Important Questions for Class 12 Chapter 3: Human Reproduction

Humans reproduce through sexual mode and are viviparous. Before the event of fertilization, a series of events take place which differs in males and females. Gametogenesis in males is called spermatogenesis whereas in females it is oogenesis, both of whose outcomes are different, i.e., sperm and an ovum respectively. The formation of the zygote is followed by the development of the blastocyst which passes through different stages of development before childbirth. Through this chapter, we get to understand the human male and female reproductive system and functionalities of various reproductive organs in depth.

Very Short Answer Type Questions

Q.1. List the following events observed in human reproduction in chronological order. Fertilization, gametogenesis, insemination, gestation, parturition, implantation.

A.1. Following is the sequence of events occurring in the process of human reproduction:

  1. Gametogenesis
  2. Insemination
  3. Fertilization
  4. Implantation
  5. Gestation
  6. Parturition

Q.2. Fill in the missing boxes exhibiting route of sperm transport.
Question - missing boxes
A.2. Following is the pathway followed by a sperm.
Answer- missing boxes

Q.3. State the significance of cervix in the female reproductive system.

A.3. The cervix is a narrow opening through which the uterus opens up to the vagina. The cervical canal is the cavity of the cervix which alongside the vagina goes on to form the birth canal.

Q.4. What is the reason for the absence of menstrual cycles during conception or pregnancy?

A.4. During pregnancy, all the events of the menstrual cycle stop and there is no menstruation. Menstruation occurs only when the egg that is released is not fertilized. But in pregnancy, the released egg is fertilized and hence the uterus lining does not shed, instead nourishes the fetus. However, a woman may experience uterine bleeding during pregnancy due to various reasons. It is not due to the period.

Q.5. Fill up the missing data in the table where Column A shows female reproductive organs and Column B shows its respective functions.

Column A
(Organs)
Column B
(Corresponding Functions)
Ovaries Ovulation
Oviduct
Pregnancy
Vagina Birth

A.5. Following are the female reproductive organs and their associated functions.

Column A
(Organs)
Column B
(Corresponding Functions)
Ovaries Ovulation
Oviduct Fertilization
Uterus Pregnancy
Vagina Birth

 

Q.6. Name the hormone crucial in parturition. Does the parturition signal originate from the mother or the fetus?

A.6. The hormone is Oxytocin. The signal originates from the placenta and fully developed fetus which initiate the foetal ejection reflex triggering the release of the hormone, oxytocin.

Q.7. State the role of epididymis in male fertility.

A.7. It is situated along the posterior surface of each testis where spermatozoa acquire motility and the capacity to fertilize the egg. The surface of the sperm is altered in response to secretions of the epididymis which is key to achieve the ability to fertilize an egg.

Q.8. List the names of the hormones, endocrine glands along with functions of the hormones that are crucial in causing spermatogenesis.

A.8. The table below provides the required data:

Name of the hormone Endocrine glands where the hormone is released Functions of the hormone
Gonadotropin-releasing hormone(GnRH) Hypothalamus Increase in secretion of GnRH initiates spermatogenesis at puberty age After acting on the anterior pituitary gland – triggers secretion of LH and FSH
Luteinising hormone(LH) Anterior pituitary gland Triggers the production and secretion of androgens
Follicle Stimulating Hormone (FSH) Pituitary gland Acts on Sertoli cells and stimulates secretion

 

Q.9. Fill in the missing boxes for the levels in the transformation of mother germ cells into a mature follicle.
Question - missing boxes
A.9. The various steps in the formation of the mature follicle are as follows:
Answer- missing boxes

Q.10. What are the events that cause the chromosome number of gametes to go from 2n, n, and again back to 2n during reproduction?

A.10. Chromosomes replicate once but divide twice. They undergo mitosis, first meiotic cell division and second meiotic cell division, the outcome of which is n number of chromosomes. They fuse with the haploid(n) sex gamete of the opposite sex to form a diploid(2n) cell during reproduction.

Q.11. How is a primary oocyte different from a secondary oocyte?

A.11. Primary oocyte is a diploid cell whereas secondary oocyte is a haploid cell. Primary oocyte is formed when oogonia are at the prophase-I of the meiotic division in the foetal ovary whereas secondary oocyte is formed from primary oocyte after meiosis – I division to produce ova in females during the stage of puberty.

Q.12. State the role of the ampullary-isthmic junction in the female reproductive tract.

A.12. In the ampullary-isthmic junction, fertilization of the ovum takes place.

Q.13. How is polyspermy checked by the zona pellucida of the ovum?

A.13. The zona pellucida is a thick layer that is girdled by corona radiata cells. During fertilization, cortical granules are released from the egg which blocks fusing of multiple sperms with an egg.

Q.14. What is the significance of LH surge through the menstrual cycle?

A.14. It triggers the rupture of Graafian follicle and causes the release of the ovum in the fallopian tube.

Q.15. During which stage of cell division are spermatids formed from the secondary spermatocytes?

A.15. The second meiotic division.

Short Answer Type Questions

Q.1. State the significance of the following stages during the lifetime of a female.

  1. Menarche
  2. Menopause

A.1. The first menstruation or onset of menstruation at puberty is referred to as menarche. It indicates the attainment of sexual maturity and the commencement of the fertile period. Menstruation cycle is the cycle of events from one up till the next menstruation and is repeated for about 28 days on an average wherein one ovum is released. Menopause, on the other hand, is when the menstruation cycle comes to a halt, indicating the end of the fertile period as the process of ovulation stops. Cyclic menstruation denotes a regular reproductive phase stretching from menarche to menopause.

Q.2.

a. How many spermatozoa does one secondary spermatocyte produce?

b. Where in zygote does the first cleavage division occur?
A.2. a. The secondary spermatocytes undergo meiotic division – II to generate four haploid spermatids which through the process of spermiogenesis are transformed into spermatozoa.

A.2. b. Cleavage occurs within the fallopian tube and is holoblastic, dividing the zygote completely into blastomeres. The first cleavage divides the zygote longitudinally into two blastomeres wherein one is slightly larger than the other.

Q.3. Why does corpus luteum stay active throughout pregnancy and in the absence of fertilization, is active only for 10-12 days?
A.3. During the luteal phase, the leftover parts of Graafian follicle transform into the corpus luteum. It discharges large quantities of progesterone hormone which is required for the maintenance of the endometrium. The endometrium is important for implantation of the fertilized egg and various other stages of pregnancy. Hence corpus luteum has a long life in pregnancy. In the absence of fertilization, upholding of the corpus luteum is not required and thus it declines within 10-12 days, which causes the lining of the endometrium to menstruate and hence the onset of the new menstrual cycle.

Q.4. What is foetal ejection reflex? How does it cause parturition?

A.4. Foetal ejection reflex is the mild uterine contractions that arise from the parturition signals from the fully developed fetus and the placenta. This reflex stimulates the release of oxytocin, which causes uterine contractions, in turn, stimulating the increased secretion of oxytocin. This action of uterine contractions and oxytocin secretion further results in stronger contractions leading to the dilation and hence expulsion of the baby out of the uterus through the cervical canal, expelling placenta along, thus the parturition or childbirth.

Q.5. What are the functions of placenta other than its endocrine function?

A.5. The placenta promotes the supply of nutrients and oxygen to the embryo. It also facilitates the elimination of excretory wastes and carbon dioxide produced by the embryo. Placenta aids in the transportation of substances to and from the embryo as it is connected to the embryo through the umbilical cord.

Q.6. Why is breastfeeding recommended during the initial stages of infant growth?

A.6. The mammary glands in females start producing milk towards the end of pregnancy through the process of lactation which helps the mother feed the newborn. Colostrum is the milk produced during the initial few days. Colostrum contains antibodies which are crucial in developing resistance in the newborns hence it is recommended by doctors to bring up a healthy baby.

Q.7. What are the different stages of the follicular phase of the menstrual cycle taking place in ovary and uterus?

A.7. In this phase, primary follicles transform into the fully mature Graafian follicle in the ovary. The endometrium of the uterus simultaneously regenerates through proliferation. Changes in the levels of ovarian and pituitary hormones induce changes in the uterus and ovaries. During this stage, the secretion of FSH and LH eventually increases and triggers the secretion and follicular development of estrogen by the growing follicles. In the middle of the cycle, both LH and FSH reach the peak level. This speedy secretion of LH at the maximum level during the mid-cycle causes rupture of Graafian follicle and hence ovulation.

Q.8. Mention the names of the hormones responsible for ovarian changes during the menstrual cycle in the boxes provided.
Question- missing boxes

A.8. Hormones responsible for the various stages of the menstrual cycle are:
Answer- missing boxes
Q.9. Draw a schematic diagram depicting oogenesis. (Label without description)
A.9.
Schematic diagram depicting oogenesis

Q.10. Mention the changes taking place during the transition of a primary follicle to Graafian follicle in the oogonia.

A.10. Oogonia or the gamete mother cells are formed within each fetal ovary. No more oogonia are formed after birth. They enter into the prophase-I stage of meiotic division when they start cell division to approach the primary oocyte stage. These primary oocytes are girdled by a layer of granulosa cells to form the primary follicle which degenerates during the stages of birth to puberty. The primary follicles are encircled by more layers of granulosa cells and a new theca known as secondary follicles. The theca is subdivided into other theca externa and an inner theca interna which secretes estrogen. The secondary follicle is then transformed into a tertiary follicle characterized by antrum, which is a fluid-filled cavity. At this phase, the primary oocyte grows in size inside the tertiary follicle to complete the first meiotic division. The tertiary follicle finally transitions to form the Graafian follicle.

Long Answer Type Questions

Q.1. Explain the role of pituitary gonadotropins during the follicular and ovulatory phases of the menstrual cycle. Describe the shifts in steroidal secretions.

A.1. The menstrual flow is due to the breakdown of the lining of the uterine endometrium and blood vessels which forms the liquid discharged from the vagina. The menstrual cycle is controlled through the pituitary gland by the hypothalamus. Changes in the ovary and uterus during the menstrual cycle is due to the fluctuation in the levels of ovarian and pituitary hormones. Towards the end of the menstrual phase, the pituitary FSH eventually increases which causes the development of the follicles inside the ovaries. Both the FSH and LH attain a peak level during the mid of the cycle. This speedy secretion of LH leads to LH surge which induces rupture of the Graafian follicle and hence the ovulation. During the maturation of follicles, more of estrogen is secreted causing a surge in FSH and LH from the anterior pituitary. The LH surge causes ovulation. The LH also induces luteinisation. The LH hormone causes the conversion of empty follicle into the corpus luteum. The Corpus luteum produces steroidal hormones – progesterone and estrogen. These hormones govern the growth and maintenance of the uterine endometrium for probable implantation.

Q.2. Explain in detail the difference between the meiotic division of oogenesis and spermatogenesis.

A.2. Spermatogenesis is the production process of sperm from the male germ cell whereas oogenesis is the production process of the eggs from the oogonia in females. Meiosis is different in spermatogenesis and oogenesis in the quantity of the end product. This unequal division is necessary to maintain the essential part of the cytoplasm. One minor part is detached as the polar body where a single daughter cell called the ovum is formed which is functional. But in spermatogenesis, four spermatids are produced which are functional and that later develops into spermatozoa.

Oogenesis Spermatogenesis
Production of eggs from oogonia Production of sperm from spermatogonia
Takes place inside the ovary in females Takes place inside the testes in males
All except the last phase takes place inside the ovary All phases occur inside the testis
Early stages observed during the fetal period. Rest stages observed between puberty and menopause A continuous process that is initiated from puberty and lasts until death
Matured from germinal epithelium overlying the ovary Developed from the germinal epithelial lining of the seminiferous tubules
Sertoli cells not found in germinal cell epithelium Sertoli cells found in germinal cell epithelium
Few oogonia divide to produce eggs, one at a time Spermatogonia are divided by meiosis to produce sperms
Lengthy growth phase in oogonia The growth phase of spermatogonia is short
Generates non-motile gametes Produces motile gametes
Primary oocyte divides to form a secondary oocyte and polar body during meiosis-I During meiosis-I, primary spermatocyte divides to form two secondary spermatocytes

Q.3. Explain in detail the various developmental stages of the zygote until implantation with suitable diagrams.

A.3. When the zygote moves through the isthmus of the oviduct, the mitotic division is initiated and is called the cleavage towards the uterus to form 2,4,8,16 daughter cells called blastomeres. The embryo containing 8 to 16 blastomeres form the morula. It continues to transform and divide into blastocysts as it further approaches the uterus. In the blastocyst, the blastomeres are organized into an outer layer referred to as the trophoblast and the inner cell mass which is an inner collection of cells attached to the trophoblast. This layer gets attached to the endometrium and the inner cell mass transforms into the embryo. After attachment, the cells of the uterus rapidly divide and covers up the entire blastocyst. This causes the blastocyst to implant in the endometrium of the uterus which leads to conception.
Developmental stages of the zygote

Q.4. With the help of a neat labelled diagram of the female reproductive system, depict the following sites:

(a)production of gamete
(b)site of fertilization
(c)site of implantation
(d)birth canal

diagram of the female reproductive system

Q.5. Explain the organization of the mammary gland with the help of a diagram.

A.5. One of the characteristics of the female mammals is that they possess functional mammary glands. They are paired structures and contain glandular tissues and fat that varies in individuals. The glandular tissue is organized into 15-20 mammary lobes in each breast. Which possess alveoli which are a cluster of cells. These alveolar cells secrete milk that is stored in the lumens or cavities of the alveoli. The alveoli open into the mammary tubules. These tubules in each of the lobes combine to form the mammary duct. Many such mammary ducts join to form a mammary ampulla that is connected to the lactiferous ducts. Through these structures, milk is sucked.

 

organization of the mammary glandTo know more about human reproduction, or any other topic, please visit BYJU’S biology.

Related Links:

 

Leave a Comment

Your email address will not be published. Required fields are marked *