Transcript Plants

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Chapter 23 and 24
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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flowers, double fertilization, endosperm, fruit
common ancestor
Flowering plants
Seed
seeds
megaphylls
Vascular
Gymnosperms
vascular
tissue
apical
growth
Seedless
Ferns and allies
microphylls
embryo
protection
Bryophytes
Mosses
Hornworts
common
green
algal
ancestor
Liverworts
Nonvascular
Lycophytes
Charophytes
550
500
450
400
350
Million Years Ago (MYA)
300
250
PRESENT
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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
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cuticle
a. Stained photomicrograph
of a leaf cross section
Plant leaves have a
Cuticle and stomata
Stomata
400 x
b. Falsely coloured scanning
Electron micrograph of leaf surface
(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 dispersal
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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
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reproduction.
Organization of Plant Body
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
terminal bud
blade
leaf
vein
petiole
axillary bud
stem
node
internode
node
vascular tissues
shoot system
root system
branch
root
root hairs
primary
root
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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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