Q.Describe the process of Fertilization in angiosperms.
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Start your 14-day free trial to unlock the full solution →In angiosperms fertilization involves pollen germination, pollen-tube growth to the embryo sac, and double fertilization: syngamy (male gamete + egg → zygote) and triple fusion (male gamete + 2 polar nuclei → primary endosperm nucleus).
Fertilization in angiosperms is the fusion of male and female gametes, and it is unique because it involves double fertilization. The process occurs in the following steps:
1. Pollination and germination of pollen grain: A compatible pollen grain landing on the stigma absorbs water and nutrients and germinates, putting out a pollen tube through one of its germ pores.
2. Growth of the pollen tube: The pollen tube grows through the tissue of the stigma and style, guided chemically (chemotropism), carrying the tube nucleus (vegetative nucleus) and the two male gametes (formed by division of the generative cell).
3. Entry into the ovule: The pollen tube reaches the ovary and enters the ovule usually through the micropyle (porogamy), and then into one of the two synergids of the embryo sac. Filiform apparatus of the synergids guides the tube.
4. Discharge of male gametes: The tip of the pollen tube bursts and releases the two male gametes into the embryo sac; the synergid degenerates.
5. Double fertilization: This is the hallmark of angiosperms — both male gametes fuse:
• Syngamy (true fertilization): One male gamete (n) fuses with the egg cell (n) to form a diploid zygote (2n), which develops into the embryo. …
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