Chapter 14Plants and Fungi

Plant Characteristics• Plants are multicellular eukaryotes.• Almost all are photosynthetic.• Evolved from green algae• Forms a multicellular embryo that forms, develops

within, and is nourished by tissues of the parental plant

Life on Land• Land plants, unlike aquatic plants and algae, face the threat of drying out and the

task of holding themselves upright• A cuticle prevents water loss by evaporation• Stomata, which can be opened or closed as needed, allow plants to balance water

conservation with the need to obtain carbon dioxide and to release oxygen during photosynthesis

• Roots anchor plants as well as a\take up water with dissolved minerals from the soil• Vascular tissues allow water and nutrients to move from the roots throughout the

plant body• Vascular plants have vascular tissues that are reinforced by lignin, an organic

compound that stiffens them and provides structural support• Leaves increase a plant’s surface area for absorbing sunlight and exchanging gases.• Not all plants have all of these adaptations!!!

Plant Life Cycle• Plants go through two multicellular stages during

their life cycle, called alternation of generations.• Diploid form = sporophyte (makes spores)• Spores develop into multicellular, haploid

gametophyte (makes eggs and sperm that combine and give rise to new sporophyte)

• The size and longevity of sporophyte vs. gametophyte varies with different types of plants.

• Spores withstand drying out better than gametes do.

Reproduction and Dispersal• Some plants still require water for fertilization.• Other plants have evolved the ability to reproduce in dry places by

releasing pollen grains (the male gametophyte) that can be delivered to eggs (female gametophyte) by wind or animals.

• In still other plants, female gametophytes form within a protective chamber on the sporophyte body. This gamete formation and fertilization produces a seed, which is an embryo sporophyte and tissues that nourish it, all encased in a protective coat.

• Seeds can lie dormant during unfavorable conditions and then germinate and produce a new sporophyte when conditions are favorable.

• Pollen and seeds not only allow plants to survive on land, but also allow them to spread into diverse habitats.

Bryophytes• Include mosses, hornworts, liverworts• No lignin-stiffened vascular tissues (no true roots, etc.) so they

don’t stand more than 8 inches tall• Instead, water and nutrients are absorbed across leaf surface• Gametophyte is largest, longest lived stage of life cycle• Need water for fertilization since flagellated sperm swim through

water to eggs• Mature sporophyte remains attached to and is dependent upon

gametophyte and produces wind-dispersed spores• Are important colonists of rocky places (primary and secondary

succession)• Mosses are the most diverse group of bryophytes. Peat mosses

can be burned for energy, producing fewer air pollutants than burning coal.

• Peat moss is also added to plant mixes to help soil retain moisture.

Bryophytes

Seedless Vascular Plants

• Include ferns, mosses, and horsetails• Evolved from bryophytes• Have flagellated sperm that require water for motility• Gametophyte is reduced in size and is short-lived• Sporophyte can live independent of gametophyte• Lignin stiffens sporophyte body and vascular tissue

transports water, sugars, and minerals throughout the body• These adaptations allow the sporophyte to be large and

complex with roots, stems, and leaves• Ferns, the most diverse group of seedless vascular plants,

may do asexual reproduction more often than sexual reproduction since it can occur even when there is little water present

• Many tropical ferns are epiphytes; they live on the trunks of trees but do not derive nutrients from it

Fern Life Cycle

Seed Plants• Evolved from a lineage of seedless vascular plants• Became dominant as the climate on Earth became drier• Microspores develop into male gametophytes (pollen

grains); megaspores develop into female gametophytes• Do not release their spores into the environment like

bryophytes and seedless vascular plants• Male and female gametophyte are reduced in size and

develop upon the sporophyte• Wind or animals deliver pollen grains to female parts of

another plant (called pollination)• A pollen tube grows out from pollen grain after pollination

and delivers the sperm to the egg- no water is needed for fertilization so seed plants can reproduce during dry times

Seed Plants• Female gametophyte form inside ovule• After pollination and fertilization, ovule develops into seed• A seed is an embryo sporophyte and some nutritive tissue inside a

protective coat• Since embryo is enclosed with nutrition inside a waterproof

protective coat and can stay dormant until conditions are favorable, seed plants have an advantage over seedless plants

• Secondary growth (growth in diameter) produces woody tissue• This woody tissue is produced when lignin-stiffened tissue called

xylem (vascular tissue that transports water and minerals) is added• Only seed plants produce true wood

Gymnosperms• Vascular seed plants that produce seeds on the surface of

ovules• Seeds are “naked” because they are not inside of fruits• Seeds may be enclosed in fleshy or papery covering• Conifers: most diverse gymnosperms; woody trees or shrubs

with needlelike/scale-like leaves; usually evergreen but a few are deciduous; a pine tree is a gymnosperm sporophyte- its gametophytes are in its cones

• Cycads and ginkgos are the only modern gymnosperms with flagellated sperm that swim in a fluid secreted by the female plant to the eggs in the plant’s ovule

• Ephedra is another gymnosperm that produces a compound with a stimulating effect on the nervous system that can be fatal

GymnospermsPine Ginkgo biloba

Cycad

Ephedra

Angiosperms• Vascular seed plants that make flowers and fruits• After fertilization, an ovule matures into a seed and the ovary

becomes the fruit. A fruit is a mature plant ovary.• Nearly 90% of all modern plants are angiosperms.• Angiosperms can survive in almost any habitat because they

grow faster than gymnosperms.• Also, the flower is another adaptation that makes angiosperms

so successful• Flowers and insects coevolved; they have a mutualistic

relationship• The plant gets pollinated and the insect gets nectar to feed on• In fact, many flowering plants evolved traits to attract specific

pollinators, such as brightly colored petals, sugary nectar, or a strong fragrance.

• Wind pollinated angiosperms don’t have these traits.

Flowers

Male part Female part

Angiosperms• Two lineages of angiosperms:• Monocots: orchids, palms, lilies, rye, wheat, corn,

rice, sugarcane, etc.; • Dicots: non-wwody plants such as tomatoes,

cabbages, roses, daisies, cacti, etc.MONOCOTS DICOTS

Embryo with single cotyledon(seed leaf) Embryo with two cotyledons Pollen with single furrow or pore Pollen with three furrows or poresFlower parts in multiples of three Flower parts in multiples of four or fiveMajor leaf veins parallel Major leaf veins reticulatedStem vacular bundles scattered Stem vascular bundles in a ringRoots are adventitious Roots develop from radicleSecondary growth absent Secondary growth often present

Angiosperms

Angiosperm Life Cycle1. Pollen forms in stamen (male part)2. Female gametophytes form in carpels (female part)3. Pollen grain lands on stigma4. Pollen tube forms down through style and into ovary5. Two sperm are delivered to the ovule, where double fertilization

occurs6. One sperm fertilizes the egg to form the embryo7. The other sperm fertilizes a cell with two nuclei, forming a

triploid cell that will become the endosperm (nutritive tissue that will nourish the embryo in the seed and is unique to angiosperms)

Economic Importance of Angiosperms

• Provide food and shelter for land animals• Provide nearly all of our food, directly or indirectly• Their fibers are used to make clothing• Furniture comes from their wood• We extract medicines and psychoactive drugs from

them

Fungi• Are more closely related to animals than plants• Are spore producing heterotrophs with cell walls made of chitin• Some are single-celled (yeast) while others are multicellular

(molds and mushrooms)• Multicellular fungi grow as a mesh of branching filaments

collectively called the mycelium; each filament is called a hypha• No specialized vascular tissue but cell walls are porous so

material can flow among cells• Some fungal bodies can be enormous- the hyphae of one soil

fungus in Oregon covers an area of over 2,200 acres and is still growing. It has been estimated to be 8,000 years old!

Fungi• All fungi obtain nutrients by extracellular digestion (done by

enzymes secreted by the fungus) and absorption.• Most fungi are free-living saprobes (organisms that feed on and

decompose organic wastes and remains).• By doing this, they keep nutrients cycling in ecosystems.• Some fungi can be parasitic, while other benefit their host. • Most plants have beneficial fungi growing on their roots.• There is one modern fungi that is mainly aquatic, having a

flagellated stage in its life cycle.• Scientists believe that fungi evolved, like plants and animals,

from an aquatic protist.

Fungi• Three types of fungi:• Club fungi: mushrooms are their reproductive parts

(fruiting bodies), appearing briefly when conditions favor sexual reproduction

• Zygote fungi: bread molds, do not make large fruiting bodies

• Sac fungi: truffles (below ground) and morels (above ground) are their fruiting bodies, both of which are highly valued as food; a single 3 pound truffle brought $160,000 in 2006.

FungiBeneficial• Mutualistic relationship with most

plants, increasing absorptive area of plants; plant shares its sugars while fungus shares its minerals

• Lichens consist of fungus and green alga/cyanobacteria-fungus shelters photosynthetic partner and receives nutrients in return-lichens are colonial species that begin primary/secondary succession-they break down rocks and form soil

• Lichens are used as an indicator species

• Are important decomposers, can break down lignin in wood and recycle nutrients, especially in forests

Harmful• Can be parasitic

• Are especially important plant pathogens

• Can infect humans, especially skin (athlete’s foot, ring worm)

• Histoplasmosis is caused when humans breathe in spores of Histoplasma capsulatum which can be fatal to the immune-suppressed and the elderly