Post on 12-Jan-2016
CHAPTER 30Plant Diversity II: The Evolution of Seed Plants
TRANSFORMING THE WORLD
Origin of Seed Plants 360 million years ago
Seeds consist of an embryo, its food supply and a surrounding protective coating
Fun Fact: seeds are analogous to a detachable and mobile version of a pregnant woman’s womb
Matured seeds dispersed from their parent by wind or other means.
Gymnosperms and angiosperms have come to dominate modern landscapes and make up the great majority of plant biodiversity.
The cultivation and harvest of plants, especially angiosperms, began 13,000 years ago.
Near East, East Asia, Africa, and the Americas is where humans began the cultivation of plants independently.
This was an important cultural change in the history of humanity.
In addition, it made possible the transition from hunter-gatherer societies to permanent settlements.
CHAPTER 30.1Seeds and Pollen Grains are key adaptations for life on land
ALL SEED PLANTS HAVE:
Reduced Gametophytes Heterospory Ovules Pollen
ADVANTAGES OF REDUCED GAMETOPHYTES Develop from spores located on the sporangia of
the parental sporophyte Protects female gametophytes from
environmental stresses Moist reproductive tissues shield against UV
Radiation and protect from drying out Dependent gametophytes ones obtain food from
sporophytes Free-living ones defend for
themselves
HETEROSPORY: THE RULE AMONG SEED PLANTS
Megasporangia produce megaspores (female gametophytes) and have only one function
Microsporangia produce vast numbers of microspores (male gametophytes)
Closest relatives of seed plants are all homosporous (single type of spore that is bisexual)
OVULES AND PRODUCTION OF EGGS
Integument: layer of sporophyte tissue that envelopes and protects the megasporangium (gymnosperm have 1 & angiosperm have 2)
Ovule: megasporangium, megaspore and their integuments
Ovules are where females produce one or more eggs
POLLEN AND PRODUCTION OF SPERM
Pollen grains consist of a male gametophyte enclosed within a pollen wall
Polymer Sporopollenin (pollen walls) protect pollen
Pollination is the transfer of pollen to part of a seed plant that contains ovules
If a pollen grain germinates it gives rise to a pollen tube
Flagellated sperm only travel a few centimeters, but sperm producing male gametophytes can be carried long distances
Living gymnosperms provide evidence of evolutionary transition to nonmotile sperm
THE EVOLUTIONARY ADVANTAGES OF SEEDS
Spores were the only protective stage in any plant life cycle before the advent of seeds
Moss spores can withstand many different conditions and are easily dispersed
Spores were the main way plants spread over Earth for the first 100 million years of plant life on land
Spores are single-celled and seeds are multi-cellular
Unlike spores, seeds have a supply of stored food
Spores have shorter lifetimes
CONTINUED…
Favorable conditions lead to the germination of seeds whose sporophyte embryos emerge as seedlings
Some seeds land close to their parent sporophyte plant, but others are transferred far distances by plants and animals
GYMNOSPERM EVOLUTION
Gymnosperms bear “naked” (not enclosed in ovaries) seeds, typically conesEarly gymnosperms lived in carboniferous
ecosystems and took over the seedless plants before (horsetails, lycophytes, ferns)
Carboniferous Period380 million years ago Plants begin to acquire characteristics of seed
plants Progymnosperms- transitional species of
seedless vascular plants 1st seed bearing plants appear in fossil record
1200 million years after the first angiosperms
GYMNOSPERM EVOLUTION
Permian period Drier climate that favored the spread of
gymnosperms Mostly changed the plant life in seas Changed terrestrial life
Amphibians decreased in diversity and replaced with reptiles
CarboniferousPermianPaleozoicMesozoic
CYCADOPHYTA
Next largest group after conifers (cone bearing conifers)
Large cones and palm-like leaves 130 species survive todays
Thrived during Mesozoic era
GINKOPHYTA
Ginkgo biloba is only surviving species Fan-like leaves that turn gold in fall Tolerates air pollution well
GNETOPHYTA PHYLUM
• Gnetum 35 species of tropical trees, shrubs, or vines Located in Africa and Asia Seeds look like fruits Leaves look like those of flowering plants
• Ephedra 40 species that inhabit arid regions worldwide Arid- extremely dry
GNETOPHYTA PHYLUM CONT.
Coniferophyta Largest phyla (600 species) Large trees Evergreens
Douglas fir, European larch, Common juniper, Wollemi pine, Bristlecone pine, Sequoia
Welwitschia 1 species = Welwitschia mirabilis Lives in deserts of southwest Africa Strap-like leaves (largest leaves ever known)
30.3: THE REPRODUCTIVE ADAPTATIONS OF ANGIOSPERMS INCLUDE FLOWERS AND FRUITS
flowering plants; seed plants that produce the reproductive structures called flowers or fruits.
Most diverse and widespread of all plants More than 250,000 species About 90% of plant species
ANGIOSPERMS
Flower: structure specialized for sexual reproduction Pollination occurs by wind, insects, and other animals Sepal: Usually green and enclose the flower before it
opens (ex: rosebud) Petals: Interior to the sepals, brightly colored and aid
in attracting pollinators Stamens: Produce microspores that develop into pollen
grains containing male gametophytes Filament: Stalk of the stamen Anther: Terminal sac of the stamen where pollen is produced
Carpels: Make megaspores and their products, female gametophytes
Stigma: Sticky tip of the carpel that receives pollen. Style: Leads from the stigma to the ovary at the base
of the carpal
Fruits: A mature ovary of a flower Fruit protects dormant seeds and often aids in their
dispersal. Can either be fleshy (oranges, grapes) or dry (beans,
nuts, and grains) Seeds are spread through animals, water (coconuts),
and wind (Maple tree helicopters)
Terms: Generative Cell: divides and forms two sperm Tube Cell: Produces a pollen tube Gametophyte: The multicellular haploid form that
produces haploid gametes by mitosis. The haploid gametes unite and develop into sporophytes
Embryo Sac: Female gametophyte Crosspollination: The transfer of pollen from an anther
of a flower on one plant to the stigma of a flower on another plant of the same species Enhances genetic variability
Endosperm: Developed from the rapid division of the fertilized nucleus of the central cell of the female gametophyte Tissue rich in starch and other food reserves that nourish the
developing embryo Double Fertilization: One fertilization event produces a
zygote and the other produces a triploid cell Unique to angiosperms
ANGIOSPERM EVOLUTION
Originated at least 140 million years ago During the late Mesozoic period, the major
branches of the clade diverged from their common ancestor
Fossils, phylogenic analyses, and developmental studies offer insights into the origin of flowers
Increased dominance of plants in Cretaceous era
TYPES OF ANGIOSPERMS Magnolids: most closely related to eudicots; more
than 8,000 species Ex: Magnolias
Basal Angiosperms: Member of a clade of 3 early-diverging lineages Ex: Water Lily, Star Anise, Amborella Trichopoda
TYPES OF ANGIOSPERMS
Monocots: 70,000 species (1/4 of angiosperms); one cotyledon (sporophyte embryo with a rudimentary root and one or two seed leaves); veins usually parallel; vascular tissue scattered; root system usually fibrous (no main root); pollen grain with one opening; floral organs usually in groups of threeEx: Orchids, Pygmy date palm, Lily, Barley
TYPES OF ANGIOSPERMS
Eudicots: 170,000 species (2/3 of angiosperms); two cotyledons, veins usually netlike; vascular tissue usually arranged in ring; taproot (mainroot) usually present; pollen grain with three openings; floral organs usually in multiples of four of five Ex: California Poppy, Pyrenean Oak, Dog Rose, Snow Pea,
Zucchini
30.4 HUMAN WELFARE DEPENDS GREATLY ON SEED PLANTS
We rely on seed plants for food, fuel, wood, and medicine. preservation of plant diversity is
critical because of our reliance on themPRODUCTS FROM SEED PLANTS
MOST OF OUR FOOD COMES FROM ANGIOSPERMS
Flowering plants provide nearly all our food.
Just six crops—wheat, rice, maize, potatoes, cassava, and sweet potatoes
yield 80% of all calories consumed by humans.
Also depend on angiosperms to feed livestock
Today’s crops are the products of a relatively recent burst of genetic change, resulting from artificial selection after the domestication of plants 13,000 years ago.
How did wild plants change so dramatically in such a relatively short time? The answer is likely a combination of
deliberate and unconscious selection for plants with desirable traits, such as large fruits and lack of toxins.
Angiosperms also provide important edible foods such as coffee, chocolate, and spices. Spices come from many plant parts such as vanilla and
mustard come from fruits and seeds Gymnosperms and angiosperms are sources of
wood, which is absent in all living seedless plants and consists of an accumulation of tough-walled xylem cells. Wood is the primary source of fuel for much of the
world. Wood pulp is used to make paper the world’s most widely used construction material.
Humans depend on seed plants for medicines. Most cultures have a tradition of
herbal medicine. Scientific research has identified
the relevant secondary compounds in many of these plants, leading to the synthesis of many modern medicines.
THREASTS TO PLANT DIVERSITY Although plants are a renewal
resource, plant diversity is not. Plant diversity is a nonrenewable
resource. **
The demand for space and natural resources are extinguishing plant species at a very fast rate because of human population Due primarily to the slash-and-burn clearing of forests
for agriculture, tropical forests may be completely eliminated within 25 years.
When the forests go so does thousands of plant species and the animals that depend on these plants.
The destruction of these areas is an irrevocable loss of these nonrenewable resources.
The rate of loss is faster than the Permian and Cambrian extinctions….forever changing the evolutionary history of land plants and many other organisms
While the loss of species is greatest in the tropics In addition to the ethical concerns that many
people have concerning the extinction of living forms, there are also practical reasons to be concerned about the loss of plant diversity.
People depend on plants for food, building materials, and medicines. We have explored the potential uses for only a tiny
fraction of the 290,000 known plant species. For example, Almost all of our food is based on
cultivation of only about two dozen species. fewer than 5,000 plant species as potential
sources of medicines The tropical rain forests and other plant communities
may be a medicine chest of healing plants that could be extinct before we even know they exist.