How do moss plants exhibit alternation of generations?
1 Answer
In moss plants gametophytic generation, represented by main plant body alternates with sporogonium, representing sporopytic generation, which is permanently attached to gametophyte.
Explanation:
In most of the plants, the life cycle is completed into two generations, i.e. gametophytic and sporophytic generations.
Gametophytic generation reproduces sexually by gametes and is haploid. Sporophytic generation reproduces asexually by meiospores and is diploid .
These two generations follow each other in alternate sequence. This phenomenon is termed alternation of generations.
Moss plant is haploid. It represents gametophytic generation as it reproduces sexually by gametes. The antheridia and archegonia are male and female gametangia, respectively.
The antheridium produces bifalgellate motile antherozoids. Archegonium produces single non-motile female gamete or oosphere.
The antherozoids after liberation from antheridium swim through thin film of water. These enter the neck of the archegonium and reach oosphere, located in venter part of archegonium.
The antherozoid fuses with oosphere or egg to form diploid oospore.
Antherozoids and oosphere are the last step of gametophytic generation and diploid oospore is the first step of sporophytic generation.
Dipoid oospore starts developing into embryo. It gets attached to gametophyte and develops into sporogonium, that is permanently attached to the tip of the female branch of moss plant.
The sporogonium in moss has chlorenchymatous tissue and can synthesize its food by photosynthesis. Sporophte is thus partially parasitic on gametophyte as it can not exist independently of gametophyte (moss plant.)
The sporogonium reproduces asexually by haploid meiospores. The meiospores get liberated from sporogonium at maturity .
Each meiospore germinates to form protonema after falling on suitable substrate. A number of leafy moss plants develop from protonema.
Thus moss plant, representing gametophytic generation and sporogonium representing sporophytic generation follow each other in alternate sequence, exhibiting alternation of generations.
