Biology 110
Plant Kingdom - Spore producers
The Plant Kingdom includes two separate evolutionary lines
and several taxonomic groups:
- Mosses and Liverworts
- Ferns, Horsetails and Lycopods
- Gymnosperms and Angiosperms
Characteristics shared with the (probable ancestral group:) Green
Algae:
- Chloroplast composition and structure
- Cell walls
- Storage product of photosynthesis
- Mechanism of mitosis
Shared characteristics of all members of the Plant Kingdom (what
makes a plant a plant?):
- Alternation of multicellular haploid (gametophyte = gamete
producing) and multicellular diploid (sporophyte = spore
producing) phases in life cycle
- Eggs are fertilized in a special structure (archegonium) and
developing embryo is protected for some time
Benefits of terrestrial life for photosynthetic organisms:
Abundant resources - Light and CO2
Environmental challenges to terrestrial life:
- Dehydration.
- Sources of mineral nutrients and water are no longer
surrounding.
- Support/
- Sexual reproduction without liquid water.
Evolutionary lineage 1: Non-vascular plants, e.g. Mosses and
Liverworts
- No cells specialized for conducting water - no true roots.
- Photosynthetic tissues are generally not covered by a waxy
cuticle.
- Haploid dominant life cycle with "parasitic" diploid phase.
- Restricted to moist places but can be tolerant of desiccation.
- Flagellate sperm swim to egg cells for fertilization in liquid
water.
Evolutionary lineage 2: Vascular plants, e.g. Ferns et al. ,
Gymnosperms and Angiosperms
- Vascular systems with cells specialized for transport of
water.
- Waxy cuticle covers photosynthetic tissue.
- True roots specialized for uptake of water and minerals from
soil solution
- Diploid dominant life cycle.
Ferns and their "allies" - Horsetails and Lycopods:
- Disperse offspring by producing haploid spores from sporangia.
- The spores germinate and grow into independent photosynthetic
autotrophic gametophytes.
- Sperm and eggs produced in special structures.
- Flagellate sperm swim to eggs for fertiliztion.