Thallophyta | CEE Academy

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PLANT LIFE CYCLE

▢ Basic Stages:

Table 1: Sporophytic and Gametophytic Stages

Stage	Ploidy	Function
Gametophyte	Haploid \((n)\)	Produces gametes by mitosis
Sporophyte	Diploid \((2n)\)	Produces spores by meiosis

▢ Life Cycle Flow: Gametophyte \((n)\) → gametes \((n)\) → fertilization → zygote \((2n)\) → sporophyte \((2n)\) → meiosis → spores \((n)\) → gametophyte \((n)\)

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Alternation of generations

▢ Definition: Regular alternation between a multicellular haploid gametophyte and a multicellular diploid sporophyte

▢ Generations:

Table 1: Alternating Generations

Generation	Ploidy	Produces	Process
Gametophyte	Haploid \((n)\)	Gametes	Mitosis
Sporophyte	Diploid \((2n)\)	Spores	Meiosis

▢ Present In:

•
Algae
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Bryophyta
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Pteridophyta
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Gymnosperms
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Angiosperms

▢ Distinct and Independent Generations: Most clearly observed in Pteridophyta

▢ Group-wise Pattern:

Table 1: Alternation of Generations in Plant Groups

Group	Dominant Generation	Dependent Generation
Bryophyta	Gametophyte	Sporophyte
Pteridophyta	Sporophyte	Gametophyte usually independent
Gymnosperms	Sporophyte	Highly reduced gametophyte
Angiosperms	Sporophyte	Highly reduced gametophyte

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Dominant plant body

Table 1: Dominant Generation in Major Plant Groups

Plant Group	Dominant Plant Body	Ploidy
Thallophyta	Usually gametophyte	Usually haploid \((n)\)
Bryophyta	Gametophyte	Haploid \((n)\)
Pteridophyta	Sporophyte	Diploid \((2n)\)
Gymnosperms	Sporophyte	Diploid \((2n)\)
Angiosperms	Sporophyte	Diploid \((2n)\)

▢ Trend in Plant Evolution: Gametophyte dominance ↓ → sporophyte dominance ↑

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THALLOPHYTA

▢ Terminology:

❖ Term 'Thallophyta': Endlicher

❖ Plant Body: Thallus → no true root, stem or leaves

▢ Main Plant Body:

❖ Nature: Usually haploid \((n)\)

❖ Generation: Gametophytic

❖ Example: Spirogyra → haploid gametophytic plant body

22Thallophyta

Table 1: Sporophytic and Gametophytic Stages

Table 1: Alternating Generations

Table 1: Alternation of Generations in Plant Groups

Table 1: Dominant Generation in Major Plant Groups

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