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Chapter 23 and 24
*Plants
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23.1 The Green Algal Ancestor of Plants
• Plants are multicellular, photosynthetic eukaryotes
• Plant evolution is marked by adaptations to a land existence.
• A land environment offers certain advantages Plentiful light for photosynthesis Carbon dioxide is present in higher concentrations
and diffuses more readily in air than in water
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The Green Algal Ancestor of Plants
• Adaptations are required for a land environment Constant threat of desiccation (drying out)
• Protect all phases of reproduction (sperm, egg, embryo) from drying out
• Seed plants disperse their embryos within the seed, which provides the embryo with food within a protective seed coat
• The water environment provides plentiful water support for the body of the plant
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The Green Algal Ancestor of Plants
• To conserve water, the land plant body is covered by a waxy cuticle. Impervious to water while still allowing carbon dioxide to enter so
that photosynthesis can continue• Vascular system transports water in the body of the land
plant.
• Plants are thought to have evolved from freshwater green algae about 450 mya
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Evolutionary History of Plants
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common ancestor
megaphylls
microphylls
seeds
flowers, double fertilization, endosperm, fruit
Flowering plants
Gymnosperms
Ferns and allies
Mosses
Lycophytes
Hornworts
Va
scu
lar
No
nv
asc
ula
r
See
dle
ss
Bry
op
hy
tes
See
d
Liverworts
Charophytes
550 400450500 350 300 250PRESENT
commongreenalgalancestor
embryoprotection
apicalgrowth
vasculartissue
Million Years Ago (MYA)
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The Green Algal Ancestor of Plants
• Additional terrestrial adaptations:
Waxy cuticle to prevent water loss
Stomata to allow gas exchange
Apical tissue, which has the ability to produce complex tissues and organs
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Leaf Adaptation
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cuticle
a. Stained photomicrographof a leaf cross section
Stomata
b. Falsely coloured scanningElectron micrograph of leaf surface
400 x
Stomata
Plant leaves have aCuticle and stomata
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(Left): © Kingsley Stern; (Right): © Andrew Syred/SPL /Photo Researchers, Inc.
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Evolution of Seed Plants: Full Adaptation to Land
• Flowers and Diversification:
Wind-pollinated flowers are usually not showy
Bird-pollinated and insect-pollinated flowers are often colorful
Night-blooming flowers attract nocturnal mammals or insects
• Usually white or cream-colored and aromatic
Fruits of flowers protect and aid in seed dispersal
• Utilize wind, gravity, water, and animals for dispersal8
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• Chapter 24
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24.1 Organs of Flowering Plants• Flowering plants, or angiosperms, are extremely diverse
but share many common structural features. • Most flowering plants possess a root system and a shoot
system The root system simply consists of the roots, The shoot system consists of the stem and leaves.
• A typical plant features three vegetative organs roots, stems, and leaves Vegetative organs are concerned with growth and
nutrition.• Flowers, seeds, and fruits are structures involved in
reproduction.10
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Organization of Plant Body
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stem
internode
leaf
petiole
blade
axillary bud
terminal bud
node
vascular tissues
root hairs
primaryroot
branchroot
shoot systemroot system
node
vein
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Organs of Flowering Plants
• Roots Generally, the root system is at least equivalent in
size and extent to the shoot system• Anchors plant in soil
• Absorbs water and minerals from the soil
• Produces hormones
Root hairs:• Projections from epidermal root-hair cells
• Greatly increase absorptive capacity of root
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