HOTs Human Reproduction Class 12 Biology

HOTs for Class 12

The Male Reproductive System

Very Short Answer Type Questions

Question. Why are the human testes located outside the abdominal cavity ? Name the pouch in which they are present. 
Answer. The human testes are located outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2- 2.5°C) lower than the normal internal body temperature, necessary for spermatogenesis.

Question. Write the location and functions of the following in human testes :
(a) Sertoli cells
(b) Leydig’s cells
Answer.
(a)The cells that nourish the germ cells in the testes are called Sertoli cells. Sertoli cells are located in the germinal epithelium of the seminiferous tubules.
(b) Leydig’s cells synthesise and secrete testicular hormones called androgens. 

Question. Why does failure of testes to descend into the scrotum produce sterility?
Answer. Sterility results because spermatogenesis requires a temperature 2–2.5°C lower than the internal body temperature, which is maintained by scrotum.

Question. What is the function of Leydig’s cells?
Answer. Leydig’s cells synthesise and secrete testicular hormones called androgens.

Question. Name the cells that nourish the germ cells in the testes. Where are these cells located in the testes? 
Answer. The cells that nourish the germ cells in the testes are called Sertoli cells. Sertoli cells are located in the germinal epithelium of the seminiferous tubules.

Question. Write the function of the seminal vesicle.
Answer. Seminal vesicle produces an alkaline secretion that helps to neutralise the acidic environment of the male urethra as well as that of female reproductive tract.

Question. Draw a diagrammatic of a sectional view of seminiferous tubule of a human.
Answer. Sectional view of human seminiferous tubule is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Give reasons for the following :
The human testes are located outside the abdominal cavity.
Answer. The human testes are located outside the abdominal cavity within a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2- 2.5°C) lower than the normal internal body temperature, necessary for spermatogenesis.

Question. Explain the role of Sertoli cells in the development of sperms. 
Answer. Sertoli cells are present in between the germinal epithelial cells of the seminiferous tubules. They provide nourishment to the developing spermatozoa and also secrete androgen binding protein that concentrates testosterone in the seminiferous tubules.

Question. Where are the Leydig’s cells present? What is their role in reproduction?
Answer. Leydig’s cells or interstitial cells are small group of cells present between the seminiferous tubules in the connective tissue.


Short Answer Type Questions

Question. Who discovered Sertoli cells? Mention their role in spermatogenesis.
Answer. Sertoli cells were discovered by Enrico sertoli,an Italian physiologist. He published a description of this cell in 1865. Sertoli cells provide nutrition to germ cells that undergo spermatogenesis to form spermatozoa. 

Question. Draw a sectional view of seminiferous tubules of human. Label Sertoli cells, spermatogonia and Leydig’s cell on it and write their function.
Answer.Sectional view of human seminiferous tubule is as follows:

HOTs Human Reproduction Class 12 Biology

Functions:
(i) Sertoli cells : The cells that nourish the germ cells in the testes are called Sertoli cells. Sertoli cells are located in the germinal epithelium of the seminiferous tubules.
(ii) Spermatogonia : During spermatogenesis, spermatogonia grow into primary spermatocytes which undergo meiosis, producing haploid cells, First secondary spermatocytes and then spermatids. The spermatids then convert into spermatozoa (sperms).
(iii) Leydig’s cell: Leydig’s cells synthesise and secrete testicular hormones called androgens.

Question. Differentiate between the location and function of Sertoli cells and Leydig’s cells.
Answer.Leydig’s cells and Sertoli cells are located in testis.
Differences between Leydig’s cells and Sertoli cells are as follows :

HOTs Human Reproduction Class 12 Biology
HOTs Human Reproduction Class 12 Biology

Question. The above diagram shows human male reproductive system (one side only).

HOTs Human Reproduction Class 12 Biology

(a) Identify ‘X’ and write its location in the body.
(b) Name the accessory gland ‘Y’ and its secretion.
(c) Name and state the function of ‘Z’
Answer. (a) X is testis. It is located outside the abdominal cavity within a pouch called scortum.
(b) Y is seminal vesicle. It produces an alkaline secretion which forms 60% of the volume of the semen.
(c) Z is epididymis. It stores the sperms and also secretes a fluid which nourishes the sperms.


Long Answer Type Questions

Question. (a) Draw a labelled diagrammatic view of human male reproductive system.
(b) Differentiate between :
(i) Vas deferens and vasa efferentia.
(ii) Spermatogenesis and spermiogenesis.
Answer.(a) Diagrammatic view of human male reproductive system is as follows:

HOTs Human Reproduction Class 12 Biology

(b) (i) Differences between vasa efferentia and vasa deferentia are as follows:

HOTs Human Reproduction Class 12 Biology

(ii) Differences between spermatogenesis and spermiogenesis are as follows:

HOTs Human Reproduction Class 12 Biology

The Female Reproductive System

Very Short Answer Type Questions

Question. Write the function of (oviducal) fimbriae.
Answer. Fimbriae help in the collection of ovum, after ovulation.

Short Answer Type Questions

Question.  Mention the names and the characteristics of different uterine wall layers in humans. Which one of them undergoes cyclic changes during menstrual cycles? 
Answer.The wall of the uterus is composed of three layers of tissues. The perimetrium is an outer thin covering of peritoneum. The myometrium is a middle thick layer of smooth muscle fibres which shows strong contraction during delivery of the baby. The endometrium is inner glandular layer that lines the uterine cavity. The endometrium undergoes cyclical changes during menstrual cycle.

Question. Draw a labelled diagram of the human female reproductive system.
Answer.Labelled diagram of human female reproductive system is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Write two major functions each of testis and ovary.
Answer. Functions of testis:
(i) It produces sperms (male gametes).
(ii) It secretes male sex hormones i.e., androgens
(e.g., testosterone).
Functions of ovary :
(i) It produces ova (female gametes).
(ii) It secretes female sex hormones e.g., estrogen and progesterone.

Question. Explain the functions of myometrium and endometrium in human females.
Answer.Myometrium is middle thick layer of smooth muscles fibres that brings about contraction of the uterus during the delivery of the baby. The endometrium is the inner glandular layer that undergoes cyclical changes during the menstrual cycle.

Question. Where are fimbriae present in human female reproductive system? Give their function.
Answer.The edges of the infundibulum possess finger like projections called fimbriae, which help in collection of the ovum after ovulation. 

Short Answer Type Questions

Question.

HOTs Human Reproduction Class 12 Biology

The diagram above shows a part of the human female reproductive system.
(a) Name the gamete cells that would be present in ‘X’ if taken from a newborn baby.
(b) Name ‘Y’ and write its function.
(c) Name ‘Z’ and write the events that take place here. 
Answer.(a) Primary oocytes will be present in ovary
(X) of a newborn baby.
(b) Y is fimbriae. 
(c) Z is the ampullary-isthmic junction. It is the site of fertilisation in humans.

Question. Name and explain the role of the inner and middle walls of the humans uterus.
Answer.The inner glandular wall of the uterus is known as endometrium.
Role – During the menstrual cycle, the endometrium wall grows into a thick, vascular (blood vessel-rich) glandular layer. This condition of the endometrium favours the implantation of the foetus. If fertilisation does not occur, the endometrium is shed during the hemorrhagic phase of the menstrual cycle.
The middle wall of the uterus is known as myometrium.
Role – It consists of smooth muscles. It exhibits contraction during delivery of the baby.

Question. Draw a diagrammatic sectional view of the female reproductive system of human and label the parts
(i) where the secondary oocytes develop
(ii) which helps in collection of ovum after ovulation
(iii) where fertilisation occurs
(iv) where implantation of embryo occurs.
Answer.Diagrammatic sectional view of female reproductive system is as follows:

HOTs Human Reproduction Class 12 Biology

Gametogenesis

Very Short Answer Type Questions

Question. Sperms have a tail whereas eggs do not. Why so?
Answer.Sperms are tailed whereas eggs do not as sperms have to move (tail helps in locomotion) through the cervix, uterus and Fallopian tube to reach to the egg already present there.

Question. Write the function of acrosome of human sperm. 
Answer.Acrosome contains enzymes called spermlysins that are used to contact and penetrate the ovum at the time of fertilisation.

Question. Define spermiogenesis. Where does it occur?
Answer.The process of transformation of spermatids into sperms is called spermiogenesis. It occurs in seminiferous tubules.

Question. Where is acrosome present in humans? Write its function. 
Answer.Acrosome is present in the head of the human sperm.Acrosome contains enzymes called spermlysins that are used to contact and penetrate the ovum at the time of fertilisation.

Question. When do the oogenesis and the spermatogenesis initiate in human females and males respectively? 
Answer.
Oogenesis begins during embryonic development stage while spermatogenesis begins during puberty.

Question. Mention the difference between spermatogenesis and spermiation. 
Answer.The process of formation of sperms is called spermatogenesis while release of sperms from the seminiferous tubules is called spermiation.

Question. List the changes the primary oocyte undergoes in the tertiary follicular stage in the human ovary. 
Answer. The primary oocyte grows in size and completes its fist meiotic division within the tertiary follicle.

Short Answer Type Questions

Question. Name the labels a, b, c, d, e, f in the diagram of seminiferous tubule.

HOTs Human Reproduction Class 12 Biology

Answer.In the given diagram of seminiferous tubule a–Spermatogonium, b–Primary spermatocyte, c–Spermatid, d–Secondary spermatocyte, e–Spermatozoa, f–Sertoli cell

Question. Draw a labelled diagram of a Graafian follicle.
Answer.The labelled diagram of Graagian follicle is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Draw and label the parts of the head region only of a human sperm. 
Answer. Labelled parts of head region of human sperm is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Mention the event of meiosis that occurs in the tertiary follicle in a human ovary.
Answer.When the secondary follicle transforms into tertiary follicle, the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body.

Question. Explain the role of pituitary and sex hormones in the process of spermatogenesis.
Answer. During spermatogenesis, gonadotropin releasing hormone (GnRH) is secreted by the hypothalamus, which stimulates the anterior pituitary gland to secrete luteinising hormone (LH) and follicle stimulating hormone (FSH). LH acts on the Leydig’s cells of the testes to secrete testosterone while FSH acts on Sertoli cells of the seminiferous tubules of the testes to secrete androgen binding protein (ABP) and inhibin. ABP concentrates testosterone and inhibin suppresses FSH synthesis. FSH also acts on spermatogonia to stimulate sperm production.

Question. Draw labelled diagram of a human sperm.
Answer.Labelled diagram of a human sperm is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Draw a diagrammatic sectional view of a human seminiferous tubule and label Sertoli cell, primary spermatocyte, spermatogonium and spermatozoa in it.
Answer.Sectional view of human seminiferous tubule is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Write the function of each of the following :
(a) Middle piece in human sperm.
(b) Luteinising hormone in human males.
Answer.(a) The middle piece in human sperm possesses numerous mitochondria, which produce energy for the movement of tail that facilitate sperm motility essential for fertilisation.
(b)Labelled parts of head region of human sperm is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Identify A, B, C and D with reference to gametogenesis in humans, in the flow chart given below.

HOTs Human Reproduction Class 12 Biology

Answer.A – Leydig’s cells, B – Sertoli cells,
C–Spermatogenesis, D – Spermiogenesis

Question. Differentiate between gametogenesis in human males and females on the basis of
(a) time of initiation of the process.
(b) Products formed at the end of the process.
Answer.Gametogenesis in human males is called spermatogenesis while it is called oogenesis in human females.
(a) Spermatogenesis is initiated at the time of puberty and oogenesis is initiated at the stage of embryonic development.
(b) In spermatogenesis, four spermatozoa are formed from one spermatogonia while in oogenesis one ovum is formed from one oogonium.

Question. Draw a detailed structure of a human sperm.Label the cellular components.
Answer.Detailed structure of human sperm with labelled cellular components is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Draw a diagram of human sperm. Label only those parts along with their functions, that assist the sperm to reach and gain entry into the female gamete. 
Answer. Diagram of a human sperm with labelled parts that assist in sperm to reach and gain entry into female gametes is as follows:

HOTs Human Reproduction Class 12 Biology

Functions:
Acrosome – It contains enzymes called spermlysins that are used to contact and penetrate the egg at the time of fertilisation.
Mitochondrial spiral – It provides energy for the movement of the sperm.
Tail – It help the sperm to reach to the egg.

Question. Draw a diagram of the microscopic structure of human sperm. Label the following parts in it and write their functions.
(a) Acrosome
(b) Nucleus
(c) Middle piece 
Answer. The diagram of a human sperm with labelled parts–acrosome, nucleus and middle piece is as follows:

HOTs Human Reproduction Class 12 Biology

Functions:
(a) Acrosome : It contains enzymes called spermlysins that are used to contact and penetrate the egg at the time of fertilisation.
(b) Nucleus : It contains chromatin material which will be responsible for the genetic make-up of the future zygote.
(c) Middle piece : It contains mitochondria that provide energy for the movement of the sperm.

Question. Explain the steps in the formation of an ovum from an oogonium in humans.
Answer. THe process of formation of a mature female gamete (ovum) is called oogenesis. It occurs in the ovaries. It consists of three phases : multiplication, growth and maturation.
(i) Multiplication phase : In the foetal development, certain cells in the germinal epithelium of the ovary of the foetus are larger than others. ese cells divide by mitosis, producing a couple of million egg mother cells or oogonia in each ovary of the foetus.
The oogonia multiply by mitotic divisions forming the primary oocytes.
(ii) Growth phase : This phase of the primary oocyte is very long. The oogonium grows into a large primary oocyte by taking food from the surrounding follicle cells.
(iii) Maturation phase : Each primary oocyte undergoes two maturation divisions, first meiotic and the second meiotic.
In the first, meiotic division, the primary oocyte divides into two very unequal haploid daughter cells – a large secondary oocyte and a very small first polar body or polocyte. In the second maturation division, the first polar body may divide to form two second polar bodies. The secondary oocyte again divides into unequal daughter cells, a large ootid and a very small second polar body. The ootid grows into a functional haploid ovum. Thus from one oogonium, one ovum and three polar bodies are formed. The polar bodies take no part in reproduction and, hence, soon degenerate. In humans, ovum is released from the ovary in the secondary oocyte stage, this process is called ovulation.

Question. Draw a diagrammatic sectional view of human ovary to show the development of follicles and ovulation. Label the different stages in the diagram. 
Answer. Diagrammatic sectional view of human ovary showing the development of follicles and ovulation is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Mention the target cells of luteinising hormone in human males and females. Explain the effect and the changes which the hormone induces in each case.
Answer.In males, luteinising hormone (LH) secreted by anterior lobe of pituitary gland acts on the Leydig’s cells of the testes to secrete testosterone. Testosterone brings about the growth of the secondary sex organs and development of secondary sexual characters.In females, luteinising hormone induces the rupture of the mature graafian follicle and thereby the release of secondary oocyte (ovulation).

Question. Draw a sectional view of human ovary. Label the following parts :
(i) Primary follicle
(ii) Ovum
(iii) Graafian follicle
(iv) Corpus luteum
Answer.Sectional view of human ovary with labelled parts is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Where does sperm mature and become motile?
Answer.The final maturation of the sperms and their motility is attained in the epididymis. Epididymis is a mass of long narrow closely coiled tubule which lies along the inner side of each testis. The epididymis stores the sperms and secretes a Thuid which is considered to nourish the sperms.

Question. Explain the development of a secondary oocyte (ovum) in a human female from the embryonic stage upto its ovulation. Name the hormones involved in this process. 
Answer. THe process of formation of a mature female gamete (ovum) is called oogenesis. It occurs in the ovaries. It consists of three phases : multiplication, growth and maturation.
(i) Multiplication phase : In the foetal development, certain cells in the germinal epithelium of the ovary of the foetus are larger than others. ese cells divide by mitosis, producing a couple of million egg mother cells or oogonia in each ovary of the foetus.
The oogonia multiply by mitotic divisions forming the primary oocytes.
(ii) Growth phase : This phase of the primary oocyte is very long. The oogonium grows into a large primary oocyte by taking food from the surrounding follicle cells.
(iii) Maturation phase : Each primary oocyte undergoes two maturation divisions, first meiotic and the second meiotic.
In the first, meiotic division, the primary oocyte divides into two very unequal haploid daughter cells – a large secondary oocyte and a very small first polar body or polocyte. In the second maturation division, the first polar body may divide to form two second polar bodies. The secondary oocyte again divides into unequal daughter cells, a large ootid and a very small second polar body. The ootid grows into a functional haploid ovum. Thus from one oogonium, one ovum and three polar bodies are formed. The polar bodies take no part in reproduction and, hence, soon degenerate. In humans, ovum is released from the ovary in the secondary oocyte stage, this process is called ovulation.
The hormones involved in this process are luteinising hormone (LH) and follicle stimulating hormone (FSH), both secreted by anterior pituitary gland under the influence of GnRH from hypothalamus. FSH stimulates the growth of Graafian follicle and also the development of egg (secondary oocyte) within the follicle. LH induces the rupture of mature Graafian follicle and thereby the release of secondary oocyte (ovulation).

Question. (a) How is ‘oogenesis’ markedly different from ‘spermatogenesis’ with respect to the growth till puberty in the humans?
(b) Draw a sectional view of human ovary and label the different follicular stages, ovum and corpus luteum. 
Answer.(a) In spermatogenesis, the growth phase is very short. The spermatogonium actively grows into a larger primary spermatocyte by obtaining nourishment from the nursing cells.
In oogenesis, the growth phase is very long. It may extend over many years. The oogonium grows into a large primary oocyte. It then gets surrounded by a layer of granulosa cells to form primary follicle. A large number of these follicles degenerate during the period from birth to puberty. So, at puberty only 60,000 – 80,000 primary follicles are left in each ovary.

Question. (a) Describe the stages of oogenesis in human females.
(b) Draw a labelled diagram of a human ovum released after ovulation.
Answer. THe process of formation of a mature female gamete (ovum) is called oogenesis. It occurs in the ovaries. It consists of three phases : multiplication, growth and maturation.
(i) Multiplication phase : In the foetal development, certain cells in the germinal epithelium of the ovary of the foetus are larger than others. ese cells divide by mitosis, producing a couple of million egg mother cells or oogonia in each ovary of the foetus.
The oogonia multiply by mitotic divisions forming the primary oocytes.
(ii) Growth phase : This phase of the primary oocyte is very long. The oogonium grows into a large primary oocyte by taking food from the surrounding follicle cells.
(iii) Maturation phase : Each primary oocyte undergoes two maturation divisions, first meiotic and the second meiotic.
In the first, meiotic division, the primary oocyte divides into two very unequal haploid daughter cells – a large secondary oocyte and a very small first polar body or polocyte. In the second maturation division, the first polar body may divide to form two second polar bodies. The secondary oocyte again divides into unequal daughter cells, a large ootid and a very small second polar body. The ootid grows into a functional haploid ovum. Thus from one oogonium, one ovum and three polar bodies are formed. The polar bodies take no part in reproduction and, hence, soon degenerate. In humans, ovum is released from the ovary in the secondary oocyte stage, this process is called ovulation.

(b) The labelled diagram of a human ovum released after ovulation is as follows:

HOTs Human Reproduction Class 12 Biology

Question. (a) Describe the events of spermatogenesis with the help of a schematic representation.
(b) Write two differences between spermatogenesis and oogenesis. 
Answer.Spermatogenesis is the process of formation of haploid spermatozoa from diploid spermatogonia inside the testes of the male. It includes following three phases :
(i) Multiplication phase – At sexual maturity, the undifferentiated primordial germ cells divide several times by mitosis to produce a large number of spermatogonia or sperm mother cells. Spermatogonia (2N) are of two types : type A spermatogonia and type B spermatogonia. Type A spermatogonia serve as the stem cells which divide to form second type of spermatogonia whenever required. Type B spermatogonia are progenitor cells which function as precursors of spermatozoa.
(ii) Growth phase – Each type B spermatogonium actively grows to a larger primary spermatocyte by obtaining nourishment from the nursing cells.
(iii) Maturation phase – Each primary spermatocyte undergoes two successive divisions, called maturation divisions. The first maturation division is reductional or meiotic. Hence, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes now undergo second maturation division which is an ordinary mitotic division to form four haploid spermatids, by each primary spermatocyte.

(b) Differences between spermatogenesis and oogenesis are as follows :

HOTs Human Reproduction Class 12 Biology

Question. Describe in sequence the process of spermatogenesis in human. 
Answer. Spermatogenesis is the process of formation of haploid spermatozoa from diploid spermatogonia inside the testes of the male. It includes following three phases :
(i) Multiplication phase – At sexual maturity, the undifferentiated primordial germ cells divide several times by mitosis to produce a large number of spermatogonia or sperm mother cells. Spermatogonia (2N) are of two types : type A spermatogonia and type B spermatogonia. Type A spermatogonia serve as the stem cells which divide to form second type of spermatogonia whenever required. Type B spermatogonia are progenitor cells which function as precursors of spermatozoa.
(ii) Growth phase – Each type B spermatogonium actively grows to a larger primary spermatocyte by obtaining nourishment from the nursing cells.
(iii) Maturation phase – Each primary spermatocyte undergoes two successive divisions, called maturation divisions. The first maturation division is reductional or meiotic. Hence, the primary spermatocyte divides into two haploid daughter cells called secondary spermatocytes. Both secondary spermatocytes now undergo second maturation division which is an ordinary mitotic division to form four haploid spermatids, by each primary spermatocyte.

Question. (a) Describe the events of oogenesis with the help of schematic representation.
(b) Write two differences between oogenesis and spermatogenesis. 
Answer.(a) The schematic representation of events of oogenesis is as follows:

HOTs Human Reproduction Class 12 Biology

(b) Differences between spermatogenesis and oogenesis are as follows :

HOTs Human Reproduction Class 12 Biology

Question. Study the following chart. Name the hormones involved at each stage. Explain their functions.
Hypothalamus

Pituitary

Testes

Sperms
Answer.

HOTs Human Reproduction Class 12 Biology

(i) GnRH : Act on pituitary gland and stimulates secretion of LH and FSH.
(ii) LH : Luteinising hormone acts at the Leydig’s cells and stimulates synthesis and secretion of androgens.
(iii) FSH : FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of spermatogenesis.
(iv) Androgen (Testosterone) stimulates the process of spermatogenesis.

Question. When does oogenesis start in humans? Name the three hormones and their source linked with oogenesis. How do they influence the process of oogenesis? Explain.
Answer. Oogenesis starts in embryonic developmental stage. The three hormones related with oogenesis are GnRH (Gonadotropin releasing hormone),luteinising hormone (LH) and follicle stimulating hormone (FSH).
THe process of formation of a mature female gamete (ovum) is called oogenesis. It occurs in the ovaries. It consists of three phases : multiplication, growth and maturation.
(i) Multiplication phase : In the foetal development, certain cells in the germinal epithelium of the ovary of the foetus are larger than others. ese cells divide by mitosis, producing a couple of million egg mother cells or oogonia in each ovary of the foetus.
The oogonia multiply by mitotic divisions forming the primary oocytes.
(ii) Growth phase : This phase of the primary oocyte is very long. The oogonium grows into a large primary oocyte by taking food from the surrounding follicle cells.
(iii) Maturation phase : Each primary oocyte undergoes two maturation divisions, first meiotic and the second meiotic.
In the first, meiotic division, the primary oocyte divides into two very unequal haploid daughter cells – a large secondary oocyte and a very small first polar body or polocyte. In the second maturation division, the first polar body may divide to form two second polar bodies. The secondary oocyte again divides into unequal daughter cells, a large ootid and a very small second polar body. The ootid grows into a functional haploid ovum. Thus from one oogonium, one ovum and three polar bodies are formed. The polar bodies take no part in reproduction and, hence, soon degenerate. In humans, ovum is released from the ovary in the secondary oocyte stage, this process is called ovulation.
The hormones involved in this process are luteinising hormone (LH) and follicle stimulating hormone (FSH), both secreted by anterior pituitary gland under the influence of GnRH from hypothalamus. FSH stimulates the growth of Graafian follicle and also the development of egg (secondary oocyte) within the follicle. LH induces the rupture of mature Graafian follicle and thereby the release of secondary oocyte (ovulation).

Question. Draw a labelled diagram of the microscopic structure of a human sperm. Explain the functions of each part.
Answer. 
Labelled diagram of a human sperm is as follows:

HOTs Human Reproduction Class 12 Biology

Sperm is a microscopic structure consisting of four parts: head, neck, middle piece and tail. A plasma membrane envelops the whole body of sperm. Head consists of large posterior haploid nucleus and a small anterior cap-like acrosome. Acrosome contains proteolytic and lysosomal enzymes popularly called sperm lysins, required to penetrate the egg at the time of fertilisation. Neck is present between the head and middle piece. It contains the proximal centriole towards the nucleus which plays a role in the first cleavage of the zygote and the distal centriole which gives rise to the axial filament of the sperm. Middle piece is a long cylindrical part of sperm which lies between the neck and tail. Axoneme or axial filament of microtubules runs through it. The same is covered by a mitochondrial spiral (nebenkern) of 10-14 turns. Mitochondrial activity helps in providing energy. The distal end bears a ring centriole or annulus of uncertain role. Tail is very long slender and tapering, and is formed of cytoplasm. Tail is vibratile part of sperm.

Question. (a) Draw a transverse section of human ovary showing the sequential development of different follicles up to the corpus luteum.
(b) Comment on the corresponding ovarian and pituitary hormone levels during these events.
Answer.Diagrammatic sectional view of human ovary showing the development of follicles and ovulation is as follows:

HOTs Human Reproduction Class 12 Biology

(b) GnRH secreted by the hypothalamus stimulates the anterior lobe of pituitary gland to secrete LH and FSH. FSH stimulates the growth of Graafian follicles and also the development of egg/oocyte within the follicle to complete the meiosis I to form secondary oocyte. FSH also stimulates the formation of estrogens. LH induces the rupture of the mature Graafian follicle and thereby the release of secondary oocyte. Thus LH causes ovulation. The remaining part of the Graafian follicle is stimulated by LH to develop into corpus luteum which secretes progesterone.
The rising level of progesterone inhibits the release of GnRH, which in turn, inhibits production of FSH, LH and progesterone.


Menstrual Cycle

Very Short Answer Type Questions

Question. Write the physiological reason, why a woman generally cannot conceive a child after 50 years of age?
Answer.A woman generally cannot conceive a child after 50 years of age as at this age menopause occurs.It is a phase in a woman’s life when ovulation and menstruation stops.

Question. Name the phase of menstrual cycle when a Graafian follicle transforms into an endocrine structure. Write its action thereafter.
Answer.Graafian follicle changes into an endocrine structure, called corpus luteum during luteal phase of menstrual cycle. Corpus luteum secretes progesterone which stimulates the uterine glands to produce increased amount of watery mucus and is also essential for maintenance of the endothelium.

Short Answer Type Questions

Question. At what stage of me nstrual cycle is corpus luteum formed in human females? When does it regress? 
Answer.Corpus luteum is formed during the luteal phase of the menstrual cycle. It regresses in the absence of fertilisation.

Question. Explain the role of pituitary and the ovarian hormones in menstrual cycle in human females. 
Answer.Menstrual cycle is regulated by certain hormones, some of which are secreted by the pituitary gland. The pituitary gland is stimulated by releasing factors produced in hypothalamus. The hormones produced by pituitary gland influence the ovaries, which in turn affect the uterus. Anterior pituitary gland secretes two hormones FSH and LH. FSH stimulates maturation of follicle and stimulate it to secrete estrogens. Rapid secretion of LH (LH surge) induces rupturing of Graafian follicle, thereby leading to release of ovum (ovulation).
Ovary secretes two hormones : estrogen and progesterone. Estrogen stimulates follicular development and proliferation of the endometrium of the uterine wall. Progesterone produced by corpus luteum helps to maintain endometrium which is required for implantation of the fertilised ovum and other events of pregnancy.

Question. Name the hormones influencing
(a) ovulation,
(b) development of corpus luteum.
Answer.(a) On the 14th day of the menstrual cycle,surge in LH causes rupturing of Graafian follicle and release of ovum (ovulation).
(b) After ovulation, the remaining cells of the ovarian follicles are stimulated by LH to develop corpus luteum.

Question. Write the effect of the high concentration of LH on mature Graafian follicle.
Answer.High concentration of LH cause rupturing of Graafian follicle and thereby the release of ovum.This is called ovulation.

Question. Mention the role of gonadotropins in menstrual cycle. On what day of the menstrual cycle do the gonadotropins reach a peak?
Answer. LH and FSH secreted by pituitary gland are called gonadotropins. The secretion of FSH and LH increase gradually during the follicular phase and stimulates the development of follicles as well as secretion of estrogens by the growing follicles. Both gonadotropins reach a peak level in the middle of the cycle (14th day). LH surge induces rupture of Graafian follicle and thereby the release of ovum (ovulation). This ovulatory phase is followed by luteal phase during which LH stimulates the remaining cells of the Graafian follicle to transform into corpus luteum which secretes large amounts of progesterone needed for maintenance of endometrium. In the absence of fertilisation, LH production gets reduced leading to degeneration of corpus luteum. THis causes disintegration of endometrium leading to menstruation. 

Question. Differentiate between major structural changes in the human ovary during the follicular and luteal phase of the menstrual cycle.
Answer.The major structural changes in human ovary during the follicular and luteal phase of menstrual cycle are as follows :

HOTs Human Reproduction Class 12 Biology
HOTs Human Reproduction Class 12 Biology

Question.

HOTs Human Reproduction Class 12 Biology

Read the graph given above and correlate the uterine events that take place according to the hormonal levels on
(i) 6-15 days
(ii) 16-25 days
(iii) 26-28 days (if the ovum is not fertilised)
(b) Specify the sources of the hormones mentioned in the graph.
Answer. (a) (i) It is the follicular phase during which FSH stimulates the ovarian follicles to secrete estrogen which in turn stimulate the proliferation of the endometrium of the uterine wall. The endometrium becomes thicker accompanied by increase of uterine glands and blood vessels.
(ii) From 16-25 days, secretion of progesterone stimulates the uterine glands to produce increased amount of watery mucus. Progesterone is also essential for the maintenance of endometrium which is necessary for the implantation of fertilised ovum and other events of pregnancy.
(iii) If the ovum does not get fertilised, corpus luteum degenerates which decrease the level of progesterone. This causes disintegration of the endometrium leading to menstruation.
(b) Estrogen is secreted by ovarian follicles and progesterone is secreted by corpus luteum.

Question. Differentiate between menarche and menopause. 
Answer.Beginning of menstruation or first menstruation is called menarche that occurs at puberty. When menstrual cycle ceases around the age of 50 years, it is called as menopause.

Question. Explain the events in a normal woman during her menstrual cycle on the following days:
(a) Ovarian event from 13-15 days
(b) Ovarian hormones level from 16 to 23 days
(c) Uterine events from 24 to 29 days
Answer.(a) During 13-15 days, FSH stimulates the ovarian follicle to secrete estrogens that further stimulate the proliferation of the endometrium of the uterine wall. On 14th day, LH surge causes ovulation.
(b) From 16 to 23 days, the corpus luteum secretes progesterone which is required for the maintenance of endometrium. In the absence of fertilisation, corpus luteum degenerates causing disintegration of endometrium leading to menstruation that takes 3-5 days.
(c) During 24 to 29 days (luteal phase of 15 to 28 days), the luteinising hormone (LH) is secreted by the anterior lobe of the pituitary gland. LH causes ovulation. The remaining cell of the ovarian follicles are stimulated by the LH to develop corpus luteum. The corpus luteum secretes large amount of progesterone. Progesterone stimulates the uterine glands to produce increased amount of watery mucus. During the secretory phase, there is also similar increase in the secretion of watery mucus by the vaginal glands and by the glands of the Fallopian tubes. Progesterone is also essential for maintenance of the endometrium which is necessary for implantation of the fertilised ovum and other events of pregnancy. In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation marking a new cycle.

Question. Explain the events in a normal woman during her menstrual cycle on the following days :
(a) Pituitary hormone levels from 8 to 12 days.
(b) Uterine events from 13 to 15 days.
(c) Ovarian events from 16 to 23 days.
Answer.(a) From 8-12 days (follicular phase), the level of gonadotropins (LH and FSH) increase gradually and stimulate follicular development as well as secretion of estrogens by growing follicles.
(b) From 13 to 15 days, the endometrium becomes thicker by rapid cell multiplication and there is increase in uterine glands and blood vessels.
(c) After ovulation, the remaining cells of the ovarian follicles are stimulated by LH to develop corpus luteum.

Question. When does the corpus luteum degenerate?
Explain the immediate consequences of its degeneration in human female. 
Answer.In the absence of fertilisation, the corpus luteum degenerates. Degeneration of the corpus luteum leads to decrease in the production of progesterone.
As progesterone is needed for the maintenance of the endometrium, its reduction leads to disintegration of endometrium thus causing menstruation.

Question. Name the muscular and the glandular layers of human uterus. Which one of these layers undergoes cyclic changes during menstrual cycle? Name the hormone essential for the maintenance of this layer. 
Answer. The muscular layer of human uterus is myometrium and glandular layer is endometrium.The endometrium undergoes cyclical changes during menstrual cycle. Progesterone is essential for the maintenance of endometrium.

Question. Enumerate the events in the ovary of a human female during:
(a) Follicular phase,
(b) Luteal phase of menstrual cycle.
Answer. (a) During follicular phase, ovarian follicle secretes estrogens under the influence of FSH secreted by anterior pituitary. Estrogens stimulate the proliferation of the endometrium of the uterine wall.
(b) During luteal phase, the remaining cells of the ovarian follicles after ovulation are stimulated by LH to develop corpus luteum. The corpus luteum secretes progesterone that stimulates the uterine glands to produce increased amount of mucus and is also essential for the maintenance of the endometrium which is necessary for implantation of the fertilised ovum.

Question. With the help of graphical illustration only, show the changes in the levels of the pituitary hormone during a menstrual cycle in humans.
Answer. The graphical representation of changes in level of pituitary hormone during menstrual cycle is as follows:

HOTs Human Reproduction Class 12 Biology

Long Short Answer Type Questions

Question. (a) Explain the menstrual phase in a human female. State the levels of ovarian and pituitary hormones during this phase.
(b) Why is follicular phase in the menstrual cycle also referred as proliferative phase? Explain.
(c) Explain the events that occur in a Graafian follicle at the time of ovulation and there after.
(d) Draw a Graafian follicle and label antrum and secondary oocyte. 
Answer.(a) In a 28 day menstrual cycle, the menses takes place on days 3-5. The production of LH from the anterior lobe of the pituitary gland is considerably reduced. The withdrawal of this hormone causes degeneration of the corpus luteum and, therefore, progesterone production from the ovary is reduced. Production of estrogens from the ovary is also reduced in this phase. The endometrium of the uterus breaks down and menstruation begins. The cells of endometrium secretions, blood and the unfertilised ovum constitute the menstrual flow.
(b) During follicular phase, follicle stimulating hormone (FSH) stimulates the ovarian follicle to secrete estrogens, which in turn stimulate the proliferation of the endometrium of the uterine wall. As a result, endometrium becomes thicker by rapid cell multiplication and is accompanied by an increase of uterine gland and blood vessels. Hence, this phase is also referred as proliferative phase.
(c) At the time of ovulation, rapid secretion of LH induces rupturing of Graafian follicle, thereby releasing ovum. After ovulation has taken place, LH stimulates cells of ovarian follicle to develop corpus luteum. Corpus luteum secretes large amount of progesterone.
(d) The structure of a mature Graafian follicle is as follows:

HOTs Human Reproduction Class 12 Biology

Question. The following is the illustration of the sequence of ovarian events “A” to “I” in a human female.

HOTs Human Reproduction Class 12 Biology

(a) Identify the figure that illustrates ovulation and mention the stage of oogenesis it represents.
(b) Name the ovarian hormone and the pituitary hormone that have caused the above mentioned event.
(c) Explain the changes that occur in the uterus simultaneously in anticipation.
(d) Write the difference between ‘C’ and ‘H’.
(e) Draw a labelled sketch of the structure of a human ovum prior to fertilisation
Answer.(a) ‘F’ illustrates ovulation. It represents secondary oocyte.
(b) Estrogen (ovarian hormone) and LH (pituitary hormone).
(c) Endometrium becomes thicker by rapid cell multiplication which is accompanied by an increase of uterine glands and blood vessels.
(d) C is developing follicle under the influence of FSH. H is regressing corpus luteum under the influence of reduction of LH.
(e) The labelled structure of a human ovum prior to fertilisation is as follows:

HOTs Human Reproduction Class 12 Biology

Question. Describe the roles of pituitary and ovarian hormones during the menstrual cycle in a human female.
Answer. Menstrual cycle in a human female consists of menstrual phase, proliferative phase (follicular phase), ovulatory phase and secretory phase (luteal phase). Days 1-5 of the cycle are known as the menstrual phase. During this phase, menstruation occurs. At the beginning of this stage, levels of progesterone and estrogen have dropped dramatically because of the degeneration of the last cycle’s corpus luteum. This triggers the shedding of endometrium. The detached portion of the endometrium as well as blood will pass through the vagina as the menstrual flow. Days 5-14 are known as the proliferative phase. Proliferative phase consists of growth of endometrium of uterus, Fallopian tube and vagina. In ovary, a Graafian follicle grows, matures and secretes estrogen during this phase. The endometrium grows thicker and becomes more vascularised and glandular. Change in the levels of pituitary and ovarian hormones bring about these changes in the ovary and uterus. The levels of LH and FSH increase gradually during the follicular phase and stimulate follicular development as well as secretion of estrogens by the growing follicles. In ovulatory phase, both LH and FSH attain a peak level in the middle of cycle (about 14th day). Rapid secretion of LH leading to its maximum level during the mid-cycle called LH surge induces rupture of Graafian follicle and thereby the release of ovum (ovulation).
After ovulation and in response to luteinising hormone, the portion of the Graafian follicle that remains in the ovary enlarges and is transformed into a corpus luteum containing yellow substance (called lutein) and the luteal phase begins. The corpus luteum secretes large amounts of progesterone which is essential for maintenance of endometrium. Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy. In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation, marking a new cycle.