CBSE Class 12 Biology (2026–27)
Chapter 2: Human Reproduction
20 Important Questions and Answers
Human reproduction involves the male and female reproductive systems, gametogenesis, menstrual cycle, fertilization, pregnancy, parturition, and lactation. These topics form the core of the CBSE syllabus.
1. Describe the structure and functions of the human testis.
Answer:
The testes are the primary male reproductive organs located in the scrotum outside the abdominal cavity. Each testis contains numerous seminiferous tubules where spermatogenesis occurs. Sertoli cells inside the tubules provide nourishment to developing sperms, while Leydig cells present between the tubules secrete testosterone. The scrotum maintains a temperature about 2–2.5°C below body temperature, which is essential for sperm production. The testes perform two major functions: production of male gametes (sperms) and secretion of male sex hormones (androgens). Testosterone regulates spermatogenesis and the development of secondary sexual characters such as facial hair, deep voice, and muscular growth.
2. Explain the functions of accessory glands in the male reproductive system.
Answer:
The male accessory glands include the seminal vesicles, prostate gland, and bulbourethral glands. These glands secrete fluids that combine with sperms to form semen. Seminal vesicles produce a fructose-rich secretion that provides energy to sperms. The prostate gland secretes an alkaline fluid that neutralizes acidity in the female reproductive tract and enhances sperm motility. Bulbourethral glands release mucus that lubricates the urethra and penis during copulation. Together, these secretions nourish, protect, and transport sperms efficiently. The alkaline nature of semen also increases sperm survival. Thus, accessory glands play an essential role in successful fertilization.
3. Describe the structure of a human sperm.
Answer:
A human sperm is a microscopic, motile male gamete consisting of four parts: head, neck, middle piece, and tail. The head contains a haploid nucleus carrying genetic material and is covered by an acrosome containing enzymes necessary for fertilization. The neck connects the head with the middle piece. The middle piece contains numerous mitochondria that generate ATP required for sperm movement. The long tail helps in locomotion through the female reproductive tract. A mature sperm carries 23 chromosomes and is specialized for reaching and fertilizing the ovum. Its streamlined structure ensures efficient movement and successful fertilization.
4. Write a note on the female reproductive system.
Answer:
The female reproductive system consists of a pair of ovaries, oviducts (fallopian tubes), uterus, cervix, vagina, and external genitalia. Ovaries produce ova and female sex hormones. The oviduct receives the ovum after ovulation and serves as the site of fertilization. The uterus is a muscular organ where implantation and fetal development occur. The cervix connects the uterus to the vagina, which acts as the birth canal. The female reproductive system is adapted for ovulation, fertilization, implantation, pregnancy, and childbirth. It also regulates the menstrual cycle through hormonal coordination involving estrogen and progesterone.
5. What are Graafian follicle and corpus luteum?
Answer:
A Graafian follicle is a mature ovarian follicle containing a fully developed secondary oocyte. During ovulation, the Graafian follicle ruptures and releases the ovum. After ovulation, the remaining follicular tissue transforms into a temporary endocrine structure called the corpus luteum. The corpus luteum secretes progesterone and a small amount of estrogen. Progesterone prepares the uterine endometrium for implantation and supports early pregnancy. If fertilization does not occur, the corpus luteum degenerates, causing progesterone levels to fall and menstruation to begin. Thus, both structures are essential for reproductive success in females.
6. Explain spermatogenesis.
Answer:
Spermatogenesis is the process of sperm formation in the seminiferous tubules of testes. It begins at puberty under hormonal control. Diploid spermatogonia divide mitotically to form primary spermatocytes. Each primary spermatocyte undergoes meiosis I to produce two haploid secondary spermatocytes. These undergo meiosis II to form four spermatids. Spermatids then differentiate into mature spermatozoa through spermiogenesis. Sertoli cells provide nourishment during development, while testosterone stimulates the process. Spermatogenesis is a continuous process throughout reproductive life and ensures the production of millions of sperms daily for successful fertilization.
7. Explain oogenesis.
Answer:
Oogenesis is the process of ovum formation in the ovaries. It begins during fetal life when oogonia multiply and form primary oocytes. These remain arrested until puberty. During each menstrual cycle, a primary oocyte completes meiosis I to form a secondary oocyte and a polar body. The secondary oocyte is released during ovulation and completes meiosis II only after fertilization. Oogenesis results in the formation of one functional ovum and polar bodies. Unlike spermatogenesis, oogenesis is discontinuous and produces only one mature gamete from each primary oocyte. It ensures the availability of a female gamete for reproduction.
8. Differentiate between spermatogenesis and oogenesis.
Answer:
Spermatogenesis occurs in the testes and produces male gametes, while oogenesis occurs in the ovaries and produces female gametes. Spermatogenesis begins at puberty and continues throughout life, whereas oogenesis starts before birth and proceeds cyclically after puberty. One primary spermatocyte forms four functional sperms, but one primary oocyte produces only one ovum and polar bodies. Spermatogenesis is continuous, while oogenesis is discontinuous with long resting phases. Sperms are small and motile, whereas ova are large and non-motile. These differences reflect the specialized roles of male and female gametes in reproduction.
9. Explain the menstrual cycle.
Answer:
The menstrual cycle is a monthly series of changes in the female reproductive system lasting about 28 days. It consists of menstrual, follicular, ovulatory, and luteal phases. During menstruation, the endometrium is shed. In the follicular phase, ovarian follicles develop under FSH stimulation. Ovulation occurs around the 14th day due to an LH surge. During the luteal phase, the corpus luteum secretes progesterone, preparing the uterus for implantation. If fertilization does not occur, hormone levels decline, causing breakdown of the endometrium and initiation of a new cycle. The menstrual cycle prepares the female body for pregnancy.
10. What is ovulation? How is it regulated?
Answer:
Ovulation is the release of a mature secondary oocyte from the Graafian follicle of the ovary. It generally occurs around the 14th day of a 28-day menstrual cycle. Ovulation is regulated by hormones secreted from the pituitary gland and ovaries. Rising estrogen levels stimulate the anterior pituitary to release a surge of luteinizing hormone (LH). This LH surge causes rupture of the mature follicle and release of the ovum. Follicle-stimulating hormone (FSH) also supports follicular development. Ovulation is a crucial event because fertilization can occur only after the ovum is released into the oviduct.
11. Define fertilization and mention its site in humans.
Answer:
Fertilization is the fusion of a haploid sperm and a haploid ovum to form a diploid zygote. In humans, fertilization usually occurs at the ampullary-isthmic junction of the fallopian tube. During fertilization, the sperm penetrates the ovum with the help of acrosomal enzymes. The fusion of nuclei restores the diploid chromosome number. Changes occur in the zona pellucida to prevent entry of additional sperms. Fertilization combines genetic material from both parents and initiates embryonic development. It is a vital step in sexual reproduction because it leads to the formation of a new individual.
12. What is implantation?
Answer:
Implantation is the attachment and embedding of the blastocyst into the endometrium of the uterus. After fertilization, the zygote undergoes repeated mitotic divisions called cleavage and forms a blastocyst. Around 6–7 days after fertilization, the blastocyst reaches the uterus and attaches to the thickened endometrial lining. Cells of the blastocyst invade the uterine tissue and establish a connection with maternal blood vessels. Successful implantation marks the beginning of pregnancy. It ensures nourishment and support for the developing embryo and initiates further developmental processes leading to fetal growth.
13. What is placenta? State its functions.
Answer:
The placenta is a temporary vascular organ formed between the developing fetus and the uterine wall. It facilitates exchange of materials between maternal and fetal blood. Oxygen and nutrients pass from the mother to the fetus, while carbon dioxide and metabolic wastes move from the fetus to the mother. The placenta also acts as an endocrine gland by secreting hormones such as hCG, hPL, estrogen, progesterone, and relaxin. These hormones help maintain pregnancy and support fetal growth. Thus, the placenta performs nutritive, respiratory, excretory, and endocrine functions essential for successful pregnancy.
14. Explain pregnancy and embryonic development.
Answer:
Pregnancy begins after implantation and lasts approximately 280 days. During this period, the embryo undergoes rapid growth and differentiation. Major organs develop during embryogenesis, while later stages involve fetal growth and maturation. The placenta provides nutrition, oxygen, and hormonal support. The embryo develops into a fetus with recognizable body structures and functional organ systems. Hormones such as progesterone and estrogen maintain the uterine environment required for fetal development. Proper embryonic development ensures normal growth of the fetus until birth. Pregnancy culminates in parturition, resulting in the delivery of a fully developed baby.
15. What is parturition? Mention the role of oxytocin.
Answer:
Parturition is the process of childbirth or delivery of the baby at the end of gestation. It is initiated by a complex neuroendocrine mechanism involving the fetus and mother. Signals from the fully developed fetus induce mild uterine contractions known as the fetal ejection reflex. This stimulates the release of oxytocin from the mother’s pituitary gland. Oxytocin causes stronger and more frequent contractions of the uterine muscles. These contractions help expel the fetus through the birth canal. Positive feedback between contractions and oxytocin release continues until delivery is completed. Thus, oxytocin plays a crucial role in childbirth.
16. What is lactation? Why is colostrum important?
Answer:
Lactation is the production and secretion of milk by mammary glands after childbirth. It is stimulated mainly by the hormone prolactin. During the initial days after delivery, the mammary glands secrete a yellowish fluid called colostrum. Colostrum is rich in proteins, vitamins, minerals, and maternal antibodies, particularly immunoglobulins. These antibodies provide passive immunity to the newborn and protect it against infections during early life. Colostrum is easily digestible and supplies essential nutrients required for growth. Therefore, breastfeeding immediately after birth is highly beneficial for the health and development of the infant.
17. Explain the role of Sertoli cells and Leydig cells.
Answer:
Sertoli cells and Leydig cells are important components of the testes. Sertoli cells are located within the seminiferous tubules and provide nourishment, support, and protection to developing sperm cells. They also help regulate spermatogenesis. Leydig cells are found in the interstitial spaces between seminiferous tubules. These cells secrete testosterone, the primary male sex hormone. Testosterone stimulates sperm production and controls secondary sexual characteristics. Both cell types work together to ensure normal reproductive function. Sertoli cells support gamete development, while Leydig cells maintain the hormonal environment necessary for male fertility.
18. Why is the scrotum located outside the abdominal cavity?
Answer:
The scrotum is a pouch-like structure that houses the testes outside the abdominal cavity. This location is essential because spermatogenesis requires a temperature slightly lower than normal body temperature. The scrotal temperature remains approximately 2–2.5°C below the body’s internal temperature. Such conditions are ideal for the production and maturation of sperms. If the testes remain at body temperature, sperm production may be adversely affected. The scrotum also helps regulate temperature by contracting or relaxing according to environmental conditions. Therefore, its external position is a crucial adaptation for male fertility.
19. What changes occur after fertilization?
Answer:
After fertilization, the sperm and ovum nuclei fuse to form a diploid zygote. The zygote undergoes repeated mitotic divisions called cleavage, producing a multicellular structure known as the blastocyst. The blastocyst moves towards the uterus and implants into the endometrium. Following implantation, embryonic tissues and extra-embryonic membranes develop. Placenta formation begins, establishing a connection between maternal and fetal blood circulation. Hormonal changes support pregnancy and prevent menstruation. These events collectively initiate embryonic development and ensure proper growth of the fetus throughout gestation.
20. What are the major events of human reproduction?
Answer:
Human reproduction involves a sequence of coordinated events. It begins with gametogenesis, the formation of male and female gametes. During insemination, sperms are transferred into the female reproductive tract. Fertilization occurs when a sperm fuses with an ovum, producing a zygote. The zygote undergoes cleavage and develops into a blastocyst, which implants in the uterus. Pregnancy follows, during which embryonic and fetal development occur. The placenta supports growth and nutrition. Finally, parturition results in childbirth, followed by lactation for nourishment of the newborn. These events ensure continuity of the human species.