(a) Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site

Question

Q. (a) Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site where fertilization takes place.

(OR)

(b)

(i) Case studies of some couples are given below. They were not able to have kids even though the parents were not taking any precautions. They also do not wish to adopt a child or take the help of donors. Study these cases and suggest an appropriate Assisted Reproductive Technology that could help them. Case I – Female – Normal Reports Male – Normal sperms but no connection between epididymis and vas deferens. Case II – Female – Normal eggs but Fallopian tube blocked. Male – Normal sperms. Male reports are normal. Case III – Female – Normal Reports. Male – Low sperm count with less motility.

(ii) Copper releasing intrauterine devices are very effective and popular contraceptive devices. Name any two copper releasing IUDs. Write two reasons that make them effective contraceptives.

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Part (a)Concept understanding — Human Reproduction

Human Reproduction: A First Look

Think about what makes you you. You have your mother's eyes, your father's laugh, a mix of traits from two people you may never have met — your grandparents. That chain of life, stretching back thousands of years, runs through one process: human reproduction. It is not a topic for biology students alone. It is the story of how every single person on this planet came to be here.

The Big Picture: Why Does Reproduction Exist?

Every living thing has one fundamental drive: to continue its kind. A mango tree grows fruit so its seeds can sprout elsewhere. A bacterium splits in two. For humans, reproduction is more complex — and more personal. It is the reason families exist, why you have siblings or cousins, and why populations grow or shrink.

At its simplest, human reproduction is the biological process by which a new human individual is created. It requires two parents — a male and a female — each contributing a special cell that fuses to form a single, new cell. That single cell then grows, divides, and develops into a baby over about nine months.

Note

Reproduction is not the same as sex. Sex is an act; reproduction is the entire sequence from cell fusion to birth. Not every act of sex leads to reproduction, and reproduction can sometimes happen with medical help (like IVF) without sex.

The Two Key Players: Male and Female Reproductive Systems

Your body, whether male or female, has a set of organs designed specifically for reproduction. These are not the same as the organs that keep you alive — they are the "spare set" dedicated to creating the next generation.

The Male System: Production and Delivery

The male reproductive system has one main job: to produce male sex cells (sperm) and deliver them to the female body. The key parts are:

Testes (two oval organs in a pouch called the scrotum): These are the factories. They produce sperm continuously from puberty onwards — millions every day. They also produce testosterone, the hormone that drives male physical changes at puberty.
Duct system (a series of tubes): Sperm travel from the testes through a long coiled tube (epididymis) where they mature, then through a muscular tube (vas deferens) that carries them toward the urethra.
Accessory glands (seminal vesicles, prostate gland, bulbourethral glands): These add fluids to the sperm to nourish them and help them swim. The mixture of sperm and these fluids is called semen.
Penis: The organ that delivers semen into the female reproductive tract.

The Female System: Production, Reception, and Nurturing

The female system has a bigger job: it produces female sex cells (eggs), receives sperm, and if fertilization occurs, houses and nourishes the developing baby for nine months. The key parts are:

Ovaries (two almond-sized organs): These produce eggs — but unlike sperm, eggs are not made continuously. A female is born with all the eggs she will ever have (about 1–2 million at birth, reducing to around 300,000–400,000 by puberty). Each month, one egg matures and is released.
Fallopian tubes (also called oviducts): These are not connected directly to the ovaries. When an egg is released, the finger-like ends of the tube sweep it inside. Fertilization — the meeting of sperm and egg — happens here, in the tube.
Uterus (womb): A hollow, pear-shaped muscular organ. If fertilization happens, the embryo implants in the lining of the uterus and grows here. If not, the lining is shed — that is menstruation.
Cervix: The lower, narrow part of the uterus that opens into the vagina. It produces mucus that changes consistency during the month to help or hinder sperm.
Vagina: A muscular canal that receives the penis during intercourse and serves as the birth canal during delivery.

Important

The female reproductive system has a monthly cycle (the menstrual cycle) that prepares the body for a possible pregnancy. This cycle is controlled by hormones and typically lasts about 28 days. The release of the egg (ovulation) happens around day 14. If no pregnancy occurs, the uterine lining is shed as menstrual blood — this is a normal, healthy process, not a "curse" or something to be ashamed of.

The Moment of Creation: Fertilization

When sperm from the male meet the egg from the female inside a fallopian tube, one sperm may penetrate the egg's outer layer. That single moment — fertilization — creates a new cell called a zygote. This zygote contains 23 chromosomes from the mother and 23 from the father, making 46 in total. That is the complete genetic blueprint for a new human being.

The zygote immediately begins to divide as it travels down the fallopian tube toward the uterus. By the time it reaches the uterus (about 5–7 days later), it has become a ball of about 100 cells called a blastocyst. This blastocyst burrows into the soft, thick lining of the uterus — a process called implantation. That is when pregnancy truly begins.

The Nine-Month Journey: Development

Once implanted, the developing human is called an embryo for the first eight weeks, and then a fetus from the ninth week until birth. During these months:

A special organ called the placenta develops, connecting the mother's blood supply to the fetus. It delivers oxygen and nutrients and removes waste — without the mother's and baby's blood ever mixing directly.
The umbilical cord links the baby to the placenta.
The baby is protected by a fluid-filled sac (amniotic sac) that cushions it.
All major organs form in the first three months (first trimester). The next three months (second trimester) are about growth and refinement. The final three months (third trimester) are about rapid weight gain and preparation for life outside the womb. …

Part (b)Concept understanding — Assisted Reproductive Technology

Imagine you have a friend who wants to have a baby, but nature isn't cooperating. Maybe the fallopian tubes are blocked, or the sperm count is very low, or the woman's age makes it difficult. For decades, that was the end of the story. But today, doctors have a toolkit of medical procedures that can step in and help — that toolkit is called Assisted Reproductive Technology, or ART.

At its simplest, ART is any medical technique that handles a human egg or sperm outside the body to help a person get pregnant. The most famous example is IVF (in vitro fertilisation), where the egg and sperm are combined in a lab dish — "in vitro" means "in glass" — and the resulting embryo is then placed into the woman's uterus. But ART is broader than just IVF. It includes everything from injecting a single sperm directly into an egg (ICSI) to using a donor's egg or sperm, or even having another woman carry the pregnancy (surrogacy).

Important

The NCERT textbook (Class 12 Biology, Chapter 4) defines ART as all techniques that involve the direct handling of gametes (sperm and eggs) or embryos outside the body to achieve pregnancy. This is the key distinction: if the procedure doesn't involve handling eggs, sperm, or embryos in a lab, it's not ART.

Why does this matter for a commerce or humanities student? Because ART is not just a medical story — it's a social, legal, and economic one. It raises questions about who can afford it (it's expensive), who gets to be a parent (single people, same-sex couples), and what happens to unused embryos (legal and ethical debates). In India, the Assisted Reproductive Technology (Regulation) Act, 2021 now governs these procedures, requiring clinics to be registered and banning commercial surrogacy for foreigners. So when you read about "test-tube babies" or "surrogacy laws" in the news, you're looking at ART in action.

Here are the main techniques you should know, as listed in the NCERT:

IVF (In Vitro Fertilisation): Egg and sperm are mixed in a lab dish. The embryo is then transferred to the uterus.
ICSI (Intracytoplasmic Sperm Injection): A single sperm is injected directly into an egg. Used when sperm count is very low.
GIFT (Gamete Intrafallopian Transfer): Eggs and sperm are placed directly into the fallopian tube, so fertilisation happens inside the body.
ZIFT (Zygote Intrafallopian Transfer): A fertilised egg (zygote) is placed into the fallopian tube. …

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Part (a): fertilisation occurs at the ampullary-isthmic junction of the fallopian tube; the zygote undergoes cleavage, morula and blastocyst stages and the blastocyst implants in the uterine endometrium (~day 7). Part (b): Case I → ICSI, Case II → IVF + embryo transfer, Case III → IUI; copper IUDs (CuT, Multiload-375) release Cu2+ that suppresses sperm motility/fertilising capacity and makes the uterus unsuitable for implantation.

Part (a)

Site of fertilisation. In humans, fertilisation normally takes place in the ampulla / ampullary-isthmic junction of the fallopian tube (oviduct) - not in the uterus. The ovulated ovum is picked up here, and it is here that a capacitated sperm meets it.

Sequence of events from fertilisation to implantation:

Fertilisation. A sperm penetrates the ovum (secondary oocyte). This induces the oocyte to complete its second meiotic division, and the male and female pronuclei fuse (syngamy) to form a diploid zygote.
Cleavage. As the zygote is moved down the tube toward the uterus by ciliary action and muscular contractions, it undergoes a series of rapid mitotic (cleavage) divisions, forming 2, 4, 8 and 16 daughter cells called blastomeres. The cells become smaller each time (no growth between divisions).
Morula. The 8-16 celled solid ball of blastomeres is the morula, which continues to divide and move towards the uterus.
Blastocyst. The morula transforms into a blastocyst: its blastomeres arrange into an outer layer, the trophoblast, and an inner group, the inner cell mass (embryoblast), enclosing a fluid-filled cavity. The trophoblast will help attach the embryo and later form part of the placenta; the inner cell mass forms the embryo proper. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

Showing the 12 most recent of 37 on this concept.

CBSE 2026Set A1 markMCQ
$Q. What is it called when an embryo having more than eight blastomeres is transferred to the uterus for development?$
(a) IVF
(b) Intrauterine Transfer
(c) Zygote Intra-fallopian Transfer
(d) ICSI
›Reveal solutionSolution

An embryo with more than 8 blastomeres is placed in the uterus by Intrauterine Transfer (IUT); an early embryo (up to 8 blastomeres) goes into the fallopian tube (ZIFT).

In assisted reproductive technologies, embryos produced in the laboratory are transferred into the female. If the embryo is at an early stage — up to the 8-blastomere stage — it is transferred into the fallopian tube by Zygote Intra-Fallopian Transfer (ZIFT). If the embryo has more than 8 blastomeres, it is transferr …

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CBSE 2026Set ZOOLOGY1 markMCQ
$Q. In the assisted reproductive technique, GIFT, the collected sperm and egg are transferred to which organ of the female?$
(a) Uterus
(b) Vagina
(c) Urethra
(d) Fallopian tube
›Reveal solutionSolution

GIFT stands for Gamete Intra-Fallopian Transfer - collected sperm and egg are transferred into the fallopian tube.

GIFT is an Assisted Reproductive Technology (ART) used to help couples who cannot conceive naturally, especially those with a healthy uterus but who cannot produce an ovum (e.g., due to ovarian issues). In this technique, an ovum from a donor female is collected and transferred, along with the sperm, into the fallopian tube (oviduct) of the recipi …

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CBSE 2026Set ANNUAL1 markMCQ
$Q. The technique by which sperm is directly injected into the ovum, is$
(a) ZIFT
(b) GIFT
(c) ZIUT
(d) ICSI
›Reveal solutionSolution
ICSI is an assisted reproductive technique where a sperm is directly injected into an ovum's cytoplasm, bypassing the need for natural sperm penetration.

Among assisted reproductive technologies (ART):

ZIFT (Zygote Intra-Fallopian Transfer) transfers an early embryo/zygote formed in the lab into the fallopian tube.

GIFT (Gamete Intra-Fallopian Transfer) transfers an ovum collected from a donor into the fallopian tube of another female who cannot produce her own ova. …
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CBSE 2026Set ANNUAL1 mark
$Q. Case Study - 1. Read the passage given below and answer the following questions : In case of an infertile couple male has abnormally low sperm count in ejaculation and female has blocked oviduct & has spermicidal secretions in vagina but can provide suitable environment for development of embryo. What is infertility ?$
›Reveal solutionSolution

Infertility is diagnosed when a couple fails to achieve conception/pregnancy despite regular unprotected sex over an extended period, and can arise from a defect/deficiency in either partner.

Infertility is defined as the inability of a couple to produce/conceive a child even after normal, unprotected sexual cohabitation for a reasonable period of time (typically taken as one year or more of regular attempts). Its causes can be physical, congenital, disease-related, drug/immunological or even purely psychological, and may lie with either the male partner (e.g. low sperm count, blocked ducts), the female partner (e.g. blocked oviducts, hormonal issues), or both. In cases such as the one described here — a male with an abnormally low sperm count and a …

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CBSE 2026Set ANNUAL1 mark
$Q. Refer to the Case Study - 1 passage above (infertile couple with low sperm count and blocked oviduct with spermicidal vaginal secretions). Suggest ART used in above case.$
›Reveal solutionSolution
Since the female's oviduct is blocked (preventing normal gamete transport and fertilisation in vivo) but her uterus can support an embryo, and the male has a low sperm count, the couple needs fertilisation to happen OUTSIDE the body, followed by placing the resulting embryo directly into the uterus (or an unblocked part of the oviduct).

Given that (i) the female partner has a blocked oviduct — meaning sperm and egg cannot naturally meet or the fertilised egg cannot travel down to the uterus — but her uterus can support embryonic development, and (ii) the male partner has a low sperm count, the appropriate ART is:

IVF (In Vitro Fertilisation): ova collected from the female and sperm from the male are made to fuse in the laboratory ('test tube baby' technique) — this fertilisation step does not require an unblocked oviduct.

ICSI (Intracytoplasmic Sperm Injection): used alongside IVF because of the male's low sperm count, a single healthy sperm is directly injected into the ovum to ensure fertilisation. …
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CBSE 2025Set X11 markMCQ
$Q. Which one among the following ART can be used to rectify if the infertility is due to low sperm count?$
(a) GIFT
(b) IUT
(c) ZIFT
(d) IUI
›Reveal solutionSolution

Intra-uterine insemination (IUI) is used to overcome infertility due to low sperm count.

In IUI, semen collected either from the husband or a healthy donor is artificially introduced into the uterus of the female. It is the assisted reproductive technology specifically recommended when the male partner is unable to inseminate the female or has a very low sperm count. GIFT transfers an ovum/gamete into the fallopian tube of a female who …
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CBSE 2025Set KH1 mark
$Q. Write the full form of abbreviation I.V.F.$
›Reveal solutionSolution

I.V.F. = In Vitro Fertilisation — fertilisation done outside the body in the lab.

Concept. In IVF, ova collected from the female and sperm from the male are combined in vitro (literally 'in glass', i.e. in a laboratory dish). The resulting zygote/early embryo is then transferred back — an embryo up to the 8-blastomere stage is placed in the fallopian tube (ZIFT) and later stages into the uterus (IU …

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CBSE 2025Set F1 markMCQ
$Q. At which of the following stages is the embryo transferred to fallopian tube?$
(a) 8-celled embryo
(b) 32-celled embryo
(c) Zygote
(d) Zygote or 8-celled embryo
›Reveal solutionSolution

Assisted transfer into the fallopian tube uses a zygote or an early embryo up to the 8-celled stage (ZIFT).

Among assisted reproductive technologies, in ZIFT (Zygote Intra Fallopian Transfer) the zygote or an early cleaving embryo with up to 8 blastomeres is introduced into the fallopian tube. (An embryo of more than 8 blastomeres is instead transferred into the uterus — IUT …

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CBSE 2025Set ANNUAL1 markMCQ
$Q. Transfer of ovum collected from a donor into the fallopian tube of another female is called$
(a) ZIFT
(b) GIFT
(c) SUZI
(d) ICSI
›Reveal solutionSolution

GIFT is the specific assisted reproductive technology procedure that transfers a donor's ovum into a recipient female's fallopian tube.

GIFT stands for Gamete Intra-Fallopian Transfer, an assisted reproductive technique in which an ovum collected from a donor female is transferred into the fallopian tube of another female who cannot produce her own ova but can carry a pregnancy. ZIFT (a) refers to transfer of a zygote (formed by in-vitro fertilization) into the fallopian tube; ICSI (d, Intracytoplasmic Sperm Injection) involves directly injecting a s …

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CBSE 2024Set 57/1/11 markMCQ
$Q. For Questions number 13 to 16, two statements are given — one labelled as Assertion (A) and the other labelled as Reason (R). Select the correct answer to these questions from the codes (A), (B), (C) and (D) as given below. (A) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). (B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A). (C) Assertion (A) is true, but Reason (R) is false. (D) Assertion (A) is false, but Reason (R) is true. Assertion (A): The laws of our country permit legal adoption and it is as yet, one of the best methods for childless couples looking for parenthood. Reason (R): Emotional, religious and social factors are no deterrents to the legal adoption of orphaned and destitute children in India.$
›Reveal solutionSolution

The Assertion is true — legal adoption is a permitted and valued method for childless couples — but the Reason is false, because emotional, religious, and social factors do act as deterrents to adoption in India.

This is an Assertion-Reason question drawn from NCERT Class-12 Biology, Chapter 4 "Reproductive Health," in the section on Infertility. The chapter notes that legal adoption is one option available to infertile couples wishing to have a child, alongside Assisted Reproductive Technology (ART) methods such as IVF, ZIFT, GIFT, and artificial insemination.

Examining the Assertion: India's legal framework — including personal-law adoption statutes and the secular Juvenile Justice (Care and Protection of Children) Act, 2015 — permits legal adoption, and it remains one of the most widely available, legitimate routes to parenthood for couples unable to conceive. The Assertion is therefore true.

Examining the Reason: The Reason claims that emotional, religious, and social factors are no deterrent to adoption. In practice, the opposite is true. Many couples in India still hesitate to adopt because of the emotional preference for a biological child, religious/cultural expectations (such as the wish for a biological heir), and the social stigma attached to a child "not of one's own blood." These are real, well-recognised deterrents — so the Reason, as stated, is false. …
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CBSE 2024Set 57/2/11 markMCQ
$Q. In humans, the secondary oocyte completes meiotic division when : (A) it gets implanted in the uterine endometrium. (B) it is released from the matured Graafian follicle. (C) it is penetrated by the sperm cell. (D) acrosomal enzymes break down the zona pellucida.$
›Reveal solutionSolution
The secondary oocyte arrests in metaphase II and completes meiosis II only upon fertilization—specifically when a sperm penetrates it. The answer is (C).

Why the secondary oocyte waits

Human oogenesis is a carefully timed process. Unlike spermatogenesis, which runs to completion once started, oogenesis has two built-in arrest points. The first is in prophase I (during fetal development), and the second is in metaphase II—right after the first meiotic division produces the secondary oocyte.

This second arrest exists because completing meiosis is metabolically expensive and produces a second polar body that will be discarded. Evolution has optimized this: why finish the division if no sperm arrives? The secondary oocyte therefore remains frozen at metaphase II, chromosomes aligned on the spindle, waiting for a signal that fertilization has begun.

That signal is sperm entry.

Walking through the oocyte's journey

Ovulation releases a metaphase II cell

When the Graafian follicle ruptures during ovulation, what is released is a secondary oocyte, not a mature ovum. This cell has already completed meiosis I (producing the first polar body) but is arrested in metaphase II. So option (B) describes the release, but meiosis II is not yet complete at this moment.

Sperm penetration triggers completion

When a sperm successfully penetrates the secondary oocyte—after the acrosome reaction has allowed it to breach the zona pellucida and the sperm head fuses with the oocyte membrane—the oocyte receives a calcium signal. This calcium wave is the trigger that releases the metaphase II arrest. The cell now completes meiosis II, extruding the second polar body and forming the mature ovum with a haploid nucleus.

What about the other options? …
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CBSE 2024Set GG1 mark
$Q. Write the full form of MTP and ZIFT.$
›Reveal solutionSolution

MTP = Medical Termination of Pregnancy; ZIFT = Zygote Intra Fallopian Transfer.

MTP (Medical Termination of Pregnancy): the intentional/induced termination of pregnancy before full term (also called induced abortion); legalised in India in 1971 and used to remove unwanted pregnancies and to safeguard the mother's health.

…

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Q.(a) Trace the events from fertilization till implantation of blastocyst in human female. Also mention the site where fertilization takes place.

Part (a)

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