PLANT DIVERSITY

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CHAPTER 19

• PLANT DIVERSITY

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Overview of Plants

• Plants are multicellular, autotrophic, eukaryotes
  which are almost exclusively terrestrial.
• They evolved from green algae
• share the same types of chlorophyll - a b
• both store food as starch
• same accessory pigments like carotene
• cell walls of cellulose

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Adapting to the Land
Before plants were able to live in terrestrial
habitats, they needed ways to

• 1. Absorb water and minerals
• developed roots to absorb water
• later, mutualistic associations like mycorrhizae
  to help with minerals

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Adapting to the Land

• Conserve water
• first land plants could only live in moist areas
• Later, they developed
• cuticle-impermeable to water
• stomata -openings to exchange gases
• guard cells - to regulate water loss through
  stomata

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Adapting to the Land

• Reproduce on land
• replaced need for sperm to swim to egg
• in drier habitats - other means of transport
  needed
• developed ways to move reproductive cells,
  through air using wind and animals (usually
  insects)
• developed spores and seeds to protect
  reproductive structures from drying out
• spore contains a haploid reproductive cell
  surrounded by a hard outer wall
• seed embryo surrounded by a protective coat
• endosperm (also contained by some seeds) a tissue
  that provides nourishment for the developing
  plant

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Adapting to the Land

• Transport materials
• developed vascular tissue that act as pipelines
  for carrying water from roots to leaves and for
  moving carbohydrates from leaves to all tissues
• two types of specialized vascular tissue
• xylem carries water and inorganic nutrients,
  usually from roots to stems and leaves
• phloem carries organic compounds, such as
  carbohydrates, in any direction, depending upon
  the plants needs

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Evolutionary History of Plant Groups
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Classifying Plants

• Twelve living plant phyla are divided into two
  groups based on the presence of vascular tissue
• Nonvascular plants (3 of 12 living phyla)
• either have no vascular tissues or very simple
  ones
• have no true roots, leaves or stems
• Vascular plants (9/12 phyla)
• have well-developed vascular tissue
• also have true roots, leaves, stems

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Plant Diversity
Vascular
Cone-bearing plants760 species
Floweringplants235,000 species
Ferns andtheir relatives11,000 species
Mosses andtheir relatives15,600 species
Nonvascular
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Alternating Life Cycles

• All plants exhibit a life cycle, known as
  alternation of generations, that involves two
  phases
• Gametophyte phase - a haploid plant that
  produces gametes
• Sporophyte phase - a diploid plant that produces
  spores
• A major difference between vascular and
  nonvascular plants is the dominant part of their
  life cycle.

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Generalized Plant Life Cycle
MITOSIS
ZYGOTE
MITOSIS
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Alternating Life Cycles

• Lower plants have a dominant gametophyte but as
  plants became more complex, the sporophyte
  generation predominates.
• In the most advanced plants, the gametophyte
  grows within the tissues of the sporophyte.

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Nonvascular Plants

• The three phyla of nonvascular plants are
  collectively called bryophytes
• most primitive plants
• lack a vascular system (?lack roots, stems and
  leaves)
• rhizoids - anchor plant absorb water
• transport all materials by osmosis and diffusion
• seedless and produce spores (asexual)
• need water for sexual reproduction sperm swims
  to egg
• small plant body (lt8 tall)

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Moss Life Cycle
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Nonvascular Plants - Bryophytes

• Types
• mosses, liverworts and hornworts
• Mosses are pioneer plants because they are
  often first to inhabit barren area
• Mosses are economically important - as Sphagnum
  moss - a.k.a. peat moss
• grows in bogs - can be dried and used as fuel
• used in gardening - superb water holding
• capacity

Moss
Liverwort
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Vascular Plants - Tracheophytes

• Vascular plants evolved 430 M yrs ago
• They can grow larger and live in more
  environments than nonvascular plants
• All vascular plants have
• dominant sporophyte generation
• specialized conducting tissue -
• phloem - soft walled conduct carbohydrates ?
• xylem - hard walled conduct water ?

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Seedless Vascular Plants

• The first vascular plants were seedless and
  required a film of water for fertilization
  because the sperm must swim to the egg.
• Spores are the mobile sexual reproductive part of
  all seedless plants.
• Examples
• ferns
• horsetails - scouring rushes - hollow silica
  stems
• whisk ferns - stems only
• club mosses - ground pine and resurrection
  plant

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Ferns

• Ferns are the most abundant and common seedless
  vascular plants.
• gametophyte reduced (less than 1 cm across)
• sporophyte is conspicuous
• drought resistant spores
• rhizomes - horizontal stems
• leaves - are fronds, fiddleheads

Fern spores
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Life Cycle of Fern
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Vascular Seed Plants

• A major advancement in the evolution of plants
  was the seed.
• It allowed plants to reproduce without the need
  for water for fertilization.
• Inside the tough outer coat of the seed is an
  embryo and nutrient supply.
• When conditions are unfavorable, the seed remains
  inactive.
• When conditions favor growth, the seed
  germinates a seedling sprouts.

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Types of Seed Plants

• The first seed-bearing plants were gymnosperms,
  which produce seeds that develop in cones
  (compose four of the five living phyla of seed
  plants)
• The fifth phylum of seed plants are the
  angiosperms, flowering plants, which produce
  seeds that develop within fruits.

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Gymnosperms

• Most living gymnosperms
• produce seeds in cones - conifers
• have needle-like leaves to reduce water loss
• have seeds that protect the embryo
• use wind pollination
• exhibit secondary growth
• growth in width of stem

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Gymnosperms

• Produce two types of cones - male and female
• large woody cones produce ovules
• smaller, softer cones produce pollen
• huge amounts of pollen because the wind is
  unpredictable

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Gymnosperms
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Gymnosperms

• Three other types of gymnosperms (conifers )
• cycads - sago palms
• ginkgoes - fan shaped leathery leaves
• a strange desert plant, Welwitschia

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Angiosperms

• Angiosperms are the most successful plants,
  comprising 90 of all living plant species.

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Angiosperms

• Adaptations that allowed success
• Flowers - reproductive structures that attract
  animal pollinators (more dependable than wind!)
• Fruits protect the seed and aid in dispersal
• Many angiosperms can go through entire life cycle
  (seed ?plant?new seeds) in one growing season
• More diverse ?can occupy more niches than
  gymnosperms

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Monocots and Dicots

• Flowering plants are divided into two classes
  monocots and dicots.
• The primary difference between these two groups
  is the number of cotyledons or seed leaves which
  store food reserves in the plant embryo.
• Monocots differ from dicots in several other ways.

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Comparing Monocots and Dicots
Dicots
Two cotyledons
Branched veins
Floral parts often in multiplesof 4 or 5
Vascularbundlesarranged ina ring
Taproot