Transcript Plant Diversity II

Plant Diversity II
The Seed Plants
Evolution and Ecology
 Derived
from a single common ancestor.
 Five phyla
 Angiosperms
(flowering plants)
 Gymnosperms (four phyla of nonflowering
plants)
 Dominated
land for 350 million years
Common Characteristics
 1N
gametophyte is reduced so much that it
acts as a reproductive organ within the 2N
sporophyte
 Female gametophyte makes eggs
 Male gametophytes are pollen grains
containing sperm.
 Waterproof,
dispersed by wind or animals
 Reproduction independent of water
Seeds consist of . . .
 Embryonic
plants
 A supply of food for the embryo as it
develops roots and leaves
 A protective coat, allowing the embryo to
remain dormant until conditions are
favorable for growth
Gymnosperms /
Coniferophytes. . .
Gymnosperms include
conifers, cycads,
ginkgoes, &
gnetophytes
 Name means “naked
seed”
 abundant in colder
latitudes and higher
dry elevations

Characteristics of Conifers
pines, firs, spruce,
hemlock, cypresses
 Adapted to dry, cold
conditions
 leaves are thin needles
with thick cuticle
 retain leaves all year
 produce antifreeze
resin in sap

Conifer Reproduction
 Sporophyte
(tree) develops male & female
cones
 Male cones are smaller and delicate,
disintegrating after releasing clouds of
pollen grains
 Female cones are large w/ woody scales
 Each scale has two 1N female
gametophytes, each producing eggs
Conifer reproduction cont. . .
 After
a pollen grain (male gametophyte)
lands on a female cone, it sends out a
slowly growing pollen tube that takes 14
months to reach the eggs.
 After fertilization, seeds develop and are
released when the female cone matures and
the scales open.
Characteristics of
Angiosperms
Flowers attract animal
pollinators
 Extremely diverse in
size, form and habitat

2 Angiospermophyte Divisions
 Hydrophytes
 Adapted
for aquatic/moist environments
 Xerophytes
 Adapted
for dry climates
Angiosperm Reproduction
Dominant sporophyte that produce and nurture
tiny male (pollen grains) and female (embryo
sacs) gametophytes within flowers.
 Gametophytes produce gametes and fertilization
occurs within ovaries of flower.
 Pollen grains dev from microsporangia in anther.
2N Microspore mother cells in microsporangia
produce microspores by meiosis wc/ develop

into pollen grains
 Diploid
ovule contains a 2N megaspore
mother cell wc/ produces 1N megaspores
 Three disintegrate, one survives, divides by
mitosis to produce 7 cells.
 One cell becomes the egg, one large central
cell has two haploid nuclei
 These will fuse with sperm to form
endosperm
Angiosperm reprod cont. . .
 Pollen
grains lands on stigma of female,
pollen tube grows thru style to ovary.
 Inside each pollen grain are 3 nuclei
 One nucleus forms pollen tube, one
fertilizes egg, other fuses with polar nuclei
to form 3N primary endosperm
 Endosperm forms food for embryo
Angiosperm reproduction. . .
 2N
zygote forms the embryo and the
endosperm is the food
 Seeds are enclosed within fruits (the ripened
ovaries of the flowers).
 Fruits entice animals to disperse seeds.
 Seeds are dispersed through animal
digestive tracts or attached to fur.
Monocots and Dicots

Monocots
 Grasses,
corns, lilies
 Seed in one piece
(cotyledons)
 Parallel veined leaves
 Flower petals in threes

Dicots
 most
trees, shrubs,
herbs
 Seeds in two pieces
(cotyledons)
 Branched veined
leaves
 Flower petals in fours
ANGIOSPERMS
The flowering
plants
Spring crocus Crocus vernus
Flower structure
 Flowers
are reproductive structures
 The have evolved to send and receive pollen
from one flower to another
 This is process of pollination
 Flowers are developed from a series of
modified leaves
 These leaves are arranged in a rings
(whorls)
Types of pollination
Wind
 Animal
 Water

Bumble bee Bombus hortorum on red clover Trifolium pratense
Yorkshire fog grass Holcus lanatus
Animal pollination
Usually insects
 Also other flying
animals
 e.g. hummingbirds or
fruit bats

Cerambycid beetle
pollinating bramble
Rubus fruticosus
Flower structure
Dog rose Rosa canina
Pollination




Pollen grains contain the
male gametes of the plant
They are picked up by a
pollinator and transferred
to another flower
Plants tend to specialize in
pollinators
This ensures the pollen is
delivered to same species
of plant
Pollination
Small skipper Thymelicus flavus on marsh thistle Cirsium palustris
Pollination
The honey bee Apis melifera on marsh thistle Cirsium palustris
© 2008 Paul Billiet ODWS
Pollination

Some flowers are
highly specialised to
encourage only one
type of insect
Fox glove flowers
Digitalis purpurea
© 2008 Paul Billiet ODWS
Pollination
 Most
species of flowering plants are
monoecious
 Pollen from a flower could land on the
stigma of the same flower or another flower
on the same plant = self pollination
 Pollen transferred from the anther on one
flower to the stigma of another flower on a
different plant = cross pollination
© 2008 Paul Billiet ODWS
Fertilisation
 Pollination
≠ Fertilization
 The male gamete (the male nucleus) has to
get to the egg cell
 The egg cell lies in an ovule in an ovary at
the centre of the plant
 The pollen grain germinates on the stigma
 It grows a pollen tube down the style
 It male nuclei travel down the pollen tube to
the ovule
© 2008 Paul Billiet ODWS
Fertilisation
Pollen grain
Stigma
Style
Ovule
Embryo sac
Ovary
© 2008 Paul Billiet ODWS
Pollen tube
Fertilization
Embryo sac
Polar nuclei
Egg cell
Micropyle
© 2008 Paul Billiet ODWS
Fertilization
Pollen grains of the daisy
Bellis perennis
© 2008 Paul Billiet ODWS
Fertilisation
Germinating pollen grains of blue
bell, Hyacinthoides non-scripta
© 2008 Paul Billiet ODWS
The double fertilization
Ovule
Pollen
tube
Male nucleus
+ 2 polar
nuclei =
endosperm
nucleus (3n)
Male nucleus
+ egg cell
= zygote (2n)
© 2008 Paul Billiet ODWS
Pollen tube
entering
micropyle
From flower to fruit
Marsh marigold Caltha palustris
© 2008 Paul Billiet ODWS
Fruits and seed dispersal
Animal dispersal Strawberry Fragaria vesca
Explosive dispersal
Bird’s foot trefoil
Lotus corniculatus
Animal dispersal
Wood avens
Geum urbanum
Wind dispersal
Ragwort Senecio
© 2008 Paul Billiet ODWS