Overview
This lecture covers the distinguishing characteristics, reproduction, and evolutionary significance of seedless vascular plants, gymnosperms, and angiosperms.
Seedless Vascular Plants
- Seedless vascular plants lack seeds but have true roots, stems, and leaves.
- Four main groups: club mosses, whisk ferns, horsetails, and true ferns.
- Early seedless vascular plants evolved before ferns and their relatives.
- The sporophyte (diploid) is the dominant and conspicuous generation.
- Haploid spores develop on the underside of sporophyte leaves.
- Water is required for reproduction so sperm can swim to eggs.
Gymnosperms
- Gymnosperms are "naked seed" plants; their seeds are not enclosed in fruit.
- Main groups: cycads, ginkgo, conifers, and gnetophytes.
- Large, conspicuous sporophytes produce spores in cones.
- Gymnosperm gametophytes are microscopic.
- Pollination brings male (pollen) and female gametophytes together; water is not needed for fertilization.
- Zygotes remain inside seeds, which protect the developing sporophyte embryo.
Angiosperms
- Angiosperms possess flowers and fruits that enclose seeds.
- Seeds develop within fruits, an evolutionary advancement over gymnosperms.
- Angiosperms are divided mainly into eudicots (most common) and monocots.
- The sporophyte is large and visible; flowers serve as reproductive structures.
- Microscopic gametophytes unite at pollination.
- Double fertilization forms both embryo and nutritive endosperm inside seeds.
- Seeds germinate when environmental conditions are favorable.
- Wind and animals play key roles in angiosperm reproduction.
Alternation of Generations
- All plants exhibit alternation of generations, alternating between multicellular haploid (gametophyte) and diploid (sporophyte) stages.
Key Terms & Definitions
- Sporophyte — Diploid plant stage that produces spores.
- Gametophyte — Haploid plant stage that produces gametes.
- Gymnosperm — Seed plant with unenclosed ("naked") seeds.
- Angiosperm — Flowering plant with seeds enclosed in fruit.
- Double fertilization — Angiosperm process producing an embryo and endosperm.
- Spore — Haploid reproductive cell capable of developing into a new organism.
Action Items / Next Steps
- Review Sections 19.3 and 19.4 for details on plant life cycles.
- Complete associated Mastering Concepts questions.
- Prepare for questions on alternation of generations and plant reproductive adaptations.