The many divisions of plants can be grouped into three main groups:

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• The many divisions of plants can be grouped into
  three main groups
• Nonvascular plants
• Seedless vascular plants
• Vascular plants with seeds
• Plants are adapted to living on land where light
  is more available and carbon dioxide diffuses
  freely.

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Common plants today
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Life Cycle of Plants

• Plants have a two-generation life cycle called
  alternation of generations.
• The sporophyte (2n) produces haploid spores and
  the spores develop into a gametophyte that
  produces the gametes.
• When the sperm fertilizes the egg, the zygote
  develops into a sporophyte.
• Some plants have a dominant gametophyte (haploid
  generation) and others have a dominant sporophyte
  (diploid generation).

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Nonvascular plant life cycle
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Seedless vascular plant life cycle
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• Seed plants are well adapted to reproduction n
  land.
• They produce heterospores microspores and
  megaspores.
• A microspore develops into a pollen grain.
• The megaspore develops into an egg-producing
  gametophyte within an ovule.
• The ovule becomes a seed enclosing the embryonic
  sporophyte.

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Seed plant life cycle
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Liverworts

• The liverwort Marchantia has a flattened, lobed
  body known as thallus.
• Rhizoids (rootlike hairs) project from the lower
  surface into the soil.
• Marchantia reproduces asexually by forming
  gemmae, groups of cells in gemmae cups on the
  upper surface of thallus.
• In sexual reproduction, umbrella-like
  gametophores produce gametes.

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Liverwort, Marchantia
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Mosses

• In the moss life cycle, antheridia produce
  swimming sperm that use external water to reach
  the eggs in the archegonia.
• Following fertilization, the dependent moss
  sporophyte consists of a foot, stalk, and a
  capsule or sporangium within which windblown
  spores are produced by meiosis.
• Each spore germinates to produce a gametophyte.

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• The gametophyte of mosses has two stages.
• First, there is the alga-like protonema, a
  branching filament of cells.
• Next, upright leafy shoots are seen at intervals
  along the protonema.
• Rhizoids anchor the shoots, which bear the
  antheridia and archegonia.

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Moss life cycle
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Adaptations and Uses of Nonvascular Plants

• Mosses are usually found in moist habitats
  because the sperm are flagellated.
• However, mosses can live in shady cracks of hot,
  exposed rocks.
• Sphagnum is bog or peat moss that is used to hold
  water in garden soil.
• Dried peat is sometimes used as fuel.

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Ferns and Their Allies

• Whisk ferns, club mosses, horsetails, and ferns
  are the seedless vascular plants that were
  prominent in swamp forests during the
  Carboniferous period.
• Their incomplete decomposition formed much of the
  coal we burn today.
• When the spores of these plants germinate, the
  larger gametophyte is independent of the
  sporophyte for nutrition.

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The Carboniferous period
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• Whisk Ferns
• Whisk ferns (psilotophytes) are represented by
  Psilotum in which an erect stem that forks
  repeatedly is attached to a rhizome.
• There are no leaves and sporangia are located at
  the ends of short branches that photosynthesize.
• It closely resembles a primitive vascular plant
  (rhyniophyte) known only from the fossil record.
• The independent gametophyte produces the gametes,
  and sperm are flagellated.

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Whisk fern, Psilotum
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• Club Mosses
• In club mosses, a branching rhizome sends up
  aerial stems less than 30 cm tall.
• The sporangia are formed on terminal clusters of
  leaves called stroboli that are club-shaped.
• These plants are common in moist temperate
  woodlands, but the majority live in the tropics
  where many of them are epiphytes.

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Club moss, Lycopodium
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• Horsetails
• Rhizomes of horsetails produce aerial stems about
  1.3 meters tall.
• Whorls of side branches give the appearance of a
  green horses tail.
• Some have stroboli on regular stems some have
  special stems for stroboli.
• Silica in cell walls provide an abrasive grit
  that made horsetails useful as an abrasive
  cleanser.

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Horsetail, Equisetum
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• Ferns
• Ferns have very large fronds (leaves) that grow
  from a rhizome ferns have vascular tissue and
  have true roots, stems and leaves.
• Sporangia are within sori on the underside of the
  leaflets of a frond meiosis occurs within a
  sporangium, producing spores.
• A windblown spore develops into a separate
  gametophyte, a heart-shaped prothallus, that
  bears both egg-producing archegonia and
  sperm-producing antheridia.

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• When a flagellated sperm fertilizes an egg, the
  zygote develops into a young sporophyte.
• Although ferns are likely to be found in moist
  habitats due to flagellated sperm, vegetative
  (asexual) reproduction is used to disperse ferns
  in dry habitats.
• Ferns are used to decorate bouquets and as
  ornamental plants in homes and gardens.
• Wood from tropical tree ferns is used as a
  building material, and fiddleheads are sometimes
  eaten as a delicacy.

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Fern diversity
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Fern life cycle
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Gymnosperms

• This group includes cycads, the ginkgo, and
  conifers.
• Cycads are palm-like, tropical and subtropical
  plants that flourished during the era of
  dinosaurs.
• The single species of ginkgo is planted in parks
  because it does well in polluted areas.
• Conifers are the largest group of gymnosperms and
  include cone-bearing pine, spruce, fir, and
  redwood trees.

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Gymnosperm diversity
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• Life Cycle of a Conifer
• The gymnosperm microspore develops into a pollen
  grain this microgametophyte develops in a pollen
  cone.
• The megagametophyte develops within an ovule
  located on the scale of a seed cone.
• Following wind pollination and fertilization that
  do not require external water, the ovule becomes
  a winged seed that is dispersed by wind.

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Pine life cycle
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• Adaptation and Uses of Conifers
• Conifers supply much of the wood used for
  construction of buildings and production of
  paper.
• Many valuable chemicals are extracted from resin,
  a substance that protects conifers from fungi and
  insects.
• The oldest trees in the world, at 4,500 years
  old, are bristlecone pines in Nevada.

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Angiosperms

• Angiosperms are flowering plants and include
  tropical and subtropical deciduous trees.
• All hardwood trees are angiosperms.
• Angiosperms are the source of clothing, food,
  medicines, and many other products used by
  humans.
• Angiosperms are divided into monoots (such as the
  grass family) and dicots (such as the maple and
  rose families).

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• Life Cycle of Angiosperms
• Like conifers, angiosperms produce heterospores,
  except angiosperms do so within their flowers.
• Microspores develop into pollen grains within the
  pollen sacs of the anther.
• The megaspore develops into an embryo sac within
  an ovule.
• Pollen is windblown or carried by bees (or other
  animals) to the pistil.

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• Double fertilization occurs where one sperm joins
  with the egg to produce a zygote, and a second
  sperm joins with the polar nuclei to produce
  triploid (3n) endosperm, which becomes stored
  food.
• The ovule develops into a seed consisting of a
  seed coat, stored food, and an embryo, but the
  ovary and adjacent parts of the flower develop
  into a fruit.
• Fruits aid in seed dispersal.

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Flowering plant life cycle
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• The Flower
• The flower accounts for the success of
  angiosperms.
• The flower both attracts animals that aid in
  pollination and produces seeds enclosed by fruits
  that aid dispersal.
• Sepals form a whorl around the colored petals.

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• The reproductive parts of a flower are the pistil
  and the stamens.
• A stamen consists of a filament and anther with
  two pollen sacs.
• The pistil consists of a stigma, style, and ovary.

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Generalized flower
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• Nonvascular plants are low-growing and lack a
  means of water transport and internal support,
  whereas vascular plants have a system that
  transports water and also provides internal
  support.
• In nonseed plants, spores disperse the species
  in seed plants, seeds disperse the species.
• In seed plants, a germinating pollen grain
  transports sperm to the egg.
• Angiosperms and gymnosperms have unique
  adaptations.