Overview
This lecture covers the evolutionary importance of plants, the major plant groups, their adaptations for terrestrial life, and focuses on bryophytes as the simplest land plants.
The Importance and Evolution of Plants
- Plants are essential for life, producing oxygen and forming the base of food chains.
- Plants evolved from green algae, sharing many molecular and cellular features.
- Green algae live in water, whereas plants are adapted to life on land.
Major Plant Groups
- Plants are classified into four groups: bryophytes, seedless vascular plants, gymnosperms, and angiosperms.
- Table 19.1 summarizes the main plant phyla.
Adaptations to Land
- Key plant adaptations include leaves, vascular tissue, roots, pollen, seeds, flowers, and fruit—all aiding survival on land.
- Leaves allow efficient photosynthesis, vascular tissue transports water and nutrients, and roots anchor plants and absorb water.
Plant Life Cycles and Alternation of Generations
- All plants have similar life cycles featuring alternation of generations: a diploid sporophyte and a haploid gametophyte.
- Sporophytes produce spores by meiosis; gametophytes produce gametes by mitosis.
- Fertilization forms a diploid zygote, which develops into the sporophyte.
- The size and dominance of gametophyte and sporophyte stages vary among plant groups.
Bryophytes: Nonvascular and Seedless Plants
- Bryophytes include mosses, liverworts, and hornworts; they are nonvascular and lack seeds.
- Bryophytes are small and compact, with a dominant gametophyte stage and a small, dependent sporophyte.
- Sexual reproduction in bryophytes requires water for sperm movement.
- Bryophytes can also reproduce asexually through fragmentation.
Key Terms & Definitions
- Bryophyte — group of nonvascular, seedless plants (mosses, liverworts, hornworts).
- Sporophyte — diploid plant generation that produces spores.
- Gametophyte — haploid plant generation that produces gametes.
- Alternation of generations — plant life cycle alternating between sporophyte and gametophyte stages.
- Vascular tissue — tissues (xylem and phloem) that transport water and nutrients in plants.
Action Items / Next Steps
- Review Table 19.1 on plant phyla.
- Answer mastering concept questions from sections 19.1 and 19.2.
- Study the figures and diagrams (e.g., Figure 19.5) in the textbook for visual understanding of plant life cycles and bryophyte structure.