01:119:116 Lecture 8: Plant Diversity I
25 Jul 2017
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Characteristics of plants: seq plant evolution, c/c charophytes, land plants. Bryophytes: c/c bryophytes, seq moss life cycle. Vascular plants: c/c vascular plants, seq fern life cycle. Modern charophytes (cid:314) sister taxon to land plants. Many charophytes live at edges of ponds. Environment sometimes dries out (cid:314) selection favors survival on dry land. Sporopollenin (cid:314) layer of polymer, surrounds zygote and prevents desiccation. Derived traits of charophytes (including land plants) (1) rings of cellulose-synthesizing proteins (2) structure of flagellated sperm. Needs to exist in water to swim (3) formation of phragmoplast (cid:314) groups of microtubules between daughter nuclei (4) presence of cell plate. Derived traits of land plants (1) alternation of generations. Plants have two distinct multicellular life stages. Haploid gametophyte (cid:314) produces gametes by mitosis. Diploid sporophyte (cid:314) produces spores by meiosis. **sporophytes (2n) produce spores (n) by meiosis. **gametophytes (n) produce gametes (n) by mitosis (2) multicellular, dependent embryo. 2n embryo retained within tissue of female gametophyte.
