22.1 Introducing the Plants
1. Plants are multicellular eukaryotes that have cellulose cell walls and use starch as a carbohydrate reserve. Most photosynthesize.
2. Plants have alternation of a sporophyte (diploid) phase and a gametophyte (haploid) phase.
3. Plants are classified by presence or absence of vascular tissue, seeds, and flowers and fruits. Bryophytes lack vascular tissue. Vascular plants have vascular tissue and may be seedless or produce seeds. Gymnosperms have naked seeds, and angiosperms have seeds enclosed in fruits.
4. Plants originated about 480 million years ago from a type of green alga, charophytes. By 360 million years ago, plants had conquered dry land. Adaptations that made this possible include a dominant sporophyte, vascular tissue (xylem and phloem), roots and leaves, lignin, a waterproof cuticle, and stomata. By 200 million years ago, the angiosperms appeared and by 90 million years ago had diversified greatly.
22.2 Bryophytes Are the Simplest Plants
5. Bryophytes are small green plants lacking vascular tissue, supportive tissue, and true leaves and stems. Lignin hardens bryophytes and rhizoids anchor them to the ground, where they absorb water and nutrients.
6. In bryophytes, the gametophyte is dominant, and sexual reproduction requires water for sperm to travel through. Sperm from an antheridium travel to eggs in an archegonium.
7. The three divisions of bryophytes are liverworts, hornworts, and mosses.
22.3 Seedless Vascular Plants
8. Seedless vascular plants have the same pigments, reproductive cycles, and starch storage mechanisms as bryophytes, but they also have vascular tissue and a dominant sporophyte generation.
9. Seedless vascular plants include club mosses, horsetails, whisk ferns and true ferns.
22.4 Seed-Producing Vascular Plants
10. The seed-producing vascular plants are the gymnosperms and angiosperms. Neither requires water for sperm to meet eggs.
11. Gymnosperm seeds are not enclosed in fruits. They have diverse leaves and reproductive structures.
12. Gymnosperms include cycads, ginkgos, conifers, and gnetophytes.
13. In gymnosperms, male cones produce pollen and females cones produce eggs inside ovules. Pollen germination yields a pollen tube, through which a sperm cell fertilizes the egg. The resulting embryo remains dormant in a seed until germination.
14. Angiosperms are mostly terrestrial. The two major groups are monocotyledons and dicotyledons. The success of the angiosperms may reflect coevolution with animals, and dinosaur foraging habits.