6 public questions tagged with this topic.
Obelia, a cnidarian, exhibits metagenesis where polyps reproduce asexually and medusae reproduce sexually.
Ref: NCERT Class 11 Biology Chapter 4: Animal Kingdom Phylum Porifera and Cnidaria
The plant life cycle has a diploid sporophytic phase and a haploid gametophytic phase that alternate with each other. The duration and independence of these phases vary among different plant groups.
Ref: NCERT Class 11 Biology Chapter 2: Biological Classification Five Kingdom Classification and Kingdom Plantae Animalia
Alternation of heteromorphic generations shows opposite polarity between major land plant lineages reflecting evolutionary transition. In bryophytes including liverworts, hornworts, and mosses haploid gametophyte forms persistent photosynthetic thallus or leafy shoot generating gametangia and dominating biomass; diploid sporophyte is unbranched, short-lived, nutritionally dependent via foot. In tracheophytes polarity reverses with dominant photosynthetic sporophyte. Angiosperms and gymnosperms display extreme reduction of gametophytes to few cells within sporophytic flowers and cones, pteridophytes show moderate independence but still sporophyte dominated. Bryophyte gametophyte dominance defines ecology.
Ref: Campbell Biology Ch 29: Bryophyte lifecycle; Shaw & Renzaglia Bryophytes; NCERT Ch3
Life cycle evolution in land plants shows progressive sporophyte dominance and gametophyte reduction correlating with vascular complexity and desiccation tolerance. In tracheophytes encompassing pteridophytes, gymnosperms and angiosperms, diploid sporophyte is large, photosynthetically independent, long-lived, branched and produces spores through meiosis inside sporangia protected by sporopollenin. Gametophyte becomes microscopic and dependent in seed plants. Bryophytes contrastingly retain dominant haploid gametophyte bearing small dependent sporophyte. Sporophyte dominance correlates with lignin, cuticle, and complex organ differentiation enabling terrestrial dominance. This structural framework illustrates phylogenetic relationships and adaptive significance highlighted in competitive examinations focusing on comparative plant morphology and systematics.
Ref: Campbell Biology 12th Ch 29-30: Alternation of generations; NCERT Class 11 Ch 3
Plant life cycles feature alternation heteromorphic where sporophyte and gametophyte differ markedly in size complexity ecological independence and morphology. In gymnosperms sporophyte extensive woody tree shrub producing sporangia inside cones via meiosis, while gametophytes highly vestigial reduced: male few cells within pollen wall exine intine, female haploid multicellular massive with archegonia inside ovule dependent entirely for nutrition water. Isomorphic alternation shows similar thallus morphology like Ulva sea lettuce, haplobiontic one multicellular generation dominant, asexual absence alternation entirely. Heteromorphic trait indicates evolutionary reduction gametophyte lineage promoting protection pollen seed dispersal advantages ultimately leading to seed habit dominance terrestrial environments globally.
Ref: Campbell Biology, 12th ed., Chapters 29-30: Heteromorphic alternation generations sporophyte dominant reduced
NCERT Class 11 Biology clearly defines that the life cycle of higher plants strictly alternates between a diploid sporophytic generation and a haploid gametophytic generation. The lengths of these phases, and whether they are free-living or dependent on each other, vary wildly among the different plant divisions. This fundamental botanical phenomenon is officially termed 'alternation of generation'.
Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.4 Kingdom Plantae
