Скачать или смотреть Alternation of Generation| General Overview| Chap: 14| Class 10 Biology| lec # 6 (PTB)

The alternation of generations is a complex life cycle that many plants and some algae undergo. It involves the alternation between two distinct multicellular phases: the haploid (n) gametophyte phase and the diploid (2n) sporophyte phase. This cycle is characteristic of plants belonging to the division Bryophyta (mosses), Pteridophyta (ferns), Gymnosperms (conifers), and Angiosperms (flowering plants).

Here's an overview of the alternation of generations life cycle:

Gametophyte Phase (Haploid, n):
The cycle begins with the haploid gametophyte generation. This phase starts with spores, which are produced by the sporophyte generation through a process called sporogenesis. The spores are released into the environment and germinate to develop into multicellular haploid gametophytes. These gametophytes are responsible for producing gametes (reproductive cells), which in plants are typically sperm and eggs.

Gamete Production:
Within the gametophyte, specialized structures develop to produce the gametes. In male gametophytes, antheridia produce sperm, while in female gametophytes, archegonia produce eggs.

Fertilization:
Fertilization occurs when a sperm cell from a male gametophyte travels to a female gametophyte and fertilizes an egg cell. This results in the formation of a diploid zygote.

Sporophyte Phase (Diploid, 2n):
The zygote develops into a diploid multicellular structure known as the sporophyte. The sporophyte is typically larger and more conspicuous than the gametophyte. It grows and matures, eventually producing spore-forming structures called sporangia.

Spore Production:
Within sporangia, diploid cells undergo meiosis, a specialized type of cell division that reduces the chromosome number by half. This process results in the formation of haploid spores.

Spore Dispersal and Germination:
The spores are released from the sporangia and are dispersed by various means, such as wind or water. When conditions are favorable, a spore germinates and develops into a new haploid gametophyte, restarting the cycle.




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