CBSE Class 12 Biology Human Reproduction Question Bank

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BIOLOGY

CHAPTER : 3 HUMAN REPRODUCTION (QUESTION BANK)

1. Name the cells which secrete androgens [1 Mark]

Answer:
1. Leydig cells, also known as interstitial cells, located in the interstitial spaces between seminiferous tubules, secrete androgens (testosterone).

Teacher's Note:
a) Leydig cells are stimulated by Luteinizing Hormone (LH) from the anterior pituitary.
b) Androgens are male sex hormones responsible for secondary sexual characters and spermatogenesis.

2. What does the head of a sperm consists of ? [1 Mark]

Answer:
1. The sperm head contains an elongated haploid nucleus and a cap-like structure called the acrosome, which is filled with enzymes helping in fertilization.

Teacher's Note:
a) The acrosome is formed from the Golgi apparatus of the spermatid.
b) It contains hydrolytic enzymes like hyaluronidase to dissolve the egg membrane during fertilization.

3. Name the structure which secretes progesterone. [1 Mark]

Answer:
1. The corpus luteum, which develops from the ruptured Graafian follicle after ovulation, secretes progesterone.

Teacher's Note:
a) Progesterone is crucial for maintaining the endometrium of the uterus for implantation.
b) During pregnancy, the placenta also takes over the secretion of progesterone.

4. Name the structures which secrete estrogen . [1 Mark]

Answer:
1. Estrogen is primarily secreted by the growing ovarian follicles and later by the corpus luteum and placenta during pregnancy.

Teacher's Note:
a) The developing Graafian follicle is the main source of estrogen during the follicular phase.
b) Estrogen promotes the regeneration of the endometrium and female secondary sex characteristics.

5. Name the site of fertilization in human beings . [1 Mark]

Answer:
1. The ampulla-isthmic junction of the Fallopian tube (oviduct) is the site of fertilization in humans.

Teacher's Note:
a) Fertilization only occurs if both sperm and ovum are transported simultaneously to this region.
b) This explains why all copulations do not lead to fertilization and pregnancy.

6. What is the main function of Sertoli cells ? [1 Mark]

Answer:
1. Sertoli cells provide nutrition and structural support to the developing germ cells (spermatozoa) during spermatogenesis.

Teacher's Note:
a) They are also known as nurse cells found inside the seminiferous tubules.
b) They secrete inhibin and androgen-binding protein (ABP) which help regulate spermatogenesis.

7. Name the outermost layer of the blastocyst [1 Mark]

Answer:
1. The trophoblast is the outermost layer of the blastocyst.

Teacher's Note:
a) The trophoblast gets attached to the endometrium during implantation.
b) It later forms the extraembryonic membranes and the fetal part of the placenta.

8. What promotes completion of second meiotic division in oogenesis ? [1 Mark]

Answer:
1. The entry of the sperm into the cytoplasm of the secondary oocyte promotes the completion of the second meiotic division.

Teacher's Note:
a) Secondary oocyte is arrested at metaphase II until fertilization occurs.
b) Completion of meiosis II results in the formation of a second polar body and a mature ovum (ootid).

9. Testes normally remain suspended in scrotum in mammals. Why? [1 Mark]

Answer:
1. The scrotum provides a lower temperature (2 to 2.5°C lower than the normal internal body temperature) which is essential for spermatogenesis.

Teacher's Note:
a) Higher intra-abdominal temperature can impair sperm production and cause sterility.
b) This is an evolutionary adaptation for efficient male gamete production in mammals.

10. How many spermatozoa will be produced from 100 primary spermatocytes and how many ova will be produced from 100 primary oocytes? [1 Mark]

Answer:
1. 400 spermatozoa and 100 ova will be produced.

Teacher's Note:
a) Each primary spermatocyte undergoes meiosis to produce 4 functional spermatozoa (100 × 4 = 400).
b) Each primary oocyte undergoes meiosis to produce only 1 functional ovum and polar bodies (100 × 1 = 100).

11. Name the three layers of embryo that give rise to all tissues and also name the cells which have the potency to give rise to all the tissues and organs. [2 Marks]

Answer:
1. The three primary germ layers are ectoderm, mesoderm, and endoderm.
2. Stem cells present in the inner cell mass of the blastocyst possess the potency to give rise to all tissues and organs.

Teacher's Note:
a) Organogenesis proceeds from these three embryonic germ layers during early development.
b) Inner cell mass cells are termed pluripotent stem cells due to their differentiation capacity.

12. What is oogenesis? Where does it occur? [2 Marks]

Answer:
1. Oogenesis is the process of formation of a mature female gamete (ovum) from the primordial germ cells in the ovary.
2. It occurs inside the ovaries of female mammals.

Teacher's Note:
a) Unlike spermatogenesis, oogenesis begins during embryonic development in females.
b) Millions of gametes are formed and stored within ovarian follicles.

13. What is ovulation? What happens to Graafian follicle after ovulation? [2 Marks]

Answer:
1. Ovulation is the release of the secondary oocyte (ovum) from the mature Graafian follicle into the peritoneal cavity.
2. The remaining part of the Graafian follicle transforms into an endocrine structure called the corpus luteum.

Teacher's Note:
a) Ovulation is triggered by a sudden surge of Luteinizing Hormone (LH surge) mid-cycle.
b) Corpus luteum secretes large amounts of progesterone to maintain the uterine lining.

14. What is colostrum? What is its importance? [2 Marks]

Answer:
1. Colostrum is the yellowish milk produced by the mammary glands during the initial few days of lactation.
2. It is important because it contains abundant antibodies (IgA) that provide passive immunity to the newborn infant.

Teacher's Note:
a) Essential for developing the infant immune system against various infections.
b) Doctors strongly recommend breastfeeding with colostrum immediately after birth.

15. Draw a labeled diagram of the following and label six parts
i) T.S. of a testes ii) T.S. of an ovary iii) Sperm iv) Ovum .
v) Embryo development (vi) Female reproductive system [3 Marks]

Answer:
1. [Figure: Detailed scientific diagrams showing transverse section of testis with seminiferous tubules and Leydig cells, transverse section of ovary with different stages of ovarian follicles, structure of human sperm showing head, middle piece and tail, structure of ovum showing zona pellucida and plasma membrane, and female reproductive system showing uterus, ovaries, oviducts, and vagina with clear labels.]
2. Each requested diagram must clearly show at least six correct anatomical labels as per NCERT textbook standards.
3. Neat, well-proportioned pencil sketches with clear pointer lines are essential for scoring full marks in diagram questions.

Teacher's Note:
a) Practice drawing these diagrams repeatedly as they frequently appear in board examinations.
b) Ensure proper labeling, making sure lines do not cross each other and point accurately to structures.
c) Use a sharp pencil and include a title for each diagram drawn.

16. Mention any three differences between spermatogenesis and oogenesis. [3 Marks]

Answer:
1. Spermatogenesis occurs in the testes and produces male gametes, whereas oogenesis occurs in the ovaries and produces female gametes.
2. One primary spermatocyte yields four functional spermatozoa, whereas one primary oocyte yields only one functional ovum and polar bodies.
3. Spermatogenesis begins at puberty and continues throughout life, whereas oogenesis begins during embryonic development and stops at menopause.

Teacher's Note:
a) Spermatogenesis involves equal cytoplasmic division, unlike unequal division in oogenesis.
b) The process of spermatogenesis is continuous, while oogenesis is cyclical and arrested at specific stages.
c) Focus on site, product yield, and timeline differences for full marks.

17. Differentiate between Leydig cells and Sertoli cells with reference to their location in the organ and their function [3 Marks]

Answer:
1. Location: Leydig cells are located in the interstitial spaces between seminiferous tubules, whereas Sertoli cells are situated inside the seminiferous tubules amongst germ cells.
2. Function of Leydig cells: They synthesize and secrete male hormones called androgens (testosterone).
3. Function of Sertoli cells: They provide nutrition and physical support to developing spermatozoa.

Teacher's Note:
a) Always structure comparisons in tabular or point-wise format specifying location and function.
b) Leydig cells are endocrine in nature, stimulated by LH.
c) Sertoli cells act as nurse cells and secrete inhibin to regulate FSH feedback.

18. What is parturition? How is it induced? Which hormones are involved in induction of parturition? [3 Marks]

Answer:
1. Parturition is the act of expelling the full-term fetus from the mother's uterus at the end of gestation.
2. It is induced by a complex neuroendocrine mechanism originating from the fully developed fetus and placenta, triggering fetal ejection reflex.
3. The primary hormones involved are oxytocin (causes uterine contractions) and cortisol, estrogens, and prostaglandins.

Teacher's Note:
a) The signals for parturition originate from the fully developed fetus and placenta inducing mild uterine contractions.
b) Oxytocin released from the maternal pituitary acts on uterine muscles causing stronger contractions.
c) A positive feedback loop is established between uterine contraction and oxytocin release leading to expulsion.

19. What is seminiferous tubule? Name the various types of cells present in it and explain its function. [3 Marks]

Answer:
1. Seminiferous tubules are highly coiled functional units located inside the testicular lobules where sperm production takes place.
2. They contain two main types of cells: male germ cells (spermatogonia) which undergo meiosis and Sertoli cells which provide nourishment.
3. Their main function is the production, maturation, and transport of male gametes (spermatozoa).

Teacher's Note:
a) Each testicular lobule contains 1 to 3 highly coiled seminiferous tubules.
b) Germ cells undergo successive mitotic and meiotic divisions to form spermatozoa.
c) Sertoli cells protect and nourish the developing germ cells throughout the process.

20. Explain different phases of spermatogenesis with schematic representation. [5 Marks]

Answer:
1. Multiplication phase: Spermatogonia (2n) multiply by mitotic division and increase in number.
2. Growth phase: Spermatogonia grow in size by nourishing themselves to form primary spermatocytes (2n).
3. Maturation phase: Primary spermatocytes undergo the first meiotic division to form two secondary spermatocytes (n), which then undergo second meiotic division to form four haploid spermatids (n).
4. Spermiogenesis: Spermatids transform into spermatozoa (sperm) by developing an acrosome, flagellum, and losing excess cytoplasm.
5. [Figure: Schematic flowchart showing multiplication phase, growth phase, maturation phase, and spermiogenesis with ploidy levels (2n and n) clearly marked at each step.]

Teacher's Note:
a) Always include ploidy levels (2n or n) in spermatogenesis flowcharts to score full marks.
b) Differentiate clearly between spermiogenesis (spermatid to sperm) and spermiation (release of sperms from Sertoli cells).
c) Ensure the sequence from spermatogonium to spermatozoon is logically connected with arrows.
d) Explain each phase briefly alongside the schematic representation.

21. Explain different phases of oogenesis with schematic representation [5 Marks]

Answer:
1. Multiplication phase: Oogonia (2n) multiply by mitotic divisions in the fetal ovary to form millions of gamete mother cells.
2. Growth phase: Oogonia accumulate yolk and grow significantly into primary oocytes (2n), which get surrounded by a layer of granulosa cells forming primary follicles.
3. Maturation phase: Primary oocyte undergoes meiosis I to form a large secondary oocyte (n) and a tiny first polar body; secondary oocyte starts meiosis II but arrests at metaphase II until fertilization.
4. Fertilization completion: Upon sperm entry, meiosis II completes, forming a mature ovum (ootid) and a second polar body.
5. [Figure: Schematic flowchart of oogenesis indicating oogonium, primary oocyte, secondary oocyte, polar bodies, and mature ovum with correct chromosome counts (2n and n).]

Teacher's Note:
a) Highlight the arrest at prophase I during fetal life and metaphase II during ovulation.
b) Emphasize unequal cytoplasmic division resulting in polar bodies.
c) Ensure the schematic diagram clearly shows the formation of primary, secondary, and tertiary follicles in the ovary.
d) Mention the ploidy (2n and n) of every stage explicitly.

22. Name the glands associated with male reproductive organs and state their functions. [5 Marks]

Answer:
1. Seminal vesicles: Secrete seminal fluid containing fructose, calcium, and enzymes that nourish and activate sperm motility.
2. Prostate gland: Secretes a milky fluid into the urethra that nourishes sperm and enhances their motility.
3. Bulbourethral glands (Cowper's glands): Secrete an alkaline fluid that lubricates the urethra and neutralizes any acidic traces of urine.

Teacher's Note:
a) These are accessory male sex glands whose secretions constitute the seminal plasma.
b) Seminal plasma along with sperms constitutes semen.
c) Mentioning all three glands with distinct functions is essential for full credit.

23. Explain the various phases of menstrual cycle with reference to changes in ovary and uterus and hormonal cycle. [5 Marks]

Answer:
1. Menstrual phase (Days 1-5): Endometrial lining of the uterus breaks down resulting in menstruation, caused by a drop in progesterone and estrogen levels.
2. Follicular/Proliferative phase (Days 6-14): Primary follicles mature into Graafian follicles in the ovary; secretion of estrogen regenerates the uterine endometrium.
3. Ovulatory phase (Day 14): Rapid surge in LH (LH surge) and FSH induces the rupture of the Graafian follicle and release of the secondary oocyte (ovulation).
4. Luteal/Secretory phase (Days 15-28): Remaining follicular cells transform into corpus luteum which secretes large amounts of progesterone, maintaining the endometrium for implantation.
5. Hormonal regulation: Gonadotropins (FSH and LH) control ovarian events, while ovarian hormones (estrogen and progesterone) regulate uterine changes.

Teacher's Note:
a) Structure the answer clearly into the four distinct phases with day ranges.
b) Correlate changes in ovary, uterus, and pituitary hormone levels for each phase.
c) Emphasize the crucial role of the LH surge on day 14.
d) Note that without fertilization, the corpus luteum degenerates, causing menstruation to restart the cycle.

24. Explain the process of fertilization. [5 Marks]

Answer:
1. Sperm capacitation and approach: Spermatozoa undergo capacitation in the female reproductive tract and reach the ampulla-isthmic junction to contact the secondary oocyte.
2. Acrosomal reaction: The sperm head releases enzymes from its acrosome, dissolving the zona pellucida and plasma membrane of the ovum.
3. Cortical reaction: Sperm entry induces a membrane change (cortical reaction) in the egg to prevent polyspermy and ensure monospermy.
4. Syngamy: Fusion of the haploid sperm nucleus with the haploid egg nucleus forms a diploid zygote (2n).

Teacher's Note:
a) Highlight the exact location of fertilization in the Fallopian tube.
b) Explain the importance of the acrosomal and cortical reactions in preventing polyspermy.
c) Conclude with the formation of the diploid zygote restoring the chromosome number.
d) Mention that sex determination of the offspring happens at the precise moment of fertilization.

25. Explain the stages of embryo development from fertilization to implantation. [5 Marks]

Answer:
1. Cleavage: The zygote undergoes rapid mitotic divisions (cleavage) as it moves down the oviduct, forming 2, 4, 8, and 16-celled stages called blastomeres.
2. Morula formation: The 8 to 16-celled solid embryonic stage is called a morula.
3. Blastocyst formation: The morula divides and transforms into a blastocyst consisting of an outer trophoblast and an inner cell mass.
4. Implantation: The blastocyst reaches the uterus and gets embedded in the uterine endometrium, establishing pregnancy.

Teacher's Note:
a) Cleavage divisions differ from normal mitosis because cells do not grow in size between divisions.
b) Emphasize the structural transition from zygote to morula to blastocyst.
c) Implantation occurs around the 7th day after fertilization.
d) Successful implantation is signaled by the secretion of hCG by the trophoblast layer.

26. Draw a diagrammatic presentation of various events during a menstrual cycle. [5 Marks]

Answer:
1. [Figure: Comprehensive chart of menstrual cycle showing pituitary hormone levels (LH, FSH), ovarian hormone levels (estrogen, progesterone), ovarian events (follicular growth, ovulation, corpus luteum), and changes in the uterine endometrial lining across a 28-day timeline.]
2. The diagram must accurately correlate the 28-day timeline with hormonal fluctuations, ovarian follicle maturation, and endometrial thickness.
3. Correct labeling of axes and phases (menstrual, proliferative, secretory) is required for full marks.

Teacher's Note:
a) This is one of the most important graphical questions in human reproduction.
b) Practice drawing the curves for LH, FSH, estrogen, and progesterone with correct peaks.
c) Align day 14 peak of LH and estrogen with ovulation.

27. What is placenta? What is its role? Justify Placenta as an endocrine tissue. [5 Marks]

Answer:
1. Definition: Placenta is a structural and functional intimate connection between the developing fetus and maternal uterine tissue.
2. Nutritional and excretory role: It supplies oxygen and nutrients to the embryo and removes carbon dioxide and excretory wastes.
3. Endocrine role: It secretes essential pregnancy hormones such as human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, and progesterone.
4. Justification: Since it secretes multiple hormones directly into the blood without ducts to regulate pregnancy and maternal metabolism, it acts as an endocrine tissue.

Teacher's Note:
a) Note that hCG, hPL, and relaxin are produced only during pregnancy.
b) Placenta also acts as a barrier protecting the fetus from harmful substances.
c) Ensure both physiological and endocrine functions are clearly distinguished.
d) Mention that relaxin is secreted by the ovary in the later phase of pregnancy.

28. What are the main features of embryonic development at various months of pregnancy? [5 Marks]

Answer:
1. End of 1st month: The heart of the embryo is formed first, which can be heard by listening to the heartbeat.
2. End of 2nd month: The fetus develops limbs and digits (fingers and toes).
3. End of 3rd month (first trimester): Most of the major organ systems are formed, and external genitalia are well-developed.
4. 5th month and 6th month onwards: First movements of the fetus (quickening) and appearance of head hair occur by the 5th month; body is covered with fine hair, eyelids separate, and eyelashes form by the end of 2nd trimester (6th month), leading to full development by 9 months.

Teacher's Note:
a) Memorize landmark developmental milestones month by month (e.g., heart in 1st month, limbs in 2nd).
b) Emphasize the end of the first trimester for major organogenesis.
c) Mention fetal movements and hair growth in the 5th and 6th months.
d) Gestation period in humans is typically 9 months.

29. Women are being blamed for giving birth to a female child. Is it correct to say that the sex of the child is determined by the woman and not by the man? Explain [4 Marks]

Answer:
1. No, it is scientifically incorrect to blame women for giving birth to a female child.
2. Chromosomal basis: Human females have two X chromosomes (XX) and produce only one type of gamete carrying an X chromosome (homogametic).
3. Male contribution: Human males have one X and one Y chromosome (XY) and produce two types of sperms, 50% carrying X chromosome and 50% carrying Y chromosome (heterogametic).
4. Conclusion: The sex of the child is entirely determined by whether the fertilizing sperm carries an X or a Y chromosome, which comes from the father.

Teacher's Note:
a) Explain human sex chromosomes clearly using XX and XY designations.
b) Emphasize that the mother contributes only an X chromosome to every child.
c) The father's sperm (bearing either X or Y) dictates the male or female sex of the zygote.
d) This question has immense societal relevance to dispel misconceptions and gender discrimination.

SECTION A

1. Name the cells which secrete androgens. [1 Mark]

Answer:
1. Leydig cells (interstitial cells) present in the interstitial spaces between seminiferous tubules secrete androgens (testosterone).
2. These hormones regulate spermatogenesis and male secondary sexual characters.

Teacher's Note:
a) Leydig cells are located outside the seminiferous tubules.
b) Androgens are the primary male sex hormones responsible for male reproductive health.

2. What are the two main components of a sperm head? [1 Mark]

Answer:
1. Haploid nucleus containing genetic material.
2. Acrosome filled with enzymes that help in fertilisation.

Teacher's Note:
a) The acrosome is formed from the Golgi apparatus.
b) The nucleus carries the paternal set of chromosomes.

3. Name the temporary endocrine gland formed in the ovary after ovulation. [1 Mark]

Answer:
1. Corpus luteum.
2. It secretes large amounts of progesterone which is essential for maintaining the endometrium.

Teacher's Note:
a) Corpus luteum develops from the ruptured Graafian follicle.
b) Degeneration of the corpus luteum leads to menstruation if fertilisation does not occur.

4. Name the structures which secrete estrogen. [1 Mark]

Answer:
1. Ovarian follicles at various stages of development.
2. These follicles provide protection and nourishment to the developing oocyte.

Teacher's Note:
a) Primordial follicles mature into primary, secondary, and tertiary follicles.
b) The final mature stage is the Graafian follicle.

5. Where does fertilisation normally take place in human females? [1 Mark]

Answer:
1. Ampullary-isthmic junction of the fallopian tube.
2. The sperm and ovum meet at this specific site for successful syngamy.

Teacher's Note:
a) Fertilisation is strictly defined as the fusion of a sperm with an ovum.
b) Movement of gametes to this junction is facilitated by peristalsis and cilia.

6. What is the primary function of Sertoli cells? [1 Mark]

Answer:
1. Provide nutrition to germ cells.
2. Support and nourish developing spermatozoa during spermatogenesis.

Teacher's Note:
a) Sertoli cells are also known as sustentacular or nurse cells.
b) They form the blood-testis barrier protecting germ cells.

7. Name the blastocyst layer that gets attached to the endometrium. [1 Mark]

Answer:
1. Trophoblast layer.
2. It facilitates implantation of the embryo into the uterine wall.

Teacher's Note:
a) The outer layer forms the trophoblast while inner cells form the inner cell mass.
b) Trophoblast cells later form the extra-embryonic membranes and placenta.

8. What event immediately follows the entry of a sperm into the ovum? [1 Mark]

Answer:
1. Entry of the sperm into the cytoplasm of the ovum through the zona pellucida membrane and plasma membrane promotes completion of the second meiotic division.
2. Completion of the second meiotic division of the secondary oocyte.

Teacher's Note:
a) Cortical granules released upon sperm entry harden the zona pellucida.
b) This ensures monospermy and normal diploid chromosome number in the zygote.

9. Testes normally remain suspended in scrotum in mammals. Why? [2 Marks]

Answer:
1. Scrotal sac maintains a low temperature (2 to 2.5°C lower than normal internal body temperature).
2. This lower temperature is necessary for spermatogenesis.

Teacher's Note:
a) Failure of testes to descend into the scrotum is called cryptorchidism.
b) Dartos and cremaster muscles regulate testicular elevation.

10. How many spermatozoa will be produced from 100 primary spermatocytes and how many ova will be produced from 100 primary oocytes? [2 Marks]

Answer:
1. 100 primary spermatocytes undergo meiosis to produce 400 spermatozoa.
2. 100 primary oocytes undergo meiosis to produce 100 eggs.

Teacher's Note:
a) Each primary spermatocyte yields four functional sperm cells.
b) Each primary oocyte yields only one functional ovum due to unequal polar body divisions.

11. Name the three primary germ layers formed during embryonic development and give one derivative of each. [2 Marks]

Answer:
1. Ectoderm - gives rise to the nervous system and epidermis.
2. Endoderm - gives rise to the lining of gut and respiratory tract.
3. Mesoderm - gives rise to muscles, circulatory system, and bones.
4. Stem cells derived from the inner cell mass can differentiate into all three layers.

Teacher's Note:
a) Gastrulation is the developmental process forming these three layers.
b) Pluripotent stem cells hold immense regenerative medicine potential.

12. What is oogenesis? Name the primary organ where it occurs. [1 Mark]

Answer:
1. Oogenesis is the process of formation of a mature female gamete.
2. It occurs primarily in the ovary.

Teacher's Note:
a) Oogenesis begins during embryonic development in females.
b) Millions of gametes are formed before birth with no further additions postnatally.

13. Define ovulation and state what the ruptured follicle transforms into. [1 Mark]

Answer:
1. Ovulation is the release of the secondary oocyte from the ovary.
2. The ruptured Graafian follicle transforms into the corpus luteum.

Teacher's Note:
a) Ovulation is triggered by a surge in luteinizing hormone (LH surge).
b) Occurs typically around the middle of the menstrual cycle (day 14 in a 28-day cycle).

14. What is colostrum? Why is it considered essential for newborn infants? [1 Mark]

Answer:
1. Colostrum is the milk produced during the initial days of lactation.
2. It contains abundant antibodies (IgA) to give passive resistance to the newborn.

Teacher's Note:
a) Colostrum is yellowish in appearance.
b) Essential for developing infant mucosal immunity.

15. Draw a labeled diagram of the following and label six parts: i) T.S. of a testes ii) T.S. of an ovary iii) Sperm iv) Ovum v) Embryo development vi) Female reproductive system [3 Marks]

Answer:
1. Structure of human sperm comprises head, neck, middle piece, and tail.
2. Head contains acrosome and nucleus.
3. Middle piece contains mitochondria providing energy for motility.
4. Labelled parts: Acrosome, Nucleus, Neck, Middle piece, Mitochondria, and Tail.

Teacher's Note:
a) Clear and neat diagrams with straight label lines fetch full marks.
b) Mitochondria spiral is a key feature of the middle piece.

16. Differentiate between spermatogenesis and oogenesis based on time of initiation and number of gametes produced per meiotic division. [3 Marks]

Answer:
1. Spermatogenesis initiates at puberty and continues throughout life, while oogenesis starts during embryonic development.
2. Spermatogenesis produces four functional sperms from one primary spermatocyte.
3. Oogenesis produces only one functional ovum and polar bodies from one primary oocyte due to unequal divisions.

Teacher's Note:
a) Spermatogenesis involves equal cytoplasmic divisions.
b) Oogenesis involves unequal cytoplasmic division conserving nutrients in the ovum.

17. Describe the location and function of Leydig cells and Sertoli cells in human testis. [3 Marks]

Answer:
1. Leydig cells are located in the interstitial spaces outside seminiferous tubules and secrete androgens.
2. Sertoli cells are located inside the seminiferous tubules and provide structural and nutritional support to germ cells.
3. Both cell types are vital for normal male reproductive function and spermatogenesis.

Teacher's Note:
a) Interstitial cells are stimulated by luteinizing hormone (LH).
b) Sertoli cells are stimulated by follicle-stimulating hormone (FSH).

18. Explain the mechanism of parturition and mention the key hormone responsible for it. [3 Marks]

Answer:
1. Parturition is the delivery of the foetus induced by a complex neuroendocrine mechanism.
2. Signals from the fully developed foetus and placenta trigger mild uterine contractions called foetal ejection reflex.
3. Oxytocin released from the maternal pituitary acts on uterine muscle to cause stronger contractions, leading to expulsion of the baby.

Teacher's Note:
a) Positive feedback loop operates between uterine contraction and oxytocin release.
b) Cortisol, estrogen, and oxytocin play synergistic roles.

19. Write a detailed note on the structure of human testis. [5 Marks]

Answer:
1. Testises are situated outside the abdominal cavity within the scrotum to maintain low temperature.
2. Each testis has about 250 compartments called testicular lobules.
3. Each lobule contains one to three highly coiled seminiferous tubules.
4. Seminiferous tubules are lined by male germ cells and Sertoli cells for sperm formation and nutrition.
5. Interstitial spaces outside tubules contain blood vessels and Leydig cells which synthesize androgens.

Teacher's Note:
a) Describe tunica albuginea and mediastinum testis for complete structure.
b) Tubules converge to form rete testis and vas efferentia.

Answer (to the question as framed in the PDF):
1. Seminiferous tubules are highly coiled tubules located in the testicular lobules, where sperm formation takes place.
2. They contain male germ cells (spermatogonia) and Sertoli cells.
3. Germ cells undergo spermatogenesis to form sperms, and Sertoli cells provide nutrition to the germ cells.

20. Trace the path of sperm development from spermatogonia to mature spermatozoa. [5 Marks]

Answer:
1. Spermatogonia (stem cells) multiply by mitotic division inside seminiferous tubules.
2. Some spermatogonia act as primary spermatocytes and undergo the first meiotic division.
3. The first meiotic division yields two equal, haploid secondary spermatocytes.
4. Secondary spermatocytes undergo the second meiotic division to form four haploid spermatids.
5. Spermatids transform into mature spermatozoa through a process called spermiogenesis.

Teacher's Note:
a) Sequence flow: Spermatogonia → Primary Spermatocyte → Secondary Spermatocyte → Spermatid → Sperm.
b) Spermiation refers to the release of sperms from Sertoli cells into the lumen.

21. Oogonia- primary oocyte , primary secondary tertiary graafian follicles - secondary oocyte - ovum [5 Marks]

Answer:
1. Oogonia multiply through mitotic division and form primary oocytes embedded in primary follicles.
2. Primary follicles get surrounded by more layers of granulosa cells and a new antrum to form secondary and tertiary follicles.
3. The tertiary follicle grows further and completes its first meiotic division to form a secondary oocyte and a first polar body.
4. The tertiary follicle changes into a Graafian follicle which releases the secondary oocyte during ovulation.
5. The secondary oocyte undergoes the second meiotic division upon sperm entry to form an ovum and a second polar body.

Teacher's Note:
a) Oogenesis starts during embryonic development in females.
b) Mention all developmental stages sequentially to secure full marks.
c) The secondary oocyte is the stage actually ovulated in humans.
d) Meiosis II is completed only after fertilization.

22. Paired seminal vesicles , a prostate gland paired bulbourethral gland , seminal plasma rich in fructose calcium enzymes , bulbourethral lubrication of penis [5 Marks]

Answer:
1. Male accessory glands include paired seminal vesicles, a single prostate gland, and paired bulbourethral glands.
2. Secretions of these glands constitute the seminal plasma which is rich in fructose, calcium, and certain enzymes.
3. Seminal vesicle fluid provides nourishment and motility to the spermatozoa.
4. Prostate gland secretions help activate the sperms and neutralize vaginal acidity.
5. Bulbourethral gland secretions help in the lubrication of the penis.

Teacher's Note:
a) Accessory gland secretions are vital for sperm transport and survival.
b) Do not confuse the endocrine and exocrine functions here.
c) Fructose is a key biochemical marker tested frequently in reproduction questions.
d) The bulbourethral glands are also known as Cowper's glands.

23. Menstrual phase - flow follicular phase - follicular growth regeneration of endometrium Ovulation , secretary phase - corpus luteum LH ,FSH role [5 Marks]

Answer:
1. Menstrual phase involves menstrual flow due to the breakdown of endometrial lining and blood vessels.
2. Follicular phase is characterized by primary follicles growing into Graafian follicles and regeneration of the endometrium.
3. Gonadotropins LH and FSH increase gradually during the follicular phase and stimulate follicular development and estrogen secretion.
4. Rapid secretion of LH induces the rupture of the Graafian follicle and release of the ovum, known as ovulation.
5. Secretory phase involves the transformation of the remaining follicle into the corpus luteum under the influence of LH, which secretes progesterone.

Teacher's Note:
a) The menstrual cycle lasts for about 28 to 29 days in human females.
b) Ensure all four distinct phases are explained with hormonal control.
c) LH surge is the specific trigger responsible for ovulation.
d) Corpus luteum maintenance is critical for establishing pregnancy.

24. Sperm come s in contact with zona pellucida , block entry of additional sperms , acrosome helps in entry , completion second meiotic division , second polar body , ootid , haploid nucleus of sperm fuses with ovum [5 Marks]

Answer:
1. During fertilization, the sperm comes in contact with the zona pellucida layer of the ovum and induces changes that block the entry of additional sperms.
2. Secretions of the acrosome help the sperm enter the cytoplasm of the ovum through the zona pellucida and plasma membrane.
3. Sperm entry triggers the completion of the second meiotic division of the secondary oocyte, resulting in a second polar body and a haploid ootid.
4. The haploid nucleus of the sperm and that of the ovum fuse together to form a diploid zygote.
5. This complete sequence successfully culminates in the process of syngamy and fertilization.

Teacher's Note:
a) Polyspermy is prevented by cortical reactions modifying the zona pellucida.
b) Write the steps chronologically from sperm contact to nuclear fusion.
c) The acrosome is a modified lysosome filled with hydrolytic enzymes.
d) Fertilization restores the diploid chromosome number in the offspring.

25. Zygote - cleavage , blastomeres ,morula ,blastocyst ,trophoblast , inner cell mass ,attached to endometrium , diiferentiate as embryo , impalntation [5 Marks]

Answer:
1. The zygote starts moving through the oviduct and undergoes rapid mitotic divisions called cleavage to form daughter cells called blastomeres.
2. The embryo with 8 to 16 blastomeres is called a morula, which continues to divide and transform into a blastocyst.
3. The blastocyst consists of an outer envelope layer called trophoblast and an inner cell mass attached to it.
4. The trophoblast layer then gets attached to the uterine endometrium, while the inner cell mass differentiates into the embryo.
5. This process of attachment of the blastocyst to the uterine wall is known as implantation, leading to pregnancy.

Teacher's Note:
a) Cleavage divisions differ from normal mitosis as there is no growth phase in between.
b) Distinguish clearly between trophoblast and inner cell mass functions.
c) Implantation marks the establishment of a successful pregnancy.
d) After implantation, the uterine cells divide rapidly and cover the blastocyst completely.

26. Schematic representation of menstrual cycle ovarian events , uterine events , hormones of pituitary , ovarian hormones [5 Marks]

Answer:
1. Ovarian events include follicular phase development, ovulation around mid-cycle, and formation of the corpus luteum.
2. Uterine events include the menstrual flow phase, proliferative regenerative phase, and secretory phase changes.
3. Pituitary hormones, namely LH and FSH, fluctuate significantly and peak around the middle of the cycle.
4. Ovarian hormones such as estrogens and progesterones show distinct cyclical variations controlling uterine preparation.
5. The coordinated interplay between pituitary and ovarian hormones regulates the entire cyclical activity.

Teacher's Note:
a) Diagrams or schematic text mapping must link hormones with respective tissue changes.
b) Avoid confusing estrogen peaks with progesterone peaks in the timeline.
c) Negative and positive feedback loops regulate pituitary hormone release.
d) The cycle stops temporarily during pregnancy and permanently at menopause.

27. Structural and functional unit between foetus and mother , supply of nutrients and oxygen removal of wastes, hCG, hPL ,estrogens, progestogens [5 Marks]

Answer:
1. The placenta is the structural and functional unit formed between the developing foetus and the maternal body.
2. It facilitates the supply of oxygen and essential nutrients to the foetus and the removal of carbon dioxide and excretory wastes.
3. The placenta acts as an endocrine tissue and produces several hormones essential for pregnancy, such as human chorionic gonadotropin (hCG) and human placental lactogen (hPL).
4. It also secretes steroid hormones like estrogens and progestogens to maintain the uterine lining.
5. Hormones like relaxin are also secreted later in pregnancy by the ovary to facilitate parturition.

Teacher's Note:
a) Placenta connects maternal blood vessels directly with embryonic chorionic villi.
b) Note that hCG, hPL, and relaxin are produced only during pregnancy.
c) The breakdown of marks is 1 mark for definition, 1 for functions, and 3 for hormones.
d) Placenta also acts as an effective barrier preventing large maternal pathogens from entering the foetus.

28. One month- heart , end of second month -limbs and digits , end of 12 weeks -major organ system - limbs genital organs fifth month movements ,second trimester fine hair eyelids separate eye lashes [5 Marks]

Answer:
1. By the end of the first month of pregnancy, the embryo's heart is formed and can be heard.
2. By the end of the second month, the foetus develops limbs and digits.
3. By the end of 12 weeks (first trimester), most of the major organ systems and external genital organs are formed.
4. During the fifth month, the first movements of the foetus and appearance of head hair are usually observed.
5. By the end of the second trimester, the body is covered with fine hair, eye-lids separate, and eyelashes are formed.

Teacher's Note:
a) Human pregnancy lasts for 9 months, divided into three trimesters.
b) Memorize key developmental milestones month by month.
c) The foetus's first movement is traditionally called quickening.
d) Premature birth complications decrease significantly after the second trimester.

29. Genuine reason [4 Marks]

Answer:
1. No, it is not correct. The sex of the child is determined by the father and not by the mother.
2. The woman has two X chromosomes (XX) and all her ova carry only an X chromosome.
3. The man has one X and one Y chromosome (XY) and produces two types of sperms, 50% carrying X and 50% carrying Y.
4. If an ovum is fertilised by an X-bearing sperm the child is a girl (XX), and if by a Y-bearing sperm the child is a boy (XY). Thus the genuine reason is the type of sperm that fertilises the ovum, so the mother cannot be blamed.

Teacher's Note:
a) The mother always contributes an X chromosome; the sex of the child depends on the father's sperm (X or Y).
b) Human females are homogametic (XX) and males are heterogametic (XY).
c) The question carries 2 x 2 marks for the genuine reason.
d) Blaming women for the sex of the child has no scientific basis.

 HUMAN REPRODUCTION IN

(MARKING SCHEME)

Q.NO Answer Marks Allotted

2 Haploid nucleus , acrosome ½ x 2

3 Corpus luteum 1

4 Ovarian follicles 1

9 Scrotum helps in maintaining low temperature , necessary for spermatogenesisc`

10 400 spermatozoa , 100 eggs 

11 Ectoderm , endoderm , mesoderm , stem cells 

12 Formation of mature female gamete , Ovary 

13 The release of secondary oocyte from ovary , transforms into graafian follicle

15 Diagram – six parts

16 At puberty / embryonic development ,four sperms / one egg ,equal division / unequal division

17 Leydig – interstitial space , androgen , Sertoli – seminiferous tubule , nutrition to germ cells

18 Delivery of foetus , foetal ejection reflex , oxytocin 

19 Highly coiled in testicular lobule ,male germ cells sertoli cells , sperm formation provide nutrition

Please click the link below to download CBSE Class 12 Biology Human Reproduction Question Bank.