Chapter 30
Plant Diversity II:
Evolution of Seed Plants
AP Biology
Seed Plants
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Sporophyte dominant
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Being diploid allows carrying recessive alleles from one
generation to the other
Eventually, these recessive alleles may be selected for
All heterosporous
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Megasporangia
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Nucellus; is solid & fleshy part of the ovule located in the ovary of
the flower
Produces megaspores (egg cells) that produce female gametophyte
Female gametophyte consists of a group of cells called the embryo
sac
Microsporangia
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Polen sacs of an anther
Contain microsporocytes (2n) that produce microspores (n) that
produce the male gametophyte
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Microspores develop into pollen grains when they divide by mitosis
and are covered with cell wall sporopollenin
Pollen grains will germinate and form male gametophyte
Seed Plants, cont.
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Embryo – multicellular sporophyte that will grow
into new plant
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Encased in protective seed coat (derived from outer
structure called integuments)
Supplied with its own source of food (endosperm or
cotyledons)
Seeds allow embryo to be moved away from parent
through wind, water, and animals
Truly land plants – not tied to water for pollination;
gametophytes or embryos do not require as much
water for support
Integument
Female
gametophyte (n)
Seed coat
(derived from
integument)
Spore wall
Egg nucleus (n)
Megasporangium
(2n)
Megaspore (n)
Unfertilized ovule
Male gametophyte
(within germinating
pollen grain) (n)
Micropyle
Fertilized ovule
Discharged
sperm nucleus (n)
Pollen grain (n)
Food supply
(female
gametophyte
tissue) (n)
Embryo (2n)
(new sporophyte)
Gymnosperm seed
Seeded Vascular Plants
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Gymnosperms – “naked
seed”
Lack enclosed chambers
(ovaries) in which seeds
develop
Seeds form naked on
surface of modified leaf
(called a scale)
Economically important
as a lumber source
About 900 species
Division: Ginkgophya (Ginkgo)
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Single extant species – Ginkgo biloba
Used in Chinese herbal medicines
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Grows wild in China
May play a role in a cure for
Alzheimer’s, memory loss, increased
circulation
Dioescious (“two houses”) – produces
pollen and seeds on separate trees
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Male and female trees
Male tree creates small pollen cone
Female seed covered by fleshy coat (not
a fruit) that smells BAD when rotting
Division: Cycadophyta
(Cycads)
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Approximately 100 species;
some threatened by habitat
loss
Palm-like appearance (ex:
Sago palm)
Beetles and bees used for
pollination – plant generates
heat and odors to attract them
Seeds are quite large, often
brightly colored (red, purple,
or yellow)
Roots possess coralloid roots
(coral-like in appearance);
contain nitrogen fixing
bacteria
Large, slow growing
Seeds of Puerto Rican cycad, Zamia portoricensis
Division: Gnetophyta
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One species in US
(Ephedra)
Gnetum and
Welwitschia other
genera
Found in southwest US,
South America, Africa
Division: Coniferophyta (Conifer)
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Cone bearers – often called
evergreens since they retain
their needle-shaped leaves
Most have woody cones;
yews and junipers have
fleshy, berry-like tissues
(called aril)
Oldest living organisms
(Bristle-cone pine)
Tallest organisms (Coast
Redwood)
Division: Coniferophyta (Conifer), cont.
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Needles have thick cuticle, sunken stomata,
mesophyll without air spaces and veins only in center
of the leaf (why might this be valuable?)
Tracheids (xylem) transport water
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Larger in summer than in winter
Have pits at ends to facilitate water movement up tissue
Have secondary cell walls
Economically important for wood, pulp, turpentine,
resins, and ornamentals
Monoecious (“one house”) – male and female cones
(actually sporophyte tissue) appear on same tree
Division: Coniferophyta (Conifer)
Male Cones
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Male cone (staminate or pollen cone)
produces microspores that develop into male
gametophytes
Each cone made up of a number of small
sporophylls (scales)
Microsporangia contain microsporocytes
that undergo meiosis to produce haploid
microspores
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Each microspore divides a number of times
to form a viable pollen grain (immature male
gametophyte)
Division: Coniferophyta (Conifer)
Female Cones
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Female cones (ovule or seed cones)
produce megaspores that develop into
female gametophytes
The megasporangium and the outer
integuments form the ovule
Megasporocyte divides meiotically to
form 4 haploid megaspores (only one
develops into female gametophyte –
other degenerate)
Within gametophyte tissue, archegonia
are formed, containing egg cell
Conifer Life Cycle
Angiosperms – “Vessel Seed”
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Division: Anthophyta
Flowering plants
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Reproductive structure of angiosperms – a cluster of
highly-specialized leaves which participate in reproduction
Diversity of species – partially attributed to
coevolution of plants with animal pollinators (specific
pollinators = edible fruits)
Nearly all our food comes from flowering plants
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Grains, beans, nuts, fruits, vegetables, herbs, spices, tea,
coffee, chocolate, wine, beer, cola
Division Anthophyta, cont.
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Two classes:
Monocotyledones (monocots)
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Ex: lily, orchid, grass, palm, yucca and grains such as
corn, oats, rice, rye, and wheat
Dicotyledones (dicots)
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Ex: sunflower, bean, snapdragon, carrot, rose
Division Anthophyta, cont.
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Have vessel elements (xylem) for water
transport instead of tracheids
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Vessel elements have perforated or absent end
plates to speed transport
Reinforced with fiber cells
Both tracheids and vessel elements are dead cells
Heterosporous
Division Anthophyta, cont.
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Gametophyte greatly reduced
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Male gametophytes (pollen) have
only two nuclei – tube nucleus and
generative nucleus
Female gametophyte is reduced to
only 7 cells and 8 nuclei
Sperm and egg nuclei fuse to
form 2n zygote that forms
embryo
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Other sperm nucleus fuses with
polar nuclei in center to form a 3n
endosperm
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Two fertilizations take place 
double fertilization
Double Fertilization
Division Anthophyta, cont.
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After fertilization, the
ovule (female
gametophyte) develops
into a seed
The endosperm is either
retained in the seed or
absorbed by developing
cotyledons
As the seed develops,
the ovary begins to
mature around the seed
to form fruit
Angiosperm Flower Anatomy
Angiosperm Life Cycle