Botany: Bacteria, Fungi, Lichens, Algae, Higher Plants
What you must understand
Bacteria are prokaryotes: no nucleus, circular DNA, cell wall, often heterotrophic, some autotrophic by chemosynthesis or photosynthesis; they reproduce by binary fission and play roles as decomposers, nitrogen fixers, pathogens.
Fungi are eukaryotic heterotrophs with chitin walls, absorbing nutrients; they reproduce by spores, and include molds, yeasts (unicellular) and cap fungi. Lichens are a symbiosis of fungus and alga or cyanobacterium: the fungus supplies water and minerals, the alga supplies carbohydrate from photosynthesis.
Algae are photosynthetic, mostly aquatic, with simple bodies (thallus); they include green, brown and red algae. Higher plants have organs (root, shoot, leaf, flower, fruit, seed) and tissues (integumentary, conductive, mechanical, ground, educational/meristematic). Life cycles alternate sporophyte (diploid, makes spores by meiosis) and gametophyte (haploid, makes gametes by mitosis). In mosses the gametophyte dominates; in ferns the sporophyte dominates but the gametophyte is free-living; in seed plants the gametophyte is reduced and dependent.
Traps
- Lichens are not a single organism; the partners are fungus plus alga.
- Fungi are not plants: no chlorophyll, chitin walls, heterotrophic.
- Mosses lack true roots and vascular tissue; ferns have vascular tissue but need water for fertilization.
- Spores are made by meiosis; gametes by mitosis.
Rule of thumb
Ask which generation is dominant and visible? - that identifies the plant group.
Worked example: A green carpet plant with rhizoids and no vascular tissue, whose visible leafy form bears sex organs, is a moss: the visible plant is the gametophyte.