NCERT Solutions for Class 12 Science Biology Chapter 3 Human Reproduction are provided here with simple step-by-step explanations. These solutions for Human Reproduction are extremely popular among Class 12 Science students for Biology Human Reproduction Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the NCERT Book of Class 12 Science Biology Chapter 3 are provided here for you for free. You will also love the ad-free experience on Meritnation’s NCERT Solutions. All NCERT Solutions for class Class 12 Science Biology are prepared by experts and are 100% accurate.
Page No 17:
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 surface
d. In the human female implantation occurs almost seven days after fertilisation
Answer:
Internal fertilization takes place inside the female body. In birds and mammals internal fertilization takes place. Colostrum is the first milk produced by the mammary glands. It is rich in IgA and other nutrients. When one egg is fertilized by more than one sperm, the condition is called polyspermy. Generally, after fusion with the first sperm, the membrane of the ovum get depolarized. This prevents polyspermy. In the human female, implantation occurs almost seven days after fertilization.
Hence, the correct answer is option c.
Page No 17:
Question 2:
Identify the correct statement from the following:
a. High levels of estrogen triggers 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 menstrual cycle.
Answer:
Post ovulatory phase or luteal phase is also known as the secretory phase. During this phase the remaining part of the Graafian follicle transforms into corpus luteum which secrets large amount of progesterone that is essential for maintenance of endometrium.
Hence the correct answer is option d.
Page No 17:
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:
rate testis, epididymis, vasa efferentia all are the parts of human male reproduction system. Whereas, isthmus is the narrow lumen part that connects the oviduct with the uterus.
Hence, the correct answer is option d.
Page No 17:
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, the fluid part of semen, is contributed by seminal vesicle, prostate gland and bulbourethral gland.
Hence, the correct answer is option b.
Page No 18:
Question 5:
Spermiation is the process of the release of sperms from:
a. Seminiferous tubules
b. Vas deferens
c. Epididymis
d. Prostate gland
Answer:
After spermiogenesis (conversion of spermatids into spermatozoa) sperm heads become embedded in the sertoli cells and are finally released from the seminiferous tubules by the process called spermination.
Hence, the correct answer is option a.
Page No 18:
Question 6:
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 day of menstrual cycle
c. 18 – 23 day of menstrual cycle
d. 24 – 28 day of menstrual cycle
Answer:
The mature Graafian follicle is generally present in the ovary of a healthy, human female around 11-17 day of menstrual cycle. During this period, rapid secretion of LH induces rupture of the Graafian follicle and release and release of ovum (ovulation).
Hence, the correct answer is option b.
Page No 18:
Question 7:
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:
During fertilization, when sperm fuses with the ovum or comes in contact with the zona pellucida layer of the ovum, it induces changes in the membrane that block polyspermy. The acrosome releases its contents like hydrolytic enzymes by exocytosis.
Hence, the correct answer is option a.
Page No 18:
Question 8:
Which one of the following is not a male accessory gland?
a. Seminal vesicle
b. Ampulla
c. Prostate
d. Bulbourethral gland
Answer:
Seminal vesicle, prostate and bulbourethral gland, all are male accessory glands that produce seminal plasma. The fluid part of semen. Ampulla is the wider part or oviduct, present in female reproductive system.
Hence, the correct answer is option b.
Page No 18:
Question 9:
The spermatogonia undergo division to produce sperms by the process of spermatogenesis. Choose the correct one with reference to above.
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:
Primary spermatocytes undergo meiosis-I to produce secondary spermatocytes, which are haploid (have 23 chromosomes). It undergoes me meiosis-II to produce four spermatids.
Hence the correct answer is option c.
Page No 18:
Question 10:
Match between the following representing parts of the sperm and their functions and choose the correct option.
Column I Column II
A. Head i. Enzymes
B. Middle piece ii. Sperm motility
C. Acrosome iii. Energy
D. Tail iv. Genetic material
options:
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:
| Column I | Column II |
| A. Head | iv. Genetic material |
| B. Middle piece | iii. Energy |
| C. Acrosome | i. Enzymes |
| D. Tail | ii. Sperm motility |
Hence, the correct answer is option b.
Page No 19:
Question 11:
Which among the following has 23 chromosomes?
a. Spermatogonia
b. Zygote
c. Secondary oöcyte
d. Oögonia
Answer:
Spermatogonia, oogonia and zygote are diploid in nature. They have 46 chromosomes. Secondary oocytes are haploid as they formed after meiosis-I and have 23 chromosome.
Hence, the correct answer is option c.
Page No 19:
Question 12:
Match the following and choose the correct options:
Column I Column II
A. Trophoblast i. Embedding of blastocyst in the endome trium
B. Cleavage ii. Group of cells that would differentiate as embryo
C. Inner cell mass iii. Outer layer of blastocyst attached to the endometrium
D. Implantation iv. Mitotic division of zygote
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:
| Column I | Column II |
| A. Trophoblast | iii. Outer layer of blastocyst attached to the endometrium |
| B. Cleavage | iv. Mitotic division of zygote |
| C. Inner cell mass | ii. Group of cells that would differentiate as embryo |
| D. Implantation | i. Embedding of blastocyst in the endometrium |
Hence, the correct answer is option b.
Page No 19:
Question 13:
Which of the following hormones is not secreted by human placenta?
a. hCG
b. Estrogens
c. Progesterone
d. LH
Answer:
Placenta also acts as an endocrine tissue and produces several hormones like human chorionic gonadotropin (HCG), human placental lactogen (HPL), estrogen, progesterone etc. LH is secreted by the anterior pituitary gland.
Hence the correct answer is option d.
Page No 19:
Question 14:
The vas deferens receives duct from the seminal vesicle and opens into urethra as:
a. Epididymis
b. Ejaculatory duct
c. Efferent ductule
d. Ureter
Answer:
The epididymis continues into vas deferens that ascends to the abdomen and loops over the urinary bladder. It receives a duet from seminal vesicle and opens into urethra as ejaculatory duct.
Hence, the correct answer is option b.
Page No 20:
Question 15:
Urethral meatus refers to the:
a. Urinogenital duct
b. Opening of vas deferens into urethra
c. External opening of the urinogenital duct
d. Muscles surrounding the urinogenial duct
Answer:
The urethra originate from the urinary bladder and extends through the penis to its external opening called urethra meatus.
Hence, the correct answer is option c.
Page No 20:
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 zygote undergoes continuous mitotic division and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8-16 blastomeres the zygote and blastocyst.
Hence, the correct answer is option a.
Page No 20:
Question 17:
The membranous cover of the ovum at ovulation is:
a. Corona radiata
b. Zona radiata
c. Zona pellucida
d. Chorion
Answer:
The membranous cover of the ovum at ovulation is corona radiata. It is made up of follicular cells. Zona pellucida is present inside the corona radiata.
Hence, the correct answer is option a.
Page No 20:
Question 18:
Identify the odd one from the following:
a. Labia minora
b. Fimbriae
c. Infundibulum
d. Isthmus
Answer:
The female external genitalia includes mons pubis, labia majora, labia minora, hymen and clitoris. Fimbriae infundibulum and isthmus are parts of the fallopian tube.
Hence, the correct answer is option a.
Page No 20:
Question 1:
Given below are the events in human reproduction. Write them in correct sequential order.
Insemination, gametogenesis, fertilisation, parturition, gestation, implantation
Answer:
ans
Page No 20:
Question 2:
The path of sperm transport is given below. Provide the missing steps in blank boxes.
Answer:
Page No 21:
Question 3:
What is the role of cervix in the human female reproductive system?
Answer:
Cervix join the vagina with the uterus. Along with the vagina, it forms birth canal. Parturition or birth of the baby occurs through this canal.
Page No 21:
Question 4:
Why are menstrual cycles absent during pregnancy.
Answer:
During pregnancy the levels of estrogen and progesterone is high in the blood, This suppresses the releases of gonadotropins which stimulate the growth of the follicles Thus, ovulation can not take place as well as menstruation.
Page No 21:
Question 5:
Female reproductive organs and associated functions are given below in column A and B. Fill the blank boxes.
Answer:
Page No 21:
Question 6:
From where the parturition signals arise-mother or foetus? Mention the main hormone involved in parturition.
Answer:
The fully developed foetus initiates foetal ejection reflex that triggers parturition. Oxytocin which is stared and released by the posterior pituitary initiates parturition.
Page No 21:
Question 7:
What is the significance of epididymis in male fertility?
Answer:
Epididymis is a coiled structure present within the scrotum. Its main role in male fertility are-
(i) Sperms mature here and their motility and fertilizing capacity increases.
(ii) It takes part in sperm transportation.
Page No 21:
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:
| Hormones | Functions | Origin |
| (i) Gonadotropin releasing hormones(GnRH) | Acts on anterior pituitary and stimulates the secretion of LH and FSH | Hypothalamus |
| (ii) Luteinising hormone (LH) | Acts on Leydig cells and secretion of spermiogenesis promoting factors | Anterior pituitary |
| (iii) Follicle stimulating hormones (FSH) | Acts on Sertoli cells and secretion of spermatogenesis promoting factors | Anterior pituitary |
Page No 21:
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:
Page No 21:
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:
Gametogenesis takes place in sexually reproducing organisms. During gamete production the chromosome number reduces to half due to meisosis . During fertilization fusion of male and female nuclei take place which restores the chromosomal number (2n) in the offspring.
Page No 21:
Question 11:
What is the difference between a primary oöcyte and a secondary oöcyte?
Answer:
Primary oocyte is formed from the oogonia after mitosis and is diploid in nature. However, secondary oocyte forms from primary oocyte after meiosis I and is haploid in nature.
Page No 21:
Question 12:
What is the significance of ampullary–isthmic junction in the female reproductive tract?
Answer:
The ampullary - isthmic junction is the place where fertilization take place. The male gametes or sperms swim to this place to meet the ovum.
Page No 21:
Question 13:
How does zona pellucida of ovum help in preventing polyspermy?
Answer:
Changes are observed in the zona pellucida layer of the ovum when a sperm comes in contact with it, preventing the entry of other sperms, Thus inhibiting polyspermy.
Page No 21:
Question 14:
Mention the importance of LH surge during menstrual cycle.
Answer:
During the menstrual cycle a rapid its surge stimulates the rupture of Graafian follicle and the ovum is released. Thus, LH surge induces ovulation.
Page No 21:
Question 15:
Which type of cell division forms spermatids from the secondary spermatocytes?
Answer:
Spermatids are formed from secondary spermatocytes via meiosis -II
Page No 22:
Question 1:
A human female experiences two major changes, menarche and menopause during her life. Mention the significance of both the events.
Answer:
Menarche: The oust of menstruation in the life of a young girl is called menarche. It is the indication of attainment of sexual maturity and begining of fertile period.
Menopause: When menstruation stops in the life of a woman it is called menopause. It marks the end of fertile period as the woman is no longer capable of producing ovum.
Page No 22:
Question 2:
a. How many spermatozoa are formed from one secondary spermatocyte?
b. Where does the first cleavage division of zygote take place?
Answer:
a. Spermatozoa are formed from are secondary spermatocyte.
b. The first cleavage division of zygote takes place in the ampullary-isthmus junction.
Page No 22:
Question 3:
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:
After ovulation the Graafian fallicle is converted into corpus luteum which secretes progesterone. This maintains the endometrium which is essential for the development of foetus. Thus, corpus luteum has a long life during pregnancy. However, if fertilization does not take place, there is no baby and no need of corpus luteum. So it remains active only for 10-12 days.
Page No 22:
Question 4:
What is foetal ejection reflex? Explain how it leads to parturition?
Answer:
When the foetus is fully development the placenta generates mild uterine contractions. This is called foetal ejection reflex. This reflex is seen at the time of parturition when the reflex triggers the release of oxytocin from the materrial pituitary. Oxytocin acts on the uterine muscle and causes stronger uterine contractions which causes expulsion or delivery of the baby or parturition.
Page No 22:
Question 5:
Except endocrine function, what are the other functions of placenta.
Answer:
Except endocrine function, the other functions of placenta are like it facilitates the supply of oxygen and nutrients to the embryo and remove carbon dioxide and excretory material produced by the embryo.
Page No 22:
Question 6:
Why doctors recommend breast feeding during initial period of infant growth?
Answer:
The mother produces an antibody rich milk during the initial days of laction. This is called colostrum which provides immunity to the baby against various diseases. Thus, doctors recommend breast feeding during the initial period of infant growth.
Page No 22:
Question 7:
What are the events that take place in the ovary and uterus during follicular phase of the menstrual cycle.
Answer:
During follicular phase of the menstrual cycle the following events take place in the ovary and uterus.
1. The primary follicle grows in the ovary and becomes mature Graafian follicle.
2. The endometrium layer of the uterus regenerates through proliferation.
3. Growing Graafian follicle secrete estrogen hormone.
Page No 22:
Question 8:
Given below is a flow chart showing ovarian changes during menstrual cycle. Fill in the spaces giving the name of the hormones responsible for the events shown.
Answer:
Page No 22:
Question 9:
Give a schematic labelled diagram to represent oögenesis (without descriptions)
Answer:
Page No 22:
Question 10:
What are the changes in the oogonia during the transition of a primary follicle to Graafian follicle?
Answer:
Following changes take place in the oogonia during the transition primary follicle to Graafian follicle.
1. Each primary oocyte gets surrounded by a layer of granulosa cells. This is called primary follicle.
2. The primary follicle again gets surrounded by another layer of granulosa cells and a new theca forming secondary follicle.
3. The secondary follicle transforms into tertiary follicle which has a fluid filled cavity called antrum. At this stage, the primary oocyte undergoes second meiotic division to form secondary oocyte and first polar body.
4. The tertiary follicle matures and changes into Graafian. A layer of zona pellucida develops around the secondary oocyte.
Page No 22:
Question 1:
What role does pituitary gonadotropins play during follicular and ovulatory phases of menstrual cycle? Explain the shifts in steroidal secretions.
Answer:
There are two pituitary gonadotropins, FSH and LH. They play an important role during follicular and ovulatory phases of the menstrual cycle.
- FSH stimulates the graafian follicle to release the ovum. It helps in the maturation of the graafian follicle.
- During this stage, the level of estradiol increases which suppresses the level of LH. Once the level of estradiol reaches to a certain level, the effect is reversed.
- Now, the level of estrogen increases which stimulates secretion of LH and we can observe LH surge. High level of LH stimulates the development of corpus luteum. It also promotes the proliferation of endometrium. Thus, it marks the begining of luteal phase.
Page No 23:
Question 2:
Meiotic division during oogenesis is different from that in spermatogenesis. Explain how and why?
Answer:
Meiotic division during oogenesis is different from that of spermatogenesis in the following ways-
⇒ In case of spermatogenesis, meiosis begins at the time of puberty. However in case of oogenesis, it begins when the female is still in the womb.
⇒ Males form spermatocytes throughout the reproductive phase of their life. However, in females formation of primary oocyte steps by the 20th week of gestation of the female child.
⇒ In spermatogenesis, all the stages of meiosis takes place quickly one after the another. There is no time bag between the stages. In oogenesis, meiosis is stalled at prophase-I.
Reasons:
1. To ensure fertilization males need to produce large number of gametes.
2. As females do not release their gametes in the external environment, there is lens chance of them to get destroyed. So fewer amount of gametes are produced. This also helps in conservation of resources available in the female body. Females can utilize these resources to nourish the baby.
Page No 23:
Question 3:
The zygote passes through several developmental stages till implantation, Describe each stage briefly with suitable diagrams.
Answer:
After fertilization the zygote passes through the following stages till implantation.
1. The embryo with 8-16 blastomeres is called a morula.
2. As the morula contirues to divide, it transforms into blastocyst that moves further into uterus.
3. The blastomeres in the blastocyst are arranged into a surface layer called trophoblast. A elusture of interior cells are aslo attached to the trophoblast. They are called inner cell mass.
4. This trophoblast layer gets attached to the endometrium and the inner cell mass differentiates into embryo.
5. The uterice wall cells divide rapidly after attachment and cover the blastocyst.
6. Finally, the blastocyst gets embedded into the endometrium. This is known as implantation.
Page No 23:
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:
Page No 23:
Question 5:
With a suitable diagram, describe the organisation of mammary gland.
Answer:
Female mammals have functional mammary glands. Every female has a pair of mammary glands. Also called breasts. They are made up of glandular tissue and variable amount of fat. Each breast is divided into 15-20 mammary lobes containing elustures of cells called alveoli. The cells of alveoli secrete milk which is stared in the human of alveoli. These alveoli open into mammary tubules which join to form a mammary duct. Several mammary ducets join to form a wider mammary ampulla which is connected to lactiferous duct through which milk is sucked out.
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