NCERT Solutions for Class 12 Science Biology Chapter 3 – Human Reproduction
Explore the comprehensive NCERT Solutions for Class 12 Science Biology Chapter 3 on Human Reproduction, featuring easy-to-follow step-by-step explanations. Widely favored by Class 12 Science students, these Biology Human Reproduction Solutions are invaluable for efficiently completing homework assignments and preparing for exams. Access free solutions to all questions from the NCERT Book of Class 12 Science Biology Chapter 3, designed to assist you in mastering the topic. Page No 55: Question 1: Fill in the blanks: (a) Humans reproduce __________. (asexually/sexually) (b) Humans are__________. (oviparous/viviparous/ovoviviparous) (c) Fertilization is __________ in humans. (external/internal) (d) Male and female gametes are __________. (diploid/haploid) (e) Zygote is __________. (diploid/haploid) (f) The process of release of the ovum from a mature follicle is called__________. (g) Ovulation is induced by a hormone called the __________. (h) The fusion of the male and the female gametes is called __________. (i) Fertilization takes place in the __________. (j) The zygote divides to form __________, which is implanted in uterus. (k) The structure which provides vascular connection between the fetus and uterus is called __________. ANSWER: (a) Humans reproduce. (b) Humans are. (c) Fertilization is in humans. (d) Male and female gametes are. (e) Zygote is. (f) The process of release of the ovum from a mature follicle is called. (g) Ovulation is induced by a hormone called the. (h) The fusion of the male and the female gametes is called. (i) Fertilization takes place in the. (j) The zygote divides to form, which is implanted in uterus. (k) The structure which provides vascular connection between the fetus and uterus is called . Page No 56: Question 2: Draw a labeled diagram of male reproductive system. ANSWER: Page No 56: Question 3: Draw a labeled diagram of female reproductive system. ANSWER: Page No 56: Question 4: Write two major functions each of testis and ovary. ANSWER: Functions of the Testis: (a) They produce male gametes called spermatozoa by the process of spermatogenesis. (b) The leydig cells of the seminiferous tubules secrete the male sex hormone called testosterone. Testosterone aids the development of secondary sex characteristics in males. Functions of the ovary: (a) They produce female gametes called ova by the process of oogenesis. (b) The growing Graffian follicles secrete the female sex hormone called estrogen. Estrogen aids the development of secondary sex characteristics in females. Page No 56: Question 5: Describe the structure of a seminiferous tubule. ANSWER: The production of sperms in the testes takes place in a highly coiled structure called the seminiferous tubules. These tubules are located in the testicular lobules. Each seminiferous tubule is lined by germinal epithelium. It is lined on its inner side by two types of cells namely spermatogonia and sertoli cells respectively. Spermatogonia are male germ cells which produce primary spermatocytes by meiotic divisions. Primary spermatocytes undergo further meiotic division to form secondary spermatocytes and finally, spermatids. Spermatids later metamorphoses into male gametes called spermatozoa. Sertoli cells are known as nurse cells of the testes as they provide nourishment to the germ cells. There are large polygonal cells known as interstitial cells or leydig cells just adjacent to seminiferous tubules. These cells secrete the male hormone called testosterone. Page No 56: Question 6: What is spermatogenesis? Briefly describe the process of spermatogenesis. ANSWER: Spermatogenesis is the process of the production of sperms from the immature germ cells in males. It takes place in seminiferous tubules present inside the testes. During spermatogenesis, a diploid spermatogonium (male germ cell) increases its size to form a diploid primary spermatocyte. This diploid primary spermatocyte undergoes first meiotic division (meiosis I), which is a reductional division to form two equal haploid secondary spermatocytes. Each secondary spermatocyte then undergoes second meiotic division (meiosis II) to form two equal haploid spermatids. Hence, a diploid spermatogonium produces four haploid spermatids. These spermatids are transformed into spermatozoa (sperm) by the process called spermiogenesis. Page No 56: Question 7: Name the hormones involved in regulation of spermatogenesis. ANSWER: Follicle-stimulating hormones (FSH) and luteinizing hormones (LH) are secreted by gonadotropin releasing hormones from the hypothalamus .These hormones are involved in the regulation of the process of spermatogenesis. FSH acts on sertoli cells, whereas LH acts on leydig cells of the testis and stimulates the process of spermatogenesis. Page No 56: Question 8: Define spermiogenesis and spermiation. ANSWER: Spermiogenesis: It is the process of transforming spermatids into matured spermatozoa or sperms. Spermiation: It is the process when mature spermatozoa are released from the sertoli cells into the lumen of seminiferous tubules. Page No 56: Question 9: Draw a labeled diagram of sperm. ANSWER: Page No 56: Question 10: What are the major components of seminal plasma? ANSWER: Semen (produced in males) is composed of sperms and seminal plasma. The major components of the seminal plasma in the male reproductive system are mucus, spermatozoa, and various secretions of accessory glands. The seminal plasma is rich in fructose, calcium, ascorbic acid, and certain enzymes. It provides nourishment and protection to sperms. Page No 56: Question 11: What are the major functions of male accessory ducts and glands? ANSWER: The male accessory ducts are vasa efferentia, epididymis, vas deferens, and rete testis. They play an important role in the transport and temporary storage of sperms. On the contrary, male accessory glands are seminal vesicles, prostate glands, and bulbourethral glands. These glands secrete fluids that lubricate the reproductive system and sperms. The sperms get dispersed in the fluid which makes their transportation into the female body easier. The fluid is rich in fructose, ascorbic acid, and certain enzymes. They also provide nutrients and activate the sperm. Page No 56: Question 12: What is oogenesis? Give a brief account of oogenesis. ANSWER: Oogenesis is the process of the formation of a mature ovum from the oogonia in females. It takes place in the ovaries. During oogenesis, a diploid oogonium or egg mother cell increases in size and gets transformed into a diploid primary oocyte. This diploid primary oocyte undergoes first meiotic division i.e., meiosis I or reductional division to form two unequal haploid cells. The smaller cell is known as the first polar body, while the larger cell is known as the secondary oocyte. This secondary oocyte …
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