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#life cycle

8 public questions tagged with this topic.

Dictyostelium

Dictyostelium slug differentiates into:

Upon grex formation, amoebae initially equivalent diverge into two major lineages arranged along anteroposterior axis, with about twenty percent anterior prestalk cells expressing extracellular matrix genes ecmA and ecmB and eighty percent posterior prespore cells expressing spore coat proteins. Prestalk cells later vacuolate and undergo programmed death forming cellulose stalk, while prespore cells mature into viable spores. Fate decision integrates cell cycle position at starvation, cAMP concentration, DIF-1 polyketide, and ammonia gradients. This binary differentiation parallels somatic ver

Ref: Gilbert, Developmental Biology, 12th ed., Chapter 22: Prestalk and prespore differentiation - cAMP, DIF, and ammonia interplay.

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Fertilization in mammals-lll

Dictyostelium slug migrates to:

After aggregation Dictyostelium forms motile multicellular slug capable of phototactic and thermotactic migration before culmination. Slug displays positive phototaxis moving toward light source guided by lens effect of slug tip focusing light onto prestalk region and via opsin-like proteins modulating ammonia and cAMP chemotaxis. Migration toward bright, warm, elevated surfaces enhances spore dispersal by wind and reduces competition. Movement to dark or nutrient-rich areas would be counterproductive for dispersal. Therefore slug phototaxis to bright regions represents adaptive strategy seeki

Ref: Fisher et al., J Cell Sci 1989: Phototactic migration of Dictyostelium slug toward light for optimal fruiting body placement.

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Plant Classification

The dominant life cycle phase of pteridophytes is

Pteridophytes, encompassing lycophytes and monilophytes including ferns and horsetails, exhibit diplobiontic haplodiplontic life cycle where diploid sporophyte forms conspicuous vegetative plant body with true roots, stems, leaves, vascular tissues, cuticle and stomata, undergoing meiosis in sporangia to produce haploid spores. Haploid gametophyte is typically small heart-shaped thalloid prothallus, short-lived, semi-independent, photosynthetic, requiring moist microhabitats for flagellated sperm dispersal. Dominant diploid phase allows accumulation of sporophytic adaptations like lignin, bran

Ref: Campbell Ch 30: Pteridophyte life cycle; Raven Ch 20; NCERT Class 11 Plant Kingdom

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Plant Classification

The life cycle of gymnosperms shows alternation of generations that is

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 abs

Ref: Campbell Biology, 12th ed., Chapters 29-30: Heteromorphic alternation generations sporophyte dominant reduced

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Plant Classification

The dominant phase in seed plants is

Alternation generations pattern haplodiplontic diplobiontic shows multicellular sporophyte diploid phase producing spores via meiosis in sporangia alternating with gametophyte haploid phase producing gametes via mitosis in gametangia. In seed plants sporophyte tremendously dominant forming tree shrub herb providing photosynthesis structural support, while gametophytes microscopic ephemeral embedded within sporophyte tissues within flower cone. Bryophytes situation reversed gametophyte dominant photosynthetic leafy thallose, sporophyte dependent short-lived, pteridophytes both independent but s

Ref: Campbell Biology, 12th ed., Chapter 30: Alternation generations sporophyte dominance seed plants

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Animal Classification

Complete metamorphosis is characteristic of

Complete metamorphosis or holometaboly characterizes Endopterygota superorder including Diptera flies, Lepidoptera butterflies moths, Coleoptera beetles, Hymenoptera bees wasps and Neuroptera lacewings. Life cycle comprises egg, actively feeding but morphologically distinct larva such as caterpillar or maggot, non-feeding pupa where larval tissues undergo histolysis and imaginal discs differentiate into adult organs, and reproductive adult imago. Larval and adult niches often diverge reducing intraspecific competition. Hemimetabolous insects show incomplete nymphal development, Apterygota amet

Ref: Campbell Biology, 12th ed., Chapter 33: Insect Metamorphosis Holometaboly; NCERT Class 11, Chap 4

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General Biology of Protists

Plasmodium completes sexual reproduction in

Plasmodium species causing malaria exhibit heteroxenous life cycle requiring vertebrate intermediate host and invertebrate definitive host. Asexual schizogony occurs in human liver and erythrocytes causing disease manifestations. Sexual phase begins with gametocyte formation ingested during blood meal by female Anopheles mosquito; within midgut gametes fuse forming diploid zygote developing into motile ookinete penetrating epithelium forming oocyst undergoing sporogony producing haploid sporozoites migrating to salivary glands for reinfection. Fertilization and meiosis completion occurs in mos

Ref: CDC Malaria sexual reproduction Anopheles mosquito; Tortora life cycle Plasmodium definitive host female Anopheles sporogony

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