BIOL 1500 Lecture Notes - Lecture 16: Gametophyte, Sporophyte, Xylem
6 Oct 2016
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Document Summary
Plants arose about 475 million years ago from ancestors resembling green algae. Major evolutionary events in plants include the origins of vascular tissue, pollen and seeds, and flowers: the presence or absence of these characteristics define the different categories of plants. Bryophytes have no vascular tissue, seeds, or flowers. The origin of vascular tissue, which transports water and nutrients in the plant, allowed pants to grow taller. Taller plants reach their neighbors in the struggle for sunlight. Vascular tissue consists of the phloem and xylem: phloem transports sugars, xylem transports water. Lignin in xylem walls supports plants, the most abundant aromatic biopolymer on earth. Useful feedstock for plastics, carbon, fibres, fuels, chemicals, and more. Modifications in vascular tissue led to the evolution of seedless vascular plants, like ferns. The origin of seeds dormant, protected plant embryos with a nutrient supply was also adaptive. Seeds might travel far from the parent and only germinate when conditions are favorable.
