Class-XII
Chapter- Human Reproduction
Important Questions
1 Mark Questions and Answers
Q1. What is parturition?
Ans: Parturition is the intense contraction of the uterus that leads to the delivery of the child
at the end of nine months of pregnancy.
Q2. Despite the presence of several sperms in the vicinity of an egg cell, only one sperm
enters the ovum. Explain?
Ans: Even though several sperms are there in the surroundings of an egg cell only one
sperm enters the ovum because when sperm has an encounter with the ovum (zona
pellucida) it instigates changes in the membrane to block the entry of the remaining
sperms.
Q3. What is the function of Leydig cells?
Ans: The Leydig cells synthesise and release testicular hormones known as androgens.
Q4. State the reason why the male testes are located outside the abdominal cavity.
Ans: Male testes are located outside the abdominal cavity called the scrotum because it
provides a lower temperature than the typical body temperature i.e(2-3℃) needed for
spermatogenesis.
Q5. How is polyspermy checked by the zona pellucida of the ovum?
Ans. The zona pellucida of the ovum is a thick layer that is surrounded by corona radiata
cells. The cortical granules are discharged from the egg which blocks the fusion of several
sperms with an egg during the process of fertilisation.
Q6. What is the importance of the cervix in the female reproductive system?
Ans. The cervix is an important part of the female reproductive system as it is a narrow
opening through which the uterus opens up to the vagina. The cervical canal is the cavity
of the cervix which alongside the vagina connects to the birth canal.
Q7. Explain the function of the epididymis in male fertility.
Ans. It is situated along the posterior surface of each testis where spermatozoa obtain
motility and the capability to fertilise the egg. The surface of the sperm is changed in
response to discharges of the epididymis, which is necessary for fertilisation of an egg.
Q8. State the role of the ampullary-isthmic junction in the female reproductive tract.
Ans. Fertilization of the ovum happens in the ampullary-isthmic junction which is an
important process of reproduction.
2 Marks Questions and Answers
Q1. Give a reason for the following statements :
•
The first half of the menstrual cycle is called the follicular phase as well as the
proliferative phase.
Ans: Primary follicles change into Graafian follicles due to FSH stimulation in the first half
of the menstrual cycle. Graafian follicles release estrogens provoking the expansion of the
Endometrium of the uterus.
•
The second half of the menstrual cycle is called the luteal phase as well as the
secretory phase.
Ans: The Corpus luteum is entirely produced and discharges an enormous quantity of
Progesterone in the second half of the menstrual cycle.
Q2. State the number of chromosomes in the following cells. Primary oocyte, secondary
oocyte, ootid, and follicle.
Ans: The number of chromosomes in the cells is:
•
Primary oocytes contain 23 pairs.
•
Secondary oocyte: 23.
•
Ootid: 23.
•
Follicles contain 23 pairs.
Q3. What is colostrum? State its importance to a newborn baby.
Ans: The milk secreted from mammary glands immediately after birth for 2 or 3 days is
known as the colostrum. It is considered to be high in proteins & low in fats. It also consists
of the antibody IgA which ensures immunity in newborn infants.
Q4. Where are the Leydig cells situated? What do they release?
Ans: The Leydig cells or interstitial cells are situated in between the seminiferous tubules.
Leydig cells release the male sex hormone named ‘testersterone’ which encourages the
development of accessory glands & regulates male secondary sexual characteristics.
3 Marks Questions and Answers
Q1. State the male accessory glands and their function.
Ans: The male accessory glands comprise a prostate gland, paired seminal vesicles, and
paired bulbourethral glands. These glands release seminal plasma rich in
calcium, fructose, and enzymes. The lubrication of the penis is facilitated by secretions of
bulbourethral glands.
Q2. Where does oogenesis occur? Explain the stages of this process.
Ans: Oogenesis is the process of formation & maturation of the ovum. During the
embryonic development of the female foetus, this process occurs in the ovary. It
comprises three phases:–
1.
Multiplication phase:- Oogonia is produced when primordial germ cells split
through meiosis. These oogonia divide lay repeated mitotic divisions forming
clusters. In each cluster, only one of them enters into the growth phase & is called
the primary oocyte.
2. Growth phase:- After the attainment of puberty, the growth phase is initiated. It
leads to an increase in the size of the oocyte to several folds & synthesis.
3. Maturation phase:- Two haploids (n) cells are formed as the outcome of the first
division is meiotic. In this division, cytokinesis is unequal, a large daughter cell with
almost all cytoplasm is known as a secondary oocyte & a smaller me with less
cytoplasm is referred to as a polar body. The secondary oocyte then goes through
a second meiotic division to form an ovum & a second polar body.
Q3. ‘A fertilised egg is the blueprint of future development’. Explain the statement.
Ans: The father’s genetic information is carried by the sperm in the form of 23
chromosomes (including the male sex chromosome X or Y), whereas the mother’s genetic
information is carried by the egg (including the female sex chromosome X). Thus during
fertilisation, the fusion of the male and the female gametes produces a new genetic
combination that introduces variation in the progeny. The zygote or the fertilised egg
contains the genetic information which accordingly controls the development of the
embryo.
Q4. A sperm has just fertilized a human egg in the fallopian tube. Write down the events
that the fertilized eggs will go through till the implantation of the blastocyst in the
uterus.
Ans: 1. Cleavage:- When the zygotes travel through the isthmus of the oviduct, the mitotic
division starts which is cleavage approaching the uterus to form 2,4,8,16 daughter cells
known as blastomeres.
2. Blastocyst:- After the process of fertilization, the morula twins into a large mass of
cells known as blastocyst Outer peripheral cells enlarge & flatten further & make
trophoblast. Trophoblast cells discharge fluid into the interior & create a cavity
named the blastocoel. The embryonic stage with blastocoel is known as a blastula.
5 Marks Questions and Answers
Q1. What is menstruation? What are the roles of FSH, LH, oestrogen & progesterone in the
menstrual cycle?
Ans: On the 28th day of the menstrual cycle due to lack of progesterone, the endometrial
lining of the female genital tract breaks down which causes bleeding. This flow of blood
that occurs monthly is known as menstruation.
There are a variety of changes that take place in the ovary under the influence of various
hormones during the menstrual cycle:•
Menstrual phase:- The endometrial lining of the uterus breaks down due to very
low levels of hormones LH, FSH oestrogen & progesterone.
•
Follicular phase:- The release of oestrogen due to an increase in the levels of
pituitary hormones FSH & LH, FSH controls the follicular phase, it promotes the
growth of follicles. When in the middle of the cycle (14th day) both FSH & LH reach
their peak level.
•
Ovulatory Phase:– The level of LH hormones reaching its peak (called LH swing)
instigates the ruptures of mature Graffian follicle which leads to the release of the
ovum.
•
Luteal phase:- The LH & FSH hormones start to drastically fall. After ovulation, the
follicle ruptures & is converted into the corpus Luteum which releases huge
quantities of progesterone.
Q2: Why are human testes located outside the abdominal cavity?
Name
the
pouch
in
which
they
are
present.
Answer: Human testes are located outside the abdominal cavity as it helps in maintaining low
temperature (2-2.5%) lower than body temperature) required for spermatogenesis.
Testes are enclosed in a pouch called scrotum.
Q3: Write the location and functions of following in human testes
(i) Sertoli cells (ii) Leydig cells
Or
Name the cells that nourish the germ cells in the testes. Where are these cells
located in the testes?
Answer: (i) Location of Sertoli cells Within the lining of seminiferous tubule of testis.
Function of Sertoli cells They provide nutrition to the developing sperms or germ cells.
(ii) Location of Leydig cells In the interstitial spaces between the seminiferous tubules.
Function of Leydig cells They synthesise and secrete male hormones, i.e. androgens,
testosterone.
Q4: Where is acrosome present in humans? Write its function.
Answer: In humans, the acrosome is present in the anterior portion of the head of
human sperm. Function Hydrolytic enzymes or sperm lysins present in acrosome help
in the penetration of sperm into egg, during fertilization.
Q5: Explain the hormonal regulation of the process of spermatogenesis in humans.
Answer: Hormonal control of spermatogenesis in human males is as follows
•
•
•
•
Gonadotropin Releasing Hormone (GnRH) is released significantly from the
hypothalamus during puberty.
GnRH stimulates anterior pituitary to secrete gonadotropins, i.e. LH and
FSH or Interstitial Cell Stimulating Hormone (ICSH).
Luteinising Hormone (LH) acts on Leydig cells to stimulate the synthesis
and secretion of androgens which then stimulate the process of
spermatogenesis.
Follicle Stimulating Hormone (FSH) acts on Sertoli cells and stimulates
them to secrete inhibin which then stimulates the process of
spermiogenesis.
Q6: What happens to corpus luteum in human female if the ovum is (i) fertilised, (ii)
not fertilised?
Or
Mention the fate of corpus luteum and its effect on the uterus in the absence of
fertilisation of the ovum in human female.
Answer:
•
•
In case of fertilisation, the corpus luteum continues secreting progesterone
which is required for the maintenance of endometrium during pregnancy.
In the absence of fertilisation, the corpus luteum degenerates and gets
converted into corpus albicans. Deficiency of progesterone causes
disintegration of the endometrium leading to menstruation and thus, a new
cycle starts.
Q7: Explain the events in a normal woman during her menstrual cycle on the following
days:
(i) Ovarian event from 13-15 days.
(ii) Ovarian hormones level from 16-23 days.
(iii) Uterine events from 24-29 days.
Answer:
(i) In the ovarian event from 13-15 days, a immature ovum (egg cell) is released from
the Graafian follicle. Both LH and FSH attain maximum peak. FSH helps Graafian follicle
to attain maturity and LH helps in its rupture. Ovum covered by a number of layer and a
yellow fat layer forms corpus luteum. It releases (secretes) progesterone.
(ii) During menstrual cycle, the period level from 16-23 days is called luteal phase
(secretory phase). The corpus luteum secretes large amount of progesterone which is
essential for the maintenance of endometrium.
(iii) Uterine events from 24-29 days are under the influence of progesterone hormone. It
influences the maintenance of the endometrium for any pregnancy to occur. In the
absence of pregnancy, the corpus luteum degenerates and endometrium sheds off. It
causes the menstrual flow or bleeding.
Q8: Explain the events in a normal woman during her menstrual cycle on the following
days
(i) Pituitary hormone levels from 12 days.
(ii) Uterine events from 13-15 days.
(iii) Ovarian events from 16-23 days.
Answer:
(i) The period of 8-12 days after the onset of menstruation is the follicular phase. During
this phase, GnRH from hypothalamus stimulates anterior pituitary to release FSH and
LH. FSH stimulates the ovarian follicles to secrete oestrogen, which in turn stimulates
the proliferation of the endometrium of the uterine wall. This causes the endometrial
lining to thicken.
(ii) The uterine events between day 13 and 15 are governed by the high LH and FSH
levels. The endometrium is intact due to the effect of these gonadotropin hormones
and also prepares itself for pregnancy, if fertilisation occurs.
(iii) During 16-23 days, ruptured Graafian follicle gets converted into corpus luteum in
the ovary. It starts secreting progesterone which maintains the endometrium, necessary
for the implantation of fertilised ovum followed by other events of pregnancy.
Q9: Arrange the following hormones in the sequence of their secretion in a pregnant woman.
hCG, LH, FSH, Relaxin
(ii) Mention their source and the function they perform. (Delhi 2017)
Answer:
(i) The sequence of secretion of the given hormones in a pregnant woman is
FSH → LH → hCG → Relaxin