Question

2. Compare and contrast sporogenesis and gametogenesis in anther and ovary (of angiosperms). You must use, but are not limited to, the following terms: anther, eggs, embryo sac, generative cell, microsporocytes, megasporocyte, microspores, pollen sacs, pollen grain, 2 nucleate, 4 nucleate, 8 nucleate, polar nuclei, sperm, synergids, tetrads, tube cell,

Answer 1

• Sporogenesis : Sporogenesis is the production of megaspores and microspores. Microspores are poroduced in anther, while megaspores are produced in ovary of angiosperms.
  • Microsporogenesis: Each anther has 4 pollen sacs which contain numerous pollen mother cells (PMC), which undergo meiosis to produce 4 haploid microspores. Each microspore mature into pollen grain mainly by thickening of the cell wall
  • Megasporogenesis : This occurs in ovules which are located inside the ovary. A single cell in each ovule differentiate into megaspore mother cell, which undergoes meiosis to produce 4 haploid megaspores. 3 of the megaspores degenerate leaving one functional megaspore per ovule.
• Gametogenesis: The production of male and female gametes in microspores, and the megaspores, respectively, is known as gametogenesis.
  • Microgametogenesis: This refers to production of male gametes. During maturation of pollen, the microspore nucleus divides mitotically to produce "Generative" and "Tube Nucleus". Pollen is generally released in binucleate stage. After pollination, the pollen germinates and pollen tube enters the stigma and grows through the style. The generative nucleus now undergoes mitotic division to produce 2 male gametes. The pollen along with the pollen tube, is known as microgametophyte.
  • Megagametogenesis : The nucleus of a functional megaspore divides mitotically to produce 4 or more nuclei. In most of angiosperms, megaspore nucleus divides 3 times to produce 8 nuclei. 3 of these nuclei move to one pole and produce a central "Egg Cell" along with 2 "Synergid cells" situated on either side of the egg cell. Another 3 nuclei migrate to the opposite pole to give rise to "Antipodal cells". The 2 nuclei remaining in the center fuse to form a secondary nucleus. The megaspore thus develops into a mature Megagametophyte or Embryo Sac.