NCERT Exemplar Class 12 Biology Solutions Chapter 3 Human Reproduction

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 the seminiferous tubules are highly motile.
d. Progesterone level is high during the post-ovulatory phase of the menstrual cycle

Answer:

Progesterone is the hormone responsible for maintaining the uterine lining post-ovulation—it prepares the body for possible implantation. Estrogen builds up earlier but does not cause an ovulatory surge; that’s the job of LH (with FSH). Also, sperms are non-motile when first released from the seminiferous tubules, and oogonia stop dividing well before birth, not at puberty.

Hence, the correct answer is option (d). Progesterone level is high during the post-ovulatory phase of the menstrual cycle.

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:

Rete testis, epididymis, and vasa efferentia are all anatomical structures associated with sperm transport in the male reproductive system. However, the isthmus is a portion of the fallopian tube and is part of the female reproductive system. So, this is a classic “odd one out” scenario.

Hence, the correct answer is option (d) Isthmus.

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:

Seminal plasma is the fluid part of semen and is secreted by the seminal vesicle (which adds fructose), the prostate gland (which adds enzymes), and the bulbourethral gland (which provides lubrication). The urethra simply transports the semen—it doesn’t contribute to its production.

Hence, the correct answer is option (b) i, ii, and iv.

Question:5

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

Answer:

Spermiation refers to the release of mature spermatozoa from the Sertoli cells into the lumen of the seminiferous tubules. This marks the final stage of spermatogenesis before the sperm begins its journey through the male duct system.

Hence, the correct answer is option (a) Seminiferous tubules.

Question:6

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

Answer:

The Graafian follicle matures in the ovary between the 11th and 17th day of the menstrual cycle, with ovulation typically occurring around day 14. This follicle houses the secondary oocyte and bursts to release it during ovulation. Before day 11, it’s still growing; after day 17, ovulation has usually already occurred.

Hence, the correct answer is option (b) 11–17 days of the menstrual cycle.

Question:7

The acrosomal reaction of the sperm occurs due to:
a. Its contact with the 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 are produced in the uterus

Answer:

The acrosomal reaction is triggered when the sperm contacts the zona pellucida of the ovum. This reaction involves the release of enzymes such as hyaluronidase and acrosin, which digest the zona pellucida and allow the sperm to penetrate the egg.

Hence, the correct answer is option (a). Its contact with the zona pellucida of the ova.

Question:8

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

Answer:

Male accessory glands include the seminal vesicle, prostate, and bulbourethral gland, which together produce the fluid part of semen. The ampulla, however, is not an accessory gland—it is part of the female reproductive system (specifically the upper fallopian tube).

Hence, the correct answer is option (b) Ampulla.

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 the second meiotic division
d. Spermatozoa are transformed into spermatids

Answer:

Spermatogenesis is a multi-stage process. Spermatogonia (2n) first undergo mitosis. Primary spermatocytes (2n) then go through the first meiotic division to form secondary spermatocytes (n), which proceed with the second meiotic division to form spermatids. Hence, secondary spermatocytes do have 23 chromosomes and are meiotically active.

Hence, the correct answer is option (c) Secondary spermatocytes have 23 chromosomes and undergo the second meiotic division.

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 head of the sperm contains the nucleus (genetic material). The middle piece is packed with mitochondria to provide energy. The acrosome at the tip of the head contains enzymes to help penetrate the egg. The tail enables motility, allowing the sperm to swim towards the ovum.

Hence, the correct answer is option (b) A–iv, B–iii, C–i, D–ii.

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 trophoblast is the outer layer of the blastocyst that attaches to the endometrium. Cleavage is the early mitotic division of the zygote. The inner cell mass forms the embryo. Implantation refers to the process of the blastocyst embedding itself in the uterine wall.

Hence, the correct answer is 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 human placenta produces hCG, estrogen, and progesterone, which are essential for maintaining pregnancy. LH, however, is produced by the anterior pituitary and not by the placenta. This makes LH the only hormone in the list that is not placental.

Hence, the correct answer is option (d) LH.

Question:14

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

Answer:

The vas deferens combines with the duct of the seminal vesicle to form the ejaculatory duct, which then empties into the urethra. This duct is a crucial passage for the transport of semen during ejaculation.

Hence, the correct answer is option (b) Ejaculatory duct.

Question:15

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

Answer:

The urethral meatus is the external opening of the male urinogenital duct. It allows for the discharge of urine and semen. This structure is located at the tip of the penis and is distinct from internal ducts or muscular tissues.

Hence, the correct answer is option (c) the 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 morula is a solid ball of cells formed after several mitotic divisions of the zygote but before it becomes a blastocyst. This stage occurs during the early days post-fertilisation, while the embryo is still moving through the fallopian tube.

Hence, the correct answer is option (a) 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:

At the time of ovulation, the ovum is surrounded by the corona radiata—a layer of granulosa cells that nourish and protect it. Zona pellucida lies just beneath this layer, and the chorion appears much later during embryonic development.

Hence, the correct answer is option (a) Corona radiata.

Question:18

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

Answer:

Fimbriae, infundibulum, and isthmus are anatomical regions of the fallopian tube, essential for capturing and transporting the ovum. Labia minora, however, is part of the external genitalia and unrelated to the internal transport of ova, making it the odd one out.

Hence, the correct answer is option (a) Labia minora.

Question:2

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

Answer:

In males, spermatogenesis begins at puberty, when meiosis starts and sperm production becomes active. In females, oogenesis begins much earlier, while the girl is still in her mother’s womb. By around the 20th week of pregnancy, all the primary oocytes are already formed, and the process pauses there.

• Begins at puberty in males
• Begins before birth in females
• Primary oocytes are formed by the 20th week of pregnancy
• Spermatogenesis continues regularly after it starts
• Oogenesis pauses after initial formation

In spermatogenesis, all stages of meiosis happen one after the other without a break. But in oogenesis, meiosis stops at Prophase I and stays paused until puberty. After that, it resumes slowly and in small batches.

• No delay in meiosis during spermatogenesis
• Meiosis pauses at Prophase I during oogenesis
• Oogenesis continues slowly after puberty

This difference exists because male gametes are needed in large numbers since most of them don’t survive. Female gametes are protected, and fewer are needed. Producing fewer eggs also helps the body save energy, which is useful later during pregnancy and the development of the baby.

• Male gametes are made in large numbers
• Female gametes are fewer in number
• Fewer eggs help conserve energy for pregnancy and foetal growth

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 the 16-celled stage.
These daughter cells are called blastomeres.
(c) The 16-celled stage is known as a 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 the 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 that 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.