NCERT Solutions Class 12 Biology Chapter 2 Human Reproduction

Human Reproduction explains gametogenesis, menstrual cycle, fertilisation, implantation, pregnancy, parturition and lactation in humans.
These NCERT Solutions help Class 12 Biology students write accurate exercise answers with correct terms, functions and biological sequence.

Class 12 Biology Chapter 2 needs careful reading because every process is linked in sequence. Spermatogenesis leads to sperm formation, oogenesis leads to ovum formation, ovulation creates the possibility of fertilisation, and implantation begins pregnancy. Students often lose marks when they mix up spermiogenesis and spermiation, or confuse the role of LH, FSH, estrogen and progesterone. These NCERT Solutions Class 12 Biology Chapter 2 explain each answer in simple exam language while keeping NCERT terms accurate. The chapter is also diagram-heavy, so labelled diagrams of the male reproductive system, female reproductive system, sperm, ovary and Graafian follicle are important for CBSE 2026 preparation.

Key Takeaways

  • Gametogenesis: Spermatogenesis forms sperms in testes, while oogenesis forms ova in ovaries.
  • Ovulation: The release of ovum from a mature Graafian follicle is induced by the LH surge.
  • Fertilisation: Fertilisation occurs in the ampullary-isthmic junction of the fallopian tube.
  • Pregnancy: Implantation of the blastocyst in the endometrium marks the beginning of pregnancy.

NCERT Solutions Class 12 Biology Chapter 2 Structure 2026

Exercise Type Topic Covered Question Count
Fill in the blanks Gametes, fertilisation, ovulation, placenta 1 set
Diagram-based answers Male system, female system, sperm, ovary, Graafian follicle 5
Short and long answers Gametogenesis, hormones, menstrual cycle, parturition 16

NCERT Solutions for Class 12 Biology Chapter 2 Exercise

Human Reproduction questions require accurate terminology and sequence. Answers should use NCERT terms such as seminiferous tubules, LH surge, corpus luteum, zona pellucida, blastocyst and placenta.

Q1. Fill in the blanks.

(a) Humans reproduce _____________ (asexually/sexually)
Answer: sexually

(b) Humans are _____________ (oviparous/viviparous/ovoviviparous)
Answer: viviparous

(c) Fertilisation is _____________ in humans (external/internal)
Answer: internal

(d) Male and female gametes are _____________ (diploid/haploid)
Answer: haploid

(e) Zygote is _____________ (diploid/haploid)
Answer: diploid

(f) The process of release of ovum from a mature follicle is called _____________
Answer: ovulation

(g) Ovulation is induced by a hormone called _____________
Answer: luteinising hormone or LH

(h) The fusion of male and female gametes is called _____________
Answer: fertilisation

(i) Fertilisation takes place in _____________
Answer: ampullary-isthmic junction of the fallopian tube

(j) Zygote divides to form _____________ which is implanted in uterus.
Answer: blastocyst

(k) The structure which provides vascular connection between foetus and uterus is called _____________
Answer: placenta

Class 12 Biology Chapter 2 Human Reproduction Diagram Answers

Diagram questions are scoring when labels are complete and placed clearly. Students should practise drawing neat outlines with correct biological terms.

Q2. Draw a labelled diagram of male reproductive system.

Answer: Draw the male reproductive system and label these parts:

  1. Testis
  2. Scrotum
  3. Epididymis
  4. Vas deferens
  5. Seminal vesicle
  6. Prostate gland
  7. Bulbourethral gland
  8. Ejaculatory duct
  9. Urethra
  10. Urinary bladder
  11. Penis
  12. Glans penis
  13. Foreskin
  14. Urethral meatus

Diagram tip: Show the testes inside the scrotum outside the abdominal cavity because testes need a temperature 2-2.5°C lower than body temperature for spermatogenesis.

Q3. Draw a labelled diagram of female reproductive system.

Answer: Draw the female reproductive system and label these parts:

  1. Ovary
  2. Fallopian tube or oviduct
  3. Infundibulum
  4. Fimbriae
  5. Ampulla
  6. Isthmus
  7. Uterus
  8. Cervix
  9. Cervical canal
  10. Vagina
  11. Endometrium
  12. Myometrium
  13. Perimetrium

Diagram tip: Show the fallopian tube extending from the ovary to the uterus. The ampullary region should be clear because fertilisation occurs there.

Human Reproduction Class 12 NCERT Solutions: Short Answers

Short answers in this chapter often ask for two functions, definitions or tissue-level structures. Keep the answer specific and avoid unnecessary description.

Q4. Write two major functions each of testis and ovary.

Answer:

Two functions of testis are:

  1. Testis produces male gametes called sperms through spermatogenesis.
  2. Leydig cells in testis secrete androgens, mainly testosterone.

Two functions of ovary are:

  1. Ovary produces the female gamete called ovum through oogenesis.
  2. Ovary secretes ovarian hormones such as estrogen and progesterone.

Q5. Describe the structure of a seminiferous tubule.

Answer: Seminiferous tubules are highly coiled tubules present inside testicular lobules of the testis.

Each seminiferous tubule is lined internally by two types of cells: spermatogonia and Sertoli cells. Spermatogonia are male germ cells that undergo meiotic divisions to form sperms. Sertoli cells provide nutrition to the developing germ cells.

The regions outside the seminiferous tubules are called interstitial spaces. These spaces contain Leydig cells, blood vessels and immunologically competent cells. Leydig cells synthesise and secrete androgens.

Q6. What is spermatogenesis? Briefly describe the process of spermatogenesis.

Answer: Spermatogenesis is the process of formation of haploid sperms from diploid spermatogonia in the seminiferous tubules of testes.

Process of spermatogenesis:

  1. Spermatogonia are present on the inner wall of seminiferous tubules.
  2. Each spermatogonium is diploid and has 46 chromosomes.
  3. Some spermatogonia become primary spermatocytes.
  4. Each primary spermatocyte undergoes meiosis I to form two haploid secondary spermatocytes.
  5. Each secondary spermatocyte undergoes meiosis II to form two haploid spermatids.
  6. One primary spermatocyte forms four haploid spermatids.
  7. Spermatids transform into spermatozoa by spermiogenesis.
  8. Sperm heads become embedded in Sertoli cells and are later released by spermiation.

Q7. Name the hormones involved in regulation of spermatogenesis.

Answer: The hormones involved in regulation of spermatogenesis are GnRH, LH, FSH and androgens.

GnRH is secreted by the hypothalamus and acts on the anterior pituitary. It stimulates the release of LH and FSH. LH acts on Leydig cells and stimulates androgen secretion. Androgens stimulate spermatogenesis. FSH acts on Sertoli cells and helps spermiogenesis.

Q8. Define spermiogenesis and spermiation.

Answer: Spermiogenesis is the process by which haploid spermatids transform into spermatozoa or sperms.

Spermiation is the process by which mature spermatozoa are released from the seminiferous tubules after spermiogenesis.

Q9. Draw a labelled diagram of sperm.

Answer: Draw a human sperm and label these parts:

  1. Head
  2. Acrosome
  3. Nucleus
  4. Neck
  5. Middle piece
  6. Mitochondria
  7. Tail
  8. Plasma membrane

Diagram tip: Show the acrosome as a cap-like structure over the head. Show many mitochondria in the middle piece because they provide energy for sperm movement.

Q10. What are the major components of seminal plasma?

Answer: The major components of seminal plasma are secretions from the seminal vesicles, prostate gland and bulbourethral glands.

Seminal plasma is rich in fructose, calcium and certain enzymes. These components support sperm survival, motility and transport.

Q11. What are the major functions of male accessory ducts and glands?

Answer: Male accessory ducts store and transport sperms from the testes to the urethra.

The male accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. They help in sperm transport and maturation. The male accessory glands include seminal vesicles, prostate gland and bulbourethral glands.

Their secretions form seminal plasma. Seminal plasma provides nutrients, supports motility and helps sperm movement. Bulbourethral gland secretions also lubricate the penis.

NCERT Solutions Class 12 Biology Chapter 2 Gametogenesis Answers

Gametogenesis is a central concept in Human Reproduction. Learn the chromosome number, sequence and difference between spermatogenesis and oogenesis.

Q12. What is oogenesis? Give a brief account of oogenesis.

Answer: Oogenesis is the process of formation of a mature female gamete or ovum from oogonia in the ovary.

Process of oogenesis:

  1. Oogenesis begins during embryonic development.
  2. A couple of million oogonia are formed in each foetal ovary.
  3. No more oogonia are formed after birth.
  4. Oogonia start division and enter prophase I of meiosis.
  5. They get temporarily arrested at prophase I and are called primary oocytes.
  6. Each primary oocyte is surrounded by granulosa cells and forms a primary follicle.
  7. Many follicles degenerate from birth to puberty.
  8. At puberty, about 60,000-80,000 primary follicles remain in each ovary.
  9. Primary follicles become secondary follicles, then tertiary follicles.
  10. The tertiary follicle has a fluid-filled cavity called antrum.
  11. The primary oocyte completes meiosis I to form a large secondary oocyte and a small first polar body.
  12. The tertiary follicle becomes a Graafian follicle.
  13. The Graafian follicle ruptures and releases the secondary oocyte during ovulation.

Q13. Draw a labelled diagram of a section through ovary.

Answer: Draw a section of ovary and label these parts:

  1. Germinal epithelium
  2. Ovarian stroma
  3. Cortex
  4. Medulla
  5. Primary follicle
  6. Secondary follicle
  7. Tertiary follicle
  8. Graafian follicle
  9. Corpus luteum
  10. Degenerating corpus luteum

Diagram tip: Show follicles in different developmental stages inside the cortex of the ovary.

Q14. Draw a labelled diagram of a Graafian follicle.

Answer: Draw a Graafian follicle and label these parts:

  1. Secondary oocyte
  2. Zona pellucida
  3. Corona radiata
  4. Antrum
  5. Granulosa cells
  6. Theca interna
  7. Theca externa
  8. Cumulus oophorus

Diagram tip: Show a large antrum because a mature Graafian follicle has a prominent fluid-filled cavity.

Q15. Name the functions of the following.

(a) Corpus luteum
Answer: Corpus luteum secretes progesterone. Progesterone maintains the endometrium for implantation and pregnancy.

(b) Endometrium
Answer: Endometrium is the inner glandular lining of the uterus. It undergoes cyclical changes during the menstrual cycle and supports implantation.

(c) Acrosome
Answer: Acrosome contains enzymes that help the sperm penetrate the zona pellucida of the ovum during fertilisation.

(d) Sperm tail
Answer: Sperm tail provides motility to the sperm and helps it move towards the ovum.

(e) Fimbriae
Answer: Fimbriae collect the ovum after ovulation and guide it into the fallopian tube.

Class 12 Biology Human Reproduction Questions and Answers

True or false questions require correction of the biological term. Replace the incorrect organ, cell or process with the correct NCERT term.

Q16. Identify True/False statements. Correct each false statement to make it true.

(a) Androgens are produced by Sertoli cells.
Answer: False. Androgens are produced by Leydig cells.

(b) Spermatozoa get nutrition from Sertoli cells.
Answer: True.

(c) Leydig cells are found in ovary.
Answer: False. Leydig cells are found in the interstitial spaces of testes.

(d) Leydig cells synthesise androgens.
Answer: True.

(e) Oogenesis takes place in corpus luteum.
Answer: False. Oogenesis takes place in the ovary.

(f) Menstrual cycle ceases during pregnancy.
Answer: True.

(g) Presence or absence of hymen is not a reliable indicator of virginity or sexual experience.
Answer: True.

NCERT Class 12 Biology Chapter 2 Solutions: Menstrual Cycle and Parturition

The menstrual cycle is controlled by pituitary and ovarian hormones. Parturition is controlled by a neuroendocrine reflex involving oxytocin.

Q17. What is menstrual cycle? Which hormones regulate menstrual cycle?

Answer: Menstrual cycle is the reproductive cycle in female primates such as monkeys, apes and humans.

In human females, it is repeated at an average interval of about 28/29 days. It begins with menarche at puberty and continues until menopause around 50 years of age.

The menstrual cycle has four major phases:

  1. Menstrual phase
  2. Follicular phase
  3. Ovulatory phase
  4. Luteal phase

Hormones regulating menstrual cycle are:

  1. GnRH
  2. FSH
  3. LH
  4. Estrogen
  5. Progesterone

FSH stimulates follicular development. Estrogen helps regenerate the endometrium. LH surge induces ovulation. Progesterone from corpus luteum maintains the endometrium for implantation.

Q18. What is parturition? Which hormones are involved in induction of parturition?

Answer: Parturition is the process of delivery or childbirth at the end of pregnancy.

Parturition is induced by a complex neuroendocrine mechanism. Signals from the fully developed foetus and placenta cause mild uterine contractions. This is called the foetal ejection reflex.

The foetal ejection reflex triggers release of oxytocin from the maternal pituitary. Oxytocin causes stronger uterine contractions. These contractions stimulate further oxytocin secretion, creating a positive feedback loop.

The main hormone involved in induction of parturition is oxytocin. Estrogens and cortisol also support the process.

Q19. In our society the women are often blamed for giving birth to daughters. Can you explain why this is not correct?

Answer: Blaming women for giving birth to daughters is scientifically incorrect because the sex of the baby is determined by the father.

Human females have XX chromosomes. Therefore, every ovum carries only one X chromosome. Human males have XY chromosomes. Therefore, sperms are of two types: X-bearing sperms and Y-bearing sperms.

If an X-bearing sperm fertilises the ovum, the zygote becomes XX and develops into a female baby. If a Y-bearing sperm fertilises the ovum, the zygote becomes XY and develops into a male baby.

So, the sperm from the father determines the sex of the baby.

Q20. How many eggs are released by a human ovary in a month? How many eggs would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?

Answer: A human ovary usually releases one egg in one menstrual cycle.

If the mother gave birth to identical twins, one egg was released. Identical twins develop from one fertilised egg that splits into two embryos.

Yes, the answer changes for fraternal twins. Fraternal twins develop when two separate eggs are released and fertilised by two different sperms. So, two eggs are released in the case of fraternal twins.

Q21. How many eggs do you think were released by the ovary of a female dog which gave birth to 6 puppies?

Answer: Six eggs were released by the ovary of the female dog.

Dogs usually produce multiple ova during one reproductive cycle. Each puppy develops from a separate fertilised egg. Therefore, six puppies usually indicate fertilisation of six eggs.

NCERT Solutions Class 12 Biology Human Reproduction: Important Concepts

Human Reproduction connects anatomy, cell division, hormones and embryology. These concepts help students answer both short and long questions.

Male Reproductive System

The male reproductive system consists of testes, accessory ducts, accessory glands and external genitalia.

Testes are present in the scrotum. The scrotum maintains a temperature 2-2.5°C lower than internal body temperature. This lower temperature is necessary for spermatogenesis.

Each testis has about 250 testicular lobules. Each lobule contains one to three seminiferous tubules where sperms are produced.

Female Reproductive System

The female reproductive system consists of ovaries, oviducts, uterus, cervix, vagina, external genitalia and mammary glands.

Ovaries produce ova and ovarian hormones. The oviducts, uterus and vagina form female accessory ducts. The uterus has three layers: perimetrium, myometrium and endometrium.

The endometrium supports implantation. The myometrium contracts strongly during delivery.

Fertilisation and Implantation

Fertilisation is the fusion of sperm and ovum to form a diploid zygote.

Sperm reaches the ampullary region of the fallopian tube after insemination. The ovum also reaches the same region after ovulation. Fertilisation occurs only when both gametes reach the ampullary-isthmic junction at the same time.

The zygote divides by cleavage to form blastomeres. The embryo passes through 2-cell, 4-cell, 8-cell and 16-cell stages. The 8 to 16 blastomere stage is called morula. Morula develops into blastocyst, which implants in the endometrium.

Pregnancy and Embryonic Development

Pregnancy begins after implantation of the blastocyst.

The trophoblast forms chorionic villi. Chorionic villi and uterine tissue form the placenta. The placenta supplies oxygen and nutrients to the embryo and removes carbon dioxide and wastes.

The placenta also secretes hCG, hPL, estrogen and progestogens. Relaxin is secreted by the ovary in the later phase of pregnancy.

Lactation

Lactation is the process of milk production by mammary glands.

The milk produced during the first few days after childbirth is called colostrum. Colostrum contains antibodies that help the newborn develop resistance against diseases.

Human Reproduction NCERT Solutions: Important Terms

These terms are useful for one-mark questions, diagram labelling and quick revision.

Term Meaning Exam Point
Spermatogenesis Formation of sperms Occurs in seminiferous tubules
Oogenesis Formation of ovum Begins during embryonic stage
Ovulation Release of secondary oocyte Induced by LH surge
Fertilisation Fusion of sperm and ovum Forms diploid zygote
Implantation Attachment of blastocyst to endometrium Leads to pregnancy
Parturition Delivery of baby Induced mainly by oxytocin
Lactation Milk production Colostrum contains antibodies

Class 12 Biology Chapter 2 Exercise Answers: Quick Hormone Chart

Hormones in this chapter should be linked with their exact source and function. This table helps in direct revision.

Hormone Source Function
GnRH Hypothalamus Stimulates anterior pituitary
LH Anterior pituitary Acts on Leydig cells and triggers ovulation
FSH Anterior pituitary Acts on Sertoli cells and ovarian follicles
Androgens Leydig cells Stimulate spermatogenesis
Estrogen Growing ovarian follicles Regenerates endometrium
Progesterone Corpus luteum Maintains endometrium
Oxytocin Maternal pituitary Causes uterine contractions
hCG Placenta Supports pregnancy

Useful Links for Class 12 Biology

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Important Questions CBSE Important Questions Class 12 Biology
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Q.1 Name the parts of an angiosperm flower in which development of male and female gametophyte take place.

Ans-

The male gametophyte or the pollen grains develop in the microsporangia (pollen chamber) of bilobed structure called anther. The female gametophyte (embryo sac) develops from functional megaspore in the structure called megasporangium or ovule.

Q.2 Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.

Ans-

The differences between microsporogenesis and megasporogenesis are:

Microsporogenesis Megasporogenesis
1. The process of formation of microspores from a pollen mother cell (PMC) through meiosis is called microsporogenesis. 1. The process of formation of megaspores from the megaspore mother cell (MMC) is called megasporogenesis.
2. It the process of formation of the male gametophyte. 2. It the process of formation of the female gametophyte.
3. It occurs inside 4 microsporangia located inside the anther. 3. It occurs inside the ovules of an angiosperm flower.
4. Several thousands of microspores or pollen grains are formed inside each microsporangium. 4. A single MMC differentiates in the micropylar region of the nucellus to form 4 megaspores; out of which three degenerate while one develops into female gametophyte (embryo sac).

Both microsporogenesis and megasporogenesis involve meiosis which results in the formation of haploid gametes from microspore and megaspore mother cells.

Microsporogenesis results in the formation of haploid microspores from the diploid microspore mother cells. Whereas, megasporogenesis results in the formation of haploid megaspore from the diploid megaspore mother cells.

Q.3 Arrange the following terms in the correct development sequence:

Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

Ans-

Male gametophytes are produced in stamens. An anther has 4 pollen sacs or microsporangia. When the anther is young, a group of compactly arranged homogenous cells called sporogenous tissue occupies the centre of each microsporangium. Each cell of the sporogenous tissue acts as a pollen mother cell and is capable of giving rise to a microspore tetrad. Each cell of the microspore tetrad is called a microspore. The microspore divides further by mitosis and forms a structure called pollen grain, which is an immature male gametophyte (containing a vegetative cell and a generative cell). This generative cell divides mitotically to give rise to two male gametes.

So, the correct developmental sequence is:

Sporogenous tissue – pollen mother cell – microspore tetrad – pollen grains – male gametes

Q.4 With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

Ans-

The ovule or megasporangium is a part of the gynoecium that represents the female reproductive part of a flower. The gynoecium consists of single or multiple pistils at the end of which is a bulged part called the ovary. Inside the ovary is the ovarian cavity where the placenta is located. Megasporangia, which are also called as ovules, arise from these placental cells inside the ovary.

Structure of ovule: The ovule is a small structure attached to the placenta by means of a stalk called funicle. The body of the ovule fuses with funicle in the region called hilum, thus serving as a junction between the ovule and funicle. Each ovule has one or two protective envelopes called integuments. The integuments encircle the ovule except at the tip where a small opening called the micropyle is organized. Opposite to the micropylar end is a region that represents the basal part of the ovule and is called chalaza.

The integuments enclose a mass of cells called nucellus. These are filled with abundant food reserve. The embryo sac or the female gametophyte is located in the nucellus. The single embryo sac located inside the ovule arises from a megaspore through reduction division.

Q.5 What is meant by monosporic development of female gametophyte?

Answer

The process of formation of embryo sac of the female flower from a single megaspore is called the monosporic development of female gametophyte. Out of the four megaspores produced as a result of the meiotic division of the megaspore mother cell (by megasporogenesis), only one remains functional while the other three degenerate. The functional megaspore develops into a female gametophyte or an embryo sac.

Q.6 With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.

Ans-

The female gametophyte (embryo sac) develops from one of the functional megaspores arising from meiotic division while the remaining three degenerate. The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, thus forming a 2-nucleate embryo sac. Mitotic division continues and forms 4-nucleate and later the 8-nucleate stages of the embryo sac. These mitotic divisions result in the division of nucleus however there is no wall formation. Only after the 8-nucleate stage, cell walls are laid down leading to the formation of a typical female gametophyte or embryo sac. Here, six out of eight nuclei are surrounded by cell walls. The remaining two nuclei, called polar nuclei are situated below the egg apparatus in a large central cell.

The cells are distributed in a very typical fashion within the embryo sac. Three cells are grouped at the micropylar end and constitute the egg apparatus. Out of these three cells, two are synergids and one is the egg cell. The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes of the pollen grains into the synergids. Three cells located at the chalazal end are called antipodals. The large central cell has two polar nuclei. Thus, a typical angiosperm embryo sac, once matured, is called 7-celled, 8-nucleate structure.

Q.7 What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.

Ans-

A flower that opens up to expose the anthers and the stigma is called a chasmogamous flower. A chasmogamous flower opens at maturity, exposing anthers (stamens) and stigma to allow fertilization.

No, cross-pollination cannot occur in cleistogamous flowers. The reason is that these flowers stay always closed which allows self-fertilization. A cleistogamous flower is usually smaller and requires less energy. The structures are such that they allow reproductive organs to make close contact, making fertilization more likely. Since the flower never opens up, no cross-pollination can occur in cleistogamous flowers, e.g., Oxalis, Viola, etc.

Q.8 Mention two strategies evolved to prevent self-pollination in flowers.

Ans-

The two strategies evolved by the flowers to prevent self-pollination are:

  1. In some species, pollen release and stigma receptivity are not synchronized. Either the pollen is released before the stigma becomes receptive or stigma becomes receptive much before the release of pollen.
  2. In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower.

Q.9 What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Ans-

Self-incompatibility is a genetic mechanism of preventing self-pollen (from the same flower or other flowers of the same plant) from fertilizing the ovules. This is achieved by inhibiting pollen germination or pollen tube growth in the pistil. Self-incompatibility is a widespread mechanism in flowering plants that prevents inbreeding and promotes outcrossing. This genetic response is controlled by one or more multi-allelic loci and relies on a series of complex cellular interactions between the self-incompatible pollen and pistil. Example: The flowers of Brassicaceae family are self-incompatible due to the presence of a receptor kinase signalling pathway that is activated in the pistil leading to pollen rejection.

In self-incompatible species, seeds are not formed in the event of self-pollination because the flowers are genetically programmed to inhibit pollen germination or pollen tube growth in the pistil. There will be no fertilization and thus, no further development leading to seed formation in such flowers.

Q.10 What is bagging technique? How is it useful in a plant breeding programme?

Ans-

There is always a need to improve the quality of food crops to achieve higher-level production with better qualities. This is achieved by artificial hybridization techniques where it is made sure that only the desired pollen grains are used for pollination and the stigma is protected from contamination (from unwanted pollens). This is achieved by the bagging technique. The female reproductive part of the flower is covered with a bag of suitable size, usually made of butter paper. This prevents contamination of its stigma with unwanted pollen. In case of a bisexual flower, anthers are removed from the flowers using a pair of forceps (emasculation) before covering the flower with bags. Once the stigma of the bagged flower attains maturity, mature pollen grains collected from anthers of the desired male parent is artificially dusted onto the stigma and the flowers are rebagged. Fruits are allowed to develop.

This is a very useful technique and has been widely utilized in plant breeding programme. This allows careful selection of parent plants with desired traits.

Q.11 What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.

Ans-

The fusion of one of the male gametes of the pollen grain with the two polar nuclei located in the central cell to produce a triploid, primary endosperm nucleus is called triple fusion. It takes place in the central cell of the embryo sac.

Process of triple fusion: The pollen grains have two cells, a vegetative cell and a generative cell. The latter divides and forms the two male gametes during the growth of the pollen tube through the style. Once it reaches the ovary, pollen tube enters the ovule through the micropyle and releases the two male gametes into the cytoplasm of synergid. One of the male gametes moves towards the egg cell and fuses with the egg cell. This results in the formation of a diploid cell called the zygote. The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid, primary endosperm nucleus. As this involves the fusion of three haploid nuclei, it is termed as triple fusion.

Three haploid nuclei; one male gamete and two polar nuclei are involved in the triple fusion.

Q.12 Why do you think the zygote is dormant for sometime in a fertilized ovule?

Ans-

The zygote is dormant for sometime in a fertilized ovule as it waits till endosperm is developed. This is because endosperm ensures an ample supply of nutrition for the embryo. The primary endosperm cell starts its division immediately after double fertilization occurs in the embryo sac. The cells of this endosperm tissue are filled with reserve food material and are used for the nutrition of the developing embryo. This tissue becomes the food that the young plant will consume until the roots have developed after germination.

Q.13 Differentiate between:
(a) hypocotyl and epicotyl;
(b) coleoptile and coleorhiza;
(c) integument and testa;
(d) perisperm and pericarp.

Ans-

(a) Hypocotyl and Epicotyl

Hypocotyl Epicotyl
1. The cylindrical portion of the embryonal axis below the level of cotyledons is called the hypocotyl. 1. The portion of the embryonal axis above the level of cotyledons is called the epicotyl.
2. It is the portion of the embryonal axis that lies between the radicle and point of attachment of cotyledons. 2. It is the portion of the embryonal axis that lies between the plumule and cotyledons.
3. It terminates within the radicle or root tip. 3. It terminates within the plumule or stem tip.
4. It forms an important part of the embryonic root system. 4. It forms an important part of the embryonic shoot system.

(b) Coleoptile and Coleorhiza

Coleoptile Coleorhiza
1. It is the conical protective sheath which encloses the shoot apex and a few leaf primordia in a monocot seed. 1. It is the undifferentiated sheath which encloses the radicle and root cap in a monocot seed.
2. It forms the portion of the embryonal axis above the level of attachment of scutellum. 2 It forms the portion of the embryonal axis below the level of attachment of scutellum.
3. It forms the shoot system in adult plant by coming out from the soil and performs photosynthesis. 3. It remains inside the soil and is non-green in colour.

(c) Integument and Testa

Integument Testa
1. The integument is the outermost layer of the ovule. It acts as a protective covering of the ovule. 1. The tesla is the outermost protective covering of the seed.
2. There are two thin integument layers called inner and outer integuments. The cells of the integument layer are living. 2. It is thick and made of dead cells.

(d) Perisperm and Pericarp

Perisperm Pericarp
1. Perisperm is the persistent remains of the nucellus (ovule) in the seed. 1. Pericarp is the wall of fruit formed by the ovarian wall.
2. It is the part of a seed. 2. It is the part of a fruit.

Q.14 Why is apple called a false fruit? Which part(s) of the flower forms the fruit?

Ans-

An apple is called a false fruit because the thalamus (an accessory part) along with ovary contributes to the fruit formation. It develops from a compound ovary but much of the fruit’s edible part comes from the thalamus, which grows around the ovary.

Q.15 What is meant by emasculation? When and why does a plant breeder employ this technique?

Ans-

Emasculation is the removal of stamens from bisexual flowers of the female parents to avoid self-pollination in these flowers. It is done before the anthers mature. This is a very useful technique and has been widely utilized in plant breeding programme.

Plant breeders employ this technique for crop improvement programmes where they wish to select parent plants with desired traits or combine desirable characters to produce commercially ‘better’ varieties. They make sure that pollen grains with desired traits are used for pollination and the stigma is protected from contamination by other pollens. Emasculation is done in cases where the plant produces bisexual flowers.

The female reproductive part of the flower is covered with a bag of suitable size, usually made of butter paper. This prevents contamination of its stigma with unwanted pollen. Anthers are removed from the flower using a pair of forceps before covering the flower with bags. Once the stigma of the bagged flower attains maturity, mature pollen grains collected from anthers of the desired male parent are artificially dusted onto the stigma and the flowers are rebagged. Fruits are allowed to develop. This allows the development of the desired traits.

Q.16 If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?

Ans-

If one can induce parthenocarpy through the application of growth substances, the fruits which contain a large number of hard seeds would be selected to induce parthenocarpy. Such fruits resemble a normally developed fruit but are seedless. Seedlessness is a desirable trait in edible fruit with hard seeds. This trait increases the commercial value as consumers prefer to eat fruits without seeds. Thus, varieties of pineapple, banana, cucumber, grape, orange, grapefruit, etc. can be selected to induce parthenocarpy. Parthenocarpy is also desirable in fruit crops that may be difficult to pollinate or fertilize, such as tomato.

Q.17 Explain the role of tapetum in the formation of pollen-grain wall.

Ans-

Tapetum is the innermost layer that surrounds the pollen grains inside the anther. The lobes of anther of a male flower develop to form pollen sacs. They extend longitudinally all through the length of an anther and are packed with pollen grains. This is surrounded by four layers namely epidermis, endothecium, middle layers and the tapetum. The three outer layers are protective whereas the tapetum, which constitutes the innermost layer, nourishes the pollen grains. The cells in this layer are large with densely packed cytoplasm and generally have more than one nuclei. This layer surrounds the sporogenous tissue occupying the centre of microsporangia. Tapetum helps in pollen wall formation, transportation of nutrients to the inner side of anther and is involved in the synthesis of callase enzyme for the separation of microspore tetrads.

Q.18 What is apomixis and what is its importance?

Ans-

The method devised by flowering plants to produce seeds without fertilisation is called apomixis. There are numerous ways by which apomixis happens:

  1. A diploid egg cell is formed without reduction division and develops into an embryo without fertilisation.
  2. The nuclear cells surrounding the embryo sac start dividing, protruding into the embryo sac and developing into the embryos; for example, Citrus and Mango.

Importance of apomixis:

Large varieties of food crops under cultivation are hybrid varieties and maintaining the hybrid characteristics in these plants is very difficult as they segregate in subsequent divisions. This is a costly process. If these hybrids are converted into apomicts (plants that carry out apomixes), there will be no segregation of characteristics as there will be no reduction division. This will allow the hybrid character to remain as it is and farmers need not buy seeds every year as they can raise hybrid seeds by themselves without losing the character.

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Related Chapters

Chapter 1 - Reproduction in Organism

Chapter 3 - Human Reproduction

Chapter 4 - Reproductive Health

Chapter 5 - Principles of Inheritance and Variation

Chapter 6 - Molecular Basis of Inheritance

Chapter 7 - Evolution

Chapter 8 - Human Health and Disease

Chapter 9 - Strategies for Enhancement in Food Production

Chapter 10 - Microbes in Human Welfare

Chapter 11 - Biotechnology: Principles and Processes

Chapter 12 - Biotechnology and its Applications

Chapter 13 - Organisms and Populations

Chapter 14 - Ecosystem

Chapter 15 - Biodiversity and Conservation

Chapter 16 - Environmental Issues

FAQs (Frequently Asked Questions)

Human Reproduction explains reproductive organs, gamete formation, menstrual cycle, fertilisation, implantation, pregnancy, parturition and lactation. It focuses on sexual reproduction in humans.

Fertilisation occurs in the ampullary-isthmic junction of the fallopian tube. The sperm and ovum must reach this region at the same time.

The LH surge induces ovulation. LH reaches its peak around the middle of the menstrual cycle and causes rupture of the Graafian follicle.

Colostrum contains several antibodies. These antibodies help newborn babies develop resistance during the early period of life.

The father determines the sex of the baby. X-bearing sperm produces a female baby, while Y-bearing sperm produces a male baby.