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ALTERNATION OF GENERATIONS
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1.Alternation of generations: haploid (n) stage that produces gametes followed by diploid (2n) stage producing spores. 2.Haploid: gametes; half the number of chromosomes in somatic cell, indicated by n, result of meiosis. 3.Diploid: somatic cells; double number of chromosomes in gametes, indicated by 2n; result of fertilisation.
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1.Gametophyte: generation producing gametes in gametangium/ gametangia sexual stage. 2.Sporophyte: generation producing spores in sporangium/ sporangia – asexual stage. NB: In higher plants the generations alternate in the life cycle of a plant; in lower plants reproduction is either through gametes (sexual) or spores etc. (asexual).
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1.A haploid gametophyte generation that produces gametes (n) by mitosis... the gametes (n) fuse to form zygote (2n), the start of... 2.A diploid sporophyte generation that produces spores (n) by meiosis.
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Mosses (Bryophyta) Ferns (Pterophyta/ Pteridophyta) Seed plants (Spermatophyta) 1. Gymnospermae (cone-bearing plants producing seeds) 2. Angiospermae (flowering plants producing seeds) Exam guidelines require study of mosses and flowering plants to highlight alternation of generations.
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Leaf-like structures of moss gametophyte Sporangium of moss sporophyte
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Fern leaf (sporophyte) with sori (groups of sporangia
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GYMNOSPERMS ANGIOSPERMS
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Female cones at different agesMale cones Gymnosperms have two types of sporangia – female and male
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Mosses Gametophyte dominant Ferns, gymnosperms and flowering plants Sporophyte dominant
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