chapter 31

Dormancy allows the...

"clock to be stopped" to survive harsh periods before germinating

Anthophyta Phylum: Examples: Key Characteristics: Approximate Number of Living Species:

-Anthophyta -flowering plants (angiosperms) -heterosprorous. sperm not motile; conducted to egg by a pollen tube. seeds enclosed within a fruit. leaves greatly varied in size and form. herb, vines, shrubs, tress. about 14,000 genera. ->300,000

Conifers Phylum: Examples: Key Characteristics: Approximate Number of Living Species:

-Coniferophyta -pines, spruces, firs, yews, redwoods, and others -heterosporous seed plants. sperm not motile; conducted to egg by a pollen tube. leaves mostly needle-like or scale like. tress, shrubs. about 50 genera. many produce seeds in cones -601

Cycads Phylum: Examples: Key Characteristics: Approximate Number of Living Species:

-Cycadophyte -cycads -heterosporous. sperm flagellated and motile but confined within a pollen tube that grows to the vicinity of the egg. palm like plants with pinnate leaves. secondary growth slow compared with that of the conifers. ten genera. seeds in cones. -206

Seed

-Embryo protected by integument *An extra layer or two of sporophyte tissue *Hardens into seed coat -Megasporangium divides meiotically inside ovule to produce haploid megaspores -Megaspore produces egg that combines with sperm to form zygote -Also contains food supply for embryo

Fruits contain 3 genotypes in 1 package

-Fruits and seed coat from prior sporophyte (2n) generation -Remnants of gametophyte (1n) generation that produced egg -Embryo represents next sporophyte (2n) generation

Ginkgophyta Phylum: Examples: Key Characteristics: Approximate Number of Living Species:

-Ginkgophyta -Ginkgo - heterosprorous. sperm flagellated and motile but conducted to the vicinity of the egg by a pollen tube. deciduous tree with fan-shaped leaves that have evenly forking veins. seeds resemble a small plum with fleshy, foul-smelling outer covering. one genus.

Gnetophytes Phylum: Examples: Key Characteristics: Approximate Number of Living Species:

-Gnetophyta -gnetophytes -heterosprorous. sperm not motile; conducted to egg by a pollen tube. the only gymnosperms with vessels. trees, shrubs, vines. three very diverse genera (ephedra, gnetum, welwitschia). -65

Fruit Dispersal occurs through a wide array of methods:

-Ingestion and transportation by birds or other vertebrates -Hitching a ride with hooked spines on birds and mammals -Blowing in the wind -Floating and drifting on water -Burial in caches by herbivores

Pollination

-Mechanical transfer of pollen from anther to stigma -May or may not be followed by fertilization -Pollen grain grows pollen tube *Guided to embryo sac by pheromones from synergids *Pollen tube enter embryo sac via micropyle -One of the two pollen grain cells lags behind *This generative cell divides to produce two sperm cells *No flagella on sperm

Pines

-More than 100 species, all in the Northern hemisphere -Produce tough needlelike leaves in clusters -Leaves have thick cuticle and recessed stomata to retard water loss -Leaves have canals with resin to deter insect and fungal attacks

Conifers (phylum Coniferophyta)

-Most familiar gymnosperm phylum -Pines, spruces, firs, cedars, and others -Coastal redwood - Tallest living vascular plant -Bristlecone pine - Oldest living tree -Found in colder and sometimes drier regions of the world -Conifers are sources of important products *Timber, paper, resin, and taxol (anti-cancer)

Double fertilization

-One sperm unites with egg to form diploid zygote New sporophyte -Second sperm unites with the two polar nuclei to form the triploid endosperm Provides nutrients to embryo

A year later, female gametophyte matures which means... 15 months after pollination, pollen tube reaches...

-Pollen tube is digesting its way through -Mature male gametophyte has two sperm cells archegonium and discharges contents One sperm unites with egg = zygote Other sperm degenerates

Single 2n megaspore mother cell in ovule undergoes meiosis

-Produces 4 1n megaspores *3 degenerate -Nucleus of remaining megaspore divides mitotically 3 times *Daughter nuclei produce 8 haploid nuclei *Together called embryo sac (female gametophyte) -Integuments become seed coat *Form micropyle

Success attributed to evolution of seed:

-Protects and provides food for embryo -Dormancy allows the "clock to be stopped" to survive harsh periods before germinating -Later development of fruits enhanced dispersal

Once a seed coat forms, most of the embryo's metabolic activities cease -> Germination cannot take place until.... Seeds of some plants have been known to....

-dormancy -water and oxygen reach the embryo - remain viable for thousands of years

Fruits Most simply defined as.... During seed formation, the flower ovary begins..... It is possible for fruits to develop without.... Bananas are propagated....

-mature ovaries (carpels) -to develop into fruit -seed development -asexually

Seeds are an important adaptation because....

1. Maintain dormancy under unfavorable conditions 2. Protect young plant when it is most vulnerable 3. Provide food for the embryo until it can produce its own food 4. Facilitate dispersal of the embryo

Seed plants first appeared ____ - ____ MYA and evolved from...

305-465 Evolved from spore-bearing plants known as progymnosperms

Embryo sac = female gametophyte

8 nuclei in 7 cells (from 3 mitotic divisions) 8 haploid daughter nuclei (2 groups of 4) 1 from each group of 4 migrates toward center Functions as polar nuclei - may fuse Egg 1 cell in group closest to micropyle Other 2 are synergids Antipodals - 3 cells at other end (no known function)

Closest living relative to the original angiosperm is __________

Amborella

Phyla of Extant Seed Plants that belong to Angiosperms:

Anthophyta

Phyla of Extant Seed Plants that belong to Gymnosperms:

Coniferophyta Cycadophyta Gnetophyta Ginkophyta

Five Phyla of Extant Seed Plants

Coniferophyta Cycadophyta Gnetophyta Ginkophyta Anthophyta

Female (mega-) gametophytes

Develop within an ovule Enclosed within diploid sporophyte tissue in angiosperms

fruit: The ovary wall is termed the pericarp With 3 layers: Their fate determines....

Exocarp - skin or rind Mesocarp - flesh or pulp Endocarp - surrounds seeds (pit) -fruit type

Pine reproduction female

Female pine cones form on the upper branches of the same tree Female cones are larger, and have "woody" scales Two ovules develop on each scale Each contains a megasporangium Each will produce 4 megaspores, but only one megaspore becomes a female gametophyte

Angiosperms

Flowering plants Ovules are enclosed/ protected in diploid (sporophyte) tissue at the time of pollination Carpel, a modified leaf that covers seeds, develops into fruit (modified ovary wall)

seeds

In many angiosperms, embryo development is arrested soon after meristems & cotyledons (embryonic leaves) differentiate Integuments develop into a relatively impermeable seed coat Encloses the seed with its dormant embryo and stored food May remain dormant for many years Germinate when conditions are favorable

Seed plants produce two kinds of gametophytes:

Male (micro-) gametophytes Female (mega-) gametophytes

Pine reproduction male

Male cones have reduced "leafy" scales Male gametophytes (pollen grains) Develop from microspores in male cones by meiosis

Flower morphology

Modified stems bearing modified leaves Primordium develops into a bud at the end of a stalk called the pedicel Pedicel expands at the tip to form a receptacle, to which other parts attach Flower parts are organized in circles called whorls

Gnetophytes (phylum Gnetophyta)

Only gymnosperms with vessels in their xylem (similar to angiosperms) Contain three (unusual) genera Welwitschia Ephedra Gnetum

Ginkgophytes (phylum Ginkgophyta)

Only one living species remains Ginkgo biloba Flagellated sperm Dioecious Male and female reproductive structures form on different trees

Angiosperm origins are a mystery

Origins as early as 145-208 MYA Oldest known angiosperm in the fossil record is Archaefructus

Carpel has 3 major regions:

Ovary - swollen base containing ovules *Later develops into a fruit Stigma - sticky tip where pollen lands Style - neck or stalk

Gymnosperms

Plants with "naked seeds" All lack flowers & fruits of the angiosperms All have ovule EXPOSED on a scale

Male (micro-) gametophytes

Pollen grains Dispersed by wind or a pollinator No need for water

Cycads (phylum Cycadophyta)

Slow-growing gymnosperms of tropical and subtropical regions Sporophytes resemble palm trees Female cones can weigh 45 kg Have largest sperm cells of all organisms!

• List the evolutionary advantages of seeds

a common ancestor that had seeds gave rise to the gymnosperms and the angiosperms. whole-genome duplication may have contributed to the rise and dominance of seen plants, including the angiosperms. seeds protect the embryo, aid in dispersal, and can allow for an extended pause in the life cycle.

• List the defining features of angiosperms

amborella, the closest living relative of the first angiosperms, provides clues to the origins of this very successful group. Although angiosperms are a clade, horizontal gene transfer has contributed genes from distantly related plant species. angiosperms are characterized by ovules that at pollination are enclosed with in an ovary at the base of a carpel, a structure unique to the phylum; a fruit develops from the ovary.

Archaefructus may be the sister clade to all other ___________

angiosperms

Pollen production occurs in the _______

anthers -It is similar but less complex than female gametophyte formation -Diploid microspore mother cells undergo meiosis to produce four functional haploid microspores (not shown) -Nuclei of all 4 microspores undergo mitosis to form binucleate pollen grains = male gametophyte 1 -> generative cell 1 -> tube cell/nucleus

• Identify the structures from which fruits develop. • Distinguish among berries, legumes, drupes, and samaras

as a seed develops, the pericarp layers of the ovary wall develop into the fruit. a berry has a fleshy pericarp; a legume has a dry pericarp that opens to release seeds; the outer layers of a drupe pericarp are fleshy; and a samara is a dry structure with a wing. animals often distribute the seeds of fleshy fruits and fruits with spines or hooks. wind disperses lightweight seeds and samara forms

the ginkgo is __________ - that is, the male and female reproductive structures are produced on separate trees.

dioecious

During the first spring, pollen grains.......

drift down between open scales Pollen grains drawn down into micropyle Scales close

• List environmental conditions that can lead to seed germination in some plants.

fire, heavy rains, or passage through an animals digestive tract may be required for germination in some species.

evolutionary innovations of angiosperms include:

flowers to attract pollinators, fruits to protect embryos and aid in their dispersal, and double fertilization, which provides endosperm to help nourish the embryo

Specific adaptations ensure that seeds will....

germinate only under appropriate conditions -Some seeds lie within tough cones that do not open until exposed to fire

• Describe the distinguishing features of a gymnosperm.

gymnosperms are mostly cone-bearing seed plants. in gymnosperms, the ovules are not completely enclosed by sporophyte tissue at pollination, and thus have "naked seeds"

Innermost whorl -

gynoecium Consists of one or more carpels House the female gametophyte

the nuclellus itself is completely surrounded by a thick layer of cells called the ___________ that has a small opening (the ___________) toward one end.

integument micropyle

the embryo is protected by an extra layer or two of sporophyte tissue called the ___________, creating the ______

integument, ovule

Antipodals have

no known function

Second whorl -

petals

in some seed plants, the sperm moves toward the egg through a growing ___________ this eliminates.....

pollen tube the need for external water

Horizontal gene transfer explains the....

presence of moss mitochondrial genes in the genome of Amborella Mosses may have been epiphytes on Amborella ancestor, increasing likelihood of gene transfer

Integuments develop into a....

relatively impermeable seed coat

• Distinguish between pollen and sperm in seed plants

seed plants produce male and female gametophytes; the male gametophyte is a pollen grain, which is carried to the female gametophyte by wind or other mean. the sperm is within the pollen grain.

Outermost whorl -

sepals

Flower whorls

sepals petals stamens (androecium) gynoecium

Third whorl -

stamens (androecium) Each stamen has a pollen-bearing anther and a filament (stalk) Pollen is the male gametophyte

• Describe four ways in which seeds help to ensure the survival of a plant's offspring

the four advantages conferred by seeds are dormancy, protection of the embryo, nourishment, and a method of dipersal

• List the four groups of living gymnosperms

the four groups of gymnosperms are confiers, cycads, gnetophytes, and ginkgophytes

within the ovule...

the megasporangium divides meiotically, producing a haploid megaspore. the megaspore produces the egg that combines with the sperm, resulting in the zygote

Female cones usually take _____ seasons to mature

two or more

_______ are a particularly efficient conducting cell type that is a common feature in angiosperms

vessels

the other flower parts typically are attached in circles called....

whorls