Step 1: Understanding the Concept:
For successful fertilization in plants, the pollen tube must grow through the style and accurately navigate into the embryo sac through the micropyle.
This navigation is governed by chemical signals produced by the female gametophyte.
Step 2: Detailed Explanation:
The female gametophyte or embryo sac of a typical angiosperm consists of seven cells and eight nuclei.
At the micropylar end, there is a group of three cells called the egg apparatus. This includes one central egg cell and two flanking cells known as synergids.
The synergids have specialized, finger-like wall thickenings at their micropylar tip called the filiform apparatus.
Analysis of Assertion (A): The filiform apparatus serves as a structural guide. It increases the surface area for the secretion of signaling molecules and helps the pollen tube enter the correct synergid cell. Without this structure, the pollen tube might miss the embryo sac entirely. Thus, the assertion is true.
Analysis of Reason (R): Synergids are metabolically active cells. They synthesize and release chemotropic agents (such as calcium ions, boron, and specific proteins/sugars) that create a chemical gradient. The tip of the pollen tube perceives this gradient and grows toward the highest concentration. This is known as chemotropism. Thus, the reason is true.
Synthesis: The reason explains {how} the filiform apparatus guides the tube—by providing the site and means for secreting the attractants mentioned in the reason. Therefore, the reason is the correct biological explanation for why the assertion is true.
Step 3: Final Answer:
Both statements are correct, and the reason provides the functional justification for the importance of the filiform apparatus.