Biology Class 12 NCERT Solutions: Chapter 3 Human Reproduction Part 2 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Q. 3 Draw a labeled diagram of female reproductive system.

Answer:

Female Reproductive System

Q. 4 Write two major functions each of testis and ovary.

Answer:

  • Functions of the Testis
  • They produce male gametes called spermatozoa by the process of spermatogenesis.
  • 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
  • They produce female gametes called ova by the process of oogenesis.
  • The growing Graffian follicles secrete the female sex hormone called estrogen. Estrogen aids the development of secondary sex characteristics in females.

Q. 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.
Seminiferous Tubule

Q. 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.
Process of Spermatogenesis

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