Human Reproduction — Class 12 Biology NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 12 Biology chapter "Human Reproduction" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 12 Biology chapter "Human Reproduction" — 8 important questions with detailed answers for CBSE board exam…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 12 Biology — Human Reproduction. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Human Reproduction — All 8 Questions Solved
Q1. Name the parts of male reproductive system and state their functions.
Male reproductive system parts and functions:
1. Testes (two): produce sperms and testosterone hormone in seminiferous tubules
2. Epididymis: stores and matures sperms; site of final sperm development
3. Vas deferens (ductus deferens): muscular tube transporting sperms from epididymis to urethra
4. Seminal vesicles: secrete alkaline fluid rich in fructose providing energy to sperms
5. Prostate gland: secretes slightly acidic fluid with enzymes, helps coagulation of semen
6. Cowper's glands (Bulbourethral glands): secrete pre-ejaculatory fluid
7. Urethra: common passage for urine and semen
8. Penis: copulatory organ with corpus cavernosum for erection and ejaculation
Q2. Draw a labeled diagram of female reproductive system and explain the parts.
Female reproductive system structure:
- Ovaries (two): almond-shaped organs producing eggs and hormones (estrogen, progesterone)
- Fallopian tubes (oviducts, two): receive egg from ovary; site of fertilization in ampulla region; transport developing embryo to uterus
- Uterus: pear-shaped muscular organ with three layers:
* Perimetrium: outer serous membrane
* Myometrium: muscular middle layer for contractions
* Endometrium: inner mucosal layer where embryo implants
- Cervix: narrow neck of uterus opening into vagina
- Vagina: elastic muscular tube for intercourse and birth canal
- External genitalia: mons pubis, labia majora, labia minora, clitoris, urethral and vaginal openings
Q3. Describe spermatogenesis with the help of a diagram.
Spermatogenesis is formation of functional sperms from spermatogonial stem cells in seminiferous tubules of testes. Duration: 74 days approximately.
Stages:
1. Mitotic proliferation phase: spermatogonium (diploid stem cell) undergoes mitosis producing primary spermatocytes (diploid)
2. Meiotic phase: Primary spermatocyte undergoes first meiotic division producing two secondary spermatocytes (haploid). Secondary spermatocytes undergo second meiotic division producing four spermatids (haploid)
3. Spermiogenesis phase: Spermatids transform into mature sperms through:
- Nucleus becomes compact
- Golgi apparatus forms acrosome
- Centrioles form flagellum
- Mitochondria concentrate around flagellar base forming middle piece
- Excess cytoplasm removed
Result: Four functional haploid sperms from one diploid spermatogonium. Sertoli cells provide nutrition and support.
Q4. What is oogenesis? Explain the stages of oogenesis.
Oogenesis is formation of functional ovum from oogonial stem cells in ovarian follicles. Begins before birth, completes at fertilization.
Stages:
1. Proliferation phase (before birth): Oogonia (diploid stem cells) undergo mitosis producing primary oocytes
2. Growth phase (from birth to puberty and after): Primary oocytes arrest in prophase I of meiosis I. Accumulate cytoplasm, organelles, and mRNA forming primary follicles
3. Maturation phase I: At puberty, primary oocyte completes meiosis I producing:
- Secondary oocyte (haploid, receives most cytoplasm)
- First polar body (haploid, degenerates)
4. Maturation phase II: Secondary oocyte arrests in metaphase II. Completes meiosis II only after fertilization producing:
- Mature ovum (haploid)
- Second polar body (degenerates)
Result: One functional ovum from one oogonium. Monthly ovulation after puberty; ends at menopause (around 50 years).
Q5. Describe the structure and function of sperm with a labeled diagram description.
Sperm is highly specialized haploid male gamete adapted for swimming and fertilizing egg.
Structure (approximately 60 micrometers long):
1. Head: Contains haploid nucleus (genetic material) and acrosome (derived from Golgi apparatus, contains enzymes)
2. Middle piece (neck): Contains mitochondria (4-8) arranged in spiral around flagellar base; mitochondria provide ATP energy for movement
3. Tail (flagellum): Long, whip-like structure for motility; contains microtubules (9+2 arrangement); can beat up to 20 times per second
Functions:
- Nucleus: carries 23 chromosomes from father
- Acrosome: releases enzymes (acrosin) to penetrate egg layers
- Mitochondria: provide energy for locomotion
- Flagellum: propels sperm through female tract to reach egg
- Plasma membrane: carries receptors for egg binding
Sperm production rate: 300 million daily; lifespan 2-3 days in female reproductive tract.
Q6. Explain the hormonal control of male reproduction.
Male reproduction controlled by hypothalamic-pituitary-testicular axis:
1. Hypothalamus: secretes GnRH (Gonadotropin-Releasing Hormone) in pulses
2. Anterior pituitary: GnRH stimulates release of:
- FSH (Follicle-Stimulating Hormone): acts on Sertoli cells in testes, promotes spermatogenesis
- LH (Luteinizing Hormone): acts on Leydig cells, stimulates testosterone production
3. Testes:
- Sertoli cells: under FSH stimulation, produce ABP (Androgen-Binding Protein) and anti-Mullerian hormone
- Leydig cells: under LH stimulation, produce testosterone (primary androgen)
4. Testosterone functions:
- Develops male secondary sexual characters
- Maintains spermatogenesis
- Develops genital tract
- Increases metabolism and muscle mass
5. Negative feedback: High testosterone inhibits GnRH and LH; inhibin from Sertoli cells inhibits FSH
This coordinated hormonal control maintains continuous spermatogenesis after puberty.
Q7. Describe menstrual cycle and the role of hormones in regulating it.
Menstrual cycle is monthly cyclic change in endometrium lasting 28 days (range 21-35 days) in non-pregnant women. Regulated by hormones:
Phases:
1. Menstruation (Days 1-5): Shedding of endometrium with bleeding; lasts 3-5 days
2. Follicular phase (Days 6-13):
- FSH from pituitary stimulates follicle growth in ovary
- Growing follicles secrete estrogen
- Estrogen stimulates endometrial proliferation
- Rising estrogen causes LH surge on day 13
3. Ovulation (Day 14):
- LH surge triggers ovulation
- Secondary oocyte released from ovary
- Ovum survives 12-24 hours
4. Luteal phase (Days 15-28):
- Ruptured follicle forms corpus luteum
- Corpus luteum secretes progesterone
- Progesterone maintains endometrium for implantation
- If fertilization does not occur, corpus luteum degenerates
- Progesterone withdrawal triggers menstruation
Hormonal regulation: FSH and LH from pituitary; estrogen and progesterone from ovary in coordinated feedback mechanism.
Q8. What is implantation? Describe the stages of embryonic development up to blastocyst formation.
Implantation is embedding of blastocyst into endometrium of uterus, occurring 6-10 days after fertilization.
Stages of early embryonic development:
1. Cleavage: Zygote undergoes rapid mitotic divisions without growth
- 2-cell stage (36 hours)
- 4-cell stage (48 hours)
- 8-cell stage (3 days)
- Forms morula (ball of 16-32 cells)
2. Blastocyst formation (days 5-6): Cells differentiate into:
- Trophoblast: outer layer, forms placenta and membranes
- Inner cell mass (embryoblast): inner cells, forms embryo and yolk sac
- Blastocoel: fluid-filled cavity
3. Implantation process:
- Blastocyst reaches uterus
- Trophoblast cells proliferate and erode endometrium
- Blastocyst sinks into endometrium
- Trophoblast cells form primary villi
- Implantation site becomes highly vascularized
- Placenta begins forming
After implantation, gastrulation occurs forming three germ layers (ectoderm, mesoderm, endoderm) from which all organs develop.
Human Reproduction — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. What is the primary function of the scrotum in the male reproductive system?
- A. Production of testosterone
- B. Storage of sperm
- C. Maintaining a lower temperature for spermatogenesis
- D. Ejaculation of semen
Answer: C. Maintaining a lower temperature for spermatogenesis — The scrotum helps in maintaining the temperature of the testes 2-2.5°C lower than the normal internal body temperature, which is essential for spermatogenesis.
MCQ 2. Which cells are responsible for secreting androgens like testosterone in the male reproductive system?
- A. Sertoli cells
- B. Spermatogonia
- C. Interstitial cells (Leydig cells)
- D. Primary spermatocytes
Answer: C. Interstitial cells (Leydig cells) — Leydig cells, also known as interstitial cells, located in the interstitial spaces between the seminiferous tubules, synthesize and secrete testicular hormones called androgens, primarily testosterone.
MCQ 3. How many secondary spermatocytes are required to produce 100 spermatozoa?
- A. 25
- B. 50
- C. 100
- D. 200
Answer: B. 50 — Each primary spermatocyte produces two secondary spermatocytes, and each secondary spermatocyte produces two spermatids, which mature into spermatozoa. Therefore, one secondary spermatocyte yields two spermatozoa, meaning 50 secondary spermatocytes are needed for 100 spermatozoa.
MCQ 4. Where does fertilization typically occur in the human female reproductive system?
- A. Uterus
- B. Ovary
- C. Fallopian tube (oviduct)
- D. Vagina
Answer: C. Fallopian tube (oviduct) — Fertilization, the fusion of sperm and ovum, most commonly takes place in the ampullary region of the fallopian tube (oviduct).
MCQ 5. At what stage of oogenesis is the oocyte arrested before puberty?
- A. Oogonium
- B. Primary oocyte in prophase I
- C. Secondary oocyte in metaphase II
- D. Ovum
Answer: B. Primary oocyte in prophase I — During fetal development, oogonia differentiate into primary oocytes, which then get arrested at the prophase-I stage of meiosis until puberty.
MCQ 6. Which hormonal condition would cause a surge in LH during the menstrual cycle?
- A. High levels of progesterone
- B. Low levels of estrogen
- C. High levels of estrogen
- D. High levels of FSH
Answer: C. High levels of estrogen — The LH surge, which triggers ovulation, is caused by a rapid increase in estrogen levels during the late follicular phase. High estrogen levels switch from negative to positive feedback on GnRH and LH secretion.
MCQ 7. The process of attachment of the blastocyst to the uterine wall is called:
- A. Fertilization
- B. Ovulation
- C. Implantation
- D. Gastrulation
Answer: C. Implantation — Implantation is the process where the blastocyst attaches itself to the endometrium (uterine wall) and gets embedded in it, marking the beginning of pregnancy.
MCQ 8. Which of the following hormones is NOT produced by the placenta?
- A. Human Chorionic Gonadotropin (hCG)
- B. Estrogen
- C. Oxytocin
- D. Progesterone
Answer: C. Oxytocin — Oxytocin is primarily produced by the posterior pituitary gland and plays a crucial role in uterine contractions during parturition and milk ejection. hCG, estrogen, and progesterone are vital hormones produced by the placenta during pregnancy.
MCQ 9. The inner cell mass of the blastocyst differentiates into the three primary germ layers. Which germ layer forms the nervous system?
- A. Endoderm
- B. Mesoderm
- C. Ectoderm
- D. Trophoblast
Answer: C. Ectoderm — The ectoderm is the outermost germ layer that gives rise to the nervous system, epidermis of the skin, hair, nails, and various glands.
MCQ 10. The powerful contractions of the uterus during parturition are stimulated by which hormone?
- A. Prolactin
- B. Estrogen
- C. Oxytocin
- D. Relaxin
Answer: C. Oxytocin — Oxytocin, secreted by the maternal posterior pituitary, causes strong uterine contractions leading to the expulsion of the baby.
MCQ 11. Which part of the human sperm contains enzymes necessary for penetrating the egg?
- A. Head
- B. Acrosome
- C. Middle piece
- D. Tail
Answer: B. Acrosome — The acrosome, a cap-like structure at the anterior part of the sperm head, contains hydrolytic enzymes that help the sperm penetrate the egg during fertilization.
MCQ 12. Which of the following statements is true regarding human gametogenesis?
- A. Both spermatogenesis and oogenesis are continuous processes from puberty.
- B. Oogenesis produces four functional ova from one primary oocyte.
- C. Spermatogenesis results in unequal cytoplasmic division.
- D. Spermatogenesis is completed in the testes, while oogenesis is completed in the fallopian tube.
Answer: D. Spermatogenesis is completed in the testes, while oogenesis is completed in the fallopian tube. — Spermatogenesis is completed in the testes, producing mature spermatozoa. Oogenesis starts in the ovary but the secondary oocyte only completes meiosis II (and becomes an ovum) upon fertilization in the fallopian tube.
MCQ 13. Which accessory gland in males contributes fluid rich in fructose, calcium, and certain enzymes to the semen?
- A. Bulbourethral glands
- B. Prostate gland
- C. Seminal vesicles
- D. Epididymis
Answer: C. Seminal vesicles — The seminal vesicles secrete a fluid that makes up a significant portion of the semen, rich in fructose (energy for sperm), calcium, and certain enzymes.
MCQ 14. During which phase of the menstrual cycle does the endometrium proliferate rapidly, and the ovarian follicles mature?
- A. Menstrual phase
- B. Luteal phase
- C. Follicular (proliferative) phase
- D. Secretory phase
Answer: C. Follicular (proliferative) phase — In the follicular (proliferative) phase, FSH stimulates the development of ovarian follicles, which in turn secrete estrogen. Estrogen causes the regeneration and proliferation of the uterine endometrium.
MCQ 15. What is the primary difference between a morula and a blastocyst?
- A. Morula is formed before fertilization, blastocyst after.
- B. Morula is a solid ball of cells, while blastocyst has a fluid-filled cavity.
- C. Blastocyst contains fewer cells than a morula.
- D. Morula implants into the uterine wall, blastocyst does not.
Answer: B. Morula is a solid ball of cells, while blastocyst has a fluid-filled cavity. — A morula is a solid ball of cells resulting from cleavage. As cleavage continues, the morula develops a fluid-filled cavity called the blastocoel, transforming into a blastocyst, which then implants.
MCQ 16. The primary female sex organs that produce ova and several steroid hormones are:
- A. Uterus
- B. Ovaries
- C. Fallopian tubes
- D. Vagina
Answer: B. Ovaries — Ovaries are the primary female sex organs. They produce female gametes (ova) and several steroid hormones (estrogen and progesterone).
MCQ 17. What is the role of Follicle Stimulating Hormone (FSH) in males?
- A. Stimulates Leydig cells to secrete androgens
- B. Stimulates Sertoli cells to secrete factors for spermatogenesis
- C. Causes testicular descent
- D. Inhibits sperm production
Answer: B. Stimulates Sertoli cells to secrete factors for spermatogenesis — FSH acts on Sertoli cells and stimulates the secretion of some factors which help in the process of spermatogenesis. LH acts on Leydig cells.
MCQ 18. Capacitation of sperm occurs in:
- A. Epididymis
- B. Vagina
- C. Uterus
- D. Female reproductive tract
Answer: D. Female reproductive tract — Capacitation is a process where biochemical changes in the sperm membrane occur, making it capable of fertilizing an egg. This process takes place in the female reproductive tract after ejaculation.
MCQ 19. The average duration of human pregnancy is about nine months, which is called the:
- A. Menstrual cycle
- B. Ovulation period
- C. Gestation period
- D. Parturition phase
Answer: C. Gestation period — The period of development of the embryo from conception to birth is known as the gestation period, which averages about nine months in humans.
MCQ 20. The signal for parturition originates from:
- A. Placenta alone
- B. Fully developed foetus alone
- C. Both the fully developed foetus and the placenta
- D. Pituitary gland alone
Answer: C. Both the fully developed foetus and the placenta — The signals for parturition originate from the fully developed foetus and the placenta, inducing mild uterine contractions called foetal ejection reflex.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.