Ch.29 Biology

  1. Angiosperms
  2. Angiosperm= “enclosed seed”; seeds are covered by fruit tissue
    • Dominant plant group today
    • Approximately 250,000 species
    • What features contribute to the success of the angiosperms?
    • Complex vascular tissue
    • Xylem composed of tracheids (slow system of transporting water) and vessel elements (pipes transporting water)
    • More efficient transport system for water and nutrients
    • Phloem composed of sieve tubes and companion cells
    • More efficient transport system for photosynthate
    • Double fertilization
    • · Two sperm in the pollen grain
    • · One fertilizes the egg à zygote (2n)
    • · The other fertilizes polar nuclei (2n) à endosperm (3n) (endosperm is nourishment)
    • The most reliable distinguishing characteristic of the angiosperms
    • Enclosed ovules and seeds
    • Ovules and seeds are contained in carpels (modified leaves) rather than exposed on scales (Carpel = Pistil)
    • The carpel also prevents self-pollination or self-fertilization
    • Flowers
    • In addition to gamete production, flowers produce nectar and promote pollen transfer
    • In the process of nectar foraging, animals become pollen vectors
    • Some relationships are highly specialized
    • Fruit
    • The ovary of a flower develops into a fruit after fertilization
    • Fruits promote seed dispersal
    • Ex: American Robin (Scientific name = Turdus Migratorius : hint hint)
    • There are two major clades of angiosperms:
    • The monocots and eudicots include the great majority of angiosperms
    • Angiosperms make profound contributions to ecosystem services
    • Among many others benefits, they are key primary producers (taking up CO2 and releasing O2 in the process)
  3. Gymnosperms
  4. “Naked seeded”; seeds are not covered by fruit tissue
    • The four gymnosperm clades bear little resemblance to one another
    • Cycad – Encephalartos sp. – 300 species—Palm-like --- Tropics/subtopics
    • Ginkgo – Gingko biloba – 1 species--- Tree – China (native)
    • Gnetophytes—Welwitschia sp. – 90 species –Variable form –wide range
    • Conifers –Hemlock (Tsuga sp.) – 700 species – Trees (cones) ---High altitudes and latitudes
    • Male and female cones are the reproductive structures
    • Megastrobilus: the larger female seed-bearing cone
    • Microstrobilus: the smaller male pollen bearing cone
    • The see is naked, but not the embryo
    • Conifer diversity may not be that great, but…
    • The oldest known living organism on Earth is a conifer
    • The largest plant on Earth is a conifer
    • The largest biome on Earth is a coniferous forest type [Northern coniferous forest (taiga)]
    • However, angiosperms are the plants group that dominates today

  5. Why are seed plants the dominant vegetation today?
  6. Key features:
    • · Secondary growth
    • The accumulation of xylem (wood) which increases the diameter
    • Provides support to grow taller (primary growth)
    • Facilitates light absorption and seed dissemination
    • Note: not all seed plant are woody
    • · Gametophytes are nourished and protected by the sporophyte
    • Evolutionary trend: change in size and autonomy of the generations*
    • Seed plants are heterosporous; two different spore sizes
    • Microspores produce microgametophytes (pollen) which produce sperm
    • Pollen ( microgametophyte) dispersed by wind (or animals)
    • Megaspores give rise to megagmetophytes which produces eggs, which are not shed
    • Key features:
    • · Secondary growth
    • · Gametophytes are nourished and protected by the sporophyte
    • · Seeds
    • A well protected dispersal and/or resting stage
    • Seed coat protects the embryo
    • Stored energy supports early growth
    • Protection of gametes and embryos is the hallmark of seed plants
    • Seed plants are divided into gymnosperms and angiosperms
    • Angiosperms have flowers – and gymnosperms don’t
Card Set
Ch.29 Biology
Angiosperms and Gymnoosperms