Class 12 Biology Chapter 3 Human Reproduction Question Answer

Class 12 Biology Chapter 3 Human Reproduction Question Answer: Explore in-depth question-answer solutions for Class 12 Biology Chapter 3 on Human Reproduction. Prepare for exams with detailed explanations, examples, and key insights covering topics such as reproductive anatomy, gametogenesis, fertilization, and reproductive health.

Class 12 Biology Chapter 3 Human Reproduction Question Answer

• Multiple Choice Questions:

1. Choose the incorrect statement from the following:
   1. In birds and mammals internal fertilisation takes place
   2. Colostrum contains antibodies and nutrients
   3. Polyspermy is prevented by the chemical changes in the egg surface
   4. In the human female implantation occurs almost seven days after fertilisation
2. Identify the wrong statement from the following:
   1. High levels of estrogen triggers the ovulatory phase
   2. Oogonial cells start to proliferate and give rise to functional ova in regular cycles from puberty onwards.
   3. Sperms released from seminiferous tubules are poorly motile/non-motile
   4. Progesterone level is high during the post-ovulatory phase of menstrual cycle.
3. Spot the odd one out from the following structures with reference to the male reproductive system:
   1. Rete testis
   2. Epididymis
   3. Vasa effereritia
   4. Isthmus
4. Seminal plasma, the fluid part of semen, is contributed by
   i. Seminal vesicle
   ii. Prostate
   iii. Urethra
   iv. Bulbourethral gland
   1. (i) and (ii)
   2. (i), (ii) and (iv)
   3. (ii), (iii) and (iv)
   4. (i) and (iv)
5. Spermiation is the process of the release of sperms from:
   1. 5-8 day of menstrual cycle
   2. 11-17 day of menstrual cycle
   3. 18-23 day of menstrual cycle
   4. 24-28 day of menstrual cycle
6. Mature Graafian follicle is generally present in the ovary of a healthy human female around:
   1. (a) 5-8 day of menstrual cycle
   2. (b) 11-17 day of menstrual cycle
   3. (c) 18-23 day of menstrual cycle
   4. (d) 24-28 day of menstrual cycle
7. Acrosomal reaction of the sperm occurs due to:
   1. Its contact with zona pellucida of the ova
   2. Reactions within the uterine environment of the female
   3. Reactions within the epididymal environment of the male
   4. Androgens produced in the uterus
8. Which one of the following is not a male accessory gland?
   1. Seminal vesicle
   2. Ampulla
   3. Prostate
   4. Bulbourethral gland
9. The immature male germ celts undergo division to produce sperms by the process of spermatogenesis.
   Choose the correct one with reference to above.
   1. Spermatogonia have 46 chromosomes and always undergo meiotic cell division
   2. Primary spermatocytes divide by mitotic cell division
   3. Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
   4. Spermatozoa are transformed into spermatids
10. Which among the following has 23 chromosomes?
    1. Spermatogonia
    2. Zygote
    3. Secondary oocyte
    4. Ogonia
11. Which of the following hormones is not secreted by human placenta?
    1. HCG
    2. Estrogens
    3. Progesterone
    4. LH
12. The vas deferens receives duct from the seminal vesicle and opens into urethra as:
    1. Epididymis
    2. Ejaculatory duct
    3. Efferent ductule
    4. Ureter
13. Urethral meatus refers to the :
    1. Urinogenital duct
    2. Opening of vas deferens into urethra
    3. External opening of the urinogenital duct
    4. Muscles surrounding the urinogenial duct
14. Morula is a developmental stage :
    1. Between the zygote and blastocyst
    2. Between the blastocyst and gastrula
    3. After the implantation
    4. Between implantation and parturition
15. The membranous cover of the ovum at ovulation is :
    1. Corona radiata
    2. Zona radiata
    3. Zona pellucida
    4. Chorion

• Very Short Question:

1. Failure of testes to descend into scrotal sacs leads to sterility. Why?
2. Both vaccine and colostrum produce immunity. Name type of immunity produced by these.
3. How many sperms will be produced from 10 primary spermatocytes and how many eggs will be produced from 10 primary oocytes?
4. The spermatogonial cell has 46 chromosomes in human male. Give the number of chromosomes in
   (a) Primary spermatocyte (b) Spermatid

5. In ovary which structure transforms as corpus luteum and name the hormone secreted by corpus luteum?
6. “Each and every coitus does not results in fertilisation and pregnancy”. Justify the statement.
7. Why are male testes located outside the abdominal cavity?
8. State the function of leydig cells.
9. Where do we find fimbriae?
10. What is semen?

• Short Questions:

1. Give the function of
   (a) Corpus luteum
   (b) Endometrium
2. What is meant by L.H. Surge? Write the role of L.H.
3. Explain significance of the condition in which the testes remain suspended in scrotum outside the abdomen.
4. Describe the structure of a sperm with a diagram.
5. Enlist any two functions of a female placenta.
6. What is the number of chromosomes in the following cells? Primary oocyte, secondary oocyte, ootid and follicle.
7. What is corpus luteum. How dose it functions as endocrine gland?
8. Where are leydig cells located? What do they secrete?

• Long Questions:

1. Briefly explain the primary male sex organs of man.
2. Draw well-labeled sketches of the front view and sagittal section of the male reproductive system of man.
3. Explain the events taking place at the time of fertilization of an ovum in a human female.

• Assertion and Reason Questions:

1) For two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.
2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
3. Assertion is true, but reason is false.
4. Both assertion and reason are false.

Assertion: All copulations do not lead to the fertilisation and pregnancy.

Reason: Fertilisation can occur only if the ovum and sperms are transported simultaneously to the ampullary-isthmic junction.

2) For two statements are given-one labelled Assertion and the other labelled Reason. Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.
2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
3. Assertion is true, but reason is false.
4. Both assertion and reason are false.

Assertion: A drop in temperature does not affect spermatogenesis..

Reason: During temperature drop, the smooth muscles contracts and bring the testes closer to the pelvic cavity.

• Case Study Questions:

1) Read the following and answer any four questions from (i) to (v) given below:

Cleavage is the series of rapid mitotic divisions in zygote and forms blastula. The 2, 4, 8, 16 daughter cells are called blastomeres. Embryo with 64 blastomeres is known as blastocyst and has blastocoel cavity. Blastocyst gets implanted in uterine wall and leads to pregnancy.

1. Solid mass of cells with 16 blastomeres is called:
   • Morula.
   • Blastula.
   • Gastrula.
   • Zygote.
2. At which stage of embryonic development, trophoectoderm develops?
   • Zygote.
   • Morula.
   • Blastula.
   • Gastrula.
3. Site of implantation is:
   • Endometrium of uterus.
   • Cervix.
   • Uterine fundus.
   • Infundibulum of oviduct.
4. Correct sequence of various structures formed during embryonic development is:
   • Morula → Embryo → Gastrula → Blastula.
   • Zygote → Embryo → Morula → Blastula.
   • Blastula → Morula → Gastrula → Embryo.
   • Zygote → Morula → Blastula → Gastrula.
5. Assertion: Side of blastocyst with inner cell mass is called animal pole.
   Reason: Inner cell mass gives rise to embryo.
   • Both assertion and reason are true, and reason is the correct explanation of assertion.
   • Both assertion and reason are true, but reason is not the correct explanation of assertion.
   • Assertion is true, but reason is false.
   • Both assertion and reason are false.

2) Read the following and answer any four questions from (i) to (v) given below:

During copulation, semen is released by the penis into the vagina. ‘The motile sperms swim rapidly, fuse with ovum in the ampullary region, resulting in fertilisation. Haploid nucleus of sperm fuse with that of ovum to form diploid zygote.

1. In female genital tract, sperms are made capable of fertilising the egg. This phenomenon of sperm activation is called:
   • Amphimixis.
   • Cortical reaction.
   • Capacitation.
   • Acrosomal reaction.
2. Select the correct sequence of various physical and chemical events that take place during fertilisation.
   • Fusion of cortical granules with plasma membrane of secondary oocyte.
   • Formation of fertilisation cone to receive sperm.
   • Release of sperm lysin from acrosome.
   • Mixing up of chromosomes of a sperm and an ovum.
   • R → Q → P → S
   • Q → S → R → P
   • Q → R → S → P
   • R → P → Q → S
3. Assertion: Only one sperm can fertilise an ovum.
   Reason: The secretion of acrosome help the sperm to enter into cytoplasm of ovum through zona pellucida and plasma membrane.

1. Both assertion and reason are true, and reason is the correct explanation of assertion.
2. Both assertion and reason are true, but reason is not the correct explanation of assertion.
3. Assertion is true, but reason is false.
4. Both assertion and reason are false

1. What is the significance of fertilisation?
   • It restores haploid number of chromosomes.
   • It produces offspring genetically identical to parents.
   • It initiates cleavage.
   • Both (b) and (c).
2. Site of fertilisation in humans is:
   • Endometrium of uterine cavity.
   • Ampullary isthmic junction of oviduct.
   • Cervix of uterus.
   • Infundibulum of fallopian tube.

Answer Key-

Multiple Choice Answers:

1. (c) Polyspermy is prevented by the chemical changes in the egg surface
2. (b) Oogonial cells start to proliferate and give rise to functional ova in regular cycles from puberty onwards.
3. (d) Isthmus
4. (c) (ii), (iii) and (iv)
5. (a) Seminiferous tubules
6. (b) 11-17 day of menstrual cycle
7. (a) Its contact with zona pellucida of the ova
8. (b) Ampulla
9. (c) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
10. (c) Secondary oocyte
11. (d) LH
12. (b) Ejaculatory duct
13. (c) External opening of the urinogenital duct
14. (a) Between the zygote and blastocyst
15. (a) Corona radiata

• Very Short Answers:

1. High temperature of abdomen kills the spermatogenic tissue of the testes, so no sperm are formed.
2. Vaccine Active immunity Colostrum Passive immunity.
3. 40 sperms, 10 eggs.
4. (a) 46 in Primary spermatocyte
   (b) 23 in spermatid.
5. Follicular cells of empty Graafian follicle transform as corpus luteum. The corpus luteum secretes a hormone called progesterone.

6. Ovum and sperm should reach simultaneously to the ampullary – isthmic junction.
7. The male testes are located in the scrotum outside the abdominal cavity as the scrotum provides low temperature than the normal body temperature required for spermatogenesis.
8. The leydig cells synthesise and secrete testicular hormones called androgens.
9. Fimbriae are finger like projections found in the edges of the infundibulum.
10.  The seminal plasma along with the sperms constitutes semen.

• Short Answer:

1.  (a) Corpus luteum: It secretes progesterone which prepares endometrium of uterus for implantation and normal development of foetus.

(b) Endometrium: It undergoes cyclic changes during menstrual cycle and prepares itself for implantation of blastocyst.

2. There are three phases in your menstrual cycle – follicular phase, ovulatory phase and luteal phase. In terms of the luteinizing hormone (LH) surge, the ovulatory phase is most important. During the follicular phase the follicle develops at the beginning of the menstrual cycle. This cycle begins with the menstrual period, the shedding of the iuterine lining and the shedding cleanses the lining of the uterus in preparation for ovulation during the ovulatory phase.
3. Human sperm cells cannot develop at body temperature. Spermatogenesis and maintenance of the seminiferous tubules requires a temperature slightly lower than that of the body. This is provided by the scrotum, which lies outside the abdominal cavity.
4. The human sperm is a microscopic structure with a head, middle piece and a tail. The head has the haploid nucleus and an anterior acrosome that contains the enzymes required for the fertilization of the egg. The middle piece has numerous mitochondria to produce the energy for the mobility of the tail of the sperm.
5. The structural and the functional unit between the developing embryo and the mother called placenta facilitates the supply of nutrients, oxygen to the embryo and also the removal of carbon dioxide and other excretory products produced by the embryo. It also acts as endocrine tissue and produces several hormones
6. The number of chromosome in the cells is as follows:

Primary oocyte: 23 pairs. Secondary oocyte: 23. Ootid: 23. Follicle: 23 pairs.

7. After ovulation, the graffian follicle ruptures & forms corpus luteum. Corpus luteum functions as endocrine glands as they secrete progesterone & estrogen in large quantities.
8. Leydig cells or interstitial cells are located in between the sominiferous tubules. Leydig cells secrete male sex hormone TESTOSTERONE which promotes development of accessory glands & control male secondary sexual characters.

• Long Answer:

1. The testes, male gonads, produce sperms that are suspended outside the abdominal cavity in a sac of skin called the scrotum. It results in maintenance of the temperature of the testis which is lower than the rest of the body. It is a condition favorable to sperm production.

Each testis is an oval-shaped structure and is composed of a large number of seminiferous tubules surrounded by connective tissue in which occurs numerous cells called Interstitial cells or Leydig cells. These cells produce a male sex hormone named testosterone. Seminiferous tubules are lined by a layer of germinal epithelial cells. In between the germinal cells, certain large cells called Sertoli cells are present. They are nutritive in function. The germinal epithelial cells produce sperms by spermatogenesis.

2. The male reproductive system of man:

3. Fertilization is the fusion of two gametic nuclei to form a diploid zygote. It involves a series of chemical and physical steps as follows:

The cortical cytoplasm of the ovum shows the physicochemical reactions called the cortical reactions:

1. Sperm lysins dissolve the membranes around the egg.
2. The Head of sperm containing a nucleus and proximal centriole physically passes into the ovum.
3. Normally these reactions result in the formation of a fertilization membrane outside the egg plasma membrane.
4. Cortical granules burst and release their contents between the egg plasma membrane and zona pellucida, i.e. perivitelline space (no fertilization membrane formation). The plasma membrane shows increased permeability for water, phosphate, and potassium.
5. The electrical potentiality of plasma membrane changes from positive to negative, NAD kinase enzyme becomes activated after fertilization for the oxidation and reduction reaction of the cell.
6. The rate of DNA synthesis increases with great pace after fertilization. Hence the ovum is now ready for mitosis (cleavage).
7. Cleavage results in multicellular individuals.

• Assertion and Reason Answers:

1) a) Both assertion and reason are true, and reason is the correct explanation of assertion.

​​​​​​​​​​​​​​​​​​​​​​Explanation:

Fertilisation can only occur if the ovum and sperms are transported simultaneously to the ampullary-isthmic junction and ovum is released only once a month. This is one of the reasons why all copulations do not lead to fertilisation and pregnancy.

2) a) Both assertion and reason are true, and reason is the correct explanation of assertion.

Explanation:

The normal temperature of the testes in the scrotum is about 2°-2.5°C lower than the internal body temperature. When the body is chilled, the smooth muscle contracts and brings the testes closer to the pelvic cavity. This movement towards the pelvic cavity allows the testes to absorb heat from the rest of the body so that the sperm cells do not become chilled and get optimum temperature for spermatogenesis.

• Case Study Answers:

1) 

1. (a) Morula.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

Embryo with 8-16 blastomeres is solid mass of cells, known as morula.

2. (c) Blastula.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:​​​​​​​​​​​​​​

Embryo with 64 cells is called blastula (blastocyst) and has blastocyst cavity. Blastocyst is composed of an outer envelope of cells called trophoblast and inner cell mass.

3. (a) Endometrium of uterus.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

Implantation is the attachment of blastocyst to the uterine wall. The portion of blastocyst where the inner cell mass is located lies against the endometrium of uterus.

4. (d) Zygote → Morula → Blastula → Gastrula.
5. (b) Both assertion and reason are true, but reason is not the correct explanation of assertion.

2)

1. (c) Capacitation.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Explanation:

The secretions of female genital tract remove coating substances deposited on the surface of the sperms. This phenomenon of sperm activation is called capacitation.

2. (d) R → P → Q → S
3. (b) Both assertion and reason are true, but reason is not the correct explanation of assertion.

​​​​​​​Explanation:

Binding of sperm to the secondary oocyte induces depolarisation of the oocyte plasma membrane. Depolarisation prevents polyspermy and ensures monospermy.

4. (c) It initiates cleavage.

​​​​​​​Explanation:

Fertilisation restores diploid number of chromosomes. It introduces variations as it combines characters of the two parents.

5. Ampullary isthmic junction of oviduct.