Q.(a) Oogenesis is a discontinuous process that begins before birth and is completed after puberty.
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Oogenesis: The Making of an Egg Cell
Think of oogenesis as the biological story of how a female body creates the single most important cell she will ever produce — the egg, or ovum. If you've ever seen a seed that contains everything needed to grow a new plant, you have the right mental picture. The egg cell is that seed for human life. But unlike a seed that sits waiting, the egg cell goes through a long, carefully timed process before it is ready.
The Everyday Intuition
Imagine a factory that makes one very special product. This factory starts its work even before the product is ordered. It prepares the raw materials, stores them for years, and then, when the time is right, finishes the product in a matter of days. That is oogenesis. A female is born with all the "raw materials" she will ever have — millions of tiny, immature egg precursors. Most of these will never be used. Only a few hundred will ever mature into eggs that can be fertilized.
The Precise Meaning
Oogenesis is the process by which the female gamete, or egg cell, is formed in the ovaries. It begins before a girl is even born, pauses for years, and then resumes each month from puberty until menopause. The entire process transforms a primitive cell called an oogonium into a mature ovum (egg) that can be fertilized by a sperm.
The word "oogenesis" comes from Greek: oion meaning "egg" and genesis meaning "origin" or "creation." So it literally means "the origin of the egg."
Why It Matters
You might wonder why a commerce or humanities student needs to know this. Here is why: oogenesis is the biological foundation of female fertility, reproduction, and even the timing of a woman's life. It explains:
- Why a woman is born with all her eggs and never makes new ones.
- Why fertility declines with age — the eggs age along with the woman.
- Why only one egg is released each month, not hundreds like sperm.
- Why the egg is so much larger than a sperm — it carries the cytoplasm, nutrients, and mitochondria that the embryo will need for its first few days.
Key Stages in Simple Terms
The NCERT textbook describes oogenesis in three main phases, but you can think of them as three acts of a play:
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Multiplication phase — Before birth, the oogonia (the stem cells) multiply rapidly. This happens only in the fetal ovary. By the time a female is born, all the oogonia have transformed into primary oocytes, and no new ones are ever made.
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Growth phase — Each primary oocyte grows in size and accumulates nutrients. But then it stops. It enters a resting state called prophase I and stays there for years — until the female reaches puberty. Some primary oocytes wait for 12, 20, or even 40 years before they resume development.
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Maturation phase — After puberty, each month a few primary oocytes start maturing. But only one usually completes the process. This phase involves two rounds of cell division (meiosis I and meiosis II) that reduce the chromosome number by half. The result is one large, functional egg and three tiny, non-functional cells called polar bodies that eventually degenerate. …
Part (b)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.
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 …
Part (a)
- Development of the gamete mother cell to ovulation. In the foetal ovary, primordial germ cells form oogonia, which enlarge into primary oocytes (the gamete mother cells). Each primary oocyte begins meiosis I but is arrested at prophase I before birth, enclosed by granulosa cells as a primary follicle. At puberty the follicle grows into a secondary and then a fluid-filled Graafian follicle. Just before ovulation the primary oocyte completes meiosis I, giving a large secondary oocyte and a tiny first polar body; the secondary oocyte begins meiosis II but is arrested at metaphase II, and is released at ovulation when the Graafian follicle ruptures. (Meiosis II is completed only if fertilization occurs.)
- Two pituitary hormones: FSH (follicle-stimulating hormone — stimulates follicle growth) and LH (luteinizing hormone — its mid-cycle surge triggers ovulation).
Part (b)
(i) The two-celled male gametophyte (pollen grain) has a large vegetative (tube) cell and a smaller generative cell lying within its cytoplasm, enclosed by the pollen wall (exine + intine).
(ii) Three layers around the cytoplasm, innermost -> outermost: plasma membrane -> intine -> exine. The plasma membrane lies immediately around the cytoplasm; the intine is the inner cellulose-pectin wall; the exine is the tough outer wall. …
Part (a): the primary oocyte (gamete mother cell) is arrested at prophase I before birth, resumes at puberty in the Graafian follicle, completes meiosis I to a secondary oocyte (arrested at metaphase II) that is released at ovulation, all under the pituitary hormones FSH and LH.
Part (b): the two-celled pollen grain has a vegetative and a generative cell; from innermost to outermost its coverings are the plasma membrane, intine and exine; the exine is sporopollenin (highly resistant, protective) and is discontinuous at the germ pores so the pollen tube can emerge.
Part (a)
(i) From gamete mother cell to release at ovulation.
- In the foetal ovary, primordial germ cells form oogonia (diploid), which enlarge into primary oocytes, the gamete mother cells.
- Each primary oocyte enters meiosis I but arrests at prophase I before birth, surrounded by granulosa cells as a primary follicle. A newborn girl already has all her primary follicles.
- At puberty, follicles are recruited each cycle; the primary follicle grows into a secondary follicle and then a mature Graafian follicle with a fluid-filled antrum.
- Just before ovulation the primary oocyte completes meiosis I, dividing unequally into a large secondary oocyte and a small first polar body; the secondary oocyte begins meiosis II but arrests at metaphase II.
- At ovulation the Graafian follicle ruptures and the secondary oocyte is released from the ovary. Meiosis II is completed only if a sperm fertilises it. …
Showing the 12 most recent of 79 on this concept.
- CBSE 2026Set 57/2/11 markMCQQ.Given below are stages of embryo sac formation from megaspore mother cell. Identify the correct option for the cell division marked a, b, c and d. (A) a – Meiosis-I, b – No division, c – Mitosis, d – Meiosis-II (B) a – Meiosis-I, b – Meiosis-II, c – No division, d - Mitosis (C) a – Mitosis, b – Meiosis-I, c – Meiosis-II, d – No division (D) a – No division, b – Mitosis, c – Meiosis-I, d – Meiosis-II
›Reveal solutionSolution
The megaspore mother cell undergoes meiosis (two divisions) to produce four haploid megaspores, of which only one survives; that functional megaspore then undergoes three mitotic divisions to form the eight-nucleate embryo sac — so the correct sequence is Meiosis-I, Meiosis-II, No division, Mitosis.
To understand this question, you need to picture the sequence of events inside the ovule of a flowering plant. The story begins with a single, large cell called the megaspore mother cell (MMC) . This cell is diploid (2n) and is the starting point for forming the female gametophyte — the embryo sac.
The MMC does not simply grow or divide by mitosis. Instead, it enters meiosis, a special type of cell division that reduces the chromosome number by half. Meiosis happens in two consecutive stages: Meiosis-I and Meiosis-II. So the very first division (marked 'a' in your diagram) is Meiosis-I. The second division (marked 'b') is Meiosis-II. After these two divisions, the original single MMC has produced four haploid (n) cells — these are called megaspores.
Now here is a critical twist. In most flowering plants, three of these four megaspores degenerate and die. Only one of them — usually the one farthest from the micropyle (the opening of the ovule) — remains functional. So after the four megaspores are formed, there is a stage where no division occurs (marked 'c' in your diagram). Instead, three cells simply break down, leaving just one functional megaspore.
That single functional megaspore is the starting point for the actual embryo sac. It is haploid and now needs to grow into a structure that contains the egg cell and other supporting cells. How does it do that? It undergoes three rounds of mitotic divisions (marked 'd'). Mitosis ensures that all the resulting nuclei remain haploid and genetically identical. The first mitosis produces two nuclei, the second produces four, and the third produces eight nuclei. These eight nuclei then arrange themselves into the typical seven-celled, eight-nucleate embryo sac (with the egg apparatus, central cell, and antipodal cells).
So, mapping this to the labels in your question:
- a = Meiosis-I (first reduction division)
- b = Meiosis-II (second division, producing four megaspores)
- c = No division (three megaspores degenerate) …
- CBSE 2026Set A1 markMCQQ.Which of the following is one of the most resistant organic materials?(a) Pectin(b) Cellulose(c) Sporopollenin(d) Chitin
›Reveal solutionSolution
Sporopollenin forms the pollen exine and is among the most resistant organic materials known.
The hard outer wall (exine) of a pollen grain is made of sporopollenin. It can withstand high temperatures and strong acids and alkalis, and no enzyme is known that can degrade it. This extreme resistance is wh …
- CBSE 2026Set A1 markMCQQ.Which of the following cells is present in pollen grain of angiospermic plants?(a) Vegetative cell(b) Generative cell(c) Antipodal cell(d) Both (A) and (B)
›Reveal solutionSolution
An angiosperm pollen grain (male gametophyte) contains a vegetative cell and a generative cell.
When a pollen grain is shed, it is usually at the 2-celled stage. It contains a large vegetative (tube) cell with abundant food reserves, and a small generative cell floating within its cytoplasm. The generative cell later divides to form two male ga …
- CBSE 2026Set A1 markMCQQ.Which of the following plays an important role in guiding the pollen tube into the synergids?(a) Antipodals(b) Filiform apparatus(c) Central cell(d) Micropyle
›Reveal solutionSolution
The filiform apparatus of the synergids guides the entering pollen tube into a synergid.
At the micropylar end of the embryo sac, the synergids bear special cellular thickenings called the filiform apparatus. This structure guides the pollen tube by directing its entry into one of the synergids. Once inside, the pollen tube bursts and releases the …
- CBSE 2026Set A1 markMCQQ.Which of the following cells is haploid?(a) Oogonia(b) Primary oocyte(c) Secondary oocyte(d) All of these
›Reveal solutionSolution
The secondary oocyte is haploid because it forms after meiosis I; oogonia and primary oocytes are diploid.
Oogenesis begins with diploid oogonia, which grow into diploid primary oocytes (2n). The primary oocyte then completes the first meiotic division (meiosis I), producing a haploid secondary oocyte (n) and a first polar body. Because chromosome number is halved in meiosi …
- CBSE 2026Set ZOOLOGY1 markMCQQ.What is the discharge of matured egg from the Graafian follicle called as?(a) Oogenesis(b) Fertilization(c) Ovulation(d) Abortion
›Reveal solutionSolution
Ovulation is the process by which a mature egg is released from the ruptured Graafian follicle.
During the menstrual cycle, a primary follicle in the ovary matures into a fully developed Graafian follicle under the influence of FSH. A surge in Luteinising Hormone (LH) around the 14th day of the cycle causes the Graafian follicle to rupture and release the secondary oocyte (egg) into the fallopian tube - this event is called ovulati …
- CBSE 2026Set ANNUAL1 markQ.What does 'A' and 'B' represent in the above mentioned diagram of the mature embryosac? Write name for each.
›Reveal solutionSolution
In the mature 7-celled, 8-nucleate embryo sac, A marks the two polar nuclei of the central cell and B marks the three-celled egg apparatus (2 synergids + 1 egg cell) at the micropylar end.
A typical angiosperm embryo sac at maturity has 7 cells and 8 nuclei, organised as: 3 antipodal cells at the chalazal end; a large central cell containing 2 polar nuclei (which fuse with a male gamete during triple fusion to form the triploid endosperm); and, at the micropylar end, the egg apparatus consisting of 1 egg cell flanked by 2 synergid cells. The synergids bear a special thickened structure at their micropylar tip called the filiform apparatus, which guides entry of the pollen tube into the embryo sac. In the given figure, going from the chalazal end (top, unlabelled antipodal cells) toward the micropylar end (bottom, where the filiform a …
- CBSE 2026Set ANNUAL1 markMCQQ.Male gametes in angiosperms are formed by the division of(a) Vegetative cell(b) Generative cell(c) Microspore mother cell(d) Megaspore mother cell
›Reveal solutionSolution
The pollen grain's generative cell divides mitotically to form two non-motile male gametes that are delivered through the pollen tube.
A mature pollen grain in angiosperms is typically 2-celled at shedding: a larger vegetative (tube) cell and a smaller generative cell, floating within the vegetative cell's cytoplasm.
- The vegetative cell has abundant food reserves and, upon germination on the stigma, forms the pollen tube that grows down through the style. …
- CBSE 2026Set ANNUAL1 markQ.Where is filiform apparatus located? What is the role of filiform apparatus?
›Reveal solutionSolution
The filiform apparatus is a set of finger-like cell-wall thickenings at the micropylar end of each synergid, and it functions to guide the entry of the pollen tube into the embryo sac.
Location: Within the mature embryo sac of an angiosperm ovule, two synergid cells flank the egg cell at the micropylar end (together forming the egg apparatus). Each synergid has specialised, finger-like thickenings of its cell wall at its micropylar tip called the filiform apparatus.
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- CBSE 2026Set ANNUAL1 markMCQQ.Pollen grains retain viability for months in plant belonging to different families given below :(i) Solanaceae(ii) Leguminosae(iii) Gramineae(iv) Rosaceae(v) Liliaceae Correct option is :(a) (i),(ii) &(v)(b) (i),(ii) &(iv)(c) (ii), (iv),(v)(d) (i), (iii), (v)
›Reveal solutionSolution
Pollen viability varies enormously by species — from 30 minutes in some cereals to months in members of Solanaceae, Leguminosae and Rosaceae.
Pollen grain lifespan depends on temperature and humidity. In many members of the family Poaceae (Gramineae) pollen viability is lost within 30 minutes of release, while in some members of Solanaceae, Leguminosae, and Rosaceae, pollen grains maintain viability for …
- CBSE 2026Set ANNUAL1 markMCQQ.The structure of bilobed anther consist of :(a) 2 thecae, 2 sporangia(b) 4 thecae, 4 sporangia(c) 4 thecae, 2 sporangia(d) 2 thecae, 4 sporangia
›Reveal solutionSolution
A typical anther is bilobed and dithecous: two lobes (thecae), each theca bearing two microsporangia (pollen sacs) — four microsporangia in total.
A mature anther consists of two lobes joined by a sterile connective. Each lobe is called a theca, so a bilobed anther has 2 thecae, making it 'dithecous'. Within each theca lie two elongated sac-like structures called microsporangia (pollen sacs), running almost the full length of the anther. So each theca contributes 2 microsporangia, giving …
- CBSE 2026Set ANNUAL1 markMCQQ.Egg apparatus is made up of :(a) 2 synergid cells + 2 egg cells(b) 1 synergid cell + 2 egg cells(c) 2 synergid cells + 1 egg cell(d) 1 synergid cell + 1 egg cell
›Reveal solutionSolution
The egg apparatus, sitting at the micropylar end of the embryo sac, is made up of 2 synergid cells + 1 egg cell.
The mature female gametophyte (embryo sac) of a flowering plant is typically 7-celled and 8-nucleate. At its micropylar end lies a group of three cells called the egg apparatus, consisting of:
- 1 egg cell (oosphere) — the female gamete, located in the centre, flanked by the two synergids. …
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