Question

Student to attempt either option-(A) or (B):
(A) Study the given diagram showing the sectional view of a seminiferous tubule.

Answer the following questions:

• [(i)] Label A, B, C and D in the figure.
• [(ii)] What will be the number of chromosomes in secondary spermatocyte and spermatid respectively?
• [(iii)] Explain the terms — Spermiogenesis and Spermiation.

OR 
(B) Study the figures given below showing initial stages in the formation of female gametophyte and answer the questions that follow.

• [(i)] Identify (P) and (Q).
• [(ii)]
  • [I.] What kind of division does cell (P) undergo to form (Q)?
  • [II.] How many (Q) cells form the embryo sac? What is the name given to such kind of development?
  • [III.] How many free nuclear mitotic divisions will the functional megaspore undergo to form the embryo sac?
  • [IV.] Describe the structure of a mature female gametophyte.

Hint:

Spermiogenesis transforms spermatids into sperm, while spermiation releases them. In female gametophyte development, monosporic development forms the embryo sac from one megaspore.

Answer 1

(A)

1. [(i)] Labels:
   • A — Spermatozoa
   • B — Secondary spermatocyte
   • C — Primary spermatocyte
   • D — Spermatogonia
2. [(ii)] Secondary spermatocyte: n = 23 chromosomes, \quad Spermatid: n = 23 chromosomes
3. [(iii)]
   • Spermiogenesis: Process by which spermatids transform into mature spermatozoa.
   • Spermiation: Release of mature spermatozoa from Sertoli cells into the lumen of seminiferous tubules.

OR (B)

1. [(i)]
   • (P) — Megaspore mother cell
   • (Q) — Functional megaspore
2. [(ii)]
   1. [I.] Cell (P) undergoes meiosis to form cell (Q).
   2. [II.] Only one functional (Q) cell develops into the embryo sac. This is called monosporic development.
   3. [III.] The functional megaspore undergoes three free nuclear mitotic divisions.
   4. [IV.] The mature female gametophyte (embryo sac) is 7-celled and 8-nucleated, consisting of:
      • 1 egg cell and 2 synergids at the micropylar end,
      • 3 antipodal cells at the chalazal end,
      • 1 central cell with 2 polar nuclei.