Download Chapter 12: Diversification of the Eukaryotes: Plants and Fungi

Chapter 12: Diversification of the Eukaryotes: Plants and Fungi
Where did all the plants and fungi come from?
What is a plant?
The plants, fungi, and animals are three kingdoms that are all eukarya and multicellular.
BUT there are defining characteristics that separate plants from the other two kingdoms.
Unlike fungi or animals, most plants carry on photosynthesis, creating their own
carbohydrates.
Plants are sessile (attached) and terrestrial (land-living).
Plants are also multicellular. They develop specialized tissues and organs, such as
roots and shoots.
The inability of plants to move shapes the way they obtain food, reproduce, and protect
themselves from predation.
Plants need sunlight, but since they cannot move they bend in place and grow toward
the light.
Finding a mate is also difficult if stationary. Some plants have a haploid stage to help
male and female gametes find each other. Other plants use the wind, or animals to
transport the gametes.
Plants also cannot run from predators. They have evolved other ways to defend
themselves, such as thorns or chemicals.
The earliest land plants were the first multicellular organism to live on land; these simple
non-vascular plants had no vessels to transport water and nutrients.
The evolution of land plants was a series of forms with characteristics that made them
increasingly independent of water.
The evolutionary history of plants reveals the progressive appearance of characteristics
that allow plants to succeed on land despite their inability to move.
The closest living relative of plants are freshwater green algae, but they live in water or
very moist land surfaces.
The closest relatives of plants are called coleochaetes (KOH-lee-oh-keets)
An individual coleochaete is about the size of a pinhead, is only one cell thick, and can
withstand exposure to air, so they survive when the water level in a lake falls and
leaves them high and dry.
Three problems for land-living plants
1) Gravity
2) Drying out
3) Finding a mate
The earliest plants did not have to grow upward, they could creep along the ground.
The material that protects land plants from drying is a waxy layer called the cuticle,
which covers the entire surface of the plant.
Non-vascular plants—mosses, liverworts, and hornworts—have scarcely evolved
beyond the stage of the earliest land plants.
12.3 Mosses and other non-vascular plants lack vessels for transporting nutrients and
water. They rely on diffusion to move materials like water and dissolved nutrients
around.
Alternation of Generations
A life cycle of alternating haploid and diploid generations in which the diploid embryo is
protected by the haploid female parent plant.
The diploid embryo matures into a plant that produces haploid spores. These spores
grow into the haploid parents.
Mating in animals is more straight forward then in land plants.
Animals are diploid (have two sets of chromosomes). They reproduce by combining the
genomes of two haploid gametes, the egg and sperm.
Land plants developed a special haploid parent (one set of chromosomes), in addition
to the diploid parent.
The haploid parents produce the eggs and sperm and nurture the resulting embryo.
This is called “Alternation of Generation”
The diploid embryo is sheltered and nurtured within the female reproductive structure
while it continues to divide by mitosis and mature.
Unfortunately these plants still need free water to reproduce.
Water collects here during rainstorms, allowing the sperm to “swim” from the male
structure to fertilize eggs in the female structure in the haploid parent.
These non-vascular plants are still widespread, especially mosses. There are more than
12,000 species of mosses in habitats extending from Arctic and alpine habitats to
the tropics.
The first vascular plants—the earliest ferns, horsetails, and some related forms—were
able to grow much taller than their non-vascular predecessors.
The evolution of vascular tissue made large plants possible because it made water and
nutrient delivery more efficient. Like a circulatory system, vessels are an effective
way to carry water and nutrients up from the soil to the leaves.
Reproduction
In many ferns, the diploid parent produces spores from sporangia located on the
underside of the leaves.
A spore grows into a tiny heart-shaped structure, the haploid parent. It produces eggs
and sperm.
Sperm “swim” through drops of rain water to fertilize an egg.
The embryo grows into an adult diploid fern.
The next big innovation in plant evolution was the seed, an embryonic plant with its own
supply of water and nutrients encased within a protective coating.
Seeds are the way plants give their offspring a good start in life and get them to leave
home.
Seed Dispersal
Only opportunity most plants have to send their offspring away from home
Seeds and seed pods have many ways to do this:
forceful send-off of exploding seed pods
seeds that hitch rides on passing animals
seeds that float in water or almost fly
Gymnosperms (pine trees and their relatives) were the earliest plants to produce a
seed, and this mode of reproduction offers advantages over the spores of earlier plants.
Pines
Firs
The reproductive structures of gymnosperms—the cones—are male or female. The
male cones produce pollen grains in small cones. Pollen grains containing the
sperm are carried by the wind to the female cone.
The female cones produce eggs in a larger woody cone.
Seed plants no longer have a free-living haploid parent. That stage in the life cycle is
compressed into a few cells living on the diploid parent plant
Seeds gave gymnosperms the boost they needed to become the dominant plants of the
early and middle Mesozoic, but they depend on wind to carry their pollen.
12.7 Conifers include the tallest and longest-living trees.
The four tallest trees in the world are conifers: a coast redwood that is 113 meters
(380 feet) tall; a Douglas fir and a Sitka spruce, each 97 meters (318 feet); and a
Sierra redwood at 95 meters (311 feet).
Bristlecone pines reach ages of more then 4800 years
How can trees grow large and live to great ages?
Woody plants can be exceptionally strong and resistant to attack by herbivores
Bark is a physical barrier of dead tissue protecting the living tissue below.
Exuding a sticky pine pitch that can engulf insects.
Conifers are the success stories among gymnosperms, with more species and a larger
geographic range than all of their relatives combined.
12.8 Angiosperms are the dominant plants today. First appeared 125 mya.
The flowering plants, or Angiosperms, dominate the plant world now, with some
250,000 species compared to the approximately 800 species of gymnosperms.
A flower houses a plant’s reproductive structures, and most flowers have both male and
female structures.
Stamens: male
Carpels: female
12.9 A flower is nothing without a pollinator.
Why are flowers so flashy?
Trickery and Bribery
Angiosperms have found a way to transfer pollen efficiently from the anthers of one
flower to the stigma of another—let an animal carry it.
Flowers are conspicuous structures that advertise their presence with colors, patterns,
movements, and odors.
1) Trickery
Plant deceit!
Orchid species
flowers that resemble female wasps
Fly orchids use trickery.
2) Bribery
Plants offer something of value for pollen transport.
Requires:
a sticky pollen
a flower that catches the attention of the pollinator
something of value to the pollinator.
Based on these structures, plants are able to trick or bribe animals into transporting
male gametes to female gametes where fertilization can occur.
Do flowers fertilize themselves?
Outbreeding versus Inbreeding
Out-breeding mechanisms
1) Male and female structures on different plants.
2) Male parts mature before female parts on the same plant.
3) Proteins on the surface of the carpel will not allow pollen from the same plant to grow
a pollen tube for fertilization.
This ensures greater genetic variation among offspring than through inbreeding.
Plants often use the assistance of animals to disperse their fruits (containing seeds),
depositing them at a new location where they can grow.
Fruits are made up from the ovary and, occasionally some surrounding tissue.
How does this system work?
Fruits are colorful.
Fruits taste good.
Fruit is good for animals.
Can seeds still sprout after being eaten by an animal?
Test it yourself!
12.12 Unable to escape, plants must resist predation in other ways.
Chemical Defenses as Medicines?
Medicinal plants
Salicin, opium, digitalin, ipecac
Bioprospecting: the search for plants with medicinal applications.
Insect Attack!
Volatile chemicals
Plants can also warn nearby plants!
methyl jasmonate (MeJa) is released by flowering plants when attacked by insect
predators like mites. It not only warns nearby plants but signals predators of
the insects.
About 900 species of plants turn the tables and eat insects to supplement the nitrogen
compounds they get from the soil.
Pitcher plants and sundews.
Genetically animals and funi are a little more similar to each other then to plants.
Both animals and fungi must digest organic material for energy and materials, but fungi
don’t have digestive systems. They absorb nutrients externally from living or dead
organisms.
12.14 Fungi have common structures, but exploit an enormous diversity of habitats.
What is a “mycelium”?
Fungi have complex life cycles, with both sexual and asexual phases; the parts of fungi
that are most often visible are their temporary spore-producing bodies.
Mushroom Delicacies
Portobello and shitake mushrooms
The white button mushroom on pizza
Truffles
sell for $1750 to $3500 per pound!
How can fungi grow in so many habitats?
Advantages of being a decomposer. There is lots around.
Fungi don’t need light
Hyphae release enzymes to digest organic matieral
Enormously important ecological role!
Speed the decay of organic material.
Fungal Invasion!
Sick-building Syndrome
Fungal Parasites
On humans?!
Mycosis is a general term for a disease causing fungus.
Lichens
Fungi and chlorophyll-containing bacteria and algae as “partners”
12.15 Most plants have fungal symbionts.
Take-home message 12.15
Mycorrhizal fungi grow in intimate association with the roots of most plants, receiving
sugar from the plant and transferring nitrogen and phosphorus to the plant.