Biology Seeded Plants

Raven Biology 13th edition, CH 30

The Evolution of Seed Plants, Seed plants have come to dominate the terrestrial landscape over the last several hundred million years

Over 400,000 species of seed plants today

The Evolution of Seed Plants, Seed plants evolved from spore-bearing plants known as

Progymnosperms

The Evolution of Seed Plants, Success attributed to evolution of seed

Protects and provides food for embryo; allows embryos to pause development and germinate after a harsh winter or dry season has passed

Seeds and the Embryo, Embryo is protected by integument

An extra layer or two of sporophyte tissue that hardens into seed coat

Seeds and the Embryo, Megasporangium divides meiotically inside ovule to produce

Haploid megaspore

Seeds and the Embryo, Megaspore divides by mitosis to produce a female gametophyte carrying

The female gamete, an egg

Seeds and the Embryo, Seeds also contain a food supply for the

Embryo

Two kinds of gametophytes, Male gametophytes are

Pollen grains

Two kinds of gametophytes, Male gametophytes are carried to female gametophyte by

Wind or a pollinator

Two kinds of gametophytes, Male gametophytes have no need for

Water

Two kinds of gametophytes, Female gametophytes develop within an

Ovule

Two kinds of gametophytes, In angiosperms, the ovule is enclosed within

Diploid sporophyte tissue

Two kinds of gametophytes, The ovule and protective tissue are the

Ovary

Two kinds of gametophytes, The ovary develops into

Fruit

Gymnosperms, Gymnosperms are plants with

“Naked seeds”

Gymnosperms, Gymnosperms encompass four of the five lineages of seed plants

Coniferophytes, Cycadophytes, Gnetophytes, Ginkgophytes

Gymnosperms, All gymnosperms have ovule exposed on a

Scale

Gymnosperms, All gymnosperms lack flowers and fruits of the fifth lineage, the

Angiosperms

Conifers (phylum Coniferophyta), Conifers are the most familiar gymnosperm phylum

Pines, spruces, firs, cedars, and others

Conifers (phylum Coniferophyta), Coastal redwood is the

Tallest living vascular plant

Conifers (phylum Coniferophyta), Bristlecone pine is the

Oldest living tree

Conifers (phylum Coniferophyta), Conifers are found in colder temperate and sometimes drier regions of the

World

Conifers (phylum Coniferophyta), Conifers are sources of important products

Timber, paper, resin, and taxol (anti-cancer)

Pines, There are more than 100 species of pine, all in the

Northern hemisphere

Pines, Pines produce tough needlelike leaves in

Clusters

Pines, Leaves have a thick cuticle and recessed stomata to

Minimize water loss

Pines, Leaves have canals with resin to deter

Insect and fungal attacks

Pines, Wood lacks some of the more rigid cell types found in other trees, which is why they are sometimes referred to as "soft" wood

"Soft" wood

Pine reproduction, Male gametophytes (pollen grains) develop from microspores in male cones by

Meiosis

Pine reproduction, Female pine cones form on the upper branches of the

Same tree

Pine reproduction, Female cones are larger and have

Woody scales

Pine reproduction, Two ovules develop on each

Scale

Pine reproduction, Each ovule contains a megasporangium that is known as the

Nucellus

Female Pine Cones, The nucellus is surrounded by the

Integument

Female Pine Cones, The micropyle is a small opening at the end of the

Integument

Female Pine Cones, The seed coat forms from a layer of the

Integument

Female Pine Cones, One megaspore mother cell within each megasporangium forms four megaspores via

Meiosis

Female Pine Cones, Three megaspores

Break down

Female Pine Cones, One megaspore slowly develops into a female gametophyte via

Mitosis

Female Gametophyte 1, At maturity, the female gametophyte may consist of

Thousands of cells

Female Gametophyte 1, The female gametophyte has 2 to 6 archegonia at the

Micropylar end

Female Gametophyte 1, Each archegonium has a single large

Egg

Conifer Pollination, Female cones usually take two or more seasons to

Mature

Conifer Pollination, During the first spring, pollen grains drift down between

Open scales

Conifer Pollination, Pollen grains are drawn down into the

Micropyle

Conifer Pollination, After pollen enters, the scales

Close

Conifer Pollination, 15 months after pollination, the pollen tube reaches the archegonium and discharges its contents

One sperm unites with egg to form a zygote; the other sperm degenerates

Cycads (phylum Cycadophyta), Cycads are slow-growing gymnosperms of tropical and subtropical

Regions

Cycads (phylum Cycadophyta), Sporophytes of most 250 known species resemble

Palm trees

Cycads (phylum Cycadophyta), Individuals make either pollen-bearing or ovule-bearing cones, not

Both

Cycads (phylum Cycadophyta), Female cones are huge, up to

45 kg

Cycads (phylum Cycadophyta), Sperm is formed in the pollen tube but released within the ovule to swim to the

Archegonium

Gnetophytes, Gnetophytes are the only gymnosperms with vessels in their

Xylem

Gnetophytes, Gnetophytes contain 65 species in three unusual genera

Welwitschia, Ephedra, Gnetum

Ginkgophytes, Only one living species of ginkgophyte remains

Ginkgo biloba

Ginkgophytes, Ginkgophytes have

Flagellated sperm

Ginkgophytes, Ginkgophytes are dioecious, meaning male and female reproductive structures form on

Different trees

Angiosperms, Angiosperms are the

Flowering plants

Angiosperms, In angiosperms, ovules are enclosed in diploid tissue at the time of

Pollination

Angiosperms, The carpel, a modified leaf that encapsulates seeds, develops into

Fruit

Angiosperm Abundance, Today there are some 300,000 species of

Flowering plants

Angiosperm Abundance, The emergence of angiosperms changed the terrain of Earth, which was previously dominated by

Ferns, cycads, and conifers

Angiosperm Abundance, Unique angiosperm features aided their abundance

Flower production, insect pollination, broad leaves with thick veins

Angiosperm origins are a mystery, Oldest known angiosperm in the fossil record is

Archaeofructus

Angiosperm origins are a mystery, Archaeofructus is at least

125 million years old

Angiosperm origins are a mystery, Archaeofructus is unlikely to have been the

First angiosperm

Angiosperm origins are a mystery, Archaeofructus had multiseeded carpels (fruits) and stamens but lacked

Sepals and petals

Closest living relative to the original angiosperm is Amboella, Horizontal gene transfer explains the presence of moss mitochondrial genes in the genome of

Amboella

Flowers House Gametophytes, Flowers are modified stems bearing

Modified leaves

Flowers House Gametophytes, Flowers originate as a primordium that develops into a bud at the end of a stalk called a

Pedicel

Flowers House Gametophytes, The pedicel expands at the tip to form a receptacle, to which other parts

Attach

Flowers House Gametophytes, Flower parts are organized in circles called

Whorls

Flower Whorls, Outermost whorl consists of

Sepals

Flower Whorls, Second whorl consists of

Petals

Flower Whorls, Third whorl consists of stamens (androecium)

Pollen is the male gametophyte

Flower Whorls, Each stamen has a pollen-bearing anther and a

Filament (stalk)

Flower Whorls, Innermost whorl is the gynoecium, which consists of one or more

Carpels

Flower Whorls, The gynoecium houses the

Female gametophyte

The Carpel, Carpel has three major regions

Ovary, stigma, and style

The Carpel, The ovary is the swollen base containing

Ovules

The Carpel, The ovary later develops into a

Fruit

The Carpel, The stigma is the tip where pollen

Lands

The Carpel, The style is the neck or stalk connecting stigma and

Ovary

Ovule, A single diploid megaspore mother cell in the ovule undergoes meiosis to produce

Four haploid megaspores

Ovule, Three of the megaspores

Disappear

Ovule, The nucleus of the remaining megaspore divides mitotically to form the

Female gametophyte

Ovule Development, Three mitotic divisions of the megaspore nucleus produces eight haploid nuclei in two groups of

Four

Ovule Development, Two nuclei (one from each group of four) migrate toward the

Center

Ovule Development, A cell wall forms around the polar nuclei to form the

Central cell

Ovule Development, The cell closest to the micropyle becomes the

Egg

Ovule Development, Two other cells in that group become

Synergids

Ovule Development, The antipodals are the three cells at the other end; they have

No apparent function

Ovule Development, Integuments become the

Seed coat

Ovule Development, The eight haploid nuclei in seven cells make up the female gametophyte, also known as the

Embryo sac

Pollen Production, Pollen production occurs in the

Anthers

Pollen Production, The process is similar but less complex than female gametophyte formation

Diploid microspore mother cells undergo meiosis to produce four haploid microspores

Pollen Production, All four microspores at first remain together as a

Tetrad

Pollen Production, The nucleus of each microspore divides once by

Mitosis

Pollen Production, Binucleate microspores become

Pollen grains

Pollination, Pollination is the mechanical transfer of pollen from anther to

Stigma