NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction

NCERT Exemplar Class 12 Biology Chapter 3 Human Reproduction Solutions- Long Answer Type Questions:

Question:1

What role do pituitary gonadotropins play during follicular and ovulatory phases of the menstrual cycle? Explain the shifts in steroidal secretions.

Answer:

Pituitary gonadotropins (FSH and LH) play a very vital role during the follicular and ovulatory phases of the menstrual cycle.

• FSH stimulates the release of ovum from the Graafian follicle. It also stimulates the development and subsequent rupture of the Graafian follicle. Thus, FSH plays a major role during the follicular and ovulatory phases.
• The above figure shows varying levels of LH. FSH and steroid hormones during follicular and ovulation phases of the menstrual cycle.
• At this stage, the level of estradiol (a steroid hormone) increases. This suppresses the level of the Luteinizing hormone (LH). Once the level of estradiol reaches a threshold level, the effect is reversed.
• After that, the level of estrogen (another steroid hormone) increases. This stimulates a surge in levels of LH. A high level of LH stimulates the development of the corpus luteum and proliferation of the endometrium, thus, marking the beginning of the luteal phases.

Question:2

Meiotic division during oogenesis is different from that in spermatogenesis. Explain how and why.

Answer:

It is true that the meiotic division during oogenesis is different from that in spermatogenesis. Following are the details about the significant differences between them:

• In the case of spermatogenesis, meiotic division begins at the time of puberty. This is the time when spermatogenesis begins in a male. On the other hand, oogenesis begins in the female when the female is still in the womb. Thus, it can be said that meiotic division during oogenesis begins when the girl child is still in the womb.
• The formation of primary oocytes stops by the 20th week of gestation of the female child. On the contrary, the production of spermatocytes continues throughout the reproductive phase of a male.
• All the stages of meiosis take place quickly after one another in case of spermatogenesis and there is no time lag between them. In the case of oogenesis, meiosis is deferred at the Prophase I state.

Meiosis resumes only once puberty begins.
Following are some possible reasons for this difference in patterns of oogenesis and spermatogenesis:

• Male gametes need to be formed in very large numbers to ensure Fertilisation.
• Female gametes are not exposed to external hazards, and hence a smaller number of them would be enough. Limiting the production of female gametes helps in the conservation of resources from the female body. The resources can then be properly utilised during the development of the foetus.

Question:3

The zygote passes through several developmental stages till implantation, Describe each stage briefly with suitable diagrams.

Answer:

The following figure shows various stages of zygote development till implantation:

(a) The zygote divides into a two-cell stage called cleavage. This development takes place when the zygote is still in the isthmus.
(b) The cleavage undergoes further rounds of mitosis to form 2, 4, 8 and finally 16-celled stage.
These daughter cells are called blastomere.
(c) The 16-celled stage is known as morula.
(d) The morula changes into a blastocyst; with more rounds of meiosis. At this stage, the blastomeres are arranged in an outer layer of cells; called trophoblast and an inner mass of cells.
(e) Implantation to the uterine wall happens at the blastocyst stage.

Question:4

Draw a neat diagram of the female reproductive system and label the parts associated with the following
(a) production of gamete,
(b) site of fertilisation
(c) site of implantation and,
(d) birth canal.

Answer:

Question:5

With a suitable diagram, describe the organisation of the mammary gland.

Answer:

Mammary glands are paired structures which contain glandular tissue and a variable amount of fat.

• Glandular tissue present in each breast is made up of 15 - 20 mammary lobes. These lobes have clusters of cells known as alveoli.
• Milk, stored in the cavities (lumens) of alveoli, is secreted from the cells of alveoli. The alveoli open in mammary tubules.
• Tubules from each lobe join to form a mammary duct.
• Many mammary ducts join to form a wider mammary ampulla.
• A mammary ampulla is connected to the lactiferous duct. Milk is sucked out through the lactiferous duct.

NCERT Exemplar Class 12 Biology Chapter 3 Human Reproduction Solutions- Short Answer Type Questions:

Question:1

A human female experiences two major changes, menarche, and menopause during her life. Mention the significance of both events.

Answer:

Menarche marks the onset of puberty (the beginning of the reproductive phase).
Menopause marks the end of the reproductive phase.

Question:2

a. How many spermatozoa are formed from one secondary spermatocyte?

b. Where does the first cleavage division of the zygote take place?

Answer:

(a) One secondary spermatocyte forms four spermatids, all of which subsequently develop into spermatozoa via the process of spermiogenesis.
(b) The first cleavage division of the zygote takes place in the ampullary-isthmus junction.

Question:4

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:

Corpus luteum is responsible for the secretion of progesterone, which is essential to maintain the endometrium and helps in the proper development of the foetus.
This is the reason for the long life of Corpus luteum when Fertilisation has occurred. However, when there is no fertilisation, it serves no purpose and thus remains active only for 10-12 days

Question:4

What is the foetal ejection reflex? Explain how it leads to parturition.

Answer:

The foetal ejection reflex is the mild uterine contraction at the time of childbirth. It triggers the release of oxytocin from the maternal pituitary, which induces strong uterine contraction and finally leads to parturition.

Question:5

Except for the endocrine function, what are the other functions of the placenta?

Answer:

The placenta is responsible for the following in addition to its endocrine function –
(A) Supply of oxygen and nutrients to foetus
(B) Removal of waste products from the foetus

Question:6

Why do doctors recommend breastfeeding during the initial period of infant growth?

Answer:

Milk produced during the initial few days of lactation is known as colostrum and contains several antibodies, which are important for the development of disease resistance in the baby. This is the prime reason why doctors recommend breastfeeding during the initial period of growth of an infant.

Question:7

What are the events that take place in the ovary and uterus during the follicular phase of the menstrual cycle?

Answer:

During the follicular phase of the menstrual cycle, the following things happen in the ovary and the uterus –

1. The primary follicle in the ovary grows into a fully mature Graafian follicle
2. Endometrium in the uterus regenerates through the proliferation
3. Estrogen is secreted by growing follicles.

Question:8

Given below is a flow chart showing ovarian changes during the menstrual cycle. Fill in the spaces giving the name of the hormones responsible for the events shown.

Answer:

Hormones responsible for various changes during the menstrual cycle are:

1. Follicle Stimulating Hormone (FSH): It is responsible for the transformation of the primary follicle into the Graafian follicle.
2. Follicle Stimulating Hormone (FSH): It is also responsible for ovulation. It works in coordination with LH and complements its function.
3. Luteinizing Hormone (LH): It is responsible for the development of the corpus luteum from the Graafian follicle.

Question:9

Give a schematic labelled diagram to represent oogenesis (without descriptions).

Answer:

Question:10

What are the changes in the oogonia during the transition of a primary follicle to a Graafian follicle?

Answer:

Following changes occur in the oogonia during the transition of a primary follicle to a Graafian follicle:
(a) Each primary oocyte is surrounded by a layer of granulosa cells; called a primary follicle
(b) Primary follicle transforms into secondary follicle by getting surrounded by another layer of granulosa cells and a new theca.
(c) The secondary follicle then transforms into the tertiary follicle. The tertiary follicle is characterised by a fluid-filled cavity called the antrum. At this stage, the primary oocyte undergoes a second meiotic division and forms a secondary oocyte and a tiny polar body.
(d) The tertiary follicle then changes into a mature Graafian follicle. During this stage, a new layer; called zona pellucida; develops around the secondary oocyte.

NCERT Exemplar Class 12 Biology Chapter 3 Human Reproduction Solutions- Very Short Answer Type Questions:

Question:1

Given below are the events in human reproduction. Write them in the correct sequential order. Insemination, gametogenesis, Fertilisation, parturition, gestation, implantation

Answer:

Gametogenesis→Insemination→Fertilization→Implantation→Gestation→Parturition

Question:2

The path of sperm transport is given below. Provide the missing steps in blank boxes.

Answer:

Question:3

What is the role of the cervix in the human female reproductive system

Answer:

The cervix and vagina together form the birth canal. Parturition happens through the birth canal.

Question:4

Why are menstrual cycles absent during pregnancy?

Answer:

Gonadotropins, which are required for the development of new follicles, are suppressed due to the high levels of progesterone and estrogen during pregnancy. This inhibits the initiation of a new menstrual cycle.

Question:5

Female reproductive organs and associated functions are given below in columns A and B. Fill the blank boxes.

Answer:

A. Fertilisation
B. Uterus

Question:6

From where do the parturition signals arise or the foetus? Mention the main hormone involved in parturition

Answer:

Parturition signals arise from the foetus. Oxytocin is the main hormone involved in parturition and is released from the maternal pituitary gland.

Question:7

What is the significance of epididymis in male fertility?

Answer:

Secretions from the epididymis, vas deferens, prostate and seminal vesicle are essential for the maturation and motility of sperms. These organs play an important role in male fertility.

Question:8

Give the names and functions of the hormones involved in the process of spermatogenesis. Write the names of the endocrine glands from where they are released.

Answer:

Question:9

The mother germ cells are transformed into a mature follicle through a series of steps. Provide the missing steps in the blank boxes.

Answer:

Question:10

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?

Answer:

Chromosome number reduces to half in gametes as, during gametogenesis, meiosis takes place resulting in the haploid number of chromosomes.
During Fertilisation, male and female gametes undergo fusion to make the diploid zygote.

Question:11

What is the difference between a primary oocyte and a secondary oocyte?

Answer:

Question:12

What is the significance of ampullary-isthmic junction in the female reproductive tract?

Answer:

The first cleavage division of the zygote occurs in the ampullary-isthmic junction in the female reproductive tract

Question:13

How does zona pellucida of ovum help in preventing polyspermy?

Answer:

Zona pellucida’s membrane undergoes changes when sperm comes into contact with it. This prevents the entry of other sperm into the ovum and thus prevents polyspermy.

Question:14

Mention the importance of LH surge during the menstrual cycle.

Answer:

The rupture of the Graafian follicle is induced by a rapid surge in LH level. Resulting in the release of ovum (ovulation)

Question:15

Which type of cell division forms spermatids from the secondary spermatocytes?

Answer:

Meiosis results in the formation of spermatids from secondary spermatocytes.

NCERT Exemplar Class 12 Biology Chapter 3 Human Reproduction Solutions- Multiple Choice Questions:

Question:1

Choose the incorrect statement from the following:
a. In birds and mammals, internal Fertilisation takes place
b. Colostrum contains antibodies and nutrients
c. Polyspermy in mammals is prevented by the chemical changes in the egg surfaced.

d. In the human female implantation occurs almost seven days after Fertilisation

Answer:

The answer is option (c) Polyspermy in mammals is prevented by the chemical changes in the egg surface
Explanation: Zona pellucida absorbs water and swells preventing further entry of sperms. So, physical change rather than chemical change is responsible for the prevention of polyspermy in mammals.

Question:2

Identify the correct statement from the following:
a. High levels of estrogen trigger the ovulatory surge.
b. Oogonial cells start to proliferate and give rise to functional ova in regular cycles from puberty onwards.
c. Sperms released from seminiferous tubules are highly motile.
d. Progesterone level is high during the post-ovulatory phase of the menstrual cycle

Answer:

The answer is option (d) Progesterone level is high during the post-ovulatory phase of the menstrual cycle
Explanation: Ovulatory surge is triggered by the high levels of LH and FSH. Sperms released from seminiferous tubules are non-motile. Oogonial cells stop their activity when the girl child is still in the womb.

Question:3

Spot the odd one out from the following structures with reference to the male reproductive system:
a. Rete testis
b. Epididymis
c. Vasa efferentia
d. Isthmus

Answer:

The answer is the option (d) Isthmus
Explanation: The Isthmus is a part of the oviduct in the female reproductive system. Others are parts of the male reproductive system

Question:4

Seminal plasma, the fluid part of semen, is contributed by.
i. Seminal vesicle
ii. Prostate gland
iii. Urethra
iv. Bulbourethral gland
(a) i and ii (b) i, ii and iv (c) ii, iii and iv (d) i and iv

Answer:

The answer is the option (b) (i), (ii) and (iv)
Explanation: Urethra has no contribution to seminal plasma

Question:5

Spermiation is the process of the release of sperm from:
a. Seminiferous tubules
b. Vas deferens
c. Epididymis
d. Prostate gland

Answer:

The answer is the option (a) Seminiferous tubules
Explanation: Seminiferous tubules

Question:6

A mature Graafian follicle is generally present in the ovary of a healthy human female around:
a. 5 – 8 day of menstrual cycle
b. 11 – 17 days of the menstrual cycle
c. 18 – 23 days of menstrual cycle
d. 24 – 28 days of the menstrual cycle

Answer:

The answer is the option (b) 11-17 day of the menstrual cycle
Explanation: After rupturing in the Graafian follicle, ovulation takes place in this period

Question:7

The acrosomal reaction of the sperm occurs due to:
a. Its contact with zona pellucida of the ova
b. Reactions within the uterine environment of the female
c. Reactions within the epididymal environment of the male
d. Androgens produced in the uterus

Answer:

The answer is the option (a) Its contact with zona pellucida of the ova
Explanation: Sperm can enter the ova only after the enzyme from the acrosome breaks down the zona pellucida

Question:8

Which one of the following is not a male accessory gland?
a. Seminal vesicle
b. Ampulla
c. Prostate
d. Bulbourethral gland

Answer:

The answer is the option (b) Ampulla
Explanation: Ampulla is part of the fallopian tube

Question:9

The spermatogonia undergo division to produce sperm by the process of spermatogenesis. Choose the correct one with reference to athe bove.
a. Spermatogonia have 46 chromosomes and always undergo meiotic cell division
b. Primary spermatocytes divide by mitotic cell division
c. Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
d. Spermatozoa are transformed into spermatids

Answer:

The answer is option (c) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
Explanation: Spermatogonia have 46 chromosomes, and they undergo meiotic cell division; primary spermatocytes undergo meiotic cell division. Spertamids and transformed into spermatozoa

Question:10

Match between the following representing parts of the sperm and their functions and choose the correct option.

a. A-ii, B-iv, C-i, D-iii
b. A-iv, B-iii, C-i, D-ii
c. A-iv, B-i, C-ii, D-iii
d. A-ii, B-i, C-iii, D-iv

Answer:

The answer is the option (b) (A) – (iv), (B) – (iii), (C) – (i), (D) – (ii)
Explanation: The nucleus is present in the head. Acrosome releases enzyme which dissolves zona pellucida. The tail helps in the swimming of sperm and the middle piece is the place where mitochondria are present

Question:12

Match the following and choose the correct options:

a. A-ii, B-i, C-iii, D-iv
b. A-iii, B-iv, C-ii, D-i
c. A-iii, B-i, C-ii, D-iv
d. A-ii, B-iv, C-iii, D-i

Answer:

The answer is the option (b) (A)-(iii), (B)-(iv), (C)-(ii), (D)-(i)

Question:13

Which of the following hormones is not secreted by the human placenta?

a. hCG
b. Estrogens
c. Progesterone
d. LH

Answer:

The answer is the option (d) LH
Explanation: LH (Luteinizing hormone) is secreted by the pituitary gland

Question:14

The vas deferens receives duct from the seminal vesicle and opens into the urethra as:
a. Epididymis
b. Ejaculatory duct
c. Efferent ductule
d. Ureter

Answer:

The answer is the option (b) Ejaculatory duct

Question:15

Urethral meatus refers to the:
a. Urinogenital duct
b. Opening of vas deferens into urethra
c. The external opening of the urinogenital duct
d. Muscles surrounding the urinogenital duct

Answer:

The answer is the option (c) External opening of the urinogenital duct
Explanation: External opening of the urinogenital duct

Question:16

Morula is a developmental stage:
a. Between the zygote and blastocyst
b. Between the blastocyst and gastrula
c. After the implantation
d. Between implantation and parturition

Answer:

The answer is the option (a) between the zygote and blastocyst
Explanation: between the zygote and blastocyst

Question:17

The membranous cover of the ovum at ovulation is:
a. Corona Radiata
b. Zona radiata
c. Zona pellucida
d. Chorion

Answer:

The answer is the option (a) corona radiata

Question:18

Identify the odd one from the following:
a. Labia minora
b. Fimbriae
c. Infundibulum
d. Isthmus

Answer:

The answer is the option (a) Labia Minora