With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of syner

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Q. With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.

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Concept understanding — Male And Female Gametophyte

Let’s start with something you already know. Think of a plant like a mango tree. It produces flowers, and those flowers eventually turn into mangoes. How does that happen? The flower is the plant’s reproductive organ, and inside it, two tiny but crucial structures are made: the male gametophyte and the female gametophyte. These are not the “male” and “female” parts of the flower themselves (like the stamen and pistil) — they are the microscopic, single-generation cells that actually carry the genetic material to form the next plant.

The everyday intuition

Imagine you are baking a cake. The male gametophyte is like the packet of dry yeast — it’s small, mobile, and needs to be added to the mixture. The female gametophyte is like the bowl of flour, eggs, and sugar — it’s larger, stationary, and provides the environment where the yeast works. Without the yeast reaching the bowl, no cake rises. Without the bowl, the yeast has nothing to act on. In a flower, the male gametophyte (pollen grain) must travel to the female gametophyte (embryo sac) for fertilisation to happen.

The precise meaning

In NCERT biology, the male gametophyte is the pollen grain. It develops inside the anther (the top part of the stamen). A mature pollen grain contains two cells: a tube cell and a generative cell. The tube cell will grow a long tube down the style of the pistil, and the generative cell will divide to form two sperm cells. So the male gametophyte is not the whole stamen — it’s the tiny, single-celled (or two-celled) structure that carries the male genetic material.

The female gametophyte is the embryo sac. It develops inside the ovule, which is located in the ovary of the pistil. The embryo sac is a seven-celled, eight-nucleate structure (though you don’t need to memorise numbers for a prose subject — just know it’s a small, organised sac). It contains the egg cell (the female gamete) and other cells that help in fertilisation and nourishment. The female gametophyte is not the whole pistil — it’s the microscopic sac inside the ovule.

Important

The male gametophyte (pollen grain) is haploid — it has only one set of chromosomes. The female gametophyte (embryo sac) is also haploid. When they fuse during fertilisation, they form a diploid zygote, which grows into the seed. This is why both are called “gametophytes” — they produce gametes (sperm and egg).

Why it matters …

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A mature angiosperm embryo sac is a 7-celled, 8-nucleate structure containing an egg cell, two synergids, three antipodal cells, and a large central cell with two polar nuclei, with synergids playing a crucial role in guiding the pollen tube.

In the fascinating world of angiosperm reproduction, the female gametophyte, commonly known as the embryo sac, is a pivotal structure. It is within this microscopic sac, nestled deep inside the ovule, that the female gamete (egg cell) resides, awaiting fertilization. Understanding its structure is key to comprehending the intricate process of sexual reproduction in flowering plants. Typically, the embryo sac develops from a single functional megaspore, a process termed monosporic development, leading to a highly organised and efficient structure ready for double fertilisation.

A mature angiosperm embryo sac is a remarkable example of cellular specialisation, characterised by its 7-celled and 8-nucleate organisation. These cells are strategically arranged within the ovule to facilitate the reproductive process. Let us explore its distinct parts:

Egg Apparatus: Located at the micropylar end (the opening through which the pollen tube enters), this apparatus consists of three cells:
- Egg Cell: This is the single female gamete, typically larger than the synergids and positioned centrally within the egg apparatus. It is the cell that will fuse with one of the male gametes from the pollen tube to form the zygote, which develops into the embryo.
- Synergids: Flanking the egg cell are two synergids. These cells are crucial for guiding the pollen tube and will be discussed in detail shortly. They are characterised by special cellular thickenings at their micropylar tip, known as the filiform apparatus.
Central Cell: This is the largest cell of the embryo sac, occupying most of its volume. It contains two polar nuclei, which initially lie free in the cytoplasm. Before fertilisation, these two polar nuclei often fuse to form a single diploid secondary nucleus (or definitive nucleus). This central cell is vital because it fuses with the second male gamete to form the primary endosperm nucleus, which then develops into the endosperm, providing nourishment to the developing embryo.
Antipodal Cells: Situated at the chalazal end (opposite to the micropylar end) of the embryo sac, there are three antipodal cells. While their exact function is not fully understood in all species, they are generally believed to provide nourishment to the embryo sac or play a role in its development. In many plants, they degenerate either before or soon after fertilisation.

Important

Remember the 7-celled, 8-nucleate structure: 1 egg cell, 2 synergids, 1 central cell (with 2 polar nuclei), and 3 antipodal cells. The central cell is counted as one cell, even though it contains two nuclei.

Role of Synergids

The synergids are far from passive companions to the egg cell; they play a dynamic and indispensable role in the fertilisation process. Their primary functions are:

Pollen Tube Guidance: Synergids are instrumental in attracting and guiding the pollen tube towards the egg cell. They achieve this by secreting specific chemical substances. The pollen tube, growing through the stigma and style, is directed towards the micropylar end of the ovule, where it typically enters one of the synergids.
Nutrient Absorption and Transfer: The filiform apparatus, a finger-like projection at the micropylar end of the synergids, is crucial for absorbing nutrients from the nucellus (the nutritive tissue surrounding the embryo sac) and transferring them to the egg cell and the central cell, supporting their metabolic activities. …

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Q.With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.

Role of Synergids

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