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Lecture 6

BIOL 111 Lecture 6-9.pdf

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Biology (Sci)
BIOL 111
Heather Roffey

LECTURE 6 EVOLUTION OF LAND PLANTS Prelecture VocabularyAlternation of generations the succession of multicellular haploid and diploid phases in some sexually reproducing organisms notably plantsGametophytein plants and photosynthetic protists with alternation of generations the multicellular haploid phase that produces the gametes 1nSporophytein plants and protists with alternation of generations the diploid phase that produces the spores 2nGametangia gametangiumAny plant of fungal structure within which a gamete is formedArchegoniumthe multicellular structure that produces eggs in nonvascular plants ferns and gymnospermsAntheridiumthe multicellular structure that produces the sperm in nonvascular plants and fernsIsogamythe condition where male and female gametes are morphologically identicalHeterogamywhere the two gametes are dissimilar in appearanceHomosporousproducing a single type of spore that gives rise to a single type of gametophyte bearing both female and male reproductive organs HeterosporousProducing two types of spores one of which gives rise to a female megaspore and the other to a male microspore Lecture notes The transition from water to land poses challenges to organismsStructural challengesPhysiological challenges the way in which a living organism or body part functionsStructural changes needed 1 to avoid dehydration of the bodywaxy covering cuticle2 to obtain water and nutrients from the soil and means to distribute them to all parts of the bodyroots shoots stomata etc vascular system3 to benefit from higher intensity of light on landincreased photosynthetic surface arealeaves with increased surface area4 Mechanical strength to support their body massspecialized with thick cell walls eg xylem vessels tracheids fibers phloem sieve elements colenchyma sclerenchyma5 Apical growth and branching to achieve maximum growth 6 With respect to reproductioni Protect gametes zygote and embryo from dehydrationarchegonium antheridium protected embryo seedii Retention of egg on the mother plantiii Mechanisms to transfer male gamete to the female gametepollination and pollination vectors7 to cope with possible environmental stressesevolve pigments to cope with increased UV light on landAll of the adaptations needed for flourishing on land did not arise at the same time during the course of evolution their sequential acquisition and be seen in various land plants6Alternation of Generations In sexually reproducing These changes will in turn affect the life cycle of the plant organisms there is aphenomenon called Alternation Alternation of Generations of generations A haploid formA haploid form called gametophyte with one set of called gametophyte with one chromosomes alternates with a diploid form called set of chromosomes alternates with a diploid form called sporophyte with two sets of chromosomessporophyte with two sets ofGametophyte produces gametes that fuse to form zygote chromosomesthat develops into sporophyteGametophyte producesThe latter forms haploid spores through meiosisgametes that fuse to formEach spore develops into a gametophyte zygote that develops into 7 sporophyte The latter forms Green algae haploid spores throughAdvanced green algae eg Chara and Coleochaete are meiosis Each spore develops into a gametophyte8
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