CBSE Class 12 Biology Reproduction In Human Beings Worksheet Set C

Very Short Answer Type Questions

Question. What is the significance of epididymis in male fertility?
Answer.  The epididymis helps the sperm in attaining maturity, acquiring increased motility and fertilising capacity. It also stores sperms for a short period before entering the vasa
deferens. The epididymis shows peristatic and segmenting contractions at intervals to push the sperm away from the testis.

Question. During reproduction, the chromosome number (2n) reduces to half (n) in the gametes and again the original number (2n) is restored in the offspring. What are the processes through which these events take place?
– Thinking Process
Gametes are haploid while zygotes are diploid.
Answer. The meiotic cell division reducers the chromosome numbers to half during gametogenesis and diploid (2n) number of chromosome is restored by the union of male and female gamete through process of fertilisation.

Question. Mention the importance of LH surge during menstrual cycle.
Answer. Rapid secretion of LH leading to its maximum level during the mid menstrual cycle (14th day) called LH surge induces rupture of Graafian follicle and thereby the release of
ovum (ovulation).
The ovulation (ovulatory phase) is followed by the luteal phase during which the remaining parts of the Graafian follicle transform as the corpus luteum. The corpus luteum secretes
large amounts of progesterone which is essential for maintenance of the endometrium.
Such an endometrium is necessary of implantation of the fertilised ovum and other events of pregnancy.

Question. Female reproductive organs and associated functions are given below in column I and II. Fill the blank blanks.
 Column I Column II
Ovaries Ovulation
Oviduct A
B Pregnancy
Vagina Birth
Answer. 
 Column I Column II
Ovaries Ovulation
Oviduct Fertilisation
Uterus Pregnancy
Vagina Birth
The female reproductive system consists of a pair of ovaries, a pair of Fallopian tubes (oviducts), uterus, vagina, external genitalia and mammary glands.
The ovaries have both an exocrine function (production of ova) and an endocrine function (secretion) of female sex hormones.
The oviduct (Fallopian tube) conveys the egg from the ovary to the uterus, and also provides the appropriate environment for its fertilisation. The uterus (womb) is a large, inverted, pear-shaped, elastic sac specialised for the development of the embryo.
The vagina is adapted for receiving the penis during copulation, allowing menstrual flow and serving as the birth canal during parturition

Question. From where the parturition signals arise-mother or foetus? Mention the main hormone involved in parturition.
Answer. Parturition is induced by a complex neuroendocrine mechanism. The signals for parturition originate from the fully developed foetus and the placenta which induce mild uterine contractions called foetal ejection reflex.
The hormone involved in parturition is oxytocin that acts on the uterine muscle and causes stronger uterine contractions. This leads to the expulsion of the baby out of the uterus through the birth canal.

Question. Given below are the events in human reproduction. Write them in correct sequential order.
Insemination, gemetogenesis, fertilisation, parturition, gestation,implanation.
– Thinking Process
Humans reproduce sexually and give birth to young babies.
Answer. The reproductive events in humans include
(i) Gametogenesis Formation of gemetes (sperm in males, ova in females).
(ii) Insemination Transfer of sperm into female reproductive tract.
(iii) Fertilisation Fusion of male and female gemetes.
(iv) Implantation Formation, development and then attachment of blastocyst to the uterine wall.
(v) Gestation Embryonic development inside female body.
(vi) Parturition Delivery of the baby.

Question. What is the difference between a primary oocyte and a secondary oocyte?
Answer. Primary oocyte is a diploid cell formed in foetal ovary when the gamete mother cell, oogonia is arrested at prophase-I of meiosis. Secondary oocyte is the haploid cell formed from primary oocyte that completes its first meiotic division, during puberty and produces the female gamete ova(n).

Question. Write the location and function of the Sertoli cells in humAnswer.
Answer. Sertoli cells are present in seminiferous tubules. They provide nutrition to the germ cells or sperms.

Question. Name the hormones produced only during pregnancy in a human female. Mention their source organ.
Answer. During pregnancy, placenta produces hormones like human chorionic gonadotropin and human placental lactogen and ovary produces relaxin.

Question. What is the significance of ampullary-isthmic junction in the female reproductive tract?
Answer. The act of fertilisation takes place in the female genital track that is at the junction of the isthmus and ampulla (ampullary – isthmic junction) of the Fallopian tube.
Note Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary – isthmic junction. All copulations do not lead to fertilisation and pregnancy.

Question. How many eggs are released by a human ovary in a month? How many eggs do you think would have been released if the mother gave birth to identical twins? Would your answer change if the twins born were fraternal?
Answer. Only one egg is released by a human (female) ovary in a month.
Only one egg is released if the mother gave birth to identical twins.
Yes. Two or more eggs are released in case fraternal twins are born.

Question. What name is given to the cells of inner cell mass, that have the potential to give rise to all tissues and organs in a human being? 
Answer. Stem cells

Question. Why are menstrual cycles absent during pregnancy?
Answer. The menstrual flow results due to breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina. Menstruation only occurs
if the released ovum is not fertillised.
During pregnancy, all events of the menstrual cycle stop and the corpus luteum secretes large amounts of progesterone which is essential for the maintenance of the endometrium.
These changes lead to no menstruation, during pregnancy.
Note Lack of menstruation may be indicative of pregnancy. However, it may also be caused due to some other underlying causes like stress, poor health, etc.

Question. Given below are the stages in human reproduction. Write them in correct sequential order.
Insemination, Gametogenesis, Fertilisation, Parturition, Gestation, Implantation
Answer. Gametogenesis, Insemination, Fertilisation, Implantation, Gestation, Parturition.

Question. How does zona pellucida of ovum help in preventing polyspermy?
Answer. When a sperm penetrates ovum, it induces changes in the membrane that make the zona pellucida layer impenetrable to additional sperms. Thus, it ensures that only one sperm can fertilise an ovum and stops polyspermy.

Question. Name the hormones involved in regulation of spermatogenesis.
Answer. GnRH (Gonadotropin releasing hormone), LH (Luteinising hormone), FSH (Follicle stimulating hormone), androgen-binding protein (ABP), inhibin and androgens.

Question. Which type of cell division forms spermatids from the secondary spermatocytes?
Answer. The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids.
Note Secondary spermatocytes are produced, when the primary spermatocytes undergo the first meiotic division (reduction division).

Question. Name the important mammary gland secretions that help in resistance of the new born baby.
Answer. Colostrum.

Short Answer Questions

Question. (a) How many spermatozoa are formed from one secondary spermatocyte?
(b) Where does the first cleavage division of zygote take place?
– Thinking Process
In testis, the spermatogonia (immature germ cells) present in the form of germinal layer on the inner wall of seminiferous tubules multiply by mitotic division and increase in numbers. Each spermatogonium is diploid and contains 46 chromosomes. Some of them periodically undergo meiosis and are called primary spermatocytes.
Answer. (a) A primary spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes (n = 23 chromosomes each). The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids (n)., each spermatids produce spermatazoa.
(b) The mitotic division called cleavage starts 30 h after fertilisation when as to the zygote moves through the isthmus the Fallopian tube (oviduct) towards the uterus and forms blastomeres.

Question. Corpus luteum in pregnancy has a long life. However, if fertilisation does not take place, it remains active only for 10-12 days. Explain.
Answer. The ruptured Graafian follicle transform into the corpus luteum and secretes large amounts of progesterone which is essential for the maintenance of the endometrium. Such an endometrium is required for the implantation of fertilised ovum (blastocyst) and other events of pregnancy.
That’s why corpus luteum in pregnancy has a long life. But in the absence of fertilisation,maintenance of endometrium is not required. Therefore, corpus luteum degenerates with in 10-12 days.

Question. What is foetal ejection reflex? Explain how it leads to parturition?
Answer. Foetal ejection reflex encompasses the mild uterine contractions in response to the signals that originate from the fully developed foetus and the placenta. This triggers release of
oxytocin from maternal pituitary. Oxytocin acts on the uterine muscle and causes stronger contractions, which in turn stimulates further secretion of oxytocin.
The stimulatory reflex between the uterine contraction and oxytocin secretion continues resulting in stronger and stronger contractions leading to the expulsion of baby out of uterus through birth canal. 

Question. Write the location and functions of myometrium and endometrium. 
Answer. Endometrium is the inner layer of uterus. It assists in cyclic changes during menstruation and implantation of embryo.
Myometrium is the middle layer of uterus. It consist of smooth muscles and thus assists in contractions of the uterus during parturition.

Question. A human female experiences two major changes, menarche and menopause during her life. Mention the significance of both the events.
Answer. In human beings, initiation of menstruation at puberty (between age 9-15 years) is called menarche. While, menstrual cycles ceases around 50 years of age, that is termed as
menopause. Menarche signifies the maturation and readiness of the female reproductive system for child bearing.
It marks the capability of the ovaries to produce mature oocyte (female gamete) that can now be fertilised by the sperm and also that the uterus is capable of supporting the foetal growth and development.
Menopause signifies the end of child bearing age. At this age supply of healthy eggs is very low, the levels of the hormones secreted by the ovaries decline and the menstruation stops.
The uterus no longer remains conductive for foetal growth.

Question. Why doctors recommend breast feeding during initial period of infant growth?
Answer. The milk produced during the initial few days of lactation is called colostrum which contains several antibodies (especially 1gA) essential to develop resistance in the new-born babies against diseases. Breast-feeding during the initial period of infant growth is recommended by doctors for bringing up a healthy baby.

Question. What are the events that take place in the ovary and uterus during follicular phase of the menstrual cycle.
Answer. The major events of the menstrual cycle are menstrual phase, follicular phase, ovulatory phase and luteal phase.
The follicular phase follows the menstrual phase. During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones. The secretion of gonadotropins (LH and FSH) increases gradually during the follicular phase and stimulates follicular development as well as secretion of estrogens by the growing follicles.
Both LH and FSH attain a peak level in the middle of cycle (about 14th day). This rapid secretion of LH leading to its maximum level induces rupture of Graafian follicle to release ovum.

Question. Except endocrine function, what are the other functions of placenta.
Answer. Placenta is structural and functional unit between developing embryo (foetus) and maternal body. Placenta acts as an endocrine tissue and produces several hormones like human Chorionic Gonadotropin (hCG), human Placental Lactogen (hPL), estrogens, progesterones, etc.
Other than the endocrine function, placenta also facilitates the supply of oxygen and nutrients to the embryo and removes carbon dioxide and excretory/waste materials produced by the developing faetus.

Question. What are the changes in the oogonia during the transition of a primary follicle to Graafian follicle?
Answer. The germinal epithelial cells divide repeatedly until many diploid oogonia are formed. The oogonia grow to form primary oocytes. Each primary oocyte then gets surrounded by a layer of granulosa cells and then called the primary follicle.
The primary follicles get surrounded by more layers of granulosa cells and called secondary follicles. The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid filled cavity called antrum.
The primary oocyte within the tertiary follicle undergoes meiotic division to become a secondary oocyte and a first polar body (haploid). The tertiary follicle further changes into the mature follicle or Graafian follicle that ruptures to release the secondary oocyte (ovum) from the ovary by the process called ovulation.

Question. Women experience two major events in their life time, one at menarche and the second at menopause. Mention the characteristics of both the events. 
Answer. Menarche represents the beginning of menstrual cycle which is an indication of attainment of sexual maturity. Menopause, on the other hand, refers to the cessation of menstruation which in turn means stoppage of gamete production, i.e., it marks the end of reproductive or fertile life of the female.

Question. Write the function of each of the following:
(a) Seminal vesicle
(b) Acrosome of human sperm. 
Answer. (a) It is responsible for storage and transport of sperms. It provides secretions for motility and nourishment of sperms.
(b) It helps the sperm to enter into the cytoplasm of the ovum through the zona pellucida and provides enzymes for fertilisation.

Question. Why does corpus luteum secrete large amount of progesterone during luteal/secretory phase of the menstrual cycle? 
Answer. The hormone progesterone is essential for the maintenance of endometrium of the uterus. It maintains the endometrial lining of uterus so that the foetus may get implanted in the uterus. So, corpus luteum secretes large amounts of progesterone during the luteal phase of menstrual cycle.

Question. What is the number of chromosomes in the following cells of a human female?
(i) Primary oocyte (ii) Ootid
(iii) Secondary oocyte (iv) Follicle cells
Answer. (i) 46 (ii) 23
(iii) 23 (iv) 46

Question. Corpus luteum in pregnancy has a long life. However, if fertilisation does not take place it remains active only for 10−12 days. Why? 
Answer. This is because of a neural signal given by the maternal endometrium to its hypothalamus in presence of a zygote to sustain the gonadotropin (LH) secretion, so as to maintain the corpus luteum as long as the embryo remains there. In the absence of a zygote, therefore, the corpus luteum degenerates.

Question. Mention the fate of corpus luteum and its effect on the uterus in absence of fertilisation of the ovum in a human female. 
Answer. In the absence of fertilisation, corpus luteum degenerates and this causes disintegration of the endometrium of ovary, leading to menstruation.

Question. Where are fimbriae present in a human female reproductive system? Give their function.
Answer. The fimbriae are the finger-like projections present on the edges of infundibulum (fallopian tubes). They help in collection of ovum after ovulation.

Question. Differentiate between menarche and menopause. 
Answer. Menarche is the beginning of menstrual cycle at puberty. It starts at the age of 13−15 years.
Menopause is the cessation of menstrual cycle. It happens around 50 years of age.

Long Answer Questions

Question. (i) Draw a sectional view of seminiferous tubule of a human. Label the following cells in the seminiferous tubule:
(a) Cells that divide by mitosis to increase their number.
(b) Cells that undergo Meiosis I.
(c) Cells that undergo Meiosis II.
(d) Cells that help in the process of spermiogenesis.
(ii) Mention the role of Leydig cells.
OR
Draw a labelled sectional view of seminiferous tubule of a human male.
Answer. (i) Refer to Fig. 3.8.
(a) Cells that divide by mitosis to increase their number—Spermatogonia
(b) Cells that undergo Meiosis I—Primary spermatocytes
(c) Cells that undergo Meiosis II—Secondary spermatocytes
(d) Cells that help in the process of spermiogenesis—Sertoli cells
(ii) Role of Leydig cells: They synthesise and secrete testicular hormones called androgens.

Question. Study the figure given below:

(i) What is being depicted in the diagram?
(ii) Name ‘a’ and ‘b’ cells. What is the difference between them with reference to the number of chromosomes?
(iii) Pick out and name the motile cells.
(iv) What is ‘f’ cell? Mention its function.
(v) Name the structure of which the given diagram is a part.
Answer. (i) The seminiferous tubule is being depicted in the diagram.
(ii) a—Spermatogonium, b—Primary spermatocyte
They both are diploid and have 46 chromosomes each.
(iii) e—Spermatozoa
(iv) f—Sertoli cell. It provides nutrition to the germ cells.
(v) Seminiferous tubule.

Question. Name the hormones influencing (i) ovulation, (ii) development of corpus luteum.
Answer. (i) Ovulation: Gonadotropins like luteinising hormone and follicular stimulating hormone, and estrogen.
(ii) Development of corpus luteum: Luteinising hormone and progesterone.

Question. Explain the steps in the formation of an ovum from an oogonium in humAnswer.
Answer. (ii) Oogenesis
The process of formation of a mature female gamete is called oogenesis. It occurs in the ovaries.
It consists of the following three phases:
(a) Multiplication phase: Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each foetal ovary. No more oogonia are formed and added after birth. These cells start division and enter into prophase-I of the meiotic division. They get temporarily arrested at this stage and are called primary oocytes.

Question. Name the stage of human embryo at which it gets implanted. Explain the process of implantation.

OR
Draw a labelled diagram of a human blastocyst. How does it get implanted in the uterus?
Answer. 
The human embryo gets implanted at blastocyst stage.
The trophoblast layer of the blastocyst get attached to the endometrium and the inner cell mass gets differentiated as the embryo. After attachment the uterine cell divides rapidly and covers the blastocyst. As a result the blastocyst becomes embedded in the endometrium of the uterus.

Question. Name the source of gonadotropins in human females. Explain the changes brought about in the ovary by these hormones during menstrual cycle.
OR
Describe how the changing levels of FSH, LH and progesterone during menstrual cycle induce changes in the ovary and the uterus in human female.
Answer. Gonadotropins (LH and FSH) are secreted by the anterior lobe of pituitary gland.

Gonadotropins (LH and FSH) increase gradually during the follicular phase (proliferative phase) of menstrual cycle and stimulate follicular development as well as secretion of estrogen by the growing follicles.

LH and FSH attain a peak level in the middle of the cycle (about 14th day) and rapid secretion of LH induces rupture of Graafian follicle followed by ovulation (release of ovum).

LH stimulates transformation of Graafian follicle into corpus luteum.