Q.Does the first polar body born out of first meiotic division divide further or degenerate?
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Oogenesis Definition
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. …
The NCERT textbook itself answers this honestly with an acknowledgment of scientific uncertainty, stated verbatim right after the question: "At present we are not very certain about this." So there is no single settled answer to quote — some sources describe the first polar body dividing (mirroring meiosis II) to give two smaller polar bodies, while others describe it degenerating directly without dividing; either way, all polar bodies eventually degenerate and take no further part in reproduction. …
NCERT explicitly flags this as scientifically unresolved: "At present we are not very certain about this." The first polar body's fate — whether it divides once more or simply degenerates — has no single confirmed answer, but either way it never becomes a gamete.
This is one of the rare places in the NCERT Class 12 Biology textbook where the book itself flags an open question rather than supplying a confident answer — worth taking at face value rather than inventing a definitive resolution the source does not give (honesty over a confident-sounding guess).
What IS established (from the rest of section 2.3 and Figure 2.8(b)): the primary oocyte's first meiotic division is unequal, producing one large secondary oocyte and one small first polar body, both haploid (23 chromosomes). Some accounts of oogenesis describe the first polar body undergoing a second, mitosis-like division (paralleling the secondary oocyte's own meiosis II) to yield two smaller polar bodies; other accounts describe it degenerating without ever dividing again. Both possibilities appear in different sources, which is exactly why NCERT hedges rather than commits to one. …
- TG EAPCET 2026Set ap-2026-05-04-FN1 markMCQQ.Four different stages that occur during meiosis are given in the following list. Select the correct sequential arrangement of the stages. I. Complete separation of chromatids II. Pairing of homologous chromosomes III. Lining up of paired chromosomes on equator plate IV. Crossing over between chromatids (A) II, IV, III, I (B) III, I, II, IV (C) III, II, IV, I (D) II, III, IV, I
›Reveal solutionSolution
The correct order of meiotic stages is pairing of homologous chromosomes, then crossing over, then lining up on the equator, then complete separation of chromatids — which corresponds to option (A).
The question asks for the sequential arrangement of four key events during meiosis. To answer correctly, you need to recall the order of phases in meiosis I and II, and understand what happens in each.
Concept and intuition: Meiosis reduces chromosome number by half through two divisions. The events listed belong mostly to meiosis I (pairing, crossing over, lining up) and one to meiosis II (complete separation of chromatids). The natural progression is: first, homologous chromosomes find each other and pair (synapsis); then they exchange genetic material (crossing over); then they align at the cell’s equator (metaphase I); finally, after anaphase II, sister chromatids fully separate. So the sequence is II → IV → III → I.
Let’s walk through each step:
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II. Pairing of homologous chromosomes — This occurs during prophase I. Homologous chromosomes (one from each parent) come together in a process called synapsis, forming bivalents. This is the very first major event in meiosis I, before any alignment or crossing over can happen.
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IV. Crossing over between chromatids — Also in prophase I, after pairing, non-sister chromatids of homologous chromosomes exchange segments. This creates genetic recombination. Crossing over cannot occur before pairing, because the chromosomes need to be physically close. …
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- TG EAPCET 2025Set ap-2025-04-30-FN1 markMCQQ.The fertilization in angiosperms (A) Parthenogamous oogamy (B) Zooidogamous oogamy (C) Siphanogamous oogamy (D) Siphanogamous zooidogamy
›Reveal solutionSolution
Fertilization in angiosperms involves the delivery of non-motile male gametes to a non-motile egg cell via a pollen tube, a process termed siphonogamous oogamy. The correct option is (C).
Fertilization is the fundamental process in sexual reproduction where male and female gametes fuse to form a zygote. In angiosperms, or flowering plants, this process has evolved specific mechanisms to ensure successful reproduction, which are distinct from those found in lower plants. Understanding these mechanisms helps us classify the type of fertilization accurately.
The key aspects of fertilization in angiosperms are:
- Gamete Nature (Oogamy): Angiosperms produce a large, non-motile female gamete (the egg cell) and small, non-motile male gametes. The fusion of such dissimilar gametes, where the female gamete is significantly larger and non-motile, is known as oogamy.
- Gamete Delivery (Siphonogamy): Unlike lower plants where motile male gametes might swim to the egg, angiosperms have evolved a pollen tube to deliver the non-motile male gametes directly to the embryo sac containing the egg cell. This mechanism of gamete delivery via a pollen tube is called siphonogamy.
Combining these two characteristics, fertilization in angiosperms is described as siphonogamous oogamy.
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Pollen Germination and Pollen Tube Formation: After a pollen grain lands on a compatible stigma, it absorbs moisture and nutrients. The generative cell within the pollen grain divides to form two male gametes, and the vegetative cell develops into a pollen tube. This tube grows through the style, navigating towards the ovule.
TipThe pollen tube acts as a conduit, eliminating the need for water as a medium for sperm transport, which is a significant evolutionary adaptation for terrestrial life.
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Delivery of Male Gametes: The pollen tube continues its growth, typically entering the ovule through the micropyle, and then penetrates one of the synergids within the embryo sac. Once inside the synergid, the tip of the pollen tube ruptures, releasing the two non-motile male gametes. This entire process of delivering male gametes via a pollen tube is the defining feature of siphonogamy. …
- TG EAPCET 2025Set ap-2025-04-30-FN1 markMCQQ.In human female, the ovum is released from the Graafian follicle at this stage (A) Primary oocyte (B) Secondary oocyte (C) First polar body (D) Ootid
›Reveal solutionSolution
The ovum released from the Graafian follicle is a secondary oocyte — it has completed meiosis I but is arrested at metaphase II until fertilization.
The question asks about the stage of the female gamete at the moment of ovulation — when the ovum is actually released from the ovary. This is a classic point of confusion in human reproduction, because the terms "ovum," "egg," and "oocyte" are often used loosely, but in biology they refer to very specific stages of meiosis.
Let’s walk through the timeline of oogenesis to see exactly where ovulation fits.
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Before birth and through childhood — the ovary contains millions of primary oocytes, each arrested in prophase I. These are diploid cells that have started meiosis but paused. They are surrounded by a single layer of follicle cells, forming a primordial follicle.
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At puberty, each menstrual cycle — a few primary oocytes resume meiosis. The follicle grows, becoming a Graafian follicle (a mature, fluid-filled follicle). The primary oocyte completes meiosis I, producing two very unequal cells: a large secondary oocyte (which gets almost all the cytoplasm) and a tiny first polar body. Both are haploid.
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Ovulation — the Graafian follicle ruptures and releases the secondary oocyte (still surrounded by the zona pellucida and some follicle cells). This secondary oocyte does not finish meiosis II unless a sperm penetrates it. It is arrested at metaphase II.
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If fertilization occurs — the secondary oocyte completes meiosis II, producing a mature ovum (or ootid) and a second polar body. Only then is the haploid female pronucleus ready to fuse with the sperm pronucleus. …
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- TG EAPCET 2023Set ap-2023-05-11-AN1 markMCQQ.The following are stages of Plasmodium in female Anopheles. Their correct sequence is (A) IV - I - III - II - V (B) II - V - III - IV - I (C) IV - V - I - III - II (D) IV - I - III - V - II
›Reveal solutionSolution
The life cycle of Plasmodium in the female Anopheles mosquito follows a fixed sequence: gametocytes → fertilization → ookinete → oocyst → sporozoites. The correct order is IV → I → III → V → II, which matches option (D).
The question tests your understanding of the sexual phase of the malaria parasite’s life cycle — the part that happens inside the mosquito. In the human host, Plasmodium multiplies asexually, but when a female Anopheles mosquito bites an infected person, it picks up the parasite’s sexual forms (gametocytes) from the blood. Inside the mosquito’s gut, these gametocytes develop into gametes, fertilization occurs, and the resulting zygote transforms through several stages until infective sporozoites reach the salivary glands. The sequence is rigid and must be memorized with the underlying biology, not just the names.
Let’s map each stage to its Roman numeral and then arrange them in order.
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Stage IV — Gametocytes
These are the sexual forms (male and female) that enter the mosquito’s gut when it takes a blood meal from an infected human. They are the starting point inside the mosquito.
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Stage I — Fertilization
In the mosquito’s midgut, male and female gametes fuse to form a zygote. This is the only diploid stage in the Plasmodium life cycle.
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Stage III — Ookinete
The zygote develops into a motile, elongated form called the ookinete. It penetrates the mosquito’s gut wall.
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Stage V — Oocyst …
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