Chapter 3: Human Reproduction – Short Answer Type Questions

CBSE Class 12 Biology – Short Answer Type Questions with Answers

Unit I: Reproduction | Chapter 3: Human Reproduction (NCERT Based)

Course & Examination Details

• Course: CBSE Class 12 Biology
• Prescribed By: Central Board of Secondary Education
• Syllabus Reference: NCERT
• Unit: Unit I – Reproduction
• Chapter: Chapter 3 – Human Reproduction
• Exam Relevance: CBSE Class 12 Board Examinations (2–3 Mark Questions)

CBSE Class 12 Biology Chapter 3 Short Answer Questions – Human Reproduction (NCERT)

Section A: Male Reproductive System

Q1. Describe the structure and function of testes.

Ans:
Testes are the primary male reproductive organs located in the scrotum. Each testis contains numerous seminiferous tubules where spermatogenesis occurs. Sertoli cells nourish developing sperms, while Leydig cells secrete testosterone. The lower temperature of the scrotum is essential for efficient sperm production and normal reproductive function.

Q2. Explain the role of the scrotum in human reproduction.

Ans:
The scrotum is a pouch of skin that holds the testes outside the abdominal cavity. It maintains the testes at a temperature about 2–2.5°C lower than body temperature, which is essential for spermatogenesis. Any increase in temperature can impair sperm formation and reduce fertility.

Q3. What are seminiferous tubules? Mention their significance.

Ans:
Seminiferous tubules are highly coiled structures present inside the testes. They are the site of spermatogenesis. These tubules contain spermatogonia and Sertoli cells, which together ensure production, nourishment, and maturation of male gametes.

Q4. State the functions of Leydig cells.

Ans:
Leydig cells, present in the interstitial spaces of testes, secrete androgens mainly testosterone. Testosterone regulates spermatogenesis, development of male reproductive organs, and appearance of secondary sexual characters such as facial hair and deep voice.

Q5. Explain the role of accessory glands in males.

Ans:
Accessory glands include seminal vesicles, prostate gland, and bulbourethral glands. Their secretions form seminal plasma, which provides nutrition, alkaline medium, and lubrication to sperms, enhancing their motility and survival.

Section B: Female Reproductive System

Q6. Describe the structure of the ovary.

Ans:
Ovaries are paired primary female reproductive organs located in the pelvic cavity. Each ovary contains ovarian follicles at different stages of development. They produce ova through oogenesis and secrete hormones such as oestrogen and progesterone, regulating menstrual cycle and pregnancy.

Q7. Explain the functions of fallopian tubes.

Ans:
Fallopian tubes transport the ovum from ovary to uterus. The infundibulum with fimbriae collects the ovum, while fertilisation usually occurs in the ampullary region. The tubes also support early cleavage of the zygote.

Q8. What is the role of uterus in reproduction?

Ans:
The uterus is a muscular organ that provides site for implantation, embryonic development, and foetal growth. Its endometrium undergoes cyclic changes to support pregnancy and is shed during menstruation if fertilisation does not occur.

Q9. Describe the function of vagina.

Ans:
The vagina is a muscular canal connecting cervix to external genitalia. It acts as the copulatory organ, receives sperms during intercourse, and serves as the birth canal during parturition.

Q10. Explain the significance of mammary glands.

Ans:
Mammary glands are modified sweat glands that produce milk after childbirth. Lactation provides nourishment and immunity to the newborn, especially through colostrum rich in antibodies.

Section C: Gametogenesis

Q11. Define gametogenesis and state its types.

Ans:
Gametogenesis is the process of formation of haploid gametes in gonads. It includes spermatogenesis in males and oogenesis in females. These processes ensure production of functional gametes required for sexual reproduction.

Q12. Describe the stages of spermatogenesis.

Ans:
Spermatogenesis includes multiplication, growth, maturation, and differentiation phases. Spermatogonia divide mitotically, grow into primary spermatocytes, undergo meiosis to form spermatids, which differentiate into sperms during spermiogenesis.

Q13. What is spermiogenesis and spermiation?

Ans:
Spermiogenesis is the differentiation of spermatids into mature sperms. Spermiation is the release of sperms from Sertoli cells into the lumen of seminiferous tubules.

Q14. Explain hormonal control of spermatogenesis.

Ans:
GnRH from hypothalamus stimulates release of FSH and LH from pituitary. LH stimulates Leydig cells to produce testosterone, while FSH acts on Sertoli cells to support spermatogenesis.

Q15. Describe oogenesis briefly.

Ans:
Oogenesis is the formation of ova from oogonia. It begins during foetal life, pauses at prophase I, resumes at puberty, and produces one ovum and polar bodies to retain maximum cytoplasm.

Section D: Menstrual Cycle

Q16. What is menstrual cycle?

Ans:
The menstrual cycle is a monthly cyclic change in ovaries and uterus of females, averaging 28 days. It prepares the body for pregnancy and includes menstrual, follicular, ovulatory, and luteal phases.

Q17. Describe the menstrual phase.

Ans:
The menstrual phase involves shedding of endometrium due to reduced progesterone levels. It lasts about 3–5 days and occurs when fertilisation does not take place.

Q18. Explain the follicular phase.

Ans:
During follicular phase, ovarian follicles mature under FSH influence. Oestrogen regenerates the endometrium, preparing uterus for implantation.

Q19. What is ovulation?

Ans:
Ovulation is the release of mature ovum from ovary around the 14th day of menstrual cycle. It is triggered by a surge in luteinising hormone.

Q20. Describe luteal phase.

Ans:
In luteal phase, corpus luteum forms and secretes progesterone, maintaining endometrium for implantation. If pregnancy does not occur, corpus luteum degenerates.

Section E: Fertilisation and Implantation

Q21. Define fertilisation and state its site.

Ans:
Fertilisation is fusion of male and female gametes forming a diploid zygote. In humans, it occurs in the ampullary region of fallopian tube.

Q22. Explain the process of implantation.

Ans:
After cleavage, blastocyst reaches uterus and attaches to endometrium. Trophoblast cells invade uterine wall, establishing placenta.

Q23. What is the significance of implantation?

Ans:
Implantation establishes physical and nutritional connection between mother and embryo, enabling pregnancy to continue.

Section F: Pregnancy and Embryonic Development

Q24. What is gestation period in humans?

Ans:
Gestation period in humans is approximately 280 days or nine months, during which embryo develops into foetus.

Q25. Describe placenta and its functions.

Ans:
Placenta is a temporary organ connecting mother and foetus. It facilitates nutrition, respiration, waste removal, and secretes hormones like hCG and progesterone.

Q26. Explain embryonic development briefly.

Ans:
Embryonic development includes cleavage, implantation, gastrulation, and organogenesis. Major organs form by end of first trimester.

Section G: Parturition and Lactation

Q27. What is parturition?

Ans:
Parturition is the process of childbirth involving expulsion of foetus from uterus, triggered by foetal ejection reflex and oxytocin.

Q28. Explain hormonal control of parturition.

Ans:
Foetal signals stimulate oxytocin release from pituitary, causing uterine contractions. This positive feedback leads to delivery of baby.

Q29. What is lactation?

Ans:
Lactation is secretion of milk by mammary glands after childbirth, providing nutrition and immunity to newborn.

Q30. State significance of colostrum.

Ans:
Colostrum is first milk rich in antibodies, providing passive immunity to newborn.

Q31. Difference between spermatogenesis and oogenesis

Answer:
Spermatogenesis is the process of sperm formation in the testes and begins at puberty, continuing throughout life. Each primary spermatocyte forms four functional sperms. Oogenesis is the formation of ova in ovaries, beginning during foetal life. It produces only one functional ovum and polar bodies. Spermatogenesis is continuous, whereas oogenesis is discontinuous and cyclic.

Q32. Role of progesterone in pregnancy

Answer:
Progesterone is essential for maintaining pregnancy. It prepares and maintains the uterine endometrium for implantation and supports embryonic development. The hormone inhibits uterine contractions, preventing premature expulsion of the embryo. Progesterone also supports placental development and suppresses ovulation during pregnancy, ensuring stable conditions for foetal growth.

Q33. Importance of amniotic fluid

Answer:
Amniotic fluid surrounds the developing embryo and foetus, providing protection against mechanical shocks. It allows free movement of the foetus, aiding proper growth and muscular development. The fluid maintains a constant temperature, prevents adhesion of foetal tissues, and facilitates normal development of organs, especially lungs and limbs.

Q34. Function of zona pellucida

Answer:
Zona pellucida is a thick, transparent glycoprotein layer surrounding the ovum. It plays a crucial role in species-specific sperm binding and fertilisation. After fertilisation, it undergoes biochemical changes that prevent polyspermy by blocking entry of additional sperms. It also protects the early embryo during cleavage stages.

Q35. Significance of sexual reproduction in humans

Answer:
Sexual reproduction produces genetic variation through meiosis and fertilisation. This variation enhances adaptability and survival of the human population in changing environments. It also ensures healthy offspring by combining genetic material from two parents, reducing harmful mutations and supporting long-term evolution and continuity of the species.

Q36. Role of hCG hormone

Answer:
Human chorionic gonadotropin (hCG) is secreted by the trophoblast after implantation. It maintains the corpus luteum, ensuring continued secretion of progesterone during early pregnancy. hCG prevents menstruation, supports endometrial maintenance, and is the hormone detected in pregnancy test kits, indicating successful implantation.

Q37. Importance of placenta as an endocrine organ

Answer:
Placenta functions as an endocrine gland by secreting hormones such as hCG, progesterone, oestrogen, and relaxin. These hormones maintain pregnancy, support foetal development, and prepare the mother’s body for childbirth and lactation. Thus, placenta plays a vital role in regulating physiological changes during pregnancy.

Q38. Effect of hormonal imbalance on menstrual cycle

Answer:
Hormonal imbalance involving oestrogen, progesterone, FSH, or LH can disrupt the menstrual cycle. It may cause irregular cycles, delayed ovulation, excessive bleeding, or absence of menstruation. Such imbalances affect follicular development, ovulation, and endometrial preparation, leading to fertility problems and reproductive health disorders.

Q39. Why only one ovum forms in oogenesis

Answer:
Only one ovum is formed during oogenesis to ensure maximum cytoplasmic content for embryonic development. Unequal cytokinesis during meiotic divisions results in one large ovum and polar bodies. This adaptation provides sufficient nutrients, organelles, and energy reserves essential for early development of the embryo.

Q40. Importance of controlled temperature for testes

Answer:
Testes require a temperature about 2–2.5°C lower than body temperature for normal spermatogenesis. Higher temperatures impair sperm production and reduce sperm quality. The scrotum maintains optimal temperature by adjusting the position of testes, ensuring proper development and maturation of male gametes.

Q41. Role of oxytocin and prolactin

Answer:
Oxytocin stimulates uterine contractions during parturition, facilitating childbirth through positive feedback mechanisms. Prolactin regulates milk production in mammary glands after childbirth. Together, these hormones ensure successful delivery of the baby and initiation of lactation, supporting newborn nutrition and maternal bonding.

Q42. Importance of uterine endometrium

Answer:
The uterine endometrium is essential for implantation and nourishment of the embryo. It thickens and becomes highly vascular under hormonal influence to support pregnancy. If implantation does not occur, the endometrium is shed during menstruation. Thus, it plays a central role in reproductive success.

Q43. Why implantation fails sometimes

Answer:
Implantation may fail due to hormonal imbalance, defective endometrium, chromosomal abnormalities in the embryo, or improper timing between embryo development and uterine receptivity. Stress, infections, and uterine abnormalities can also prevent successful attachment of the blastocyst to the endometrium.

Q44. Significance of embryonic membranes

Answer:
Embryonic membranes such as amnion, chorion, yolk sac, and allantois support embryonic development. They provide protection, nutrition, respiration, and waste removal. These membranes also contribute to placenta formation and ensure a stable internal environment for proper growth of the embryo.

Q45. How human reproduction ensures genetic variation

Answer:
Genetic variation arises through meiosis during gamete formation and random fertilisation. Crossing over and independent assortment of chromosomes create new gene combinations. This variation enhances adaptability, disease resistance, and evolutionary success, ensuring long-term survival of human populations.

Q46. Overall importance of reproductive health

Answer:
Reproductive health ensures proper functioning of reproductive systems, safe pregnancy, healthy offspring, and prevention of reproductive disorders. Awareness and maintenance of reproductive health reduce infertility, maternal mortality, and sexually transmitted diseases, contributing to individual well-being and societal development.