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EVOLUTION AND PLANT DIVERSITY
Chapter 29
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Evolution of Green Algae
Plants share many characteristics with many protists Multicellular, eukaryotic,
and photoautotrophs Cell walls of cellulose Chloroplasts with
chlorophylls a and b Charophytes are only algae
that share 4 distinctive traits with land plants Identified lineage as closest
relatives to land plants
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Charophytes Traits
Rosette-shaped cellulose-synthesizing complexes Proteins in the PM that synthesize cellulose in cell wall
Peroxisome enzymes Help minimize loss of organic products from
photorespiration Flagellated sperm structure
Similar structure in land plants with and charophyceans
Formation of a phragmoplast Microtubules that form between daughter nuclei to
create new cell wall in dividing cells Doesn’t imply land plants are descendents
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Land Move Adaptations
Charophyte algae inhabit shallow waters Dessication is a problem Natural selection chose individuals that could
survive Sporopollenin is a polymer layer to prevent
spores from drying out during dispersal Allowed 1st land plants to survive terrestrially
Brighter sunlight, more CO2, and mineral rich Needed to overcome challenges
Scarce water and little structural support 4 adaptations specific to land plants
Not unique to (convergent evolution) and not all plants have
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Alternation of Generations Each generation gives rise
to the other Gametophyte generation
From 1n spore by mitosis Produce gametes by mitosis Gametes combine in
syngamy to form 2n zygote Sporophyte generation
From 2n zygote by mitosis Produces spores by meiosis
Generations can look different Plants we see usually
sporophyte
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Other Derived Traits
* Walled spores produced in sporangia.
Multicelled organs where sporocytes (2n) produce spores via meiosis.
* Multicellular gametangia
Archegonia: female, pear-shape with non-motile eggAntheridia: male, release sperm to environment
* Apical meristems
Localized regions of cell division at tips of shoots and roots
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Additional Characteristics
Epidermis covered by a cuticle to protect leaves from desiccation
Early plants without true roots and leaves benefited from mycorrhizal associations with fungi Review: 2 types are?
Secondary compound production to prevent against herbivores, parasites, and UV radiation Human source of spices and medicines
E.g tannin in red wines from grape skin, stem, and seed; responsible to dry, pucker taste/sensation of good reds
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Diversification of PlantsNonvascular: unclear monophylogeny
No vascular tissue, true roots, stems, or leaves
Small, grow low, moist environments
Vascular: exist in smaller clades (phyla)
Seedless are paraphyletic
Seeds are embryos with nutrients in a protective shell
Gymno: naked seeds
Angio: flowering plants
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Nonvascular Plants
Phylum Hepatophyta (liverworts) Marchantia has ‘thalloid’ shape gametophyte
Gametangia appear as mini trees from which sporophytes hang Plagiochilla has ‘leafy’ looking gametophytes
Phylum Anthocerophyta (hormworts) Long, tapered sporophyte with an open sporangium Gametophyte grows horizontally, 1st to colonize open area
Phylum Bryophyta (mosses) Mainly see gametophyte stage, carpet-like Sporophytes visible and tall, green when young, tan to
release spores
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Nonvascular Plants Life Cycle
Gametophyte is dominant stages Protonemata produce
‘buds’ Develop into
gametophores with rhizoids = anchors
Antheridia or archegonia Can be bi- (not mosses)
Sporophyte results Dependent on parent Develop foot, stalk
(seta), and capsule (sporangium)
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Importance of Mosses
Colonize bare, sandy soil and help retain nitrogen
Moist environments and extreme ones Mountaintops, tundra, and deserts
Survive despite loss of water and rehydrate when conditions improve
Sphagnum forms deposits of dead organic material = peat Good for water absorbing and gardening;
dried as fuel
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Evolution of Seedless Vascular Plants
Sperm is flagellated like nonvascular plants so must move through films of water to fertilize egg Common in moist
environments Branched sporophytes
not dependent on gametophytes for nutrition
Branching allowed for multiple sporangia
Ancestors lacked roots, but shared other traits
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Seedless Vascular Plant Life Cycle Compare with nonvascular life cycle Sporophyte generation is larger and more complex In ferns is what is seen
Gametophytes grow on or in soil Gametophytes reduced as evolution to seed plants
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Vascular Transport Tissue Xylem conducts most
water and minerals Usess tracheids (tube-
shaped cells) to move root to tip
Cell walls strengthened with lignin, a polymer
Phloem distributes sugars, amino acids, and other organics through cells arranged as tubes
Evolutionary adaptations Taller Cover other plants
(dominance) Evolution of trees
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Roots and Leaves Appear
Roots absorb from the soil and provide support Resemble stem tissue
Leaves increase SA and serve as photosynthetic organs Stomata to regulate gas and water exchange Microphylls: small, spine-like leaves, single
vascular tissue Phylum lycophyta only
Megaphylls: highly branched vascular tissue More photosynthetic
Stems move water and minerals to leaves and organics from leaves to roots
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Sporophylls
Modified leaves that bear sporangia
Vary in structure between phyla of vascular plants
Most seedless vascular plants are homosporous
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Phylum Lycophytes
Club mosses, spike mosses, and quillworts
Sporophylls clustered together as cone-like structures called strobili
Club mosses all homosporous while others are heterosporous
Club moss spores are rich in oil Photographers ignited
them to create light
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Previously represented as 3 separated phyla All homosporous Ferns Sporophytes produce fronds that grow as fiddlehead
uncoils Gametophytes die after sporophyte detaches Horsetails Separate fertile (cone-bearing) and vegetative stems Stems have joints with small leaves emerging from
them Stem is main photosynthetic organ
Whisk ferns Sporophytes have branched stems, but no roots 3 fused sporangia on stems