Chapter 29Chapter 29Plant Diversity I: Plant Diversity I: The Colonization of LandThe Colonization of Land

AP BiologyAP Biology

Requirements for Requirements for Successful Life on LandSuccessful Life on Land

Supporting mechanism (vascular tissue, Supporting mechanism (vascular tissue, lignin)lignin)

Absorptive structures (above & below Absorptive structures (above & below ground)ground)

Conducting tissues (move fluids)Conducting tissues (move fluids) Anti-desiccation (drying out) adaptations Anti-desiccation (drying out) adaptations

for body of plant (cuticle) & gametes for body of plant (cuticle) & gametes (pollen & spores)(pollen & spores)

Airborne gamete dispersalAirborne gamete dispersal

General Characteristics General Characteristics of Plantsof Plants

Includes mosses, ferns, conifers, Includes mosses, ferns, conifers, flowering plantsflowering plants

Multicellular, eukaryotic, photosynthetic Multicellular, eukaryotic, photosynthetic autotrophautotroph

Chlorophyll a, b, and carotenoidsChlorophyll a, b, and carotenoids CelluloseCellulose StarchStarch

Alternation of generations (more next)Alternation of generations (more next) Most have stomata for gas exchange Most have stomata for gas exchange

(Liverworts the exception)(Liverworts the exception) Secrete cuticle to reduce desiccationSecrete cuticle to reduce desiccation Most have vascular tissue for bulk transport of Most have vascular tissue for bulk transport of

water and materialswater and materials Exchange of materials between adjacent cells Exchange of materials between adjacent cells

through opening in cell walls (plasmodesmata)through opening in cell walls (plasmodesmata) Most have seeds (embryo with food & Most have seeds (embryo with food &

protective covering)protective covering)

General Characteristics General Characteristics of Plants, cont.of Plants, cont.

Alternation of Alternation of GenerationsGenerations Gametes produced & Gametes produced &

protected within protected within gametangia (non- (non-reproductive cells to reproductive cells to prevent desiccation & for prevent desiccation & for protection)protection)

Fertilization of egg takes Fertilization of egg takes place here (Female = place here (Female = archegonium; Male = archegonium; Male = antheridium)antheridium)

Sporophyte & gametophyte are structurally Sporophyte & gametophyte are structurally (look & develop) different ((look & develop) different (heteromorphic))

Both structures are multicellular (unlike Both structures are multicellular (unlike animals)animals)

Sporophyte dominant in most speciesSporophyte dominant in most species Meiosis in sporophyte produces haploid Meiosis in sporophyte produces haploid

reproductive cells (spores)reproductive cells (spores) Spores can develop into a new organism Spores can develop into a new organism

without fusing with another cellwithout fusing with another cell

Alternation of Alternation of Generations, cont.Generations, cont.

Proposed Ancestors of Proposed Ancestors of PlantsPlants

Charophyceans are the green algae most related Charophyceans are the green algae most related to land plantsto land plants

Several lines of evidence support this including:Several lines of evidence support this including: Homologous chloroplasts, cell walls, Homologous chloroplasts, cell walls,

peroxisomes, spermperoxisomes, sperm Phragmoplasts – microtubules form perpendicular Phragmoplasts – microtubules form perpendicular

to cell plate and guide deposition of cellulose to to cell plate and guide deposition of cellulose to form wallform wall

Molecular systematicsMolecular systematics Charophyceans had a layer of sporopollenin to Charophyceans had a layer of sporopollenin to

prevent exposed zygotes from drying out until prevent exposed zygotes from drying out until they are in water againthey are in water again

Classified Into 2 Major Classified Into 2 Major GroupsGroups

1. Nonvascular plants (aka Bryophytes) Bryophyta: mossesBryophyta: mosses Anthocrophyta: HornwortsAnthocrophyta: Hornworts Heptophyta: LiverwortsHeptophyta: Liverworts

2. Vascular Plants (aka Tracheophytes) Seedless vascular plants (Pteridophytes)

Lycophyta: LycophytesLycophyta: Lycophytes Pterophyta: Ferns & HorsetailsPterophyta: Ferns & Horsetails

Seeded vascular plants Naked seeded plants Naked seeded plants

(Gymnosperms)(Gymnosperms) Coniferophyta: ConifersConiferophyta: Conifers Cycadophyda: CycadsCycadophyda: Cycads Gnetophyta: GnetaeGnetophyta: Gnetae Ginkgophyta: GinkoGinkgophyta: Ginko

Flowering plants and Flowering plants and enclosed seeds enclosed seeds (Angiophyta)(Angiophyta)

Flowering plantsFlowering plants

Nonvascular Plants: Nonvascular Plants: BryophytesBryophytes Gametophyte dominant formGametophyte dominant form Lack vascular tissuesLack vascular tissues

Limits size (can’t grow tall)Limits size (can’t grow tall) Rely on diffusionRely on diffusion

Rhizoids – analogous to roots; used for anchorage– analogous to roots; used for anchorage Male flagellated sperm produced by the gametangium Male flagellated sperm produced by the gametangium

(antheridium)(antheridium) Female egg produced by the gametangium (archegonium)Female egg produced by the gametangium (archegonium) Sporophyte produces haploid spores within sporangiumSporophyte produces haploid spores within sporangium 3 Divisions:3 Divisions:

BryophytaBryophyta (mosses); ex: (mosses); ex: SphagnumSphagnum (peat moss) (peat moss) Heptophyta Heptophyta (Liverworts); sexual and asexual reproduction(Liverworts); sexual and asexual reproduction Anthocerophyta Anthocerophyta (hornworts)(hornworts)

Vascular Plants: Vascular Plants: TracheophytesTracheophytes Key adaptations to success on land:Key adaptations to success on land: Seeds – protect embryo & provide Seeds – protect embryo & provide

food for initial growthfood for initial growth Pollen – airborne dispersal; Pollen – airborne dispersal; Sporopollenin in walls of spores in walls of spores

Sporophyte dominantSporophyte dominant Vascular tissues – phloem & xylem; Vascular tissues – phloem & xylem;

specialization of parts of plant for specialization of parts of plant for specific functions (true roots, stems, specific functions (true roots, stems, and leaves)and leaves)

Ligninfied cell walls – supports plant Ligninfied cell walls – supports plant in airin air

Seedless Vascular PlantsSeedless Vascular Plants Division LycophytaDivision Lycophyta Club mossesClub mosses Many are Many are epiphytes – grow on other – grow on other

plants but not parasiticplants but not parasitic Sporangia produced on specialized Sporangia produced on specialized

leaves for reproduction called leaves for reproduction called sporophylls

Most species are Most species are homosporous – – produce a single type of spore that can produce a single type of spore that can produce a gametophyte with antheridia produce a gametophyte with antheridia and archegoniaand archegonia

Heterosporous species – have species – have sporophytes that produce separate sporophytes that produce separate sporesspores Megaspores – produce female Megaspores – produce female

archegonia on female gametophytearchegonia on female gametophyte Microspores – produce male antherdia on Microspores – produce male antherdia on

male gametophytemale gametophyte

Division SphenophytaDivision Sphenophyta Horsetail (Horsetail (EquisetumEquisetum) – only ) – only

extant genusextant genus HomosporousHomosporous Silica in cell walls make Silica in cell walls make

stems abrasivestems abrasive Gametophyte is free-living; Gametophyte is free-living;

can photosynthesize and can photosynthesize and not dependent on not dependent on sporophyte for nutrientssporophyte for nutrients

Seedless Vascular PlantsSeedless Vascular Plants

Seedless Vascular PlantsSeedless Vascular Plants Division PterophytaDivision Pterophyta Ferns – dominant seedless vascular Ferns – dominant seedless vascular

plantplant Large leaves (fronds) – compound Large leaves (fronds) – compound

with smaller leafletswith smaller leaflets Leaves are Leaves are megaphylls – leaves – leaves

with branched vascular with branched vascular tissues/veinstissues/veins

HomosporousHomosporous Sporangia develop on specialized Sporangia develop on specialized

sporophyllssporophylls Sporangia grow in clusters (Sporangia grow in clusters (sori) on ) on

undersideunderside Flagellated sperm – require water & Flagellated sperm – require water &

fertilization of egg in archegoniumfertilization of egg in archegonium Sporophyte protected in Sporophyte protected in

archogonium and emerges from archogonium and emerges from ground as ground as fiddlehead