Pls explain alternation of generation in Bryophytes Pteridophytes??
Alternation of generation in bryophytes
A clear alternation of generation is present in all bryophytes. They are the first plant to have heteromorphic alternation of generation. All bryophytes exhibit haplo- diplontic life cycle of heteromorphic type i.e. the plants represents two morphologically distinct generations ( gametophytic and sporophytic) with dominant independent gametophytic phase. Sporophyte is dependent on gametophyte for food. Hence, it remains attached to the gametophyte.
The haploid generation is called the gametophyte because it undergoes sexual reproduction to produce gametes. Production of gametes involve mitosis, so the gametes are also haploid. The gametes fuse to form a diploid zygote which grows into the next generation, the diploid sporophyte generation (2n). Sporophyte is dependent on gametophyte and remains attached to it. It is called sporophyte because it undergoes asexual reproduction to produce spores. Production of spores involves meiosis, so that there is return to the haploid condition. The haploid spores give rise to the gametophytic generation.
Alternation of generation in pteridophytes
Pteridophytes also show heteromorphic alternation of generation like bryophytes but the dominant phase is sporophyte.
Haploid generation called gametophyte undergoes sexual reproduction to produce gametes. Production of gametes involve mitosis, so the gametes are also haploid. The gametes fuse to form a diploid zygote which grows into the next generation, the diploid sporophyte generation (2n). Zygote( diploid oospore) develops into embryo which produces well-differentiated, multicellular sporophyte. Sporophyte is well-differentiated into true stem, leaves, and roots. Sporophyte produces spores all which can be of similar type or of two types. Spores germinate to form small, multicellular, non-vascular free-living photosynthetic thalloid haploid gametophyte called prothallus.
A clear alternation of generation is present in all bryophytes. They are the first plant to have heteromorphic alternation of generation. All bryophytes exhibit haplo- diplontic life cycle of heteromorphic type i.e. the plants represents two morphologically distinct generations ( gametophytic and sporophytic) with dominant independent gametophytic phase. Sporophyte is dependent on gametophyte for food. Hence, it remains attached to the gametophyte.
The haploid generation is called the gametophyte because it undergoes sexual reproduction to produce gametes. Production of gametes involve mitosis, so the gametes are also haploid. The gametes fuse to form a diploid zygote which grows into the next generation, the diploid sporophyte generation (2n). Sporophyte is dependent on gametophyte and remains attached to it. It is called sporophyte because it undergoes asexual reproduction to produce spores. Production of spores involves meiosis, so that there is return to the haploid condition. The haploid spores give rise to the gametophytic generation.
Alternation of generation in pteridophytes
Pteridophytes also show heteromorphic alternation of generation like bryophytes but the dominant phase is sporophyte.
Haploid generation called gametophyte undergoes sexual reproduction to produce gametes. Production of gametes involve mitosis, so the gametes are also haploid. The gametes fuse to form a diploid zygote which grows into the next generation, the diploid sporophyte generation (2n). Zygote( diploid oospore) develops into embryo which produces well-differentiated, multicellular sporophyte. Sporophyte is well-differentiated into true stem, leaves, and roots. Sporophyte produces spores all which can be of similar type or of two types. Spores germinate to form small, multicellular, non-vascular free-living photosynthetic thalloid haploid gametophyte called prothallus.