Ch. 29
Plant Diversity I
How Plants Colonized Land
Jan 24­7:37 PM
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Essential Question
How did plants make the transition from water to land?
Jan 24­7:39 PM
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Plant history
­cyanobacteria (algae) on land 1.2 billion years ago
­500 million years ago ­ plants on land
­currently about 290,000 species
locations ­ all except mountain tops, some desert and polar regions
­important for other organisms to survive
­stabilize landscapes, supply oxygen, base of food chain
Jan 24­7:42 PM
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Characteristics that land plants have in common with protists
(algae)
1. brown, green , red algae
multicellular
eukaryotic
photoautotrophic
2. green algae, dinoflagellates, brown algae
cell walls ­ cellulose
3. green algae, euglenoids, some dinoflagellates
chloroplasts ­ chlorophyll a and b
Jan 24­7:46 PM
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Charophyceans
closest relative of land plants
green algae
traits that land plants share with only charophyceans
A. Structural/biochemical evidence
1. rosette cellulose­synthesizing complexes
­rose shaped proteins in plasma membrane
­other plants = linear
­higher % of cellulose
Jan 24­7:54 PM
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2. peroxisome enzymes = peroxisomes
­lower loss of organic products by photorespiration
3. Flagellated sperm
­ land plants with sperm and charophyceans is similar
4. Phragmoplast
­cytoskeletal elements that help form cell plate in mitosis
http://botit.botany.wisc.edu/images/130/Meiosis/Lilium_microsporogenesis/Phragmoplast_Cell_Plate.html
Jan 24­7:59 PM
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B. Genetic evidence
­nuclear and chloroplast gene comparison between plant and algae closest to charophyceans (Charo and Coleochaete)
Jan 24­8:03 PM
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C. Adaptations for land
­charophyceans live on pond/lake edges
­edges can dry
­form a sporopollenin ­ polymer
­prevent desiccation
­could live on land
­once on land
­ample sunlight, carbon dioxide, soil nutrients, lack of herbivores & pathogens
Jan 24­8:08 PM
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A. Traits of land plants that Charophyceans do not have
­evolved as derived traits
1. Apical meristems ­ regions of cell division
tips of shoots and roots
­cells become surface epidermis
­shoot apical meristems ­ generate leaves
Jan 24­8:15 PM
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2. Alternation of Generations
­reproductive cycle
­derived characteristic of land plants (not present in relative of land plants and charophyceans)
­both multicellular haploid and multicellular diploid stages
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gametophyte­haploid
reproduce by mitosis to make eggs and sperm
sporophyte ­ diploid
produce spores (haploid by meiosis)
Jan 29­8:19 AM
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3. walled spores produced in Sporangia
sporangia = produce spores spores made by sporocytes by meiosis
wall of spores = sporopollenin
fern spore
Jan 24­8:45 PM
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4. Multicellular gametangia
gametes have multicellular organs called gametangia
female gametangia = archegonia
male gametangia = antheridia
Antheridium
Archegonium
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5. Multicellular, dependent embryos
develop from zygotes in female
placental transfer cells in embryo ­ help nutrients get from maternal tissue to embryo
Jan 24­8:57 PM
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other adaptations for land
a. adaptations of water conservation
1.cuticle ­ polmers of polyesters and waxes
­ waterproofing to prevent desiccation
2. stomata ­ pores
areas of gas exchange, and water evaporation
stomata of begonia
Cuticle
http://employees.csbsju.edu/ssaupe/images/stomata/mettler.jpg
Jan 24­9:21 PM
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b. Adaptations of water transport (vascular tissue*) xylem ­ carry water and minerals up from roots
­made of dead cells
phloem ­ carry nutrients (sugars, amino acids, other organic
products
* absent in bryophytes (mosses)
Jan 24­9:30 PM
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c. secondary compounds
­products of secondary metabolic pathways (branches off primary metabolic pathways)
­alkaloids
­terpenes
­tannins
bitter ­ help against herbivores
­phenolics (flavenoids) ­ absorb UV rays, symbiotic relationships with soil microbes
Jan 24­9:41 PM
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Bryophytes ­ "nonvascular plants"
liverwort
moss
moss
hornwort
Jan 24­9:49 PM
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life cycle of moss
Jan 28­8:33 PM
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moss life cycle
Jan 29­8:32 AM
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In life cycle ­ gametophyte stage is dominant stage
Sperm needs water (dew droplets) to get sperm to eggs
Protonemata ­ mass of green, branched, one­
celled thick filaments that absorb water, cell to cell or some have conducting tissue
Mar 10­8:33 AM
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Sphagnum moss (peat moss)
peat bog
closeup
leaf
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mummy found in peat bog
Mar 10­8:22 AM
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origin of vascular plants
carboniferous period ­ vascular plants began to diversify and seed plants not evolved yet
420 million years ago
­no taller than 50 cm. ­branched sporophytes
Jan 28­8:37 PM
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main traits of vascular plants:
1. life cycles­ dominant sporophytes (larger) than gametophyte
2. transport in vascular tissues
xylem­ water/minerals
­has tracheids­tube­shaped cells (dead cells)
that carry water/minerals up from roots
­ have lignin in cell walls
phloem ­ sugar conducting cells (living)
­arranged in tubes
­transport sugar, amino acids
Mar 10­8:16 AM
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3. Evolution of roots
­organs that anchor plants, absorb water and nutrients from soil
4. Evolution of leaves
­organs that increase surface area for collecting solar energy for photosynthesis
­microphylls ­ small spine shaped leaves with single vein
410 million years ago
­megaphylls ­ leaves with highly vascular system; 370 million years ago
Jan 28­8:48 PM
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Hypothesis for evolution of leaves
May have originated from sporangia
May have evolved from the fusion of branched stems
Jan 29­8:36 AM
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­evolution of sporophylls (modified leaves with sporangia)
homosporous ­ one type of sporophyll with one type of spore
heterosporous ­ two types of sporophylls and two kinds of spores
megasporophylls ­ produce megaspores ­ make female gametophytes
microspores ­ develop into male gametophytes
Jan 28­8:59 PM
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Pteridophytes
Club moss
Whisk fern
fern
horsetail
Jan 28­8:36 PM
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Lycophyte
Jan 29­8:36 AM
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Life cycle of a fern
Jan 28­9:07 PM
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fern sorus
Jan 29­8:38 AM
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Fern gametophyte
Jan 29­8:39 AM
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fern sporophytes
Jan 29­8:40 AM
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Artist's conception of carboniferous forest based on fossil evidence
Jan 29­8:41 AM
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­only plants with vascular tissue can have true roots, stems, and leaves
Feb 25­10:10 AM
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So ­ what adaptations allowed plants to grow on land?
Mar 10­9:21 AM
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Mar 15­10:41 AM
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