CBSE Class 12 Biology Chapter 3: Human Reproduction NCERT Solutions

Solution: (a) Humans reproduce sexually. This means that new individuals are produced through the combination of genetic material from two parents. (b) Humans are viviparous. Viviparous organisms give birth to live young, with development occurring inside the mother's body. (c) Fertilization is internal in humans. Internal fertilization occurs within the female's body. (d) Male and female gametes are haploid. Gametes (sperm and ovum) contain half the number of chromosomes (n) compared to somatic cells. (e) Zygote is diploid. The fusion of a haploid sperm and a haploid ovum results in a diploid zygote (2n). (f) The process of release of the ovum from a mature follicle is called ovulation. This is a key event in the menstrual cycle. (g) Ovulation is induced by a hormone called the luteinizing hormone (LH). A surge in LH levels triggers ovulation. (h) The fusion of the male and the female gametes is called fertilization. This process restores the diploid number of chromosomes. (i) Fertilization takes place in the fallopian tube (also known as the oviduct). This is where the sperm typically meets the ovum. (j) The zygote divides to form blastocyst, which is implanted in the uterus. The blastocyst is an early stage of embryonic development. (k) The structure which provides vascular connection between the fetus and uterus is called placenta. The placenta facilitates nutrient supply and waste removal for the developing fetus.

Solution: The male reproductive system is responsible for producing male gametes (sperm) and delivering them into the female reproductive tract. A labeled diagram would typically include the following key structures:

Key Structures to Label:

• Testis: The primary male reproductive organ, responsible for spermatogenesis and testosterone production.
• Scrotum: The sac that holds the testes outside the body, maintaining an optimal temperature for sperm production.
• Epididymis: A coiled tube located on the back of the testis where sperm mature and are stored.
• Vas deferens (Ductus deferens): A tube that carries sperm from the epididymis to the ejaculatory duct.
• Seminal vesicles: Glands that produce a fluid rich in fructose, which nourishes sperm and contributes to semen volume.
• Prostate gland: Secretes a milky fluid that helps activate sperm.
• Bulbourethral glands (Cowper's glands): Produce a pre-ejaculate fluid that lubricates the urethra and neutralizes any acidic urine residue.
• Urethra: The tube that carries urine from the bladder and semen from the ejaculatory ducts out of the body through the penis.
• Penis: The external male reproductive organ responsible for delivering sperm into the female reproductive tract during intercourse.
• Urinary bladder: Stores urine.
• Ureter: Tube carrying urine from the kidney to the bladder.

(Note: A visual diagram is required for a complete answer. The text above lists the components that should be labeled.)

Solution: The female reproductive system is responsible for producing female gametes (ova), receiving sperm, facilitating fertilization, and supporting the development of a fetus. A labeled diagram should include:

Key Structures to Label:

• Ovary: The primary female reproductive organ, producing ova and female hormones (estrogen and progesterone).
• Fallopian tube (Oviduct): Tubes that extend from the uterus towards the ovaries, serving as the site of fertilization and transporting the ovum to the uterus.
• Fimbriae: Finger-like projections at the end of the fallopian tube near the ovary that help sweep the ovum into the tube after ovulation.
• Uterus: A muscular organ where the fertilized egg implants and the fetus develops. Its wall has three layers:
• Endometrium: The inner lining, which thickens cyclically and is where implantation occurs.
• Myometrium: The thick middle layer of smooth muscle, responsible for contractions during labor.
• Perimetrium: The outer serous layer.
• Cervix: The lower, narrow part of the uterus that opens into the vagina.
• Cervical canal: The passage through the cervix.
• Vagina: A muscular tube connecting the cervix to the outside of the body; it receives the penis during intercourse and serves as the birth canal.
• Uterine fundus: The upper, rounded part of the uterus.
• Uterine cavity: The space within the uterus.

(Note: A visual diagram is required for a complete answer. The text above lists the components that should be labeled.)

Solution: Functions of the Testis: 1. Production of Male Gametes: The testes produce male gametes, called spermatozoa or sperm, through a process known as spermatogenesis. This is essential for sexual reproduction. 2. Secretion of Male Sex Hormones: The Leydig cells, located in the seminiferous tubules of the testes, secrete the primary male sex hormone, testosterone. Testosterone is crucial for the development and maintenance of male secondary sexual characteristics (e.g., deep voice, facial hair, muscle mass) and plays a role in spermatogenesis. Functions of the Ovary: 1. Production of Female Gametes: The ovaries produce female gametes, called ova or eggs, through a process called oogenesis. One ovum is typically released each menstrual cycle. 2. Secretion of Female Sex Hormones: The ovaries secrete the primary female sex hormones, estrogen and progesterone. Estrogen is responsible for the development of female secondary sexual characteristics and plays a role in the menstrual cycle. Progesterone is essential for preparing the uterus for pregnancy and maintaining it during gestation.