AP BIOLOGY (UNIT 10) CH. 29 & 30
Plant Diversity I & II: Ch. 29 & 30
The Colonization of Land & The Evolution of Seed Plants
Requirements for successful life on Land.
Supporting mechanism (vascular tissue and lignin).
Absorptive structures (above and below ground).
Conducting tissues (move fluids).
Anti-desiccation adaptations for body of plant (cuticle) and gametes
(sporopollenin in pollen and spores)
Airborne gamete dispersal.
General Characteristics of Plants.
• Includes mosses, ferns, conifers, flowering plants
• Multicellular, eukaryotic photosynthetic autotroph
• Chlorophyll a, b and caroteniods.
• Cellulose
• Starch
• Exhibit ALTERNATION OF GENERATIONS (Sporophyte (2n) and gametophyte (n)
generation)
• Gametes produced and protected within Gametangia (non-reproductive cells to
prevent dessication and for protection);
fertilization of egg usually takes place within
gametangia. [Female = archegonium; male =
antheridium]
• Sporophyte and gameteophyte are structurally
(look and develop) different (heteromorphic).
Both structures are multicellular, unlike
animals
• Sporophyte dominant in most species.
• Meiosis in sporophyte produces haploid
reproductive cells (spores) that can develop into
a new organism without fusing with another
cell.
• Most have stomata (except Liverworts) for gas exchange.
• Secrete cuticle to reduce desiccation.
• Most have vascular tissue for bulk transport of water and nutrients. Materials can be
exchange between adjacent cells through opening in the cell wall called
• Most have seeds (embryo with food and protective covering) for protection of
embryo.
Plant Diversity I & II (Ch 29 & 30) Introduction
1
AP BIOLOGY (UNIT 10) CH. 29 & 30
Proposed Ancestors of Plants
™ Charophyceans are the green algae most closely related to land plants.
™ Several lines of evidence support the phylogenetic connection between land plants and
green algae, especially the charophyceans, including:
¾ Homologous chloroplasts. The chloroplasts of land plants are most similar to the
plastids of green algae. Contain chlorophyll b and beta-carotene and thylakoids stacked as
grana. DNA sequences in chloroplasts similar.
¾ Homologous cell walls. Cell walls formed in similar manner with similar amounts of
cellulose.
¾ Homologous peroxisomes. Help to reduce effects of photorespiration.
¾ Phragmoplasts. Microtubles form perpendicular to cell plate and guide deposition of
cellulose to form wall.
¾ Homologous sperm. Some plants have flagellated sperm similar in structure to
charophycean sperm
¾ Molecular systematics. Similar nuclear and chloroplast genes.
¾ A layer of sporopollenin prevents exposed charophycean zygotes from drying
out until they are in water again. Sporopollenin integral for success of
terrestrial plants.
Classified into:
™ Nonvascular Plants (aka Bryophytes)
• Bryophyta: mosses
• Hepatophyta: Liverworts
™ Vascular Plants (aka
Traecheophytes)
¾ Seedless vascular plants
(Pteridophytes)
♦ Lycophyta: Lycophytes
♦ Pterophyta: Ferns and Horsetails
¾ Seeded vascular plants
ƒ Naked seeded plants
(Gymnosperms)
¾ Coniferophyta: Conifers
¾ Cycadophyta: Cycads
¾ Gnetophyta: Gnetae
¾ Ginkgophyta: Ginkgo!
ƒ Flowering plants and enclosed
seeds (Angiosperms)
¾ Anthophyta: Flowering plants
Plant Diversity I & II (Ch 29 & 30) Introduction
2
AP BIOLOGY (UNIT 10) CH. 29 & 30
Bryophytes and Seedless Vascular Plants
Nonvascular Plants
Bryophytes.
™ Gametophyte is dominant form.
™ Lack vascular tissues. Limits size (cannot grow tall). Rely on
diffusion.
™ Rhizoids are analogous to roots and used for anchorage. [Roots,
stems and leaves or vascular tissues only]
™ Male flagellated sperm produced by the gametangium,
antheridium.
™ Female egg produced by the gametangium, archegonium.
Fertilization take place within archegonium and sporophyte grows
out of archegonium.
™ Sporophyte produces haploid spores within sporangium.
™ 3 divisions:
¾ Bryophyta (mosses) e.g. Sphagnum. (aka peat moss). Burned to
provide energy
¾ Heptophyta (liverworts) sexual and asexual (through gemmae) reproduction.
¾ Anthocerophyta (hornworts)
Vascular Plants (aka Traecheophytes)
™ Key adaptations to success on land:
¾ Seeds (protect embryo and provide food for initial growth)
¾ Pollen (airborne dispersal). Sporopollenin in walls of spores.
¾ Sporophyte dominant
¾ Vascular tissues (phloem & xylem; specialization of parts of plant for specific
functions [true roots, stems and leaves])
¾ Ligninfied cell walls (supports plant in air)
Seedless vascular plants.
Division Lycophyta
• Club mosses. Many are epiphytes (grow on other plants but not parasitic).
• Sporangia produced on specialized leaves for reproduction called sporophylls.
• Most species are homosporous. Produce a single type of spore that can produce a
gametophyte with antheridia and archegonia.
Plant Diversity I & II (Ch 29 & 30) Introduction
3
AP BIOLOGY (UNIT 10) CH. 29 & 30
• Heterosporous species have sporophytes that produce separate spores. Megaspores
produce female archegonia on female gametophyte. Microspores produce male
antherdia on male gametophyte.
Division Sphenophyta.
• Horsetail (Equisetum). Only extant genus.
• Homosporous
• Silica in cell walls makes stems abrasive. (sometimes called
“scouring rush”)
• Gametophyte is free-living (can photosynthesize) and not
dependent on sporophyte for nutrients.
Division Pterophyta.
• Ferns (dominant seedless vascular plant)
• Large leaves (called fronds) are compound
with smaller leaflets. Leaves are examples of
megaphylls (leaves with branched vascular
tissues/veins).
• Homosporous.
• Sporangia develop on specialized sporophylls.
Sporangia grow in clusters on underside to for
sori.
• Flagellated sperm require
water and fertilized egg in
archegonium. Sporophyte
protected in archegonium
and emerges from ground
as Fiddlehead.
Plant Diversity I & II (Ch 29 & 30) Introduction
4
AP BIOLOGY (UNIT 10) CH. 29 & 30
Evolution of Seed Plants
PLANT DIVERSITY II (CH. 30)
Seed Plants
™ Sporophyte dominant. Recall that being diploid allows you to carry recessive
alleles from one generation to another. Eventually, these recessive alleles may be
selected for in the homo.-rec. form.
™ All heterosporous
¾ Megasporangia (nucellus; is solid and fleshy and part of the ovule that is located
in the ovary of a flower) produce megaspores (egg cells and others) that produce
female gametophyte. The female gametophyte consists of a group of cells called
the embryo sac.
¾ Microsporangia (pollen sacs of an anther) contain cells called microsporocytes
(2n) that produce microspores (n) that produce male gametophyte.
[ Microspores develop into pollen grains when they divide by mitosis and are
covered with cell wall (
). Pollen grains will germinate
and form male gametophyte.
™ Embryo (multicellular sporophyte that will grow into new plant) encased in
protective seed coat (derived from outer structure called integuments) and 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; their gametophytes or embryos
do not require as much water for support.
Seeded Vascular Plants
The 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 lumber source.
♦ About 900 species.
Plant Diversity I & II (Ch 29 & 30) Introduction
5
AP BIOLOGY (UNIT 10) CH. 29 & 30
Division: Ginkgophyta: Ginkgo! (As you should know, my favorite tree!)
‰ Single extant species (Ginkgo biloba); (aka. Maidenhair tree).
‰ Used in Chinese herbal medicines. Grows wild in China. Today thought to play role
in cure for Alzheimer’s, memory loss, increased circulation.
‰ Dioecious (“two houses”, producing pollen and seeds on separate trees. Male tree
produces small, inconspicuous pollen cone. Female seed covered by fleshy coat (it’s
not a fruit though) that, when rotting, gives off butyric acid.
Division: Cycadophyta: Cycads
‰ Approximately 100 species. Some threatened by habitat loss.
‰ Palm-like appearance (Sago palm)
‰ Beetles and bees may be used for pollination. Plant can generate heat and odors to
attract animals.
‰ Seeds of cycads are quite large, and are often brightly colored; red, purple, and
yellow seeds are common.
‰ Cycad plants are dioecious (i.e. male and female reproductive structures are borne on separate plants)
‰ Roots possess coralloid roots (coral-like in appearance) containing nitrogen fixing
cyanobacteria. [mutualism]
‰ Large, slow growing. Used in landscaping locally.
Division: Gnetophyta
‰ one species in US (Ephedra/Mormon tea)
‰ Gnetum and Welwitschia other genera
‰ Found in southwest US, South America, Africa.
Division: Coniferophyta. (Pine, Larch, Yew, Juniper, Cedar, Fir, Hemlock, Spruce.
‰ “Conifer”- cone-bearer. Often called evergreens since they retain their needle-shaped
leaves. Most confirs have woody cones; yews and junipers have fleshy, berry-like
tissues (called aril) instead.
‰ Oldest living organisms (Bristle-cone pine), tallest organisms (Coast Redwood)
‰ Needles have thick cuticle, sunken stomata, mesophyll w/o air spaces and veins only
in center of leaf. Why is this valuable….?
‰ Male and female cones (actually sporophyte tissue) appear on same tree (monoecious“one-house”).
• Male cone (staminate or pollen cone) produces microspores that develop into male
gametophytes. Each cone is made up of a number of small sporophylls (scales).
Microsporangia contain microsporocytes that undergo meiosis to produce haploid
microspores (each microspore divides a number times to form a viable pollen grain
(immature male gametophyte).
Plant Diversity I & II (Ch 29 & 30) Introduction
6
AP BIOLOGY (UNIT 10) CH. 29 & 30
‰
‰
• Female cones (ovulate 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
Tracheids (xylem) transport water and are larger in summer than in winter. Tracheids
have pits at ends to facilitate water movement up tissue. Have secondary cell walls.
Economically important for wood, pulp, turpentine, resins and ornamentals.
Life-Cycle of a Conifer. (Diagram)
The Angiosperms “vessel seed”
Division: Anthophyta.
: Flowering plants. Reproductive structure of angiosperms. A cluster of highlyspecialized leaves which participate in reproduction
: Diversity of species is partially attributed to coevolution of plants with animal
pollinators. (specific pollinators, edible fruits)
: Nearly all of our food comes from flowering plants; grains, beans, nuts, fruits,
vegetables, herbs and spices almost all come from plants with flowers, as do tea,
coffee, chocolate, wine, beer, tequila, and cola.
: Two classes:
ƒ Monocotyledones (monocots) e.g. lily, orchid, grass, palm, yucca and grains
(corn, oats, rice, rye, wheat)
ƒ Dicotyledones (dicots) e.g. sunflower,
bean, snapdragon, carrot, rose
: Have vessel elements (xylem) for water
transport instead of tracheids. Vessel
elements have perforated or absent end
plates to speed transport. Reinforced with
fiber cells. Both tracheids and vessel
elements are dead cells.
: Heterosporous.
: Gametophyte is greatly reduced. 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. Other sperm nucleus
fuses with polar nuclei in center to form a 3n endosperm. Two fertilizations take
place Î Double Fertilization.
: 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.
Plant Diversity I & II (Ch 29 & 30) Introduction
7
AP BIOLOGY (UNIT 10) CH. 29 & 30
Life-Cycle of an Angiosperm. (Diagram)
Plant Diversity I & II (Ch 29 & 30) Introduction
8