuments encircle the nucellus except at the tip where a small opening called the micropyle is organised."

A. Monocarpellary:
- This term refers to the condition where the gynoecium (the female parts of a flower) consists of a single pistil.
- A pistil is a single or fused carpel, and the carpel is the individual unit of the gynoecium.
- Hence, option A (Monocarpellary) matches with 2 (Refers to the condition where gynoecium consists a single pistil).
B. Syncarpous:
- This term is used to describe the condition where multiple pistils are fused together.
- The pistils could be completely fused, or they could maintain separate ovaries but share a common style or stigma.
- Therefore, option B (Syncarpous) matches with 1 (Refers to the condition where pistils are fused together).
C. Micropyle:
- Micropyle is a small opening in the ovule of a seed plant.
- It's through this opening that the pollen tube enters during fertilization.
- The micropyle allows for the sperm cells carried within the pollen tube to reach the ovule and fertilize it, leading to the formation of a seed.
- As a result, option C (Micropyle) matches with 3 (The small opening in the ovule through which pollen tubes enter).
So, the correct matching is: A - 2, B - 1, C - 3. Therefore, the answer is D.
Topic in NCERT: The Pistil, Megasporangium (ovule) and Embryo sac
Line in NCERT: "The gynoecium may consist of a single pistil (monocarpellary) or may have more than one pistil (multicarpellary). When there are more than one, the pistils may be fused together (syncarpous)." "The ovules have a stalk called funicle, protective integument(s), and an opening called micropyle."

The correct answer is: D: Statement I is incorrect, Statement II is incorrect.
- The spindle formation as seen in Asymmetric during microspore maturation.
- The larger cell (B) is  the vegetative cell, and the smaller cell (C) is  the generative cell. 

Diagram from NCERT:

In monosporic development, only one megaspore out of the four produced from the megaspore mother cell (MMC) develops into the female gametophyte. The other three megaspores typically degenerate. Therefore, the assertion is correct. However, the reason is incorrect as it states that all four megaspores become functional, which is not the case in monosporic development.
Topic in NCERT: Female gametophyte development
Line in NCERT: "Only the functional megaspore develops into the female gametophyte (embryo sac). This method of embryo sac formation from a single megaspore is termed monosporic development."

Here's a detailed explanation:
- The diagram depicts the different stages of embryo sac development.
- Statement I is correct because it accurately describes the content of the diagram, showing two, four, and eight nucleate stages of the embryo sac.
-  Statement II is correct as the divisions in embryo sac development are typically  free nuclear.
Topic in NCERT: Formation of the Embryo Sac
Line in NCERT: "The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. It is of interest to note that these mitotic divisions are strictly free nuclear, that is, nuclear divisions are not followed immediately by cell wall formation."

A synergid cell wall forms a highly thickened structure called the filiform apparatus at the micropylar end consisting of numerous finger-like projections into synergid cytoplasm. These synergid cells are necessary for pollen tube guidance in the ovule.