lab+notes+for+bryophytes+to+flowering+plants-std+version -...

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Plants Evolutionary history of plants I. Plants first appear in the Ordovician period, about 450 MYA. (This is AFTER most animal phyla evolved, in the Cambrian). Whereas animals made jump onto land several times, plants only made the leap once. Most likely source is the green algae of a type called charophytes. This is based on comparisons between modern plants and modern charophytes. -Both contain the accessory pigments Chlorophyll B and beta-carotene -Plant and alga chloroplast DNA most similar -Structure of grana as stacks of thylakoids the same -Algal peroxisomes have same enzymes as plant peroxisomes -cell walls of charophytes contain most cellulose -similar cell division steps (disappearance of nuclear envelope during late prophase, cell plate formation and mitotic spindle similar) -similar sperm structure -DNA and rRNA similarities Charophytes live in shallow water. Towards the end of the Ordovician (440 MYA) repeated glaciations and other climatic changes caused water levels to fluctuate. Natural selection would have favored shallow water plants tolerant to occasional drying. These adaptation would also have been useful for totally terrestrial living, including: -waxy cuticles to prevent drying -protection for gametes
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lab+notes+for+bryophytes+to+flowering+plants-std+version -...

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