Please refer to Human Reproduction Class 12 Biology Important Questions with solutions provided below. These questions and answers have been provided for Class 12 Biology based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 12 Biology for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 12.
Class 12 Biology Important Questions Human Reproduction
Very Short Answer Questions
Question. Mention the location and the function of Leydig cells in humans.
Ans. Leydig cells are present in the regions called interstitial spaces outside the seminiferous tubules.
They synthesise and secrete androgens (testosterone).
Question. Mention the function of mitochondria in sperm.
Ans. Provide energy for the movement of sperm tail.
Question. Identify the figure given below and the part labelled “A”.
Ans. The figure is of blastula/blastocyst.
A—Trophoblast.
Question. When do the oogenesis and the spermatogenesis initiate in human females and males respectively?
Ans. Oogenesis in human females initiate at the foetal/embryonic stage.
Spermatogenesis in human males starts at puberty.
Question. What is the role of cervix of the human female system in reproduction?
Ans. Cervix helps in regulating the passage of sperms into the uterus and forms the birth canal to facilitate parturition.
Question. What are the major functions of male accessory ducts and glands?
Ans. Male accessory ducts include rete testes, vasa efferentia, epididymis and vas deferens. These ducts store and transport the sperms from the testes to the outside through urethra. Male accessory glands include paired seminal vesicles, prostate gland and paired bulbourethral glands. Secretion of these glands constitute the seminal plasma which is rich in fructose, calcium and certain enzymes. The secretions of bulbourethral glands also help in the lubrication of the penis.
Question. Draw a labelled diagram of a section through ovary.
Ans.
Question. Write two major functions each of testis and ovary.
Ans. Functions of testis:
(i) Production of sperms by seminiferous tubules.
(ii) Production of male sex hormone, testosterone, by Leydig cells.
Functions of ovary:
(i) Production of ova (eggs).
(ii) Production of female sex hormones, estrogen and progesterone.
Question. Draw a labelled diagram of a Graafian follicle.
Ans.
Short Answer Questions
Question. Why are the human testes located outside the abdominal cavity? Name the pouch in which they are present.
Ans. The human testes need lower temperature, 2 – 2.5°C less than the body temperature, for the formation of sperms which is provided outside the body.
Testes are present in scrotal sac or scrotum.
Question. (i) How many spermatozoa are formed from one secondary spermatocyte?
(ii) Where does the first cleavage division of zygote take place?
Ans. (i) Two
(ii) During the passage of zygote from fallopian tube to the uterus.
Question. Draw a diagram of a human sperm. Label only those parts along with their functions, that assist the sperm to reach and gain entry into the female gamete.
Ans.
Question. Given below is a flow chart showing ovarian changes during menstrual cycle. Fill in the spaces with the hormonal factor(s) responsible for the events shown.
Ans. a: FSH and estrogen
b: LH
c: Progesterone
Question. Differentiate between major structural changes in the human ovary during the follicular and luteal phase of the menstrual cycle.
Ans.
| S.No. | Follicular phase | Luteal phase |
| (i) | During this, primary follicles grow to become fully mature Graafian follicle | During this, remaining part of Graafian follicle transforms into corpus luteum. |
| (ii) | Endometrium regenerates through proliferation. | Endometrium further thickens secreting progesterone for implantation after fertilisation.If fertilisation does not occur, corpus luteum degenerates. |
Question. Where is acrosome present in humans? Write its function.
Ans. Acrosome is present on the sperm head. It has enzymes to help the sperm enter into the cytoplasm of ovum through zona pellucida and plasma membrane to facilitate entry of sperm nucleus for fertilisation.
Question. Write the function of each of the following:
(a) Middle piece in human sperm.
(b) Luteinising hormone in human males.
Ans. (a) Provides energy for movement as it contains mitochondria.
(b) Stimulates synthesis and secretion of androgens or male hormones for spermatogenesis.
Question. What is spermatogenesis? Briefly describe the process of spermatogenesis.
Ans. The process of formation of spermatozoa (sperms) from diploid spermatogonia is called spermatogenesis. The male germ cells of seminiferous tubules multiply mitotically to increase in numbers. Spermatogonia grow and increase in size to form primary spermatocyte (2n). The primary spermatocytes undergo the first meiotic division and produce two haploid secondary spermatocytes (n). Each secondary spermatocyte undergoes the second meiotic division and produces 4 equal haploid spermatids. The spermatids are finally transformed into spermatozoa by the process of spermiogenesis.
Question. Define spermiogenesis and spermiation.
Ans. Spermiogenesis: The process involving transformation of spermatids into spermatozoa is called spermiogenesis.
Spermiation: After spermiogenesis, sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process called spermiation.
Long Answer Questions
Questions. Draw a labelled diagram of the embryonic stage that gets implanted in the human uterus.
State the functions of the two parts labelled.
• Trophoblast helps in implantation or attachment to endometrium.
• Inner cell mass gets differentiated into an embryo.
QuestionsQ. 10. (a) At which stage of life does gametogenesis begin in human male and female respectively?
(b) Name the organs where gametogenesis gets completed in human male and female, respectively.
Ans. (a) Gametogenesis, i.e., spermatogenesis in males starts at puberty and oogenesis in females, start during embryonic development at foetal stage.
(b) In human males, the process is completed in the testes (seminiferous tubules) whereas in females, it is completed in the fallopian tube (oviduct).
Questions. Meiotic division during oogenesis is different from that in spermatogenesis. Explain how and why?
Ans. Unequal cytoplasmic division of the oocyte is to ensure the retention of bulk of cytoplasm in one cell called secondary oocyte instead of sharing it with two. It has to provide nourishment for the developing embryo during early stages, so it is essential to retain as much cytoplasmic materials it could in a single daughter cell.
Questions. Given alongside is the diagram of a human ovum surrounded by a few sperms. Observe the diagram and answer the following questions: (Image 108)
(a) Compare the fate of sperms shown in the diagram.
(b) What is the role of zona pellucida in this process?
(c) Analyze the changes occurring in the ovum during the process.
(d) Mention what helps in the entry of sperm into the ovum.
(e) Specify the region of female reproductive system where the event represented in the diagram takes place.
Ans. (a) A is able to penetrate/fertilize the ovum, whereas B and C are unable to penetrate/fertilise B and C will degenerate.
(b) Zona pellucida ensures the entry of only one sperm into the ovum
(c) Induces completion of meiotic division of the secondary oocyte, formation of second polar body and a haploid ovum
(d) Enzymes of acrosome
(e) Ampullary-isthmic junction of the fallopian tube
Questions. (a) When and how does placenta develop in human female?
(b) How is the placenta connected to the embryo?
(c) Placenta acts as an endocrine gland. Explain.
Ans. (a) Placenta develops after implantation of embryo in human female in the uterus. After implantation, finger-like projections called chorionic villi are surrounded by the uterine tissue and maternal blood. The chorionic villi and uterine tissue become interdigitated with each other and together form a structural and functional unit between developing embryo and maternal body called placenta.
(b) An umbilical cord connects placenta with the embryo.
(c) The placenta also acts as an endocrine gland as it secretes the following hormones:
(i) Human chorionic gonadotropin (hCG)
(ii) Human placental lactogen (hPL)
(iii) Progestogens
(iv) Estrogens
The increased production of these hormones during pregnancy is essential for supporting the foetal growth and metabolic changes in the mother.
Questions. (a) Describe the stages of oogenesis in human females.
(b) Draw a labelled diagram of a human ovum released after ovulation.
Ans. (a)
(ii) Oogenesis
• The process of formation of a mature female gamete is called oogenesis. It occurs in the ovaries.
It consists of the following three phases:
(a) Multiplication phase: Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia) are formed within each foetal ovary. No more oogonia are formed and added after birth. These cells start division and enter into prophase-I of the meiotic division. They get temporarily arrested at this stage and are called primary oocytes.
(b) Growth phase: Each primary oocyte then gets surrounded by a layer of granulosa cells. This structure is called the primary follicle. A large number of these follicles degenerate during the phase from birth to puberty. At puberty, only 60,000 to 80,000 primary follicles are left in each ovary. The primary follicles get surrounded by more layers of granulosa cells and a new theca to form secondary follicles.
(c) Maturation phase: In the first maturation phase, the secondary follicle soon transforms into a tertiary follicle. The primary oocyte within the tertiary follicle grows in size and completes
its first meiotic division to form a large, haploid, secondary oocyte and a tiny first polar body. The tertiary follicle changes into a mature follicle—the Graafian follicle—which ruptures to
release the secondary oocyte (ovum) from the ovary by a process called ovulation. The second maturation phase occurs after fertilisation when the meiotic division of the secondary oocyte is complete. This second meiotic division results in the formation of a second polar body and a
(b)
Questions. Enumerate the events in the ovary of a human female during:
(i) Follicular phase
(ii) Luteal phase of menstrual cycle.
Ans. (i) In the follicular phase, following events occur:
1. The primary follicles in the ovary grow to form a fully mature Graafian follicle.
2. The endometrium of uterus regenerates through proliferation.
3. The secretion of gonadotropins (LH and FSH) gradually increases.
(ii) In the luteal phase, following events occur:
1. The parts of Graafian follicle remaining after the rupture, transform into the corpus luteum.
2. The corpus luteum secretes large amounts of progesterone.
Questions. It is commonly observed that parents feel embarrassed to discuss freely with their adolescent children about sexuality and reproduction. The result of this parental inhibition is that the children go astray sometimes.
(i) Explain the reasons that you feel are behind such embarrassment amongst some parents to freely discuss such issues with their growing children.
(ii) By taking one example of a local plant and animal, how would you help these parents to overcome such inhibitions about reproduction and sexuality?
Ans. (i) The reasons behind this embarrassment are illiteracy, their conservative attitude, misconceptions, social myths and generation gap.
(ii) It can be seen in animals such as honey bee and plants such as orchid ophrys flower that sexual attraction is a natural phenomenon. The male honey bee assumes the petal of orchid as its female partner and pseudocopulates with it. So, sexuality is a natural phenomenon and parents should speak to their children about it.
Questions. Distinguish between:
(a) Corona radiata and Zona pellucida
(b) Blastula and Gastrula
Ans. (a) Differences between corona radiata and zona pellucida
| S.No. | Corona radiata | Zona pellucida |
| (i) | It consists of follicle cells. | It is a single membrane. |
| (ii) | It envelops the egg outside the zona pellucida. | It is above the vitelline membrane making the membrane thick. |
| (iii) | The cells provide nourishment to the egg at the time of release from the ovary. | It protects the egg and shows changes that block entry of additional sperms. |
(b) Differences between blastula and gastrula
| S.No. | Blastula | Gastrula |
| (i) | It is a hollow ball of cells with trophoblast and inner cell mass. | It is a three-layered embryo—3 germ layers being ectoderm, mesoderm and endoderm. |
| (ii) | The cavity of the blastula is known as the blastocoel. | The cavity of the gastrula is known as archenteron. |
| (iii) | It results after the cleavage. | It is formed from blastula due to the movement of cells into 3 germ layers. |
Questions. (a) Arrange the following hormones in sequence of their secretion in a pregnant woman.
(b) Mention their source and the function they perform:
hCG, LH, FSH, Relaxin
Ans. (a) The sequence of secretion of hormones is:
(i) FSH (ii) LH (iii) hCG (iv) Relaxin
(b)
| Hormone | Source | Function |
| (i) FSH | Anterior pituitary lobe. | Stimulates growth of ovarian follicles and maturation of primary oocytes. |
| (ii) LH | Anterior pituitary lobe. | Induces ovulation and maintains corpus luteum. |
| (iii) hCG | Chorionic cells of placenta | Maintains the corpus luteum and stimulates it to secrete progesterone. |
| (iv)Relaxin | Ovary | Helps during child birth by relaxing the pelvic muscles as well as muscles of the cervix. |
Questions. The graph given below shows the variation in the levels of ovarian hormones during various phases of menstrual cycle:
(a) Identify ‘A’ and ‘B’.
(b) Specify the source of the hormone marked in the diagram.
(c) Reason out why A peaks before B.
(d) Compare the role of A and B.
(e) Under which condition will the level of B continue to remain high on the 28th day?
Ans. (a) A – Estrogen
B – Progesterone
(b) A – Maturing ovarian follicle/Graafia n follicle
B – Corpus luteum
(c) Formation of Graaffian follicle (releases estrogen) is followed by the formation of corpus luteum (releases progesterone)
(d) Role of A (Estrogen): leads to changes in the ovary and uterus / regeneration of endometrium through proliferation Role of B (Progesterone): Maintenance of endometrium for implantation of the fertilized ovum/maintenance of other events of pregnancy
(e) In case of pregnancy.
Questions. Explain the ovarian and uterine events that occur during a menstrual cycle in a human female, under the influence of pituitary and ovarian hormones respectively.
Ans. Release of gonadotropins (FSH and LH) from pituitary, during follicular phase or 5-14 days of menstrual cycle leads to growth of primary follicle to Graafian follicle (GF.) in the ovary. Estrogen from growing follicle helps in proliferation of uterine endometrium or its repair. High level of LH at middle, i.e., 14th day of the menstrual cycle, leads to rupture of GF causing release of ovum. This is called ovulation. The remaining cells of GF transform into corpus luteum (CL) under the influence of LH. CL secretes progesterone that maintains endometrium in preparation for pregnancy. Level of FSH and LH fall due to rise of progesterone and estrogen (25th day of the cycle), leading to degeneration of CL. Level of progesteron falls, leading to disintegration of uterine endometrium and menstruation starts (0-5 day of the cycle).
Questions. Write the duration and the events that occur in the ovary and the uterus during follicular and luteal phases of the menstrual cycle in humans.
How do pituitary and ovarian hormones influence these two phases ?
Ans.
(ii) Follicular Phase/Proliferative Phase
• The primary follicles in the ovary grow and become a fully mature Graafian follicle.
• The endometrium of the uterus is regenerated due to the secretion of LH and FSH from anterior pituitary and ovarian hormone, estrogen.
• It lasts for about 10 to 14 days.
(iv) Luteal Phase/Secretory Phase
• In this phase the ruptured follicle changes into corpus luteum in the ovary and it begins to secrete the hormone progesterone which is essential for maintenance of endometrium.
• The endometrium thickens further and their glands secrete a fluid into the uterus.
• If ovum is not fertilised, the corpus luteum undergoes degeneration and this causes disintegration of the endometrium leading to menstruation.
• Estrogen and progesterone levels rise during this phase.
• It lasts for only 10–14 days.
Refer to question above.
