Download Chapter 24: Evolution and Diversity of Plants

Chapter 24: Evolution and Diversity of Plants
Evolutionary History
Alternation of Generations
Nonvascular Plants
Vascular Plants
Seedless
Seed
Angiosperms
Monocots and Eudicots
Flowers
Evolutionary History of Plants
More than 98% of all biomass is plants
Multicellular photosynthetic eukaryotes
280,000 known species
Thought to have evolved from freshwater algae over 500 mya
Evolution of plants marked by four evolutionary events associated with four major groups of
plants
Nonvascular Plants
Advent of nourishment of a multicellular embryo within the body of the female plant
Seedless vascular plants
Advent of vascular tissue
Vascular Seed Plants – Gymnosperms and angiosperms
Produce seeds
Gymnosperms – “Naked seeds”
Angiosperms – Flowering Plants
Attract pollinators that give rise to fruits
Representatives of the Four Major Groups of Plants
Alternation of Generations
Life cycle involves alternation of generations
Multicellular 1n individuals (gametophytes) produce multicellular 2n individuals
(sporophytes)
Multicellular 2n individuals (sporophytes) produce multicellular 1n individuals
(gametophytes)
Sporophyte (2n):
Multicellular individual that produces spores by meiosis
Spore is haploid cell that will become the gametophyte
Gametophyte (1n):
Multicellular individual that produces gametes
Gametes fuse in fertilization to form zygote
Zygote is a diploid cell that will become the sporophyte
Alternation of Generations – cont’d
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Appearance of generations varies widely
In ferns, female portions are archegonia and are fertilized by flagellated sperm
In angiosperm, female gametophyte (embryo sac), consists of an ovule
Following fertilization, ovule becomes seed
In seed plants, pollen grains are mature sperm-bearing male gametophytes
Reduction in Size of the Gametophyte
Other Terrestrial Adaptations
Vascular tissue transports water and nutrients to the body of the plant
Cuticle provides an effective barrier to water loss
Stomata bordered by guard cells that regulate opening, and thus water loss
Protection of Eggs and Embryos
Leaves of Vascular Plants
Nonvascular Plants (bryophytes)
Lack specialized means of transporting water and organic nutrients
Do not have true roots, stems, and leaves
Gametophyte is dominant generation
Produces eggs in archegonia
Produces flagellated sperm in antheridia
Sperm swim to egg in film of water to make zygote
Non-vascular Plant Examples:
Hornworts (Division Anthocerophyta) have small sporophytes that carry on photosynthesis
Liverworts (Division Hepatophyta) have either flattened thallus or leafy appearance
Mosses (Division Bryophyta) usually have a leafy shoot, although some are secondarily flattened
Can reproduce asexually by fragmentation
Dependent sporophyte consists of foot, stalk, and sporangium
Hornwort
Liverwort, Marchantia
Moss (Polytrichum) Life Cycle
Vascular Plants
Xylem conducts water and dissolved minerals up from roots
Phloem conducts sucrose and other organic compounds throughout the plant
Lignin strengthens walls of conducting cells in xylem
Most seedless vascular plants are homosporous
Windblown spores are dispersal agents
All seed plants are heterosporous and have male and female gametophytes
Seeds disperse offspring
Cooksonian Fossil
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Vascular Tissue
Seedless Vascular Plants
Club Mosses (Division Lycophyta)
Typically, branching rhizome sends up short aerial stems
Leaves are microphylls (have only one strand of vascular tissue)
Sporangia occur on surfaces of sporophylls
Grouped into club-shaped strobili
Club Moss, Lycopodium
Ferns and Allies
Horsetails (Division Sphenophyta)
Rhizome produces tall aerial stems
Contains whorls of slender, green branches
Small, scalelike leaves also form whorls at the joints
Horsetail, Equisetum
Ferns
Whisk Ferns (Division Psilotophyta)
Branched rhizome has rhizoids
utualistic mycorrhizal fungus helps gather nutrients
Ferns (Division Pterophyta)
Large conspicuous fronds
Divided into leaflets
Dominant sporophyte produces windblown spores
Whisk fern, Psilotum
Diversity of ferns
Fern Life Cycle (see Handout)
Vascular Seed Plants
Seed plants are the most plentiful plants in the biosphere
Seed coat and stored food allow an embryo to survive harsh conditions during long period
of dormancy
Heterosporous
Drought-resistant pollen grains
Ovule develops into seed
Gymnosperms
Gymnosperms have ovules and seeds exposed on the surface of sporophylls
Confiers
Cycads
Ginkgoes
Gnetophytes
Conifers
Conifers, as well as other gymnosperm phyla, bear cones
Tough, needlelike leaves of pines conserve water with a thick cuticle and recessed stomata
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Considered a “soft” wood because it consists primarily of xylem tissue
Pine Life Cycle
Cycads
Cycads (Division Cycadophyta)
Large, finely divided leaves that grow in clusters at the top of the stem
Pollen and seed cones on separate plants
Pollinated by insects
Cycad Cones
Ginkgoes
Ginkgoes (Division Ginkgophyta)
Dioecious
Some trees producing seeds
Others producing pollen
One surviving species (Gingko biloba)
The Ginkgo Tree
Gnetophytes
Gnetophytes (phylum Gnetophyta)
Have similarly structured xylem
None have archegonia
Strobili have similar construction
Ephedra
Welwitschia miribilis
Angiosperms
Angiosperms (Division Anthophyta)
An exceptionally large and successful group of plants
Ovules are always enclosed within diploid tissues
Became dominant group of plants in the late Cretaceous and early Paleocene periods
Amborella trichopoda – genetic data suggests that this plant is most closely related to earliest
flowering plants
Monocots and Eudicots
Two classes of flowering plants
Monocotyledones (Monocots)
One cotyledon in seed
Eudicotyledones (Dicots)
Two cotyledons in seed
Flower Diversity
The Flower
Peduncle (flower stalk) expands at tip into a receptacle
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Bears sepals, petals, stamens, and carpels, all attached to receptacle in whorls
Calyx (collection of sepals) protect flower bud before it opens
Corolla (collection of petals)
The Flower
Each stamen consists of an anther and a filament (stalk)
Carpel has three major regions
Ovary - Swollen base
Fruit
Style - Elevates stigma
Stigma - Sticky receptor of pollen grains
Generalized Flower - Diagram
Flowering plant life cycle
Flowers and Diversification
Wind-pollinated flowers are usually not showy
Bird-pollinated flowers are often colorful
Night-blooming flowers attract nocturnal mammals or insects
Usually white or cream-colored
Fruits of flowers protect and aid in dispersal
Utilize wind, gravity, water, and animals for dispersal
Review
Evolutionary History
Alternation of Generations
Nonvascular Plants
Vascular Plants
Seedless
Seed
Angiosperms
Monocots and Eudicots
Flowers
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