The Plant Kingdom
► Plants are photosynthetic eukaryotes that develop from embryos protected by parental tissue. Like the green algae, they use chlorophylls a and b and store carbohydrates as starch. Review Figure 29.1
► Plant life cycles feature alternation of gametophyte (haploid) and sporophyte (diploid) generations. Both generations include multicellular organisms. Review Figure 29.2
► There are ten surviving phyla of plants. The three basal phyla are nontracheophytes, and the remaining seven phyla are tra-cheophytes. Review Table 29.1
► Plants arose from a common green algal ancestor in the charophyte clade, either a stonewort or a member of the group that includes Coleochaete. Descendants of this ancestral charo-phyte colonized the land.
► The acquisition of a cuticle, gametangia, a protected embryo, protective pigments, thick spore walls with a protective polymer, and a mutualistic association with a fungus are all defining characters of plants, and all are associated with the adaptation of plants to life on land.
► Tracheophytes are characterized by possession of a vascular system, consisting of water- and mineral-conducting xylem and nutrient-conducting phloem. Nontracheophytes lack a vascular system. Review Figure 29.4
The Nontracheophytes: Liverworts, Hornworts, and Mosses
► Nontracheophytes either lack vascular tissues completely or, in the case of certain mosses, have only a rudimentary system of water- and food-conducting cells.
► The nontracheophyte sporophyte generation is smaller than the gametophyte generation and depends on the gametophyte for water and nutrition. Review Figures 29.5, 29.6. See Web/CD Tutorial 29.1
► The nontracheophytes include the liverworts (phylum Hepatophyta), hornworts (phylum Anthocerophyta), and mosses (phylum Bryophyta).
► Hornwort sporophytes grow at their basal end.
► Hornworts, mosses, and tracheophytes have surface pores (stomata) that allow gas exchange and minimize water loss.
► In mosses and tracheophytes, the sporophytes grow by apical cell division.
► The hydroids of mosses, through which water may travel, may be ancestral to tracheids, the water-conducting cells of the tracheophytes.
► The tracheophytes have vascular tissue with tracheids and other specialized cells designed to conduct water, minerals, and products of photosynthesis.
► Present-day tracheophytes are grouped into seven phyla. The two basal phyla are nonseed tracheophytes, and the rest are seed plants. Review Figure 29.10
► In tracheophytes, the sporophyte is larger than the gameto-phyte and independent of the gametophyte generation.
► The earliest tracheophytes, known to us only in fossil form, lacked roots and leaves. Review Figure 29.12
► Roots may have evolved from rhizomes or from branches that penetrated the ground. Microphylls are thought to have evolved from sporangia, and megaphylls may have resulted from the flattening and reduction of an overtopping, branching stem system. Review Figure 29.13
► Heterospory, the production of distinct female megaspores and male microspores, evolved on several occasions from homosporous ancestors. Review Figure 29.14. See Web/CD Activities 29.1 and 29.2
The Surviving Nonseed Tracheophytes
► Club mosses (phylum Lycophyta) have microphylls arranged spirally.
► Among the pteridophytes (phylum Pteridophyta), horsetails have reduced megaphylls in whorls. Whisk ferns lack roots; one genus has minute scales rather than leaves, and the other has reduced megaphylls with vascular tissue. Leaves with more complex vasculature are characteristic of all other phyla of tra-cheophytes.
► The ferns are not a clade, although 97 percent of fern species do constitute a clade. Ferns have megaphylls with branching vascular strands. Review Figure 29.20. See Web/CD Activity 29.3
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.