introduction to plants ap biology invading land conditions to overcome: buoyancy of water is...
TRANSCRIPT
Invading Land
• Conditions to overcome: buoyancy of water is missing, no longer bathed in a nutrient solution, air dries things out
Invading Land
• Those adverse conditions favored evolution of: structures that support, vessels that transport, and structures that conserve water
• See handout
Three major groups
• Bryophytes: small nonvascular plants– Mosses, liverworts
• Seedless, vascular plants –ferns, horsetails
• Seed bearing plants– Usually divided into two classes:– Gymnosperms (“naked seeds”) and
Angiosperms (flowering plants)
What is vascular tissue?
• Tissues that conduct water and food throughout the plant
• Equivalent of blood vessels in higher animals
• Xylem conducts water• Phloem conducts food
How do bryophytes survive without vascular tissue?
• Must remain small• Must have water for
reproduction• Must live in moist
areas• Rely on diffusion and
primitive rootlike structures to absorb water
Invading Land• Evolutionary order:
bryophytes first—410 million years ago
• Ferns—by 360 million years ago
• Conifers—by 290 million years ago
• Angiosperms—138 million years ago
Bryophytes
• Mosses, liverworts, hornworts
• 18,600 species• Small• Moist environments• No vascular tissue (no
xylem or phloem)• Rhizoids are rootlike
Bryophytes
• “Alternation of generations” means a gametophyte plant produces a sporophyte plant, which then produces a gametophyte
• Sporophyte remains attached to the gametophyte
Bryophytes
• The stages are named after what they produce
• A sporophyte produces spores
• A gametophyte produces gametes
Sporophyte
capsules
Bryophytes
• Sperm must swim to the egg, so water must be available
• Also need water because they do not have true roots or vascular tissue
antheridium
archegonium
Ferns
• 12,000 species• Mostly tropical• Very diverse• Range is size from 1
cm to 25 meters tall• Have vascular tissue,
but do not produce seeds
Ferns
• Dominant stage is the sporophyte (2n)
• Alternation of generations
• Sporophyte produces haploid spores (n) which grows into a gametophye
Sori contain spores
Ferns
• Germinating spores develop into small gametophyes, the plant’s stage which produces gametes
• The gameotyphyte plant is very small and hard to notice
• Heart shaped: called a prothallus
Gametophyte
• Antheridia are sperm producing structures
• Archegonia are egg producing structures
• Fertilization forms a zygote (2n), which develops into a sporophyte plant (2n)
• The sporophyte develops into the leafy fern we recognize, and will go on to produce haploid spores
Gymnosperms : Naked Seeds(not enclosed in a fruit)
• 4 Major groups:
• Cycads: mostly tropical or subtropical regions
• Gingkoes: native to Southeastern China
• Conifers: cone bearing
• Gnetales: resemble angiosperms, but no flower
CycadsMost common in equatorial regions, some subtropical areas
Gnetales• Small leaves that
resemble angiosperm leaves
• No flowers• Cones may be fleshy
and brightly colored• Some consider them to
be a “bridge” to angiosperms
Conifers• Trees and shrubs that
have needles or scale like leaves
• Bear seeds on exposed cone scales
• Most are evergreen• Examples: pine, fir,
cypress, redwood, pacific yew
Conifers
• Both male and female cones are produced
• Male cones produce pollen, which drifts and lands on ovules of female cones
• Pollen sprouts a tube which grows to the eggs inside the ovule
Conifers
• After fertilization, the zygote develops into a seed.
• The seed becomes a mature sporophyte (2n), producing male and female cones
• The cones produce haploid spores which become pollen and eggs
Conifers
• Slow to reproduce• After pollen lands,
may be a year before fertilization occurs
• This is a competitive disadvantage
Angiosperms
• Flowering plants
• The flower is the reproductive structure
• Sporophyte is the dominant generation
• Gametophyte generation is small (microscopic) ; this offers protection and nutrition, and is a competitive advantage.
Angiosperms
• Coevolved with pollinators
• Birds• Insects: bees,
butterflies, moths, etc.• Bats• Mutually beneficial
Angiosperms
• Zygote (embryo) forms in the base of the female ovary in an ovule
• Each ovule becomes a seed; the whole ovary becomes the fruit, or part of the fruit