Transcript most massive plants

origin of seeds
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late Devonian, 360 mya
seed = embryo + food + protective coat
advantage:
protection from desiccation
wait for good conditions
own food to get started
reproductive adaptations
of seed plants
• gametophytes smaller
• female gametophyte retained on
parent sporophyte
• male gametophyte transports sperm
• water not required for fertilization
• seeds are means of dispersal
2 types of seed plants
• 1. Gymnosperms “naked seeds”
– seeds exposed (on cones)
• 2. Angiosperms “vessel seeds”
– seeds inside fruits
gymnosperm life cycle
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heterospory w/2 types of cones:
1) small cones w/microsporangia
microspores develop into pollen
pollen = immature male gametophyte
reduced in size—no antheridia
whole gametophyte travels (pollination)
fertilization without water
gymnosperm life cycle
• 2) large cones have megasporangia
• megasporangium protected by
integuments
• ovule = megasporangium + integuments
• seed = mature ovule
• integuments become seed coat
• megaspore stays in megasporangium
gymnosperm seed
example: Pine
•seed coat (2n)
female gametophyte (n)
embryo (2n)
embryo is new sporophyte
female gametophyte is stored food
pine life cycle
• 3 years to make seed
• pollination & seed dispersal by wind
gymnosperms--cycads
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prominent w/dinosaurs
today 11 genera 130 sp
tough leaves
look like ferns
but have cones w/seeds
roots assoc. w/cyanobacteria
plants defended by toxic compounds
gymnosperms--Ginkgo
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only genus in group Ginkgophyta
thought extinct
good urban tree
stinky seeds
veins dichotomously
branched
gymnosperms--Gnetophyta
3 very different genera, 70 sp
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1) Ephedra
desert
“mormon tea”
ephedrine
gymnosperms--Gnetophyta
• 2) Gnetum
• tropical vine
• flat leaves
gymnosperms--Gnetophyta
• 3) Welwitschia mirabilis
• Namib desert, 2 leaves, ~1500 yrs old
gymnosperms--conifers
• very successful. 50 genera, 550 sp
• most evergreen
• needle leaves adapted for drought
– small surface area, thick cuticle
– stomata sunken in valleys
Taxodium distichum
bald cypress
Heron Pond,
Cache River State
Natural Area , S IL
deciduous
relative of redwoods
& sequoias
•oldest plants
•Bristlecone Pines 4600 years old
gymnosperms--conifers
• most massive plants
• Giant Sequoia 26 m circumference,
(8.3 m diameter!) 3000 years old
• tallest living plants
• Coast Redwoods 367 ft tall,
600-800 yrs old
• Watterson Towers only 281 ft
types of growth
• primary growth (up or down):
shoot & root apical meristems
• secondary growth (out): cambium—
meristem makes shoot & root thick
secondary growth
• vascular cambium:
– xylem to inside, phloem to outside
• wood is secondary xylem
• cork cambium makes cork to outside
• bark = cork + phloem
– everything outside of vascular cambium
tree rings: seasonal changes in
xylem cell size
dendrochronology
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tree rings date historical events
similar patterns in neighboring trees
overlap rings: to get complete record
need consistent rings
regular wet &
dry cycles
Plant tissue culture Fig 38.14
• plant cells are totipotent:
– any cell can grow into whole new plant
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new plant is clone (same genes)
examples: leaf cutting, Wollemi Pine
callus = undifferentiated tissue (wound)
develops roots and shoots
balance of hormones required
biotech: insert gene into callus