Plant Diversity II The Seed Plants Evolution and Ecology u Derived from a single common ancestor. u Five phyla u Angiosperms (flowering plants) u Gymnosperms

Plant Diversity IIPlant Diversity II

The Seed Plants

Evolution and EcologyEvolution 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 CharacteristicsCommon 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 . . . 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 / Gymnosperms / Coniferophytes. . . Coniferophytes. . .

Gymnosperms include conifers, cycads, ginkgoes, & gnetophytes

Name means “naked seed”

abundant in colder latitudes and higher dry elevations

Characteristics of ConifersCharacteristics 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 ReproductionConifer 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. . . 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 Characteristics of AngiospermsAngiosperms

Flowers attract animal pollinators

Extremely diverse in size, form and habitat

2 Angiospermophyte Divisions2 Angiospermophyte Divisions

Hydrophytes Adapted for aquatic/moist environments

Xerophytes Adapted for dry climates

Angiosperm ReproductionAngiosperm 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. . . 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. . . 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 DicotsMonocots 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

ANGIOSPERMSANGIOSPERMS

The flowering plants

Spring crocus Crocus vernus

FlowerFlower structure 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 pollinationTypes of pollination Wind Animal Water

Bumble bee Bombus hortorum on red clover Trifolium pratense

Yorkshire fog grass Holcus lanatus

Animal pollinationAnimal pollination

Usually insects Also other flying

animals e.g. hummingbirds or

fruit bats

Cerambycid beetle pollinating bramble Rubus fruticosus

Flower structureFlower structure

Dog rose Rosa canina

PollinationPollination

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


Small skipper Thymelicus flavus on marsh thistle Cirsium palustris


The honey bee Apis melifera on marsh thistle Cirsium palustris© 2008 Paul Billiet ODWS


Some flowers are highly specialised to encourage only one type of insect

Fox glove flowers Digitalis purpurea

© 2008 Paul Billiet ODWS


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


FertilisationFertilisation

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



Style

StigmaPollen grain

Ovule

Embryo sac

Pollen tubeOvary


FertilizationFertilization

Egg cell

Polar nuclei

Embryo sac

Micropyle


FertilizationFertilization

Pollen grains of the daisy Bellis perennis



Germinating pollen grains of blue bell, Hyacinthoides non-scripta


The double fertilizationThe double fertilization

Pollen tube

Pollen tube entering micropyle

Male nucleus + egg cell

= zygote (2n)

Male nucleus + 2 polar nuclei = endosperm nucleus (3n)

Ovule


From flower to fruitFrom flower to fruit

Marsh marigold Caltha palustris


Fruits and seed dispersalFruits and seed dispersalAnimal dispersal Strawberry Fragaria vesca

Wind dispersal Ragwort Senecio

Explosive dispersal Bird’s foot trefoil Lotus corniculatus

Animal dispersalWood avens Geum urbanum


Documents

Plant Diversity II The Seed Plants Evolution and Ecology u Derived from a single common ancestor. u Five phyla u Angiosperms (flowering plants) u Gymnosperms