Plants are multicellular eukaryotes. Nearly all are photosynthetic, and most are terrestrial (some are secondarily aquatic). Plants contain a variety of cell types that are specialized to perform different functions: the aerial parts generally have a waxy cuticle to prevent water loss, but the roots don’t so they can absorb water. The photosynthetic pigments include chlorophylls A and B plus various carotenoids. Plant cells have cell walls which are made of cellulose. Plants grow by mitosis, and reproduce by meiosis and alternation of generations with special adaptations of the gametes and embryos to survive in a non-aquatic environment. The gametes are produced ingametangia. The male gametangium is called an antheridium (anthe = flower), while the female gametangium is an archegonium (arche = first, beginning; goni = seed). The eggs are fertilized within the female archegonium to reduce desiccation, and often stay within the archegonium to continue their development. In all plant groups except Division Bryophyta, the 2n sporophyte is the dominant generation.
| The various Divisions (remember botanists use Division = Phylum) of plants are classified based on presence/absence of a vascular system and/or seeds. If seeds are present, the location of the seeds (whether on the surface of a reproductive structure or within some type of ovary) becomes significant. |
- Division Bryophyta, the mosses and liverworts:
- (bryo = moss; phyto = plant; wort = herb, plant) These are terrestrial, but live in very damp, shady places. They have no vascular system so must directly absorb water from the soil. Mosses have root-like rhizoids (rhizo = root; -oid = like, form) and leaf-like structures, but these are not true roots/leaves because they have no vascular system. The dominant generation in the life cycle is the 1n gametophyte. In addition to the “usual” sexual reproduction, liverworts also reproduce asexually by means of small, cup-like structures called gemma cups containing small pieces of liverwort calledgemmae (sing. = gemma). When it rains, the gemmae are splashed out and can grow into new liverworts.
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