CBSE Class 12 Biology Reproduction In Human Beings Worksheet Set B

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. 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.

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

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. 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. 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.

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. 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. 

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. 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.

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. 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.

Short Answer Type Questions

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 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. 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. 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. 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. (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. 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. 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. 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. 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. 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. 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. 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. 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. 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.