What do you understand by alternation of generation? Explain it with the example of moss.

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Feb 10, 2018

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Alternation of generations is the phenomenon in which two generations, i.e. sporophytic and gametophytic generations in a plant follow each other in alternate sequence.

Explanation:

Life cycle of moss is completed in two generations, i.e. gametophytic and sporophytic.

Funaria plant represents gametophytic generation and is haploid.
It reproduces sexually by male and female gametes. Male gametes or antherozoids are biflagellate and motile, produced in large number in antheridium..

The female gamete or oosphere is non-motile produced one in archegonium.

The male gametes on liberation from antheridium swim to reach archegonium. One of the male gametes entering archegonum fuses with oosphere to form diploid oospore.

Antherozoids (n) and oosphere (n) are last step of gametophytic generation and oospore (2n) is first step of sporophytic generation.

Oospore start developing into embryo inside the archegonium and gets attached to the tip of female branch where archegonia are located. The embryo develops into sporogonium, representing sporophytic generation.

Sporogonium is partially parasitic on gametophyte as it is dependent on it for support and absorption of water and minerals from the soil. It can synthesize its own organic food materials by photosynthesis due to the presence of chlorophyll containing tissue in capsule part of sporogonium.

At maturity it reproduces asexually by meiospores. Meiosore is haploid (n) and is the first step of gametophytic generation. Each meiospores germinates to from protonema from which a number of leafy plants develop.

Funaria plant and sporogonium represent gametophytic (n) and sporophytic (2n) generations, which follow each other in alternate sequence. This phenomenon is termed alternation of generations.

In Funaria, main plant represents gametophytic generation and is haploid. Sporogonium represents sporophytic generation, which is permanently attached to funaria plant and is partially parasitic on it.

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