NCERT Solutions

1. Humans reproduce sexually.
2. Humans are viviparous.
3. Fertilisation is internal in humans.
4. Male and female gametes are haploid.
5. Zygote is diploid.
6. The process of release of ovum from a mature follicle is called ovulation.
7. Ovulation is induced by a hormone called Luteinizing Hormone (LH).
8. The fusion of male and female gametes is called fertilization.
9. Fertilization takes place in ampullary-isthmic junction (ampulla) of the oviduct.
10. Zygote divides to form blastocyst which is implanted in uterus.
11. The structure which provides vascular connection between foetus and uterus is called placenta.

• Testis: Primary sex organ.
• Scrotum: Pouch containing testes.
• Epididymis: Stores sperm.
• Vas Deferens: Transports sperm.
• Seminal Vesicle, Prostate, Bulbourethral glands: Accessory glands.
• Urethra: Common passage for urine and semen.
• Penis: External genitalia.

• Ovaries: Primary sex organs.
• Fallopian Tubes (Oviducts): Infundibulum, Ampulla, Isthmus.
• Uterus: Fundus, Body, Cervix.
• Uterine Wall: Perimetrium, Myometrium, Endometrium.
• Vagina: Birth canal.

1. Spermatogenesis: Production of male gametes (sperms) in seminiferous tubules.
2. Hormone Secretion: Leydig cells secrete androgens (Testosterone) which regulate male secondary sexual characters.

1. Oogenesis: Production of female gametes (ova/eggs).
2. Hormone Secretion: Secretion of Estrogen and Progesterone which regulate menstrual cycle and female secondary sexual characters.

Each testis contains about 250 testicular lobules, and each lobule contains 1-3 highly coiled seminiferous tubules.

• Lining: Lined by two types of cells – Male Germ Cells (Spermatogonia) and Sertoli Cells.
• Male Germ Cells: Undergo meiotic divisions to form sperms.
• Sertoli Cells: Provide nutrition to the germ cells.
• Interstitial Space: The region outside the tubules containing small blood vessels and Leydig cells (Interstitial cells). Leydig cells synthesize and secrete testicular hormones (Androgens).

Spermatogenesis is the process of formation of haploid sperms (spermatozoa) from diploid spermatogonia in the male testis. It begins at puberty.

1. Multiplication Phase: Spermatogonia (2n) multiply by mitosis to increase in number.
2. Growth Phase: Some spermatogonia grow to form Primary Spermatocytes (2n).
3. Maturation Phase (Meiosis):
   • Primary Spermatocyte (2n) undergoes Meiosis I to form two equal haploid Secondary Spermatocytes (n).
   • Secondary Spermatocytes undergo Meiosis II to form four equal haploid Spermatids (n).
4. Spermiogenesis: The transformation of non-motile spermatids into motile spermatozoa (sperms).

1. GnRH (Gonadotropin Releasing Hormone): From Hypothalamus. Stimulates anterior pituitary.
2. LH (Luteinizing Hormone): Acts on Leydig cells to stimulate synthesis and secretion of Androgens.
3. Androgens (Testosterone): Stimulate the process of spermatogenesis.
4. FSH (Follicle Stimulating Hormone): Acts on Sertoli cells to stimulate secretion of factors helping in spermiogenesis.

• Spermiogenesis: The process of transformation of spermatids into spermatozoa (sperms).
• Spermiation: The release of sperms from the seminiferous tubules after their heads become embedded in the Sertoli cells.

• Head: Contains haploid nucleus and Acrosome (filled with enzymes for fertilization).
• Neck: Connects head to middle piece.
• Middle Piece: Contains numerous Mitochondria (powerhouse) for energy for motility.
• Tail: Facilitates sperm motility essential for fertilization.

Seminal plasma is the fluid secreted by the accessory glands (Seminal vesicles, Prostate gland, Bulbourethral glands).

Components: It is rich in Fructose, Calcium, and certain Enzymes. It provides a medium for sperm transport and nutrition.

• Accessory Ducts (Rete testis, Vasa efferentia, Epididymis, Vas deferens): Store and transport sperms from the testis to the outside through urethra.
• Accessory Glands (Seminal vesicles, Prostate, Bulbourethral): Secrete seminal plasma which helps in lubrication (Bulbourethral) and provides nutrition and motility medium for sperms.

Oogenesis is the formation of a mature female gamete (ovum). Unlike spermatogenesis, it begins during embryonic development.

1. Fetal Life: Oogonia (2n) divide to form Primary Oocytes (2n). They enter Prophase-I of meiosis and get arrested.
2. Puberty: Primary Oocyte (surrounded by granulosa cells – Primary Follicle) completes Meiosis I (unequal division) to form a large Secondary Oocyte (n) and a tiny First Polar Body.
3. Ovulation: The Secondary Oocyte is released from the Graafian follicle.
4. Fertilization: Only upon entry of sperm, Meiosis II is completed, forming the Ovum (n) and a Second Polar Body.

• Primary Follicle
• Secondary Follicle
• Tertiary Follicle (with Antrum)
• Graafian Follicle (Mature)
• Ovum (released)
• Corpus Luteum

• Antrum: Fluid-filled cavity.
• Secondary Oocyte: The gamete.
• Zona Pellucida: Membrane surrounding the oocyte.
• Theca layers: Theca interna and Theca externa.
• Cumulus oophorus: Granulosa cells supporting the oocyte.

• (a) Corpus luteum: Secretes large amounts of Progesterone which is essential for maintenance of the endometrium (pregnancy).
• (b) Endometrium: Inner lining of uterus. Undergoes cyclical changes during menstrual cycle and is the site of implantation of the blastocyst.
• (c) Acrosome: Cap-like structure on sperm head containing enzymes (hyaluronidase) that help fertilization by penetrating the ovum.
• (d) Sperm tail: Provides motility to the sperm to swim towards the ovum for fertilization.
• (e) Fimbriae: Finger-like projections at the infundibulum of oviduct. Help in collection of the ovum after ovulation.

1. (a) Androgens are produced by Sertoli cells. -> False. (Produced by Leydig cells).
2. (b) Spermatozoa get nutrition from Sertoli cells. -> True.
3. (c) Leydig cells are found in ovary. -> False. (Found in Testis).
4. (d) Leydig cells synthesize androgens. -> True.
5. (e) Oogenesis takes place in corpus luteum. -> False. (Takes place in Graafian follicle/Ovary).
6. (f) Menstrual cycle ceases during pregnancy. -> True.
7. (g) Presence or absence of hymen is not a reliable indicator of virginity. -> True.

Menstrual Cycle: The reproductive cycle in the female primates (e.g., monkeys, apes, humans) is called menstrual cycle. It repeats on average every 28/29 days.

• Pituitary Hormones:
  • FSH: Stimulates follicular development.
  • LH: Surge causes ovulation (Day 14).
• Ovarian Hormones:
  • Estrogen: Secreted by growing follicles; repairs endometrium.
  • Progesterone: Secreted by Corpus Luteum; maintains endometrium.

Parturition: The process of delivery of the foetus (childbirth) at the end of pregnancy due to vigorous contraction of the uterus.

• Oxytocin: Released from maternal pituitary. Acts on uterine muscle to cause strong contractions.
• Relaxin: Relaxes pelvic ligaments.
• Cortisol & Estrogen: Involved in the fetal ejection reflex.

This is scientifically incorrect because the sex of the baby is determined by the father (sperm), not the mother (ovum).

• A female produces only one type of gamete (Ovum) with X chromosome (Homogametic).
• A male produces two types of gametes (Sperms): 50% carry X and 50% carry Y (Heterogametic).

If an X-sperm fertilizes the egg (X+X), it is a girl. If a Y-sperm fertilizes the egg (X+Y), it is a boy. Thus, it is a matter of chance dependent on the male parent.

• Usually, one egg is released by one of the ovaries in a month.
• For Identical Twins (Monozygotic): Only one egg was released. It was fertilized by one sperm to form a single zygote, which later split into two separate embryos.
• For Fraternal Twins (Dizygotic): Two eggs would have been released and fertilized by two separate sperms.

Dogs are polyovulatory animals. If a female dog gave birth to 6 puppies, her ovaries must have released at least 6 eggs (ova), each of which was fertilized by a separate sperm to form 6 zygotes.