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Bio1020, Diversity of Life: February 28.docx

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BIOL 1020
Robert Laird

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February 28, 2014 – Biology Origin of vascular plants • Bryophytes were prevalent for first 100 million years of plant evolution • Vascular plants originated in the Silurian and underwent great diversification during the Devonina and Carboniferous periods (dominant types of plants) • Vascular plants now dominant non-vascular plants • Greater bio mass today • Paraphyletic group • Early vascular plants o 425 millions years ago o Tiny o Independent, branching sporophytes o Living vascular plants have…  Life cycles with dominant sporophytes  Vascular tissues called xylem and phloem  Well-developed roots and leaved • Early vascular plants lacked roots  Dichotomous branching (symmetrical): even branching (earlier)  Overtop branching (asymmetrical): upright, taller quickly (modern) • Evolutionary innovation: vascular tissue o Vascular tissue allowed these plants to grow tall (competition for sunlight), limits the evolution of plant height? (falling over, shallow soil) increased in volume to height diameter : height. o Unlike bryophytes, in which lacks of specialized conductive tissues severely limits size • Seedless vascular plants o The first vascular plants were seedless o Recall that a seed consists of an embryo and its food supply surrounded by protective coat o Main groups: both originate from a seedless vascular plant  Lycophytes • Club mosses (not true mosses) • Spike mosses (not true mosses) • Quillworts  Pterophytes • Ferns • Horsetails • Whisk ferns o Flagellated sperm, and are usually restricted to moist environments (not as seriously as the bryophytes) Life cycles of seedless vascular plants • Sporophyte is dominant, gametophyte (small, live flat on the ground or below the soil) • Figure 29.13 o Spore -> young gametophyte -> bisexual gametophyte (has both antheridium and archegonium) (egg and sperm do not mature at the same time to reduce inbreeding) -> zygote grows by mitosis -> sporophyte is a diploid -> growth of the sporangium (inside there is meiosis which creates spores Transport in vascular tissue • Xylem: water, minerals, through dead cells (tracheids) • Water-conducting cells are strengthened by lignin and proved structural support • Phloem consists of living cells and distributes sugars, amino acids, and other organic products • This evolution allowed the first forests to occur (carboniferous forest) Evolution of roots and leaves • Roots o Organs that anchor vascular plants o Enable vascular plants to absorb water and nutrients from the soil o Roots may have evolved from subterranean stems (not agreed if they only have one origin or multiple) • Leaves o Organs that increa
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