Class 12 Biology Chapter 3 Human Reproduction Notes
3.1 Human Reproduction – Basic Features
Humans reproduce by sexual reproduction and show viviparous mode of development.
Key Points:
Fertilisation is internal
Male and female gametes are haploid (n)
Zygote is diploid (2n)
Ovulation is the release of ovum from ovary
Ovulation is induced by LH (Luteinising Hormone)
Fertilisation occurs at ampullary–isthmic junction of fallopian tube
Zygote develops into blastocyst
Blastocyst implants in uterus
Placenta provides vascular connection between foetus and uterus
3.1 The Male Reproductive System
Main Components:
Testes – primary male sex organs
Accessory ducts – rete testis, vasa efferentia, epididymis, vas deferens
Accessory glands – seminal vesicles, prostate, bulbourethral glands
External genitalia – penis
Functions of Testes:
Production of sperms (spermatogenesis)
Secretion of testosterone (male sex hormone)
Structure of Seminiferous Tubule
Structural unit of testis
Lined by:
Sertoli cells – provide nourishment
Spermatogenic cells – form sperms
Leydig cells present between tubules
Secrete testosterone
3.3 Spermatogenesis
Spermatogenesis is the process of formation of haploid sperms from diploid spermatogonia.
Site:
Seminiferous tubules of testis
Phases:
Multiplication phase – mitotic division of spermatogonia
Growth phase – formation of primary spermatocytes
Maturation phase – meiosis I & II → spermatids
Spermiogenesis – spermatids → spermatozoa
Spermiation – release of sperms into tubule lumen
👉 One primary spermatocyte produces 4 sperms
Hormonal Regulation of Spermatogenesis
GnRH – from hypothalamus
LH – stimulates Leydig cells → androgens
FSH – acts on Sertoli cells
Androgens – maintain spermatogenesis
Structure of Sperm
Parts:
Head – contains nucleus & acrosome
Middle piece – mitochondria (energy)
Tail – helps in motility
Seminal Plasma
Components:
Sperms
Secretions of:
Seminal vesicles
Prostate gland
Bulbourethral glands
Rich in:
Fructose
Enzymes
Calcium
Prostaglandins
3.2 The Female Reproductive System
Components:
Ovaries
Fallopian tubes
Uterus
Cervix
Vagina
Functions of Ovaries:
Production of ova
Secretion of estrogen & progesterone
Oogenesis
Oogenesis is the formation of female gamete (ovum).
Nature:
Discontinuous process
Begins before birth
Resumes after puberty
Phases:
Multiplication phase – oogonia formation
Growth phase – primary oocyte formation
Maturation phase – meiosis I & II
👉 Ovum is released as secondary oocyte under LH influence
3.4 Menstrual Cycle
Menstrual cycle is a monthly cyclic change in female reproductive system (≈28 days).
Phases:
Menstrual phase
Follicular phase
Ovulatory phase
Luteal phase
Hormones Involved:
FSH
LH
Estrogen
Progesterone
Menstrual cycle stops during pregnancy.
3.5 Fertilisation and Implantation
Fertilisation = fusion of male & female gametes
Occurs in fallopian tube
Forms diploid zygote
Zygote → morula → blastocyst
Blastocyst implants in uterus
3.6 Pregnancy and Embryonic Development
Placenta develops from foetal & maternal tissues
Functions of placenta:
Nutrition
Respiration
Waste removal
Hormone secretion
3.7 Parturition and Lactation
Parturition:
Process of childbirth
Occurs around 280 days
Induced by:
Oxytocin
Estrogen
Cortisol
Lactation:
Milk secretion after childbirth
Provides immunity & nutrition to newborn
Important Functions (Quick Revision)
Corpus luteum – secretes progesterone
Endometrium – implantation
Acrosome – fertilisation enzymes
Sperm tail – motility
Fimbriae – collect ovum
Sex Determination in Humans
Female: XX
Male: XY
Ovum always carries X
Sperm carries X or Y
👉 Father determines sex of child, not mother.
Twins
Identical Twins:
One zygote splits
Same genetic makeup
Fraternal Twins:
Two ova + two sperms
Genetically different
Multiple Births in Animals
Dogs release multiple ova
Each fertilised ovum forms a puppy
Hence, 6 puppies = ~6 eggs released
3.8 Summary (Exam Gold ✨)
Humans show sexual reproduction
Gametogenesis produces haploid gametes
Fertilisation is internal
Placenta supports embryo
Hormones regulate entire reproductive cycle
📝 PYQs (Previous Year Questions)
🔹 1️⃣ Very Short Answer Questions (1 Mark)
What type of reproduction is seen in humans?
Name the hormone responsible for ovulation.
Where does fertilisation occur in humans?
Name the structural and functional unit of testis.
Which cells secrete testosterone?
What is spermiogenesis?
Name the hormone secreted by corpus luteum.
Which part of sperm contains mitochondria?
What is the chromosomal constitution of human female?
Who determines the sex of the child in humans?
🔹 2️⃣ Short Answer Questions (2–3 Marks)
Define spermatogenesis. Mention its site.
Name the phases of spermatogenesis.
Describe the structure of sperm.
What are the functions of testes?
Write two functions of placenta.
What is oogenesis? Why is it called a discontinuous process?
Name the phases of menstrual cycle.
What is fertilisation? Mention its site.
Distinguish between identical and fraternal twins (any two points).
Why does menstrual cycle stop during pregnancy?
🔹 3️⃣ Long Answer Questions (3–5 Marks)
Describe the male reproductive system in humans.
Explain spermatogenesis with the help of a flowchart.
Describe the female reproductive system.
Explain the menstrual cycle in humans.
Describe fertilisation and implantation in humans.
Explain pregnancy and embryonic development in humans.
Describe parturition and lactation.
🔹 4️⃣ Difference-Based PYQs (Very Important)
Spermatogenesis vs Oogenesis
Identical twins vs Fraternal twins
Ovum vs Sperm
Estrogen vs Progesterone
Menstrual phase vs Luteal phase
🔹 5️⃣ Assertion–Reason / Concept-Based PYQs
Spermatogenesis is hormonally regulated. Explain.
Placenta acts as an endocrine gland. Justify.
Humans are called viviparous animals. Give reason.
Father determines the sex of the child. Explain.
Parturition is a hormonally controlled process.
🔹 6️⃣ Diagram / Flowchart Based PYQs
Draw a labelled diagram of human sperm.
Draw a labelled diagram of seminiferous tubule.
Flowchart of spermatogenesis.
Flowchart showing stages from zygote to blastocyst.
✍️ Top 10 Short Question–Answers
Q1. What type of reproduction is seen in humans?
Answer: Humans show sexual reproduction and are viviparous.
Q2. What is ovulation?
Answer: Ovulation is the release of ovum from the ovary.
Q3. Which hormone induces ovulation?
Answer: Luteinising Hormone (LH).
Q4. Where does fertilisation occur in humans?
Answer: At the ampullary–isthmic junction of the fallopian tube.
Q5. What is the chromosomal nature of human gametes?
Answer: Male and female gametes are haploid (n).
Q6. What is the function of testes?
Answer: Production of sperms and secretion of testosterone.
Q7. What is spermatogenesis?
Answer: Formation of haploid sperms from diploid spermatogonia.
Q8. Name the structural unit of testis.
Answer: Seminiferous tubule.
Q9. Which hormone is secreted by corpus luteum?
Answer: Progesterone.
Q10. Who determines the sex of the child in humans?
Answer: Father determines the sex of the child.
📝 Long Answer Questions
Q1. Describe the male reproductive system in humans.
Answer:
The male reproductive system consists of the following parts:
Primary sex organs:
Testes – produce sperms and testosterone
Accessory ducts:
Rete testis
Vasa efferentia
Epididymis
Vas deferens
Accessory glands:
Seminal vesicles
Prostate gland
Bulbourethral glands
External genitalia:
Penis
Q2. Explain spermatogenesis in humans.
Answer:
Spermatogenesis is the process of formation of sperms.
Site: Seminiferous tubules of testis
Phases:
Multiplication phase: Mitotic division of spermatogonia
Growth phase: Formation of primary spermatocytes
Maturation phase: Meiosis I & II form spermatids
Spermiogenesis: Spermatids → spermatozoa
Spermiation: Release of sperms into lumen
👉 One primary spermatocyte produces four sperms.
Q3. Describe the menstrual cycle in humans.
Answer:
Menstrual cycle is a monthly cyclic change in female reproductive system.
Duration: About 28 days
Phases:
Menstrual phase
Follicular phase
Ovulatory phase
Luteal phase
Hormones involved:
FSH
LH
Estrogen
Progesterone
Menstrual cycle stops during pregnancy.
❓ FAQs (5)
FAQ 1. Why are humans called viviparous?
Because embryo develops inside the mother’s uterus.
FAQ 2. Why is oogenesis called a discontinuous process?
Because it begins before birth and resumes after puberty.
FAQ 3. What is the role of placenta?
It provides nutrition, respiration, waste removal and hormone secretion.
FAQ 4. Why does zygote develop into blastocyst before implantation?
Because blastocyst is the stage that implants in the uterus.
FAQ 5. Why do identical twins have same genetic makeup?
Because they develop from the splitting of a single zygote.
| Chapter No. | Chapter Name | Visit |
|---|---|---|
| 1 | Reproduction in Organisms | Visit |
| 2 | Sexual Reproduction in Flowering Plants | Visit |
| 3 | Human Reproduction | Visit |
| 4 | Reproductive Health | Visit |
| 5 | Principles of Inheritance and Variation | Visit |
| 6 | Molecular Basis of Inheritance | Visit |
| 7 | Evolution | Visit |
| 8 | Human Health and Disease | Visit |
| 9 | Strategies for Enhancement in Food Production | Visit |
| 10 | Microbes in Human Welfare | Visit |
| 11 | Biotechnology: Principles and Processes | Visit |
| 12 | Biotechnology and its Applications | Visit |
| 13 | Organisms and Populations | Visit |
| 14 | Ecosystem | Visit |
| 15 | Biodiversity and Conservation | Visit |
| 16 | Environmental Issues | Visit |
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