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Ch. 30 Plant Diversity II

The Evolution of Seed plants

ancient squash seed

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Essential Question:

How did the emergence of seed plants change the course of evolution?

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Common traits of all seed plants

1. gametophyte reduction in size

2. heterospory

3. Ovules and production of eggs

4. Pollen and production of sperm

5. Seeds

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Common traits of all seed plants:

1. reduced gametophytes ­ can be microscopic

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advantages of reduced gametophyte

a. protection of female gametophytes from environmental changes

b. help prevent drought

c. protect from UV radiation

d.can obtain nutrients from sporophytes

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2. Heterospory

• each megasporangia produces 1 megaspore (spore from a heterosporous plant species that develops into a female gametophyte)

• each microsporangia produces many microspores (a spore from a hetersporous plant species that develops into a male gametophyte)

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3. Ovules and production of eggslayers of integument enclose megasporegymnosperms ­ 1 integumentangiosperms ­ two integumentswhole structure = ovule

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4. Pollen and production of sperm• microspores become pollen grains (male gametophytes)• protected by sporopollenin (tough coat polymer)• carried by wind, animals for pollination• Purpose: reproduction over long distances• advantages: long distance, no motility needed

yellow iris pollen

http://www.microscopy­uk.org.uk/mag/indexmag.html?http://www.microscopy­uk.org.uk/mag/artjul99/pollen.html

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5. Evolution of seeds

Advantages:• multicellular layer of tissue (seed coat) ­ extra protection for embryo ­can resist harsh conditions

• Supply of food within ­ can remain dormant for years

• disperse widely

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Gymnosperms = plants that have naked seedsnot enclosed in ovaries

evolution of gymnosperms360 million years ago, became extinctCarboniferous period started, then Permian period (more dry

so favored gymnosperms)­needle shaped leaves, thick cuticles helped with water conservation

dominate the Mesozoic Era

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Phylum Cycadophyta

http://www.ucmp.berkeley.edu/seedplants/cycadophyta/cycads.html

Have large cones and palmlike leaves

most prevalent duringMesozoic era

~130 species today

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Phylum Ginkophyta

Ginkgo biloba

fanlike leaves that turn gold in autumn

ornamental tree

seeds smell rancid when decay

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Phylum Gnetophyta

Welwitschia ­ SW Africa

Gnetum subtropical Africa/Asia

some tropical and desert species

3 genera

Ephedra Desert shrubsproduce ephedrine (decongestant)

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Phylum Coniferophyta

SequoiaDouglas Fir

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Largest of gymnosperm phyla

600 species

most are evergreens

bristlecone pineoldest living tree4,600 years old

Pacific yew ­ source of taxolovarian cancer drug

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Life Cycleof a pine

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male pollen cone

female cones

http://oregonstate.edu/trees/con/spp/big/lppbg064.GIF

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Angiosperms ­ Flowering plants

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Angiosperms ­ are seed plants that produce reproductive structures called flowers or fruits

Evolution140 million years ago ­ late Mesozoic

hypothesis of carpel from early reproductive leaf

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flower ­ specialized for sexual reproduction

sepals ­ enclose flower before it opens

petals ­ aid to attract pollinators

stamen ­ produce microsporesthat develop pollen grains

carpels ­ make megaspores which make female gametophytes

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Fruits= mature ovary

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Types of fruit:

fleshy = wall of ovary is soft during ripeningEx. oranges, plums, grapes

Dry fruits = wall is hard during ripeningEx. beans nuts, grains

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fleshy fruit

dry fruit

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Pollinator relationships

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adaptations for dispersal:

• parachutes/propellers ­ dandelions, maples

• water dispersal ­ coconuts

• barbs ­ so animals carry them

• animals eating ­ seeds come out in feces

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Life cycle of angiosperm

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double fertilization

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Angiosperm Diversity

Monocots ­ species with on cotyledon

Eudicots ­ species with two cotyledons

Basal Angiosperms ­ three lineages, formerly grouped with dicots; oldest lineages

Magnoliids ­ evolved later; more closely related to eudicots and monocots

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Basal Angiosperms

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magnoliids

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Monocots Dicots

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Monocots Dicots

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Monocots

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Dicots

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Products from seed plants for Humans

1. food

2. tea, coffee

3. spices (ex. cloves, saffron, vanilla, black pepper)

4. sources of wood

5. medicinesex. atropine (pupil dilator) ­ belladonna plant menthol (cough medicines)­ eucalyptus tree

morphine (pain reliver) ­ Opium poppydigitalin (heart medication) ­ Fox glove

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How did the emergence of seed plants change the course of evolution?

39Feb 25­8:48 AM