Important Questions for CBSE Class 12 Biology Chapter 2 - Human Reproduction 2024-25

1 Marks Questions

1. Failure of testes to descend into scrotal sacs leads to sterility. Why?

Ans: The high temperature of the abdomen kills the spermatogenic tissue of the testes, so no sperm are formed.

2. Both vaccine and colostrum produce immunity. Name the type of immunity produced by these.

Ans: Vaccine Active immunity Colostrum Passive immunity.

3. How many sperms will be produced from 10 primary spermatocytes and how many eggs will be produced from 10 primary oocytes?

Ans: 40 sperms, 10 eggs.

4. The spermatogonial cell has 46 chromosomes in a human male. Give the number of chromosomes in:

a. Primary spermatocyte

Ans: 46 in primary spermatocyte 

b. Spermatid 

Ans: 23 in spermatid.

5. In ovary, which structure transforms as corpus luteum and names the hormone secreted by corpus luteum?

Ans: Follicular cells of empty Graafian follicle.

The hormone secreted by the Corpus luteum is Progesterone.

6. “Each and every coitus does not result in fertilisation and pregnancy”. Justify the statement.

Ans: The ovum and sperm should arrive at the ampullary – isthmic junction at the same time.

7. Why are male testes located outside the abdominal cavity?

Ans: Because the scrotum provides a lower temperature than the typical body temperature required for spermatogenesis, the male testes are situated outside the abdominal cavity in the scrotum.

8. State the function of leydig cells.

Ans: The Leydig cells synthesise and secrete testicular hormones called androgens.

9. Where do we find fimbriae?

Ans: Fimbriae are finger-like projections found in the edges of the infundibulum.

10. What is semen?

Ans: Semen is the combination of seminal plasma and sperms.

11. Define parturition.

Ans: The vigorous contraction of the uterus that results in the delivery of the child at the end of pregnancy is called parturition.

12. Where does fertilization normally takes place in a human female.

Ans: Ampulla (fallopian tube).

13. Name the substance present in the sperm acrosome & which help in sperms entry into egg.

Ans: Acrosome contains enzymes e.g. hyaluronidase that helps in dissolving the membrane of the ovum.

14. Name the layer of cells that forms the outer wall of blastocyst.

Ans: Trophoblast.

15. At what stage is the mammalian embryo implanted in uterus?

Ans: Blastocyst stage.

16. Despite the presence of So many sperms in the vicinity of an egg cell, only one sperm enters the ovum. Why?

Ans: Because when sperm comes in contact with ovum (zona pellucida) & induces changes in membrane to block entry of other sperms.

17. How many polar bodies are given out in production of one egg during cogenesis?

Ans: Two polar bodies are given out in production of one egg during cogenesis.

2 Marks Question

1. Give the function of

1. Corpus luteum

Ans: Corpus luteum: It secretes progesterone which prepares the endometrium of the uterus for implantation and normal development of the fetus.

2. Endometrium

Ans: Endometrium: It undergoes cyclic changes during the menstrual cycle and prepares itself for implantation of the blastocyst.

2. In the given figure, give the name and functions of parts labeled A and B.

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Ans: A = Trophoblast Gets attached to the endometrium and draws nutritive material secreted by uterine endometrium gland.

B = Inner cell mass Differentiates as Embryo.

3. Given below is an incomplete flow chart showing the influence of hormones on gametogenesis in male. Observe the flow chart carefully and fill in the blank A, B, C and D.

Ans: A = Testosterone; B = Spermatogenesis C = Sertoli cells; D Spermiogenesis

4. Give reason for the following :

1. The first half of the menstrual cycle is called the follicular phase as well as the proliferative phase.

Ans: In the first half of the menstrual cycle, primary follicles transform into Graafian follicles under FSH stimulation. Graafian follicles secrete estrogens stimulating the enlargement of the Endometrium of the uterus.

2. The second half of the menstrual cycle is called the luteal phase as well as the secretory phase.

Ans: In the second half of the menstrual cycle, the Corpus luteum is fully formed and secretes a large quantity of Progesterone.

5. What is meant by L.H. Surge? Write the role of L.H.

Ans: The three phases of the menstrual cycle are–

Follicular phase, Ovulatory phase, and Luteal phase.
The ovulatory phase becomes most important in the terms of luteinizing hormone (LH) surge. In the follicular phase, at the beginning of the menstrual cycle, the follicle is developed. This cycle begins with the menstrual period, the shedding of the uterine lining and the shedding cleanses the lining of the uterus in preparation for ovulation during the ovulatory phase.

6. Explain the significance of the condition in which the testes remain suspended in the scrotum outside the abdomen.

Ans: The development of human sperm cells is not possible at body temperature. Spermatogenesis and maintenance of the seminiferous tubules require a temperature slightly lower than that of the body. Hence, the scrotum provides this which lies outside the abdominal cavity.

7. Describe the structure of a sperm with a diagram.

Ans: The sperm of the human is of a microscopic structure with a head, middle piece, and tail. The head comprises the haploid nucleus and an anterior acrosome which contains the enzymes required for the fertilization of the egg. The middle piece contains numerous mitochondria which are responsible to produce the energy for the mobility of the tail of the sperm.

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8. Enlist any two functions of a female placenta.

Ans: The Placenta is the structural and functional unit between the developing embryo and the mother which facilitates the supply of nutrients, oxygen to the embryo and is also responsible for the removal of carbon dioxide and other excretory products produced by the embryo. It also functions as an endocrine tissue, producing a variety of hormones.

9. What is the number of chromosomes in the following cells? Primary oocyte, secondary oocyte, ootid, and follicle.

Ans: The number of chromosomes in the cells is as follows:

Primary oocyte: 23 pairs. Secondary oocyte: 23. Ootid: 23. Follicle: 23 pairs.

10. What is corpus luteum? How does it function as an endocrine gland?

Ans: After ovulation, the graffian follicle ruptures & forms the corpus luteum. The Corpus luteum functions as endocrine glands as they secrete progesterone & estrogen in large quantities.

11. Where are leydig cells located? What do they secrete?

Ans: The location of Leydig cells or interstitial cells is in between the seminiferous tubules. Leydig cells secrete the male sex hormone TESTOSTERONE which promotes the development of accessory glands & control male secondary sexual characters.

12. Draw a well labeled diagram of T.S. of ovary?

Ans:

13. Why are testes of human males considered extra abdominal? 

Ans: Testis in human males is called extra-abdominal because testis is located outside the abdominal cavity in a pouch called the scrotum which provides a temperature 2-3 oC lower than the body temperature necessary for spermatogenesis.

14. Draw a diagram of the T.S. of seminiferous tubule of testis of an adult human male & label any four parts in it.

Ans:

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15. What is colostrum? What is its significance to a newborn baby?

Ans: The colostrum is the milk secreted from mammary glands just after birth for 2 or 3 days. It is rich in proteins & low in fats. It also contains the antibody IgA which provides immunity to newborn infants.

3 Marks Question

1. Mention the name and role of hormones which are involved in regulation of gamete formation in human male.

Ans: GnRH: Stimulates apophysis to secrete gonadotropins.

GSH: Stimulates Sertoli cells to secrete factors while helping in spermatogenesis.

ICSH: Stimulates interstitial cells to secrete testosterone.

2. Three of the steps of neuroendocrine mechanism in respect of parturition are mentioned below.

Write the missing steps in proper sequence.

1. Signals originate from fully developed foetus and placenta.

2. 
   
3. 
   

4. Oxytocin causes strong uterine contraction

5. Uterine contraction stimulates the further secretion of oxytocin.

6.  

Ans: b. Foetal ejection reflex

c. The reflex triggers the release of oxytocin

f. Expulsion of the baby out through the birth canal.

3. The events of the menstrual cycle are represented below. Answer the following questions.

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(i) State the levels of FSH, LH, and Progesterone simply by mentioning high or low around the 13th and 14th day and 21st to 23rd day.

Ans: 13-14th day 21st -23rd day FSH - High Low

LH - High Low Progesterone -Low High

(ii) In which of the above-mentioned phases does the egg travel to the fallopian tube?

Ans: End of the follicular or proliferative phase.

(iii) Why is there no menstruation after fertilization?

Ans: Menstruation does not occur during pregnancy upon fertilization due to high levels of progesterone secreted by persisting Corpus luteum and Placenta.

4. (a) Read the graph given below. Correlate the ovarian events that take place in the human female according to the level of the pituitary hormone during the following day.

(I)10th - 14th days
Ans: Gonadotropins and FSH increases

(ii) 14th -15th days

Ans: LH attains peak level but FSH decreases

(iii) 16th - 23th days

Ans: LH and FSH level decreases

(iv) 25th - 29th days (If the ovum is not fertilized)

Ans: LH remains low and FSH decreases.

(b) What are the uterine events that follow beyond the 29th day if the ovum is not fertilizer?

Ans: After the 29th day there is a menstrual flow involving the discharge of blood and cast off endometrium lining.

5. T.S. of mammalian testis revealing seminiferous tubules show different types of cell.

1. Name the two types of cells of germinal epithelium.

Ans: The germinal epithelium has two types of cells. 

1. Spermatogonium. 2. Sertoli cells

(ii) Name of cells scattered in connective tissue and lying between seminiferous tubules. Differentiate between them on the basis of their functions.

Ans: Leydig cells or interstitial cells.

Functions:

Spermatogonium undergoes meiotic division leading to sperm formation. 

Sertoli cell: Nourishes germ cells.

Leydig cell: Synthesise and Secrete hormone androgen.

6. What are the various male accessory glands? Give their function.

Ans: The male accessory glands is made up of paired seminal vesicles, a prostate gland, and paired bulbourethral glands. These glands secrete seminal plasma rich in fructose, calcium, and certain enzymes. Secretions of bulbourethral glands aid in the lubrication of the penis.

7. Explain the menstrual cycle with a diagram.

Ans: The menstrual cycle has three phases: menstrual, proliferative, and secretory.

1. Menstrual Phase: In females, the menstrual phase lasts for 3-5 days and during this period the endometrial lining of the uterus is cast off and is slowly passed out from the vagina as a mixture of blood.

2. Proliferative or Follicular Phase: Between the 6th and 16th day of the cycle, it lasts 11 days. One ovarian follicle is converted to a Graafian follicle during this phase, and the endometrial layer is regenerated, as well as the burst blood vessels are repaired. Estrogen levels rise. It comes to an end with ovulation.

3. Secretory Phase: It exists for 12 days and between 17-28 days. The Graafian follicle gets converted to Corpus Luteum. The endometrium grows and thickens further. Progesterone increases. It ends with the conversion of the corpus luteum to corpus albican.

8. Differentiate between spermatogenesis and oogenesis.

Ans: Below given are the differences between spermatogenesis and oogenesis:-

9. ‘A fertilized egg is the blueprint of future development’. Explain

Ans: The 23 chromosomes in the sperm, including the male sex chromosome X or Y, carry the genetic material from the father, whereas the egg carries the material from the mother (including the female sex chromosome X). Hence, during conception, the union of the male and female gametes creates a novel genetic combination that adds variety in the progeny. The genetic material that regulates how the embryo develops is found in the zygote or fertilised egg.

10. Briefly describe the stages of spermatogenesis in humans?

Ans: Spermatogenesis consists of two phases:-

1. Formation of Spermatids:- It further consists of 3 phases

1. Multiplication phase:-  Sperm mother cells or Spermatogonia are produced by the repeated division of undifferentiated germ cells.

2. Growth phase:- Spermatogonia increase in volume & is now called Primary Spermatocytes.

3. Maturation phase: - primary spermatocyte undergoes meiosis I to produce small size haploid secondary spermatocyte divided by meiosis – II & forms haploid Spermatids.

II. Formation Of Sperms:- The transformation or differentiation of spermatids into spermatozoa or sperm is called spermiogenesis & occurs under the influence of FSH.

11. Describe the hormonal control of the human male reproductive system with the help of a flow chart & highlight the inhibitory & stimulatory directions in it?

Ans: i) Spermatogenesis is initiated due to an increase in the secretion of Gonadotropin releasing hormone from the hypothalamus at the age of puberty.

1. The increased levels of GnRH act on the anterior pituitary stimulate the secretion of two gonadotropins i-e. luteinizing hormone (LH) & follicle-stimulating hormone (FSH)

2. LH stimulates the Leydig cells to secrete testosterone

3. FSH acts on Sertoli cells & stimulates the secretion of some factors that help in spermatogenesis.

12. A sperm has just fertilized a human egg in the fallopian tube. Trace the events that the fertilized eggs will undergo upto implantation of the blastocyst in the uterus.

Ans: 1. Cleavage:- The fertilized egg starts dividing lay specific mitotic divisions called cleavage. The zygotes undergo mitotic division in the isthmus of the oviduct to form daughter cells, the cells formed as a result of cleavage called a blastomere.

2. Blastocyst:- 3-4 days after fertilization, the morula twins into a large mass of cells called blastocyst Outer peripheral cells enlarge & flatten further & form trophoblast. Trophoblast cells secrete a fluid into the interior & form a cavity called the blastocoel. The embryonic stage with blastocoel is called a blastula.

13. Where oogenesis does take place. Describe the stages of this process?

Ans: The process of formation & maturation of the ovum is called oogenesis. It takes place in the ovary & is initiated during the embryonic development of the female fetus. It consists of 3 phases:--

1. Multiplication phase:- Oogonia is produced when primordial germ cells split through meiosis. These oogonia divides lay repeated mitotic divisions forming clusters. In each cluster, only one of them enters into the growth phase & is called the primary oocyte.

2. Growth phase:- Growth phase occurs only after attainment of puberty. It involves – increases in the size of the oocyte to many folds & synthesis of you.

3. Maturation phase:- The first division is meiotic as a result two haploid (n) cells are produced. In this division, cytokinesis is unequal, a large daughter cell with almost all cytoplasm is called a secondary oocyte & a smaller me with less cytoplasm is called a polar body. The secondary oocyte then undergoes a second meiotic division to form an ovum & a second polar body.

5 Marks Questions

1. 

Ans:

(i) ’D’ Spermatids = undergo spermatogenesis

2. ‘A’= Spermatogonium; B = Primary spermatocyte

3. ‘B’ = Diploid 'E' = Haploid

4. ‘F’ = Sertoli cells - Nutrition to germ cells

5. Mitosis in Cell ‘A’, Meiosis in cell ‘B’

2. Explain the development of human embryos with diagrams.

Ans: The Fusion of the sperm and the egg in humans results in the formation of the diploid structure called a zygote. The zygote undergoes mitotic division as it travels through the oviduct into the uterus to form 2,4,8,16 daughter cells which are called blastomeres. The stage is called a morula. The Morula divides further and differentiates into blastocysts. The outer layer of blastomeres called the trophoblast gets attached to the endometrial layer of the uterus.

The blastocysts are divided and encased by the uterine wall, which is referred to as implantation. The embryo is formed by the inner layer of blastomeres in the blastocysts.

3. What is menstruation? What are the specific actions of FSH, LH, estrogen & progesterone in the menstrual cycle?

Ans: During the menstrual phase of the menstrual cycle which starts on the 28th day, the endometrial lining of the female genital tract breaks down due to lack of progesterone As a result bleeding occurs. This monthly flow of blood is called menstruation.

During menstrual cycles, the various changes occur in the ovary under the influence of various hormones:-

1. Menstrual phase:- The levels of hormones LH, FSH estrogen & progesterone is very less which results in the breakdown of the endometrial lining of the uterus.

2. Follicular phase:- In this phase, the levels of pituitary hormones FSH & LH increase which causes ovarian hormone estrogen to release, FSH controls the follicular phase, it stimulates the growth of follicles. Both FSH & LH reach their peak level in the middle of the cycle (14th day)

3. Ovulatory Phase:- The level of LH hormones reaching its peak (called LH swing) induces the ruptures of mature Graffian follicle & thereby release of ovum.

4. Luteal phase:- The LH & FSH hormones begin to decline. After ovulation, the follicle ruptures & is transformed into the corpus Luteum which secretes large quantities of progesterone.

4. A woman has conceived & implantation has occurred within her uterus. Discuss the sequence of changes up to parturition which will take place within her body under the influence of various hormones.

Ans: The following changes take place in the body of women after implantation:-

1. The trophoblast differentiates into two layers; the outer layer secretes enzymes to dissolve the endometrium of the uterus.

2. The inner layer grows out as finger-like projections called chorionic villi into the uterine stroma. The chorionic villi & the uterine tissue become interdigitated to form a structural & functional unit called the placenta.

3. Placenta secretes hormones like HCG, HPL, estrogen & progesterone that are necessary to maintain pregnancy

4. The umbilical cord, the structure that connects the placenta with the fetus is formed.

5. Simultaneously, inner cell mass differentiates into an outer layer called ectoderm & an inner layer called endoderm. & a middle layer called mesoderm appears between ectoderm & endoderm.

6. The primary germ layers give rise to all the tissues & organs of the adults e.g. after one month the heart is formed & after the second month the digits & limbs are formed.

7. By the end of the ninth month of pregnancy, the foetus is completely developed & is ready for delivery.

8. During parturition, the ovary secretes a hormone called relaxin that facilitates parturition which softens the connective tissue. Mild contraction called foetal ejection reflex is induced. This triggers the release of oxytocin from the posterior pituitary. Oxytocin induces stronger leads to the expulsion of the baby from the uterus, through the birth canal.

CBSE Class 12 Biology Chapter 2 Important Questions - Free PDF Download

Introduction - Human Reproduction Class 12

In-depth explanations of the chapter's concepts, rules, key questions, and exam-relevant subjects are provided by Vedantu. Subject matter experts from Vedantu have selected these crucial topics and questions. The chapter's key questions as well as the exam format are revealed in Chapter 2 of Biology for Grade 12. Some topics also have PDF versions that students can download to any device and practise at any time. Vedantu topic teachers have outlined the crucial ideas and key questions of the chapter, which is part of CBSE biology chapter 2 for class twelve.

Human Reproduction class 12 chapter 2 continues with the understanding of the human reproduction system that students have already cleared in earlier classes. More new concepts are introduced in class 12.

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Human Reproduction Chapter 2 Class 12 - Biology

Humans are sexually reproducing. The reproductive results in humans include the formation of gametes (sperms in males and eggs in females). The event results in the transfer of sperms into the female genital tract and fusion of male and female genital tract leading to the formation of zygote. This is also known as insemination and fertilization respectively. This process is followed by the formation and development of blastocytes and their attachment to the uterine wall, also known as implantation. The embryonic development is known as gestation and the delivery of the baby as parturition.

The male reproductive system consists of two types of sex organs 1. Primary ( a pair of testes suspended in a scrotum ) and 2. Secondary sex organs. ( pair of ducts and associated glands )

The female reproductive system consists of the following:

1. Primary sex organs ( a pair of ovaries )

2. Secondary sex organs ( duct system consisting of pair of fallopian tube, uterus, cervix, and vagina )

3. External genitalia

4. Mammary glands

Female external genitalia includes:

1. Mons pubis - a cushion of fatty tissues

2. Labia majora - Fleshy fold that surrounds the vaginal opening

3. Labia Manora - It is the paired fold of tissue located under labia majora.

4. The opening of the vagina is covered by a membrane called the hymen. The tiny finger-like projection present at the upper junction is termed the clitoris.

Mammary glands are paired structures that contain glandular tissues and fats. 15 to 20 mammary lobes are present in each mammary gland. These lobes containing alveoli secrete milk. Mammary ducts join to form the mammary ampulla. 

Structure of sperm: Sperm is a microscopic structure composed of a head, neck, middle body, and tail. The acrosome is a covered cap-like structure on sperm. 

The human male ejaculates about an average of 200 to 300 million sperms during sexual intercourse.

Process of reproduction: The process of reproduction starts as phase-wise and is discussed below in brief:

1. Pre fertilization: Here gametes are formed and transferred

2. Fertilization: Formation of zygote takes place after the sperm fertilizes the egg

3. Post fertilization: Embryo is formed from the result of the mitotic division of the zygote. The reproductive stage is referred to as embryogenesis.

Duration and Stages of Pregnancy:

Human gestation lasts for an average of 9 months and these intervals are called trimesters.

Let us discuss the phases of pregnancy in brief:

1. First trimester - pre embryonic and embryonic development ( First 3 months or week 1 to 12 )

2. Second trimester - This phase begins with fetal development ( The next 3 months or week 13 to 24 )

3. The third trimester - At this stage, the baby continues to grow and mature. Babygrows its organs ( the next 3 months or week 25 to the birth of the baby )

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Human Reproduction Class 12 - Important Questions

Q1. Describe the Term Parturition and Lactation?

Ans. Parturition is the term used for the process of a fully developed fetus. Signals of parturition originate from a fully developed fetus and placenta inducing mild uterine contractions. These contractions are named as Foetal ejection reflex.

It also triggers the release of oxytocin from the maternal pituitary.

Lactation is the term used when the mammary glands of a female start producing milk. It happens to end the pregnancy by the process called lactation. The milk produced during the initial days of lactation is called colostrum which contains several antibodies useful for the baby.

Q2. Discuss in Detail the Menstrual Cycle and Its Phases

Ans. Menstrual cycle: The reproductive cycle that starts in female primates is known as the menstrual cycle. It starts from puberty and is termed menarche. It undergoes four phases during its cycle namely:

1. Menstrual phase - The menstrual cycle usually range from 28 to 35 days. In a menstrual cycle, the menses take place on cycle days of 3 to 5. In this process, the production of LH from the anterior lobe of the pituitary gland is reduced and causes degeneration of the corpus luteum. It results in the following:

1. Progesterone production is reduced

2. Production of estrogen is reduced

3. Menstruation begins after the endometrium of the uterus breaks down

4. The menstrual flow consists of cells of endometrium secretion, blood, and unfertilized ovum

2. Follicular phase - This phase includes cycle days 6 to 13 on a 28 days cycle. The following changes are observed:

1. The FSH secreted stimulates the ovarian follicle to secrete estrogens.

2. Estrogen stimulates the proliferation of the uterine wall

3. The endometrium becomes thicker and this is accompanied by an increase in uterine glands and blood vessels.

3. Ovulatory phase - In this phase:

1. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) attain the peak level during the middle stage of the cycle

2. Estrogen concentration in blood increases

3. LH causes ovulation

4. Rapid release of Lh results in the release of the ovum.

4. Luteal phase - In this phase:

1. It includes cycle days of 15 to 28

2. Progesterone is secreted by corpus luteum

3. Endometrium thickens

4. Uterine glands become secretory

Conclusion

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