Download Plant Diversity II

PLANT DIVERSITY II
Chapter 30
FERTILIZATION OF SEED PLANTS VIA POLLEN

Microspore develop into pollen grains, the male
gametophyte covered by sporopollenin
Carried by wind or animals
 Pollination when pollen reaches ovule part of plant


Pollen grain germinates and produces a pollen tube


Allows fertilization across long distances


Two sperm released into female gametophyte
Water film no longer necessary
Some gymnosperms retain flagellated condition of
sperm, though no longer necessary
THE SEED PLANTS
A seed is an embryo
and its food supply that
is surrounded by a
protective coat
 Able to survive away
from parent plant


Can remain dormant
for different periods of
time
Dominant producers on
land
 Enormous impact on
human society

SEED PLANTS HAVE REDUCED GAMETOPHYTES
Develop from
spores kept in
sporangia of
parental
sporophyte
 Nutrients from
parent
 Protects seed
from
environmental
stresses

Seed Plants are Heterosporous
Most seedless plants
are homosporous
Produces 1
hermaphroditic
gametophyte
Seed plants are
heterosporous



Produce megaand
microsporangia
Female and male
spores
SEED PLANTS PRODUCE OVULES

Consists of the megasporangium, megaspore, and
integuments

Layer of sporophyte tissue to envelop and protect the
megasporangium
Gymnosperms with 1 integument
 Angiosperms with 2 integuments


Female gemetophyte from megaspore produce 1+ eggs
GYMNOSPERMS

Naked seed plants


Ovules and seeds on develop of surfaces of leaves, usually
as cones (strobili)
Four phyla with uncertain relationships

Phylum Cycadophyta


Phylum Gnetophyta


Large cones and palm-like leaves
3 genera: Welwitschia (largest leaves), Ephedra (ephedrine), and
Gnetum (tropical plants that resemble angiosperms)
Phylum Ginkophyta
Ginkgo biloba only surviving species
 Ornamental species, but only males planted due to seed odor


Phylum Coniferophyta
Largest phyla commonly called conifers
 Most are evergreens and retain leaves year round, others are
deciduous

PHYLUM CONIFEROPHYTA
L
LIFE CYCLE OF A PINE
Pine tree is a sporophyte
Separate types of cones for
each gametophyte
Pollen cones undergo
meiosis to develop
pollen grains
Ovulate cone with many
scales, each with 2 ovules
Haploid cells produced
become megaspores
with some developing
into gametophytes
3 years for cones to form
mature seeds
Ovulate cone separates
and seeds dispersed by
wind
ANGIOSPERMS

Reproductive structures are flowers and fruits

Seeds contained in fruits, the mature ovaries
Most diverse and widespread plants
 All placed in phylum Anthophyta
 Previously divided into monocots and dicots

1 or 2 cotyledons, seed leaves, in embryo respectively
 Monocots form a clade, but most dicots now eudicots
 Rest of ‘dicots’ as basal angiosperms (oldest) and
magnoliids


Water lilies and kudzuu
FLOWERS




Specialized structure with up to 4
circles of modified leaves
Sepals at base, usually green, and
enclose bud before opening
Petals brightly colored and aid in
attracting pollinators
Stamens are sporophylls that
produce microspores = pollen


Filament is the stalk and anther is the
terminal sac
Carpals are sporophylls that produce
megaspores
Stigma is sticky and receives pollen
 Style leads to ovary at base with ovules

FRUITS

Mature ovaries resulting from
thicken ovary walls
Triggered by hormonal changes
 Wall is the pericarp

Forms only following pollination
 Can be fleshy or dry



Pericarp softens as ripens or
adheres to seed coat
Adapted to disperse seeds
Winged seed by wind
 Modified burrs to cling to animals
 Edible so animals eat, but seed
passes unharmed with natural
fertilizer

ANGIOSPERM LIFE CYCLE
•Pollen
grains develop in
anthers of stamens
•
2 haploid cells produced: 1
to sperm other to pollen
tube
•Ovule develops into embryo
sac
•
Few cells: 1 is egg
•Anther releases pollen to
sticky stigma on carpel
•
Some flowers selfpollinate, but many
cross-pollinate
•
Stamens and carpels
develop at different times
or arrangement unlikely
•Pollen tube into style to
penetrate ovule integument
•1 sperm fertilizes egg = 2n
zygote
•1 sperm into other cells to
form endosperm, becomes
food source for embryo
•Embryo with basic root and
cotyledons
HUMAN DEPENDENCE ON SEED PLANTS

Most food from angiosperms

Wheat, rice, maize, potatoes,
cassava, and sweet potatoes
contribute 80% of human
calorie consumption
Angiosperms feed livestock
 Other foods



Coffee, tea, cocoa, and spices
Sources of wood and
medicines