Reproduction Class 12 Biology Notes | Complete Chapter with MCQs & FAQs

Reproduction is one of the fundamental life processes that ensures the continuity of life on Earth. It is the biological process through which living organisms give rise to new individuals of their own kind. Without reproduction, life would cease to exist after a single generation. In Class 12 Biology, the chapter on Reproduction explains its types, significance, processes in plants, animals, and humans in detail.

Reproduction can be broadly divided into asexual reproduction and sexual reproduction, each with its unique mechanisms, advantages, and limitations. In higher organisms, reproduction involves complex systems and structures such as the reproductive organs, gametogenesis, fertilization, and embryonic development.

This article provides a comprehensive explanation of reproduction, with every point clearly covered for easy understanding and exam preparation.

Reproduction Class 12 Biology Notes | Complete Chapter with MCQs & FAQs

Types of Reproduction

Asexual Reproduction

Asexual reproduction is a type of reproduction in which a single parent is involved, and there is no gamete formation or fusion. The offspring are genetically identical to the parent and are called clones.

Characteristics of Asexual Reproduction

1. Involves only one parent.

2. Gametes are not formed.

3. Offspring are genetically identical (clones).

4. Faster mode of reproduction.

5. Common in unicellular organisms and some plants.

Methods of Asexual Reproduction

• Binary Fission: Parent cell divides into two equal halves (e.g., Amoeba, Paramecium).

• Budding: Small outgrowths (buds) develop into new individuals (e.g., Hydra, Yeast).

• Fragmentation: Parent body breaks into fragments, each fragment grows into a new organism (e.g., Spirogyra).

• Vegetative Propagation: Seen in plants using roots, stems, or leaves (e.g., potato, ginger, Bryophyllum).

• Sporulation: Formation of spores (e.g., fungi, algae).

Sexual Reproduction

Sexual reproduction involves the fusion of two gametes (male and female) from two parents, resulting in offspring that show genetic variations.

Characteristics of Sexual Reproduction

1. Involves two parents.

2. Formation of male and female gametes.

3. Fertilization occurs (fusion of gametes).

4. Genetic variation in offspring.

5. Slower process but evolutionary significant.

Phases of Sexual Reproduction

1. Pre-fertilization events

   • Gametogenesis (formation of gametes)

   • Gamete transfer

2. Fertilization (syngamy – fusion of gametes)

3. Post-fertilization events

   • Zygote formation

   • Embryogenesis

   • Seed and fruit formation in plants

Reproduction in Organisms

Reproduction in Plants

Asexual Reproduction in Plants

• Natural methods: Rhizome (ginger), tuber (potato), bulb (onion), leaf buds (Bryophyllum).

• Artificial methods: Cutting, grafting, layering, tissue culture.

Sexual Reproduction in Plants (Angiosperms)

1. Floral Structure

   • Androecium (male part – stamens)

   • Gynoecium (female part – carpel)

2. Pollination

   • Transfer of pollen grains from anther to stigma.

   • Types: Self-pollination and cross-pollination.

   • Agents: Wind, water, insects, birds.

3. Fertilization

   • Double fertilization (unique to angiosperms):

     • One male gamete + egg cell → zygote.

     • Other male gamete + polar nuclei → endosperm.

4. Post-fertilization changes

   • Ovary → fruit

   • Ovules → seeds

Reproduction in Animals

Asexual Reproduction in Animals

• Binary fission in protozoans.

• Budding in Hydra.

• Fragmentation/regeneration in Planaria, sponges.

Sexual Reproduction in Animals

• Involves gametes (sperm and ova).

• Internal or external fertilization.

• Development may be oviparous (egg-laying) or viviparous (giving birth to young ones).

Human Reproduction

Male Reproductive System

1. Primary sex organs: Testes (produce sperm and testosterone).

2. Accessory ducts: Epididymis, vas deferens, ejaculatory duct, urethra.

3. Glands: Seminal vesicles, prostate gland, bulbourethral glands.

4. External genitalia: Penis, scrotum.

Female Reproductive System

1. Primary sex organs: Ovaries (produce ova and hormones).

2. Accessory ducts: Fallopian tubes, uterus, cervix, vagina.

3. External genitalia: Vulva, clitoris.

4. Glands: Mammary glands (for lactation).

Gametogenesis

Spermatogenesis

• Process of sperm formation in testes.

• Diploid spermatogonia → primary spermatocytes → secondary spermatocytes → spermatids → spermatozoa.

Oogenesis

• Process of ovum formation in ovaries.

• Oogonia → primary oocyte → secondary oocyte → ovum.

Menstrual Cycle

• Average cycle: 28 days.

• Phases:

  1. Menstrual phase (1–5 days): Shedding of endometrium.

  2. Follicular phase (6–13 days): Growth of follicles under FSH.

  3. Ovulation (14th day): Release of ovum under LH surge.

  4. Luteal phase (15–28 days): Corpus luteum formation, progesterone secretion.

Fertilization and Embryonic Development

Fertilization

• Fusion of sperm and ovum in the ampulla of fallopian tube.

• Results in zygote formation.

Embryonic Development

• Zygote → Cleavage → Morula → Blastocyst → Implantation in uterus.

• Embryo develops into fetus.

• Placenta forms, which provides nourishment and oxygen.

Significance of Reproduction

1. Ensures continuity of species.

2. Maintains genetic stability.

3. Provides genetic variation (in sexual reproduction).

4. Plays a role in evolution.

MCQs (Multiple Choice Questions)

Q1. Which of the following is not a method of asexual reproduction?

a) Binary fission
b) Budding
c) Fertilization
d) Fragmentation

Answer: Fertilization

Q2. The offspring produced by asexual reproduction are:

a) Identical to parent
b) Genetically different
c) Always sterile
d) Haploid

Answer: Identical to parent

Q3. Double fertilization is a characteristic feature of:

a) Gymnosperms
b) Angiosperms
c) Algae
d) Bryophytes

Answer: Angiosperms

Q4. Male gametes in humans are produced in:

a) Epididymis
b) Testes
c) Vas deferens
d) Prostate gland

Answer: Testes

Q5. Ovum in human females is released from:

a) Uterus
b) Cervix
c) Ovary
d) Fallopian tube

Answer: Ovary

Q6. The functional unit of the ovary is:

a) Graafian follicle
b) Corpus luteum
c) Endometrium
d) Follicle-stimulating hormone

Answer: Graafian follicle

Q7. Spermatogenesis occurs in:

a) Leydig cells
b) Seminiferous tubules
c) Epididymis
d) Vas deferens

Answer: Seminiferous tubules

Q8. In humans, fertilization takes place in:

a) Uterus
b) Ovary
c) Ampulla of fallopian tube
d) Cervix

Answer: Ampulla of fallopian tube

Q9. Which hormone is responsible for ovulation?

a) FSH
b) LH
c) Progesterone
d) Prolactin

Answer: LH

Q10. Which one is viviparous?

a) Frog
b) Hen
c) Human
d) Lizard

Answer: Human

Q11. Vegetative propagation in Bryophyllum occurs through:

a) Roots
b) Stem
c) Leaves
d) Flowers

Answer: Leaves

Q12. The zygote in humans is:

a) Haploid
b) Diploid
c) Triploid
d) Polyploid

Answer: Diploid

Q13. Which layer of uterus is shed during menstruation?

a) Myometrium
b) Endometrium
c) Perimetrium
d) All layers

Answer: Endometrium

Q14. Which of the following is a unisexual flower?

a) Mustard
b) Hibiscus
c) Papaya
d) China rose

Answer: Papaya

Q15. Which of the following is an external fertilization example?

a) Human
b) Frog
c) Cow
d) Dog

Answer: Frog

Q16. The male reproductive gland that produces alkaline secretion is:

a) Prostate gland
b) Seminal vesicle
c) Bulbourethral gland
d) All of the above

Answer: Prostate gland

Q17. The process of release of ovum from ovary is called:

a) Menstruation
b) Fertilization
c) Ovulation
d) Implantation

Answer: Ovulation

Q18. Which of the following is a post-fertilization event in plants?

a) Pollination
b) Double fertilization
c) Seed formation
d) Gametogenesis

Answer: Seed formation

Q19. The placenta is formed by:

a) Uterus only
b) Embryo only
c) Both maternal and embryonic tissues
d) Cervix

Answer: Both maternal and embryonic tissues

Q20. Which one is a secondary sex organ in male?

a) Testes
b) Epididymis
c) Ovary
d) Oviduct

Answer: Epididymis

Short Answer Questions

Q1. What is the significance of reproduction?

Answer: Reproduction ensures the continuity of species, maintains genetic stability, and introduces variations essential for evolution.

Q2. Define parthenogenesis with an example.

Answer: Parthenogenesis is the development of a new organism from an unfertilized egg, e.g., honeybee drones.

Q3. What is double fertilization?

Answer: In angiosperms, one male gamete fuses with the egg to form a zygote and another fuses with polar nuclei to form endosperm. This is double fertilization.

Q4. What are gametes?

Answer: Gametes are specialized haploid sex cells (sperm in males and ova in females) that fuse during fertilization to form a zygote.

Q5. Name the phases of menstrual cycle.

Answer: Menstrual phase, follicular phase, ovulation, and luteal phase.

Q6. Distinguish between oviparous and viviparous animals.

Answer: Oviparous animals lay eggs (e.g., hen), while viviparous animals give birth to young ones (e.g., human).

Q7. What is implantation?

Answer: Implantation is the process by which the blastocyst attaches to the uterine wall for further development.

Q8. What is vegetative propagation?

Answer: A form of asexual reproduction in plants where new plants grow from roots, stems, or leaves.

Q9. Define spermatogenesis.

Answer: Spermatogenesis is the process of formation of haploid sperm from diploid spermatogonia in testes.

Q10. What is the role of placenta?

Answer: Placenta supplies nutrients and oxygen to the fetus and removes waste products from fetal blood.

Long Answer Questions

Q1. Explain asexual reproduction in plants with examples.

Answer: Asexual reproduction in plants occurs through vegetative parts like roots, stems, and leaves. Natural methods include rhizomes (ginger), tubers (potato), bulbs (onion), and leaf buds (Bryophyllum). Artificial methods include cutting, grafting, layering, and tissue culture. These methods help in rapid propagation and maintaining desirable traits.

Q2. Describe the male reproductive system in humans.

Answer: The male reproductive system consists of testes (produce sperm and testosterone), accessory ducts (epididymis, vas deferens, ejaculatory duct, urethra), glands (seminal vesicles, prostate gland, bulbourethral glands), and external genitalia (penis, scrotum). Together, they ensure sperm production, maturation, and delivery.

Q3. Explain the menstrual cycle in detail.

Answer: The menstrual cycle lasts 28 days and includes four phases:

1. Menstrual phase (1–5 days) – shedding of endometrium.

2. Follicular phase (6–13 days) – follicle growth and estrogen secretion.

3. Ovulation (14th day) – release of ovum triggered by LH surge.

4. Luteal phase (15–28 days) – corpus luteum secretes progesterone, preparing uterus for implantation.

Q4. What is fertilization? Explain the process in humans.

Answer: Fertilization is the fusion of male and female gametes. In humans, it occurs in the ampulla of fallopian tube. Sperm penetrates the ovum, haploid nuclei fuse to form a diploid zygote. The zygote undergoes cleavage and develops into an embryo.

Q5. Describe gametogenesis.

Answer: Gametogenesis is the formation of gametes. Spermatogenesis produces sperm in seminiferous tubules through mitosis, meiosis, and differentiation. Oogenesis forms ova in ovaries; primary oocytes undergo meiosis and maturation to form haploid ovum.

Q6. Explain the process of pollination and fertilization in plants.

Answer: Pollination is the transfer of pollen grains from anther to stigma by agents like wind, insects, or water. Fertilization occurs when male gametes reach ovule through pollen tube. One male gamete fuses with egg (zygote) and another with polar nuclei (endosperm). This double fertilization is unique to angiosperms.

Q7. What are the phases of sexual reproduction?

Answer: Sexual reproduction includes pre-fertilization (gametogenesis, gamete transfer), fertilization (fusion of gametes), and post-fertilization (zygote development, embryogenesis, seed/fruit formation).

Q8. Discuss embryonic development in humans.

Answer: After fertilization, zygote undergoes cleavage to form morula, then blastocyst, which implants in uterus. Gastrulation forms three germ layers. Organs develop progressively into fetus. Placenta forms to provide nourishment until birth.

Q9. Explain the female reproductive system in humans.

Answer: The female reproductive system includes ovaries (produce eggs and hormones), fallopian tubes (site of fertilization), uterus (supports embryo), cervix, and vagina. External genitalia and mammary glands also play roles in reproduction and lactation.

Q10. Differentiate between asexual and sexual reproduction.

Answer:

• Asexual: single parent, no gametes, offspring are clones, rapid process, no variation (e.g., binary fission, vegetative propagation).

• Sexual: two parents, gamete fusion, genetic variation, slower but evolutionary significant (e.g., humans, flowering plants).

FAQs

Q1. Why is sexual reproduction considered better than asexual reproduction?

Answer: Sexual reproduction introduces genetic variation, which helps species adapt and evolve, unlike asexual reproduction that produces identical offspring.

Q2. What is the site of fertilization in humans?

Answer: Fertilization occurs in the ampullary-isthmic junction of the fallopian tube.

Q3. What is the difference between oviparous and viviparous animals?

Answer: Oviparous animals lay eggs outside (e.g., birds), while viviparous animals give birth to young ones (e.g., humans).

Q4. Why is double fertilization unique to angiosperms?

Answer: Because it involves two fusions – one forms zygote, another forms endosperm – both essential for seed development.

Q5. How many chromosomes are present in human gametes?

Answer: Human gametes are haploid and contain 23 chromosomes.

Q6. What is corpus luteum?

Answer: Corpus luteum is a temporary endocrine structure formed from the ruptured Graafian follicle after ovulation, secreting progesterone.

Q7. What is the role of seminal vesicles?

Answer: Seminal vesicles secrete fructose-rich fluid that provides energy to sperms and aids in semen volume.

Q8. Why is reproduction essential for survival of species?

Answer: It ensures continuity of life, maintains population size, and introduces variations for adaptation and evolution.

Conclusion

Reproduction is an essential biological process that ensures survival and perpetuation of life. While asexual reproduction produces genetically identical offspring, sexual reproduction ensures variations, which drive evolution. In humans, reproduction is a highly complex process involving specialized systems, gametogenesis, fertilization, embryonic development, and ultimately the birth of a new individual. Understanding reproduction is crucial not only for academics but also for appreciating the continuity of life.

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