Plants

1
Plants

• Chapter 13

2
Setting the Stage for Plants

• Earths atmosphere was originally oxygen free
• Ultraviolet radiation bombarded the surface
• Photosynthetic cells produced oxygen and allowed
  formation of a protective ozone layer

3
The Plant Kingdom

• Nearly all are multicelled
• Vast majority are photoautotrophs
• Energy from sun
• Carbon dioxide from air
• Minerals dissolved in water

4
Nonvascular Plants

• Bryophytes
• Fewer than 19,000 species
• Three groups
• Liverworts
• Hornworts
• Mosses

5
Vascular Plants or Trachaeophytes

• Majority of plants
• Have internal tissues that carry water and
  solutes
• Two groups
• Seedless vascular plants
• Seed-bearing vascular plants

6
Adaptations to Land in vascular plants

• Root systems
• Shoot systems
• Vascular tissues
• Waxy cuticle

7
Seedless Vascular Plants

• First Tracheophytes
• Produce spores but no seeds
• Four main groups, including Ferns.

8
Seed-Bearing Vascular Plants

• Gymnosperms (no flowers) arose first
• Angiosperms (flowering plants) arose later

9
Evolutionary relationships between plants

• See separate diagram
• Bryophytes arose separately from vascular plants
• Major evolutionary advancements among vascular
  plants were
• Pollen and Seeds
• Flowers

10
All land plants reproduce in a complex process
called alternations of generations, which they
inherited from their green alga ancestors

• Haploid (n) phase alternates with diploid (2n)
  phase
• Sporophyte (2n) produces spores by meiosis.
• Spores are haploid (n)
• Spores divide by mitosis to produce gametophyte
  (n)
• Gametophyte produces gametes by mitosis (!)
• Gametes fuse to produce zygote (2n), which is
  first cell of sporophyte.

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Moss Life Cycle
Zygote grows, develops into a sporophyte while
still attached to gametophyte.
mature sporophyte
zygote
Diploid Stage
Meiosis
Fertilization
Haploid Stage
Spores germinate.
sperm-producing structure
male gametophyte
egg-producing structure
female gametophyte
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Bryophytes

• Small, nonvascular, nonwooody
• Gametophyte dominates life cycle has leaflike,
  stemlike, and rootlike parts
• Usually live in wet habitats
• Flagellated sperm require water to reach eggs

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Types of Bryophytes

• Mosses (most common)
• Liverworts (simplest)
• Hornworts

14
Peat Mosses

• 350 species
• Sphagnum is an example
• Grow in acidic bogs important ecosystems of cold
  and temperate regions
• Peat can be harvested and burned as fuel

15
Alternation of generations in flowering plants

• Pollen grains are male gametophytes which are
  transported by wind or pollinators.
• Sperm have no flagella and do not swim to egg
• Pollination transfer of pollen male part of
  flower to female part of flower on same or
  different flower or plant.

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Vocabulary to know

• The plant and its flowers are sporophytes (2n)
• Sepal
• Petals
• Stamen anther and filament
• Carpel (pistil) stigma, style, ovary, ovule
• Be able to recognize and/or sketch flower parts

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Steps in Reproduction in flowering plants

• In Ovary, in an ovule
• meiosis in a diploid (2n) cell produces 4 haploid
  spores
• Three die
• The fourth divides 3 times by mitosis to produce
  8 haploid nuclei in 7 cells. One of these cells
  is an egg cell.
• One cell contains two polar nuclei
• These 7 cells are the female gametophyte.

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Ovules

• Female reproductive structures that become seeds
• Consist of
• Female gametophyte with egg cell
• Nutrient-rich tissue
• Jacket of cell layers that will form seed coat

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Steps in Reproduction in flowering plants

• In the Anther
• Meiosis in a diploid (2n) cell forms 4 spores (n)
• Each spore divides once to form one cell with two
  haploid (n) nuclei.
• This cell develops a thick, protective wall and
  becomes know as a pollen grain
• This is the male gametophyte.

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Pollen

• Pollen grains are sperm-bearing male gametophytes
  that develop from spores
• Allows transfer of sperm to egg without water
• Can drift on air currents or be carried by
  pollinators

21
Steps in Reproduction in flowering plants

• Pollination transfers pollen grains to the stigma
• Pollen grain germinates and grows a pollen tube
  through tissue of style and down to ovule. This
  growth is directed by one of the nuclei in the
  pollen grain called the tube nucleus.
• The other nucleus in the pollen grain divides to
  form 2 sperm nuclei
• One sperm fertilizes the egg (nn2n)
• The other sperm unites with the polar nuclei to
  form a triploid endosperm nucleus (nnn3n)
• This is called double fertilization

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Steps in Reproduction in flowering plants

• The zygote divides by mitosis to form an embryo
  plant, with tiny root, stem, and leaves (see
  page340).
• The endosperm divides to form cotyledons or seed
  leaves, which contain stored food.
• When mature, the embryo and its cotyledon(s) are
  surrounded by a seed coat, and become a seed.
• A seed is a mature ovule.

23
Comparison of Moss and Flowering Plant
reproduction

• Similarities
• Meiosis produces spores
• There are sporophytes and gametophytes
• Differences
• Fertilization does not require water
• Sporophyte is large, gametophyte is only a few
  cells
• Gametophyte is dependent on the sporophyte

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Flowering Plant Life Cycle
sporophyte
Diploid
Double fertilization
Meiosis
Meiosis
Haploid
mitosis without cytoplasmic division
microspores
pollination
two sperm enter ovule
female gametophyte
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Seedless Vascular Plants

• Like bryophytes
• Live in wet, humid places
• Require water for fertilization
• Unlike bryophytes
• Sporophyte is free-living and has vascular tissues

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Ancient seedless tracheophytes

• Now extinct
• Formed dense forests before the age of the
  dinosaurs
• Many died and were converted to the fossil fuels
  we use today.
• Thus fossil fuels are the result of long-ago
  photosynthesis
• See page 343 for sketches of these ancient trees

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Living Seedless Vascular Plants

• Lycophytes (Lycophyta)
• Whisk ferns (Psilophyta)
• Horsetails (Sphenophyta)
• Ferns (Pterophyta)

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Ferns (Pterophyta)

• 12,000 species, mostly tropical
• Most common sporophyte structure
• Perennial underground stem (rhizome)
• Roots and fronds arise from rhizome
• Mature fronds divided into leaflets
• Spores form on lower surface of some fronds
• Tiny, free-living gametophyte develops from
  spores, produces gametes, but requires water for
  fertilization

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Traits of Seed-Bearing Plants

• Pollen grains
• Arise from spores
• Develop into male gametophytes
• Can be transported without water
• Seeds
• Embryo sporophyte inside nutritive tissues and a
  protective coat
• Can withstand hostile conditions

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Seed-Bearing Plants

• Pollen and seeds are both significant adaptations
  to life on land.
• Plants knows as Gymnosperms produce pollen and
  seeds without flowers

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Gymnosperms

• Plants with naked seeds
• Seeds dont form inside an ovary
• Four groups
• Conifers Ginkgos
• Cycads Gnetophytes (wont discuss)

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Conifer Characteristics

• Widest known, largest number of living species
• Woody trees or shrubs
• Most are evergreen
• Bear seeds on exposed cone scales
• Most produce woody cones

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Conifer Distribution

• Reproduce more slowly than angiosperms at
  competitive disadvantage in many habitats
• Still dominate in far north, at higher
  elevations, and in certain parts of southern
  hemisphere

34
Cycads

• Most diverse during age of dinosaurs
• Only 100 living species
• Palmlike appearance
• Pollen-bearing and seed-bearing cones on
  different plants

Do not post on Internet
Strobilus of a female cycad
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Ginkgos

• Diverse during age of dinosaurs
• One surviving species, Ginkgo biloba
• Deciduous trees are male or female

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Angiosperms

• Flowering plants
• Dominant land plants (260,000 species)
• Ovules and (after fertilization) seeds are
  enclosed in an ovary
• Two main groups monocots, and dicots

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Double Fertilization

• Distinctive feature of angiosperms
• Male gametophyte delivers two sperm to an ovule
• One fertilizes egg other fertilizes a cell that
  gives rise to endosperm

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Evolutionary Trend
Figure 23.2Page 386
zygote
SPOROPHYTE (2n)
GAMETOPHYTE (n)
GREEN ALGA
BRYOPHYTE
FERN
GYMNOSPERM
ANGIOSPERM
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Flowers/pollinators

• Some flowers resemble female insects. As the
  male attempts to mate with the flower, he
  transfers pollen
• Odor some flowers smell like rotting flesh to
  attract carrion eaters like flies, which
  pollinate them (examples, skunk cabbage and
  corpse flower). Others have sweet scents to
  attract other types of pollinators,
• Brightly colored petals attract pollinators.
• Lines on petals point to nectar.
• Flower parts designed to transfer pollen as
  insect sips nectar
• Some shapes fit their pollinators exactly.

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Fruits/seed dispersal

• Once seeds are produced, they must be dispersed
  so that they dont compete with parents!
• Roll, glide, fly, float, stick to animals fur or
  feathers (see page 351).
• Tasty fruits or seeds are eaten by animals, and
  in not digested, can be deposited in droppings
  far from the parent.