Plant Evolution & Diversity – Ch. 22-25
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Transcript of Plant Evolution & Diversity – Ch. 22-25
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Plant Evolution & Plant Evolution & Diversity – Ch. 22-25Diversity – Ch. 22-25
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Kingdom Protista: Algae & Protozoa
• Organisms in this Kingdom don’t fit clearly into what we call plant, animal, or fungi.
• Most diverse eukaryotic Kingdom (>60,000 species). • We are interested in this Kingdom because of the
Chlorophytes & Charophyceans - green algae.
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The line between Kingdom Protista and Kingdom Plantae is still being discussed……
Fig 29.4
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Origin of Plants
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Characteristics of Green Algae - Chlorophytes
• There are unicellular and multicellular forms• Can live symbiotically with fungi as lichens
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Fig 28.30
Volvox - freshwater
Caulerpa - intertidal
Ulva – sea lettuce
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Characteristics of Green Algae - Charophyceans• fresh water ponds• They are considered to be the closest ancestors of true
plants. Evidence:1. .
2. .
3. .
4. Both form a cell plate during cell division5. Genetic evidence – charophyceans share a greater %
of similar DNA with true plants than any other algae
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Plants
• So how are they different from Charophyceans??
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What challenges did plants face when they “moved” onto land?
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Adaptation to life on Land:
1. .
2. .
3. .
4. Multicellular gametangia5. Multicellular, dependent embryos
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1. Apical Meristems –
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2. Alternation of Generations
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• 2 multicellular life stages:1. Sporophyte:
• Diploid• Divides by meiosis to form spores• Spores – haploid cells that can grow into a
new, multicellular, haploid organism (the gametophyte) without fusing to another cell.
2. Gametophyte: • Haploid• Divides by mitosis to form the gametes (egg
and sperm)• Egg & sperm fuse to form the diploid zygote,
which divides by mitosis to form the sporophyte
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3. Walled spores produced in sporangia
• Sporopollenin protects the spore from harsh environmental conditions
• Sporangia =
• Sporocytes = the diploid cells within the sporangia that divide by meiosis to form the haploid spores
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sporocytes
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4. Multicellular gametangia• Gametangia =
• 2 types of gametangia:1. Archegonia – 2. Antheridia –
• Sperm travel to the egg, fertilizing it within the archegonia.
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5. Multicelluar, dependent embryos
• Zygote divides by mitosis to become the sporophyte.
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Other examples of adaptations to life on land: (not all plants have the following):
1. Cuticle –
2. Secondary compounds –
3. Roots –
4. Shoots - stems and leaves to make food. 5. Stomata – openings in the leaf surface to allow gas exchange for
photosynthesis and to regulate water loss.
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More Adaptations
4. .
5. A vascular system that transports food & water from roots to shoots and vice versa.
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Fig 29.7
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Nonvascular Land Plants: Bryophytes
• Earliest land plants• 3 Phyla:
1. Hepatophyta – 2. Anthocerophyta – 3. Bryophyta -
• .
• Peat moss (sphagnum): doesn’t decay rapidly, stores 400 bil tons of carbon
• Gametophyte is the dominant generation:
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Fig 29.8
Moss life cycle
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Phylum Hepatophyta – liverworts
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Phylum Anthocerophyta – hornworts
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Phylum bryophyta - mosses
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Peat bogs – sphagnum
moss
Fig 29.10
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Vascular Plants
• Vascular tissue:– Xylem = water & mineral transport– Phloem = food (carbohydrates) transport
• .
• Sporophytes branched, independent of gametophyte parent
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Seedless Vascular Land Plants
-Egg & sperm need moist environment to fertilize (similar to bryophytes)
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Two phyla of seedless vascular plants:
1. Phylum Lycophyta (Club Mosses)
- flammable spore clouds- were tree-like in the Carboniferous period
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Phylum Lycophyta: clubmosses, spikemosses, quillwarts
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2. Phylum Pterophyta
a) Whisk ferns –
b) Horsetails –
c) Ferns – produce clusters (sori) of sporangia on underside of leaves (fronds)
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Phylum Pterophyta: ferns, horsetails, whisk ferns
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Fig 29.12 Life cycle of a fern
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Forests of the Carboniferous period (290-360 mil years ago):
• Heat + pressure + time ----> coal• Pulled lots of CO2 out of atmosphere, cooling the earth &
forming glaciers• Larger species died out when climate became drier
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Terrestrial Adaptations of Seed Plants1. Seeds replace spores as main means of dispersal.
• Why?
2. Gametophytes became reduced and retained within reproductive tissue of the sporophyte
3. Heterospory –
4. Zygote develops into an embryo packaged with a food supply within a protective seed coat.
5. Pollen & Pollination - freed plants from the requirement of water for fertilization.
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1. Seeds replace spores as main means of dispersal.• old way (ferns & mosses) =
• new way: the sporophyte RETAINS its spores within the sporangia & the tiny gametophyte develops within the spore.
• ovule =
• after fertilization, the ovule becomes the seed• seed = sporophyte embryo + food supply (mature ovule
tissues)
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2. Reduction of the gametophyte:
Similar to Fig 30.2
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3. Heterospory – separate male & female gametophytes
• Old way: sporangia spores bisexual gametophyte (antheridia sperm, archegonia -> eggs)
• New way:
• Microsporangia microspores male gametophyte sperm
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4. Ovules and seed production
• Megasporangia protected by layers of tissue called integuments.
• Ovule =
• After fertilization, embryo develops, ovule becomes a seed
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Fig 30.3
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5. Pollen & Pollination
• Microsporangia microspores male gametophyte sperm
• Pollen =• Pollination =
• Pollen tube brings sperm to egg within the ovule
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Two types of seed plants:
1. Gymnosperms •Evolved first•“naked seed” –
• 2. Angiosperms
•Evolved from gymnosperms: Sporophylls rolled together to form ovaries.
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Gymnosperms
• Four phyla:1. Ginkophyta – 2. Cycadophyta – 3. Gnetophyta – 4. Coniferophyta –
Dominate forests of the N. hemisphere Most are evergreen Needle-shaped leaves to reduce water loss
during drought
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Phylum Cycadophyta
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Phylum Ginkophyta
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Phylum Gnetophyta
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Phylum Coniferophyta
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Fig 30.6
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Angiosperms
• One phylum: Anthophyta
• Formerly only 2 classes: monocots & dicots. Now 4 clades (evolutionary lines):
1. Basal angiosperms2. Magnoliads3. Monocots4. Eudicots
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Evolutionary success of Angiosperms due to:
1. .
2. Flowers – attract pollinators3. Fruits – many forms for variety of dispersal
mechanisms
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Fig 30.3
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Notice the triploid stage!•Each pollen grain (male gametophyte) produces two sperm•Sperm travel down the pollen tube & into the ovule.•Double fertilization –
•Ovule matures into the seed – contains sporophyte embryo & endosperm (food).•Ovary (female sporangium tissues) matures into the fruit.
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Kingdom Fungi (A tiny bit of Ch. 21)
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But Fungi:
• their bodies are filamentous
• the organization of large structures such as mushrooms and morels is completely different from plants, • they are heterotrophs (aquire nutrients by absorption)• Hence the boot!!
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Ecological Roles of Fungi:
1. Decomposers –
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Ecological Roles of Fungi:
2. Parasites – absorb nutrients from living hosts.
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Ecological Roles of Fungi:
3. Mutualists with plants –
. ex. mycorrhizae
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•Lichens: symbiotic association of cyanobacteria or green algae and fungi.
–Lichens are very sensitive to air pollution; used as indicators of air quality.
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Lifestyles of Fungi, continued
• Mycorrhizae: mutualistic association of plant roots and fungi.
– Fungus receives food from the root exudates.
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