Chapter 2: Human Reproduction Long Questions | biology Class 12 CBSE

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Chapter 2: Human Reproduction Long Questions | biology Class 12 CBSE | ByteNotes.in

Long Answer

Hard difficulty • Structured explanation

Hard

Question 1

Long Form

Compare and contrast spermatogenesis and oogenesis with respect to location, initiation, meiotic divisions and the number of functional gametes produced.

Spermatogenesis occurs in the seminiferous tubules of the testis and begins at puberty; oogenesis occurs in the ovaries and is initiated during embryonic development itself.
In spermatogenesis, each primary spermatocyte undergoes two meiotic divisions to produce four equal haploid spermatids; in oogenesis, the divisions are unequal, producing one large secondary oocyte and a tiny first polar body (meiosis I), then a haploid ovum and second polar body (meiosis II).
Spermatogenesis is a continuous process producing millions of sperms; oogenesis produces one mature ovum per cycle, and meiosis II completes only after fertilisation.
After spermiogenesis, spermatids transform into spermatozoa and are released by spermiation; in oogenesis, the secondary oocyte (not a mature ovum) is released at ovulation.
Androgens (via LH and FSH) regulate spermatogenesis; oogenesis is regulated by FSH, LH, estrogens and progesterone during each menstrual cycle.

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Long Answer

Hard difficulty • Structured explanation

Hard

Question 2

Long Form

Analyse the hormonal regulation of the menstrual cycle, tracing the events from the follicular phase through the luteal phase.

During the follicular phase, FSH and LH levels gradually increase, stimulating primary follicle growth into a mature Graafian follicle and secretion of estrogens, which promote endometrial proliferation.
Both LH and FSH peak around day 14; the rapid LH surge induces rupture of the Graafian follicle, resulting in ovulation of the secondary oocyte.
After ovulation, the luteal phase begins: remnants of the Graafian follicle become the corpus luteum, which secretes large amounts of progesterone.
Progesterone maintains the endometrium in a secretory state suitable for implantation of the fertilised ovum.
If fertilisation does not occur, the corpus luteum degenerates, progesterone and estrogen levels fall, the endometrium breaks down, and menstruation begins, starting a new cycle.

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Long Answer

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Medium

Question 3

Long Form

Describe the structure of the male reproductive system, tracing the path of sperm from formation in the testis to ejaculation.

Sperms are produced in the highly coiled seminiferous tubules inside testicular lobules; each testis has about 250 such lobules housed in the scrotum at a temperature 2–2.5°C below body temperature.
From seminiferous tubules, sperms pass into the rete testis, then through vasa efferentia into the epididymis located on the posterior surface of the testis, where sperms mature.
The vas deferens ascends from the epididymis, loops over the urinary bladder and receives a duct from the seminal vesicle to form the ejaculatory duct.
The ejaculatory duct opens into the urethra, which originates from the urinary bladder and passes through the penis to the urethral meatus.
Secretions from the seminal vesicles, prostate and bulbourethral glands form the seminal plasma (rich in fructose, calcium and enzymes); sperms plus seminal plasma constitute semen that is ejaculated through the urethra.

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Long Answer

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Question 4

Long Form

Trace the events from fertilisation to implantation, explaining the structural changes in the embryo at each stage.

Fertilisation occurs in the ampullary region of the fallopian tube when a sperm penetrates the zona pellucida of the secondary oocyte using acrosomal enzymes; zona pellucida changes block polyspermy.
The entry of the sperm triggers completion of meiosis II in the secondary oocyte, forming a haploid ovum and second polar body; fusion of sperm and ovum nuclei forms a diploid zygote.
The zygote undergoes cleavage (mitotic divisions) while moving through the isthmus toward the uterus, forming 2, 4, 8, 16 blastomeres; an 8–16 blastomere embryo is called a morula.
The morula continues dividing and transforms into a blastocyst, with an outer trophoblast layer and an inner cell mass attached to it.
The trophoblast attaches to the endometrium; uterine cells rapidly cover the blastocyst, embedding it in the endometrium — this is implantation, which establishes pregnancy.

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Long Answer

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Hard

Question 5

Long Form

Describe the structure and functions of the placenta, and explain why it is considered both a nutritive and an endocrine organ.

The placenta is formed by interdigitation of chorionic villi (arising from the trophoblast) with uterine tissue and maternal blood after implantation.
As a nutritive organ, it facilitates supply of oxygen and nutrients from maternal blood to the embryo and removes carbon dioxide and waste materials produced by the embryo.
The embryo is connected to the placenta via the umbilical cord, through which all exchange of substances occurs.
As an endocrine organ, the placenta produces hCG, hPL, estrogens, progestogens; hCG and hPL are produced only during pregnancy and are unique to the placenta.
These placental hormones are essential for supporting fetal growth, inducing metabolic changes in the mother and maintaining pregnancy; relaxin secreted by the ovary in later pregnancy also aids in preparing for delivery.

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Long Answer

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Medium

Question 6

Long Form

Describe the structure of a mature spermatozoan and relate each structural component to its specific function.

The sperm head contains an elongated haploid nucleus that carries the paternal genetic information to be contributed to the zygote.
The anterior portion of the head bears a cap-like acrosome filled with enzymes that facilitate penetration of the zona pellucida and plasma membrane of the ovum during fertilisation.
The neck connects the head to the middle piece and acts as a flexible junction enabling movement.
The middle piece contains numerous mitochondria that generate ATP through cellular respiration, providing energy for sperm motility.
The tail (flagellum) uses the ATP produced by mitochondria for its whip-like movement, propelling the sperm towards the ovum; a plasma membrane envelops the entire sperm body.

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Long Answer

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Hard

Question 7

Long Form

Explain the process of oogenesis from the formation of oogonia in the fetal ovary to the release of the secondary oocyte at ovulation.

During embryonic development, a few million oogonia (diploid gamete mother cells) are formed in the fetal ovary; no additional oogonia are added after birth.
Oogonia enter prophase I of meiosis and are temporarily arrested as primary oocytes; each is surrounded by granulosa cells forming a primary follicle.
Many primary follicles degenerate between birth and puberty; at puberty, approximately 60,000–80,000 remain per ovary.
Under FSH stimulation, primary follicles develop into secondary follicles (additional granulosa layers + theca) and then tertiary follicles (fluid-filled antrum); the primary oocyte resumes and completes meiosis I, forming a large secondary oocyte and a first polar body.
The tertiary follicle matures into the Graafian follicle; the LH surge induces its rupture (ovulation), releasing the secondary oocyte surrounded by zona pellucida; meiosis II is completed only upon fertilisation.

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Long Answer

Medium difficulty • Structured explanation

Medium

Question 8

Long Form

Describe the structure of the female reproductive system, emphasising the structural adaptations of each organ to its reproductive function.

The paired ovaries (2–4 cm long) are connected by ligaments and produce ova and ovarian hormones; they contain follicles at various stages embedded in the stroma.
Each fallopian tube (10–12 cm) has a fimbriated infundibulum for collecting the released ovum, an ampulla where fertilisation occurs and an isthmus that joins the uterus.
The uterus (inverted pear-shaped) has a thick myometrium for forceful contractions during delivery and an endometrium that undergoes cyclical changes and supports implantation; the cervix forms the birth canal with the vagina.
The external genitalia (mons pubis, labia majora, labia minora, clitoris) protect the internal structures and play roles in sexual response.
Mammary glands with 15–20 lobes of alveoli produce milk stored in alveolar lumens, which flows through tubules, ducts, mammary ampulla and lactiferous ducts to the nipple for feeding the newborn.

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Long Answer

Medium difficulty • Structured explanation

Medium

Question 9

Long Form

Analyse the developmental milestones of the human embryo and foetus during the nine months of pregnancy.

After implantation, the inner cell mass differentiates into three germ layers (ectoderm, mesoderm, endoderm) that give rise to all tissues and organs; stem cells in the inner cell mass have full developmental potency.
By the end of the first month, the heart is formed and its beat can be detected; by the end of the second month, limbs and digits are visible.
By the end of 12 weeks (first trimester), most major organ systems including external genitalia are well-developed and the sex of the foetus can be determined.
During the fifth month, the first foetal movements are felt and hair appears on the head; these milestones indicate normal neurological and musculoskeletal development.
By the end of the second trimester (24 weeks), the body is covered with fine hair, eyelids separate and eyelashes form; by nine months the foetus is fully developed and ready for delivery.

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Long Answer

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Hard

Question 10

Long Form

Explain parturition and lactation, detailing the hormonal and physiological mechanisms involved in each process.

Parturition is triggered by signals from the fully developed foetus and placenta, initiating the foetal ejection reflex — mild uterine contractions that mark the onset of labour.
The foetal ejection reflex stimulates oxytocin release from the maternal pituitary; oxytocin induces stronger uterine (myometrial) contractions in a positive feedback loop until the foetus is expelled through the birth canal.
After the baby is delivered, the placenta is also expelled; cortisol, estrogens and oxytocin are identified as the key hormones involved in induction of parturition.
Lactation begins towards the end of pregnancy as mammary glands differentiate and start producing milk; milk flows through alveoli, mammary tubules, ducts, and lactiferous ducts to the nipple.
The first milk (colostrum) is rich in antibodies providing passive immunity to the newborn; breast-feeding is recommended for the initial months to ensure healthy infant development.

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Chapter 2: Human Reproduction | Long Questions

Compare and contrast spermatogenesis and oogenesis with respect to location, initiation, meiotic divisions and the number of functional gametes produced.

Analyse the hormonal regulation of the menstrual cycle, tracing the events from the follicular phase through the luteal phase.

Describe the structure of the male reproductive system, tracing the path of sperm from formation in the testis to ejaculation.

Trace the events from fertilisation to implantation, explaining the structural changes in the embryo at each stage.

Describe the structure and functions of the placenta, and explain why it is considered both a nutritive and an endocrine organ.

Describe the structure of a mature spermatozoan and relate each structural component to its specific function.

Explain the process of oogenesis from the formation of oogonia in the fetal ovary to the release of the secondary oocyte at ovulation.

Describe the structure of the female reproductive system, emphasising the structural adaptations of each organ to its reproductive function.

Analyse the developmental milestones of the human embryo and foetus during the nine months of pregnancy.

Explain parturition and lactation, detailing the hormonal and physiological mechanisms involved in each process.

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