Plant Diversity

Plant Diversity

Chapter 22

22-1 Introduction to PlantsOldest fossil evidence-470 million years

agoPlants dominate the landscapeProvide the base for food chains on landProvide shade, shelter and oxygen for

animals of all sizes

What is a Plant?Members of the Kingdom Plantae.Multicellular eukaryotesCell walls of celluloseDevelop from multicellular embryosCarry out photosynthesis using chlorophyll

a and bMost are autotrophs, few are parasites or

saprobes (feed on decaying organisms)

How have plants become so successful if they can’t move to get away from predators or to get food?

Think of plants as “Stationary animals that eat sunlight”

The Plant Life CycleTwo alternating phases known as the

alternation of generationsDiploid (2N)- the sporophyte plant or spore

producingHaploid (N)- the gametophyte plant or gamete

producingPhyte-means plant

HaploidDiploid MEIOSIS

Spores(N)

Gametophyte Plant (N)

FERTILIZATION

Sperm(N)

Eggs(N)

Section 22-1

Generalized Plant Life Cycle

Sporophyte Plant (2N)

Mosses and Ferns- Require water to reproduce

Seed Plants- reproduce without waterMany plants also have vegetative or

asexual reproduction

What Plants Need to SurviveDeveloped adaptations to survive as

sessile organismsPlants need sunlight, water & minerals,

gas exchange and transportation of water and minerals through the plant body

SunlightNeed sunlight to carry out photosynthesis.Adaptations to gather sunlight

Leaves broad and flatArrangement on stem to maximize light

absorption

Water and MineralsNeed a constant supply of waterNeed to get water to all cells, above

ground tooStructures to limit water loss Minerals absorbed with the water needed

for plant growth

Gas ExchangeRequire oxygen to carry out respiration

and carbon dioxide for photosynthesisCan’t lose water vapor in the process

Movement of Water and Nutrients

Specialized tissues that carry water up from the soil and distribute food through the plants

Simple plants do this by diffusion

Early PlantsMost of Earth’s history-no plantsAlgae and photosynthetic prokaryotes

provided the planets oxygen and foodPlants appeared, life on Earth changedNew ecosystems, soil formed, organisms

developedHow did plants adapt to land, how did they

evolve structures to allow life on land?

Origins in the WaterFirst plants evolved from an organism

much like the green algae todayAlgae have size, color and appearance of

plantsSimilar reproductive cyclesCell walls and photosynthetic pigments

like plants

The First PlantsDNA sequencing confirms that plants are

closely related to certain groups of green algae.

Oldest known fossils of plants, 450 million years ago-similar to today’s mosses (cooksonia)

Suggest that they were still dependent on water to complete life cycle.

From plant pioneers two lineagesMosses and their relativesAll other plants on Earth today

Evolved different adaptations to living on dry land.

Floweringplants

Cone-bearingplants

Ferns andtheir relatives

Mosses andtheir relatives

Green algaeancestor

Flowers; SeedsEnclosed in Fruit

Seeds

Water-Conducting(Vascular) Tissue

Overview of the Plants KingdomPlants divided into four major divisions

based on three featuresWater conducting tissuesSeedsFlowers

Mosses, Ferns, Cones, FlowersToday classified more precisely by DNA

sequencing

Mosses andtheir relatives15,600 species

Ferns andtheir relatives11,000 species

Cone-bearing plants760 species

Floweringplants235,000 species

22-2 Bryophytes Nonvascular plants- No vascular tissue to

conduct water and nutrients Life cycles that depend on water for

reproduction No vascular tissue so they draw up water by

osmosis only a few cm’s above ground This keeps them very small Produce sperm that swim to reach eggs Have to live where rain or dew for part of yr.

Groups of BryophytesMost recognizable feature is that they are

low growing plants in moist shaded areasPlants thrive in areas where water is in

regular supplyThree separate phyla.

Mosses or BryophytaLiverworts or HepaticophytaHornworts or Anthocerophyta

MossesMost common Bryophyte.Grow abundantly in areas with water and

nutrient poor soilTolerate low temperatures, most abundant

plants in the polar regionsVary in appearance from mini evergreen

trees to filament plants that form carpet of green

Gametophyte of moss looks like a stem with tiny leaves-one cell thick so lose water quickly

Reproduce with a thin stalk with a capsule that contains spores-sporophyte

No true roots-rhizoids anchor to the ground and absorb water and minerals

Water moves from cell to cell through rhizoids to rest of plant

Capsule

StalkSporophyte

Gametophyte

Stemlikestructure

Leaflikestructure

Rhizoid

LiverwortsFlat leaves attached to the ground is what

these plants look like.Named because some species look like a

flattened liverLeaf forms an umbrella shaped object that

produces the sperm and eggs.Some form gemmae that are in cuplike

structures that wash out and produce new individual

HornwortLook very much like the liverwortOnly difference is that the sporophyte

looks like a tiny green hornMost found where soil is moist year round

Life Cycle of BryophytesLife cycle involves alternation of

generationsGametophyte is dominant, recognized

form and carries out the plants photosynthesis

Sporophyte is dependent on the gametophyte for water and nutrients

Dependence on WaterSperm must swim to the egg to fertilizeBryophytes must live in habitats where

water is available at least part of the year

Life Cycle of Moss When spore lands in a moist place it germinates

and forms a protonema-mass of tangled green filaments.

Protonema grows to form rhizoids (rootlike structures and shoots that grow into the air.

Shoots form the familiar green part of the plants. The gametophyte

At the tips of the gametophyte are the archegonia (eggs) or antheridia (sperm).

Life cycle of Moss Some have both on the same gametophyte

some have separate gametophytes When sperm and egg fuse and fertilization takes

place the diploid zygote is formed This zygote develops into the sporophyte part of

the moss. It grows right out of the gametophyte part of the plant and depends on the gametophyte for food and water

When sporophyte matures it produces haploid spores in a capsule by meiosis and the capsule ruptures and releases the spores into the air and the cycle continues.

Go to Section:

Haploid (N)

Diploid (2N) MEIOSIS

FERTILIZATION

Maturesporophyte

(2N)

Gametophyte(N)

Gametophyte(N)

Youngsporophyte(2N)

Zygote(2N)

Sperm(N)

Sperm(N)

Egg(N)

Spores(N)

Capsule(sporangium)

Protonema(young gametophyte)(N)

Malegametophyte

Femalegametophyte

Antheridia

Archegonia

Section 22-2

Figure 22–11  The Life Cycle of a Moss

Human Uses of MossSphagnum moss grow in acidic water of

bogsThe dead sphagnum moss are called peat

and accumulate in thick layers.Peat can be harvested and used as fuel or

in gardening to retain moisture near the plants or to increase the acidity of the soil near the plants.

22.3 Seedless Vascular PlantsBryophytes can only move water from cell

to cell by osmosis.420 million years ago moss were joined by

plants up to a few meters highHow did they grow that tall.New transport system with vascular tissue.Able to get water to a higher height

Evolution of Vascular Tissue: A Transport System

Tracheids-new type of cell that allows transport of fluids and nutrients in plantsMakes up xylem-the system of plants that

transports water.Def.-hollow cells with thick cell walls to

resist pressureConnected end to end like straws so that

the water flows through themMore efficient movement than by diffusion

Evolution-cont.2nd type of vascular tissue is PhloemUsed to transport solutions of nutrients

and carbohydrates produced by photosynthesis

Both xylem and phloem move nutrients through the plant even against gravity

Combination of xylem and lignin enables plants to grow much higher

Ferns and their Relatives Include the club moss, horsetails and fernsAll have true roots, stems and leavesRoots-underground organs that absorb

water and nutrients. Xylem in center of root

Stems-supporting structure to connect root with the leaf

Leaves-Photosynthetic organs of the plants

Club Mosses-Phylum LycophytaOnce very large and ancient group of land

plantsNow much smaller phylum containing club

mossesAncients grew up to 35 meters tall and

made some of the Earth’s first forests that are now huge beds of coal.

Look like miniature pine trees so also called the ground pines.

HorsetailsOnly living genus is Equisetum that grows

about 1 meter tall.Has true leaves, stems and leaves which

are nonphotosynthetic.Leaves are nonphotosynthetic, scalelike

and are arranged in whorlsScouring rush looks like a horses tail and

has crystals of silica and used to scour pots and pans

Ferns Phylum Pterophyta evolved 350 mya when the

club moss forests covered the Earth. Ferns survived in greater numbers than any

other spore-bearing vascular plants Have true vascular tissues, strong roots

creeping stems called rhizomes and large leaves called fronds

Can thrive in areas of little light and most abundant in wet or seasonally wet habitats

Often found in forests of larger trees

Life Cycle of FernsLarge plant that we recognize as the fern

is the diploid sporophyte and is the dominant state.

Develop haploid spores in structures called sporangia in clusters called sori and are usually on the underside of the fronds

When spores germinate they develop into a haploid gametophyte.

Small gametophyte develops rootlike rhizoids and then flattens into a thin, heart shaped green structure that is the mature gametophyte

Small , tiny and develops independently from the sporophyte

Antheridia and archegonia are found on the underside of the gametophyte. Why??

Fertilization requires at least a thin film of water so sperm can swim to eggs

The zygote produced immediately develops into a new sporophyte plant

As the sporophyte develops the gametophyte withers away.

The sporophytes can live for many years as the fronds produced in spring die in the fall but the rhizomes live through the winter and produce new leaves

Go to Section:

Haploid gametophyte (N)

Diploid sporophyte (2N)

MEIOSIS

FERTILIZATION

Maturesporophyte(2N)

Gametophyte(N)

Frond

Sperm

Egg

Spores(N)

Antheridium

Archegonium

Developingsporophyte(2N)

Sporophyteembryo(2N)

Maturegametophyte(N)

Younggametophyte(N)

Sporangium(2N)

Section 22-3

Figure 22–17  The Life Cycle of a Fern

Go to Section:

Comparing Spore-Bearing Vascular Plants

CharacteristicsWatertransportation

Structure

Section 22-3

Compare/Contrast Table

Club MossesBy vasculartissue

Look like miniature pine trees; scalelike leaves

HorsetailsBy vasculartissue

True leaves, stems, and roots

FernsBy vasculartissue

Creeping or underground rhizomes (stems); fronts (leaves); some have no roots or leaves

22.4 Seed Plants Whether acorns, pine nuts, dandelion seeds, or

kernels of corn seeds are found everywhere. Plants with this single trait have evolved to

become the most dominant group of photosynthetic organisms on land

Two major groups- Gymnosperms-bear seeds on surface of cones Angiosperms-flowering plants bear seeds inside a

layer of tissue that protects the seed

Reproduction Free From WaterLike all plants-alternation of generations

Gametophyte and sporophyte stageDifference from moss/ferns in that they

don’t need water for fertilization of gametes

Because of this they can live everywhereAdaptations that allow this

Flowers or cones, transfer of sperm by pollination, protection of embryo in seeds

Cones and FlowersGametophytes of seed plants grow and

mature in sporophyte structures called cones or flowers.Cones are seed bearing structures of

gymnospermsFlowers are angiosperms seed bearing

structures

PollenThe entire male gametophyte is contained

in a tiny structure called a pollen grain.Doesn’t travel through waterCarried to the female reproductive

structure by WindInsectsAnimals

Transfer of pollen to female is called pollination

SeedsDef.-Seed is the embryo of a plant that is

encased in a protective covering and surrounded by a food supply.

Embryo-organism in an early stage of development

Plant embryo is diploid and is the early developmental stage of the sporophyte plant

Seed food supply provides nutrients to the growing embryo

Seed coat-surrounds and protects the embryo and keeps it from drying out

Seeds may have specialized structures to help with dispersal to other habitats

Embryos in seeds can remain dormant for long periods of time and start growing again only when the conditions are good for survival

Evolution of Seed PlantsFossil record shows that ancestors of

seed plants evolved adaptations (seed) in order to survive in places where moss/ferns couldn’t

Fossils show that the first seed plants existed 360 mya and that they resembled ferns

Remains exist as large coal deposits

Gymnosperms-cone bearersMost ancient surviving seed plants Include the Gnetophytes, Cycads,

Ginkgoes and the ConifersSeeds are all exposed- naked seeds

Gnetophytes70 species are knownReproductive scales are clustered in

conesWelwitschia-representative species

CycadsCycadophyta-palmlike plants with large

cones1st appeared 225 mya9 genera existFound in tropics and subtropics

GinkgoesOne species left-Ginkgo bilobaCommon during dinosaur reignLiving fossil-looks just like ancestorsTough and resistant to air pollution

ConifersOver 500 speciesPines, spruce, firs, cedars, sequoias etcSome live long others grow tall

Ecology of ConifersThrive in a wide variety of habitatsLeaves have adaptations to survive dry

conditionsLong thinWaxy coating

Most are evergreen-retain leaves throughout year

Replaced every 2-14 years

Go to Section:

Comparing Features of Seed Plants

FeatureSeeds

Reproduction

Examples

Section 22-4

Compare/Contrast Table

Gymnosperms Angiosperms

Bear their seeds on cones

Can reproduce without water; male gametophytes are contained in pollen grains; fertilization occurs by pollination

Conifers, cycads, ginkgoes, gnetophytes

Bear their seeds within flowers

Can reproduce without water; male gametophytes are contained in pollen grains; fertilization occurs by pollination

Grasses, flowering trees and shrubs, wildflowers, cultivated flowers

22.5 Angiosperms—Flowering Plants

Members of the Phylum AnthophytaAppeared 135 mya, most recent of plantsOriginated on land and dominate the plant

life on EarthMost have reproductive method involving

flowers and fruit

Flowers and FruitAngiosperms develop unique reproductive

organs known as flowersFlowers are an advantage because they

attract animals which then transport pollen from flower to flower.

Much more efficient than wind pollination of the gymnosperms

Flowers contain ovaries that surround and protect the seeds.

After pollination the ovary develops into a fruit which protects the seed and aids in dispersal

Fruit-a wall of tissue surrounding the seedAnother adaptation that led to success of

angiospermsSpreads plants over large areas of land

Diversity of AngiospermsVery diverse group with many ways to

classify themMonocots vs. DicotsWoody vs. HerbaceousAnnual vs. Perennial vs. Biennial

Categories can overlapJust provides a way to organize them

Monocots and DicotsTwo classes in the angiosperms

Monocotyledonae-single seed leaf or cotyledons

Dicotyledonae-two seed leavesCotyledon is the first leaf or first pair of

leaves that are produced by the embryo.See chart in next slide for different

characteristics of Monocots vs. dicots

Go to Section:

Monocots Dicots

Seeds

Leaves

Flowers

Stems

Roots

Single cotyledon

Parallel veins

Floral parts often in multiples of 3

Vascularbundlesscattered throughout stem

Fibrous roots

Two cotyledons

Branched veins

Floral parts often in multiplesof 4 or 5

Vascularbundlesarranged ina ring

Taproot

Section 22-5

Figure 22–25 Comparison ofMonocots and Dicots

Woody and Herbaceous PlantsCharacteristics of the stems of these

plants puts them into these two categoriesWoody-have cells with thick cell walls to

support the plantEx. Trees, shrubs, vines

Herbaceous-stems are smooth and nonwoody.Produce no wood as they grow

Annuals, Biennials & PerennialsCategories based on life spansAnnuals-complete a life cycle in one

growing seasonMany garden plants

Biennials-Complete a life cycle in two years

Perennials-plants that live for more than two yearsSome herbaceous, most are woody