Evolution of Plants
Chapter 16
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Outline
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Adapting to Terrestrial Life
Vascular Plants
Seedless Vascular Plants
Seed Plants
 Gymnosperms
 Angiosperms
- Flowers
 Dicots and Monocots
 Seed Dispersal
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Adapting to Terrestrial Living
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Green algae that were probably the
ancestors of today’s plants are aquatic
organisms not well-adapted to living on land.
 Had to overcome three challenges:
- Minerals absorption from rocky surfaces
- Water conservation
- Reproduction on land
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Adapting to Terrestrial Living
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Mineral Absorption
 Plants require relatively large amounts of
six inorganic minerals:
- Nitrogen, potassium, calcium,
phosphorus, magnesium, and sulfur.
 Mycorrhizae
Water Conservation
 Cuticle - watertight outer covering.
- Stomata - gas and vapor exchange.
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Adapting to Terrestrial Living
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Reproduction on Land
 Due to immobility, gametes must avoid
drying while they are transferred by wind or
insects.
- Spore Development
 Generation alteration
- Sporophytes - diploid generation
- Gametophyte - hapolid generation
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Generalized Plant Life Cycle
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Evolution of Vascular System
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Terrestrial plants are required to carry water
up from roots to leaves, and carbohydrates
down from leaves to roots.
 Vascular System
- Specialized strands of connected hollow
cells.
 Nine of Twelve living plant phyla are
vascular.
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Nonvascular Plants
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Only two phyla of living plants lack a vascular
system:
 Liverworts (Hepaticophyta)
 Hornworts (Anthocerophyta)
Simple Vascular Systems
 Mosses were first plants to evolve strands
of specialized conduction cells.
- No specialized wall thickening.
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Moss Life Cycle
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Evolution of Vascular Tissue
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Appeared approximately 430 mya.
 Grew by cell division at the tips of stem
and roots (Primary Growth).
About 380 mya vascular plants developed a
growth in which a cylinder of cells beneath
the bark divides, producing new cells around
plant’s periphery (Secondary Growth).
 Necessary for tall trees with thick trunks.
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Leaf Vascular System
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Seedless Vascular Plants
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Most abundant of the four phyla of seedless
vascular plants contain ferns with about
12,000 living species.
 Have both gametophyte and sporophyte
individuals, each independent and selfsufficient.
- Gametophyte produces eggs and sperm.
- Sporophyte bears and releases hapolid
spores.
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Fern Life Cycle
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Seed Plants
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Seed - Embryo cover that offers protection of
embryonic plant at its most vulnerable stage.
 Male and Female gametophytes
- Male - microgametophytes (pollen
grains) arise from microspores.
- Female - megametophytes contain eggs
and develop from megaspores produced
within ovule.
 Pollination - transfer of pollen.
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Seed Plants
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Five living phyla of seed plants:
 Four are gymnosperms - ovules not
completely enclosed by sporophyte tissue
at time of pollination.
 Fifth is angiosperms - ovules completely
enclosed by vessel of sporophyte tissue
(carpel) at time of pollination.
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Seed Structure
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Seed Plants
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Adaptive value of seeds:
 Dispersal
- Facilitate migration and dispersal
 Dormancy
- Wait for favorable conditions
 Germination
- Synchronization with environment
 Nourishment
- Energy source for young plants
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Gymnosperm Phyla
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Coniferophyta (Conifers)
 Trees that produce seeds in cones.
- Most familiar of four gymnosperm phyla.
- Seeds develop on scales within cones
and are exposed at time of pollination.
Cycadophyta (Cycads)
Ginkgophyta (Ginkos)
Gnetophyta (Gneetophytes)
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Conifer Life Cycle
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Rise of Angiosperms
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Comprise 90% of all living plants.
 Use roots to anchor plants in one place to
obtain nutrients.
 Produce tiny male gametes that are easily
transported.
Flower - reproductive organs that employ
bright colors to attract pollinators and nectar
to induce entrance into the flower to contact
pollen grains.
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Flowers
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Structure consists of four distinct whorls:
 Outermost - Protects flower from physical
damage (sepals).
 Second - Attracts pollinators (petals).
 Third - Produces pollen grains (stamens
and anther).
 Fourth - Produces Eggs (Carpel)
- Ovary
- Style
- Stigma
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Angiosperm Flower
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Why Different Kinds of Flowers
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Different pollinators are attracted to specific
types of flowers.
 Bees most numerous insect pollinators.
- Becomes coated with pollen while inside
the flower.
 Butterflies
 Moths
 Hummingbirds
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Double Fertilization
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Angiosperms produce a highly nutritious
tissue (endosperm) within their seeds.
 Male gametophyte contains two sperm.
- Second fuses to form endosperm cell
(double fertilization).
 Dicotyledons - Embryos with two seed
leaves.
 Monocotyledons - Embryos with one seed
leaf.
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Angiosperm Life Cycle
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Dicots and Monocots
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Seed Dispersal - Fruits
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Fruit - mature, ripened ovary containing
fertilized seeds, surrounded by a carpel.
 Fleshy fruits encourage predation.
- Berries - Many seeded forms on inner
carpel wall. (Grapes, Tomatoes)
- Drupes - Stony inner layer adhering to
single seed. (Peaches, Olives)
- Pomes - Fleshy portion comes from
petals and sepals. (Apples, Pears)
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Review
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Adapting to Terrestrial Life
Vascular Plants
Seedless Vascular Plants
Seed Plants
 Gymnosperms
 Angiosperms
- Flowers
 Dicots and Monocots
 Seed Dispersal
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies
Permission required for reproduction or display
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies