From the statements given below, choose the options that are true for a typical female gametophyte of a flowering plant. (i) It is 8-nucleate and 7-celled at maturity.
(ii) It is free-nuclear during the development.
(iii) It is situated inside the integument but outside the nucellus.
(iv) It has an egg apparatus situated at the chalazal end.

Question

Pollen pistil interaction involves all events from the landing of pollen grains on the stigma until the pollen tube enters the embryo sac (when the pollen is compatible). When a pollen tube grows through the style and enters into the ovules, it finally discharges two male gametes in one of the synergids. Syngamy and triple fusion are two fusion events that occur in angiosperms. Thus, angiosperms exhibit double fertilization. The products of these fusions are the diploid zygote and triploid primary endosperm nucleus. Zygote develops into embryo and primary endosperm cell forms the endosperm tissue. The developing embryo passes through different stages before maturation.

Answer 1

Step 1 : Understanding the Question
This question focuses on the developmental biology and structural organization of the angiosperm female gametophyte, commonly known as the embryo sac. It requires an understanding of megagametogenesis, which is the process where a functional megaspore undergoes mitotic divisions to form a mature embryo sac. The question specifically asks us to validate statements regarding the cellular count, the nature of nuclear division, and the spatial orientation of the components within the ovule.
Step 2 : Detailed Explanation

Nuclear and Cellular Organization: During the formation of the embryo sac, the nucleus of the functional megaspore undergoes three sequential mitotic divisions. This results in eight nuclei. After these divisions, cell walls are laid down for six of the nuclei, forming three antipodal cells at the chalazal end and an egg apparatus (one egg cell and two synergids) at the micropylar end. The remaining two nuclei (polar nuclei) stay in the large central cell. Thus, the structure is 8-nucleate but 7-celled. Statement (i) is true.

Free-Nuclear Development: In the early stages of megagametogenesis, nuclear divisions occur without the immediate formation of cell walls. This phase is characterized by nuclei moving to opposite poles while floating in a common cytoplasm. Cell wall formation only begins after the 8-nucleate stage is reached. Therefore, development is free-nuclear. Statement (ii) is true.

Location in the Ovule: The embryo sac develops from a megaspore that is embedded deep within the nucellus tissue. The nucellus itself is protected by one or two layers called integuments. Therefore, the embryo sac is situated inside both the integuments and the nucellus. Statement (iii) is false because it claims the sac is outside the nucellus.

Polarity of the Egg Apparatus: In a typical ovule, the egg apparatus (consisting of the egg and synergids) is always located at the micropylar end, which is the opening where the pollen tube enters. The chalazal end is the base of the ovule where the antipodal cells are found. Statement (iv) is false due to incorrect orientation.

Step 3 : Final Answer
Based on the structural and developmental facts of angiosperms, statements (i) and (ii) are the only correct descriptions. Thus, option (C) is the correct choice.

Show Hint

The Correct Option is C

Solution and Explanation

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