Revision: Reproduction >> Human Reproduction Biology (Theory) ISC (Science) ISC Class 12 CISCE

Puberty is the process of physical and hormonal changes by which a child’s body matures into an adult body capable of sexual reproduction to enable fertilization.

Reproduction is a process that results in the formation of new individuals of the same kind, though usually with slight genetic, structural and physiological variations.

The two sexes, male and female, often show outwardly differentiating features called secondary sexual characters.

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The characters by wnich we can differentiate between male and female sexes externally are called secondary sexual characters.

The sex organs that do not produce gametes but assist in reproduction by supporting, transporting, or nourishing gametes are called secondary sex organs.

The sex organs which produce gametes and sex hormones are called primary sex organs.

The process of expulsion of semen from the urethra is called ejaculation.

The secretion of glands with spermatozoa is a whitish viscous fluid known as seminal fluid or semen.

Spermatogenesis is the process of formation and development of sperm cells (spermatozoa) in the testes from spermatogonial stem cells through mitosis and meiosis.

Hernia is an abnormal condition that is caused when the intestine, due to the pressure in the abdomen, bulges into the scrotum through the inguinal canal.

A pair of oval male reproductive glands that produce sperms and secrete testosterone is called testes.

The condition in which one or both testes fail to descend into the scrotum is called cryptorchidism.

The fibrous cord extending from the caudal end of the testis to the scrotal wall that helps in testicular descent is called gubernaculum.

The fold of peritoneum that supports and attaches the testis is called mesorchium.

The two testes (popularly called testicles) are oval organs which are contained in a thin-walled sac of skin called scrotum (or scrotal sacs).

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The testes of a male remain suspended in a pouch, called scrotum.

Seminiferous tubules (semini: sperm, ferous: bearing) where the sperms are produced. The process is called spermatogenesis.

The opening of the vagina in young females is partially closed by a thin membrane called the hymen (or virgin knot).

The external female genitalia is called the vulva.

A maturing egg contained in a cellular sac is called the follicle.

When the follicle enlarges and fills with fluid as the egg grows, it is called a Graafian follicle.

The remnant of the follicle persists for sometime to convert . into a yellow mass called corpus luteum (corpus: body, luteum: yellow).

The white fibrous tissue formed by degeneration of the corpus luteum when fertilization does not occur is called the corpus albicans.

The series of changes in the ovary involving follicle development, ovulation, and formation and degeneration of the corpus luteum is called the ovarian cycle.

The process by which a mature Graafian follicle ruptures and releases the secondary oocyte from the ovary into the fallopian tube is called ovulation.

A structure in the ovary consisting of an ovum surrounded by layers of granulosa cells that supports the growth and maturation of the ovum is called an ovarian follicle.

The funnel-shaped opening of the oviduct that picks up the released egg with the help of cilia is called the oviducal funnel.

The lower part of the uterus is very narrow and is called cervix.

The thin membrane partially covering the vaginal opening in young females is called the hymen.

The glandular tissue is divided into 15–20 mammary lobes that radiate outward from the nipple and contain clusters of milk-producing glands, called alveoli.

A projection overlies the central part of the areola that is known as nipple.

The skin over the centre of the elevation has a darkly pigmented circular area called areola.

Spermiogenesis is the process of transforming spermatids into mature, flagellated spermatozoa (sperms).

The process of transformation of a circular spermatid to a spermatozoon is called spermiogenesis.

Gametogenesis is the process by which male and female gametes are formed from germinal cells in the gonads through a series of developmental stages.

Spermiation is the process of releasing mature spermatozoa. In this, spermatozoa are shed into the lumen of the seminiferous tubule for transport.

After spermiogenesis, sperm heads become embeded in sertoli cells from which they obtain their nutrition and finally get released into the lumen of seminiferous tubules. This process of release of mature sperms from sertoli cells is called spermiation.

Gametogenesis is the process of formation of gametes i.e., sperms and ovary from the primary sex organs in all sexually reproducing organisms. Meiosis plays the most significant role in the process of gametogenesis.

Formation of haploid sperms (male gametes) from diploid spermatogonia (sperm mother cells) is called spermatogenesis.

The process of release of mature sperms from Sertoli cells into the lumen of seminiferous tubules is called spermiation.

The formation of ova in the ovary from primordial germinal cells is said to be oogenesis.

Adolescence is the time period between the beginning of puberty and adulthood. During this period, the body undergoes several changes alongside reproductive maturity. It begins around the age of 11 and lasts till 18 or 19 years of age. The period of adolescence may vary from person to person.

Puberty is the period during which immature reproductive system of boys and girls matures and becomes capable of reproducing.

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The period during adolescence when the reproductive tissues mature and the body undergoes changes to attain sexual maturity is called puberty.

The release of the ovum from the ovary is called ovulation.

It is the stage when a girl menstruates for the first time.

The rhythmic series of changes in the sex organs throughout the reproductive life of a female primate (e.g., monkeys, apes, and human beings) from puberty to menopause is called the menstrual cycle (L. mensis = month, lunar month).

Menarche is the onset of menstruation in a young female at about the age of 13 years (arche: beginning).

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The appearance of the first menstrual flow in the life of a girl is called menarche.

Menopause is the permanent stoppage of menstruation in females at about the age of 45 years (pause: stop).

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The permanent disappearance of menstrual cycles in the life of a woman is called menopause.

A solid, mulberry-like ball of cells formed after cleavage is called morula.

The process of formation of blastula from morula is called blastulation.

A hollow embryonic stage formed after morula; in humans it is called blastocyst.

An extra-embryonic sac involved in waste storage and placental development is called allantois.

A series of rapid mitotic divisions of the zygote without increase in size is called cleavage.

Cleavage is the process of early mitotic division of the zygote to generate a multicellular morula stage.

A study of the development of an organism from fertilization to the formation of young one is known as embryogeny.

Union of a male gamete with the egg cell to form a zygote is called fertilization.

The formation of a zygote by the union of male and female gametes is known as fertilization.

The fusion of the male gamete (sperm) and female gamete (ovum) to form a zygote is called fertilisation.

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Formation of zygote by union of sperm and ovum is called as fertilization.

A disc-like structure attached to the uterine wall that supplies food and oxygen to the foetus and removes waste is called placenta.

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The intimate connection established between the foetal membrane and the uterine wall is known as placenta.

After nine months of pregnancy, the fully developed foetus is ready for delivery. The process of childbirth is called parturition.

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Parturition is the act of expelling the full term foetus from the mother's uterus at the end of gestation.

The term lactation refers to the secretion and ejection of milk by the mammary glands.

1. Human reproductive organs are divided into primary (gonads) and accessory parts.
2. Primary gonads: Testes in males produce sperms; ovaries in females produce eggs.
3. Accessory organs include ducts and glands that aid in fertilisation and embryo development.
4. Secondary sexual characters (e.g., beard, breasts) are not reproductive parts, as they do not directly participate in reproduction.

• The male reproductive system is located in the pelvic region and consists of testes, ducts, glands, and external genitalia.
• A pair of testes present in the scrotum produce sperms in seminiferous tubules and secrete the hormone testosterone.
• Accessory ducts—rete testis, vasa efferentia, epididymis, vas deferens, and ejaculatory duct—transport and mature sperms.
• Accessory glands (seminal vesicles, prostate gland, and bulbourethral glands) add secretions that nourish sperms and aid their movement.
• The penis, containing the urethra, acts as the external genital organ for the delivery of sperms during ejaculation.

• Each testis is enclosed by three protective layers—tunica vaginalis, tunica albuginea, and tunica vasculosa.
• Internally, each testis is divided into about 250 testicular lobules.
• Each lobule contains highly coiled seminiferous tubules, which are the site of spermatogenesis.
• The wall of seminiferous tubules is lined by germinal epithelium consisting of spermatogonia, Sertoli cells, and interstitial cells.
• Spermatogonia are diploid male germ cells that undergo meiosis to form haploid sperms.
• Sertoli cells act as nurse cells, providing nourishment and support to developing sperms, while Leydig cells secrete testosterone.
• Sperms move from seminiferous tubules into efferent ducts, then to the epididymis for maturation and temporary storage before entering the vas deferens.

1. The female reproductive system includes a pair of ovaries, oviducts (fallopian tubes), a uterus, a vagina, and Bartholin’s glands.
2. All reproductive organs are located inside the abdominal cavity.
3. Ovaries release one ovum (egg) monthly after puberty, alternating between each ovary.
4. The egg enters the oviduct through its funnel-shaped end and is pushed towards the uterus by cilia.
5. Fertilisation usually occurs in the oviduct; the zygote implants in the uterus lining if formed.
6. The placenta connects the embryo to the mother for nutrient and waste exchange until birth.

• Ovaries are the primary female sex organs that produce ova and secrete the hormones estrogen and progesterone.
• They are almond-shaped, solid structures located in the lower abdominal cavity and attached by the mesovarium.
• Each ovary is covered by germinal epithelium and internally divided into cortex and medulla.
• The cortex contains ovarian follicles with immature oocytes, supported by granulosa cells.

• Mammary glands are paired structures in female mammals that develop fully after puberty and consist of lobes, alveoli, ducts, nipple and areola.
• The glandular tissue contains alveoli that produce milk, which is transported through ducts and released via the nipple.
• Milk secretion is stimulated by prolactin, while milk ejection (let-down reflex) is controlled by oxytocin after childbirth.
• The first milk secreted, called colostrum, is rich in antibodies and nutrients; after lactation or menopause, the glands undergo atrophy.

• The menstrual cycle is regulated mainly by five hormones: GnRH, FSH, LH, estrogen, and progesterone, acting in a coordinated manner.
• GnRH released from the hypothalamus stimulates the anterior pituitary to secrete FSH and LH.
• FSH promotes growth of ovarian follicles and estrogen secretion, while estrogen repairs and thickens the uterine endometrium.
• A mid-cycle surge of LH induces ovulation and converts the ruptured follicle into the corpus luteum, which secretes progesterone.
• Progesterone maintains the endometrium for implantation; if fertilization does not occur, hormone levels fall, leading to menstruation and initiation of a new cycle.

1. Fertilisation is the union of sperm and ovum to form a zygote and is internal in humans.
2. During copulation, millions of sperms are ejaculated into the vagina, but only one sperm fertilises the ovum in the oviduct.
3. The acrosome of the sperm releases enzymes that help it penetrate the egg membrane; chemical changes then prevent entry of other sperms.
4. Fusion of sperm nucleus and egg nucleus restores the diploid chromosome number (46) in the zygote.
5. From puberty to menopause (45–50 years), only about 400 ova are released; ageing oocytes may lead to chromosomal abnormalities if fertilised.
6. Gametes are formed by meiosis: sperms are of two types (22+X or 22+Y), while ova are of one type (22+X); meiosis in ova completes during fertilisation.