Biology 051: Final Exam (28-31)

Diploid sporophytes produce unique haploid spores using ___________, so gametophytes must produce haploid gametes using ___________.

Meiosis, mitosis

Plant Growth: apical meristems

Meristems: perpetually undifferentiated tissue that divides when conditions permit •apical meristems→tips of roots, shoots, axillary buds •cause primary growth→increases in length, breadth

Seedless Vascular Plants Lycophytes, Monilophytes:

Vascular tissue: tube-shaped cells transport water (xylem), sugar (phloem) throughout plant, allowed plants to grow tall → key adaptation

Apical meristems

localized regions of cell division in tips of roots, shoots;source of directional growth toward resources

Archaeplastida Supergroup

monophyletic group, includes Charophytes(green algae): -closest relatives of plants, shared derived characters: •Rings of cellulose-synthesizing proteins in plasma membrane →make cellulose for cell wall (chlorophytes have linear proteins) •Structure of flagellated sperm→in plants with flagellated sperm, closely resemble charophyte sperm •Formation of phragmoplast during cell division structure of microtubules forming between nuclei of dividing daughter cells, causing cell plate to develop →becoming new cell wall •Nuclear, chloroplast DNA→supports morphological evidence

explain why alternation of generations is a shared derived character for plants but cellulose in cell walls is not?

-Cellulose in cell walls has evolved independently in different groups →molecule itself is not unique-All plants share unique variations in alternation of generations process →variations not present in other groups (each has their own)

What's So Great About Seeds?

-Ovules, pollen→no longer tied to moist habitats(poor sperm can take a break!) •Seeds can disperse over large distances, remain dormant over long periods •can colonize wide variety of habitats •wait out unsuitable conditions -Seeds provide food, protect embryo •dessication, predators, UV light

Structure of Plants: Tissues

3 tissue-system: grounds, dermal, vascular •Ground: performs most metabolic functions •Dermal: protects plant; cuticle,outer epidermis(external layer of tightly packed cells); may have hairs = trichomes→protect plant from insects, reduce water loss, contain secondary compounds •Vascular: xylem and phloem→transport water, nutrients between roots, shoots

Following the collapse of the giant lycophyte and monilophyte forests about 300 mya, gymnosperms underwent many speciation events and quickly diversified. This is an example of:

A) Adaptive radiation B) Macroevolution

If first plants had no roots, how did they get nutrients and water from new environment?

A) Through diffusion B) With help from their mycorrhizae

Which of the following is true of Monilophytes and Lycophytes?

A)They caused an ice age! B)They each evolved roots independently C)They are the first plants to have true leaves

Seedless Vascular Plants: Leaves

Leaves evolved to carry reproductive structures; sporophylls: leaves that bear sporangia •most lycophytes and monilophytes = homosporous:one type of sporangium, develops into bisexual gametophyte most seed plants = heterosporous: two types of sporangia, produce two kinds of spores: megaspore→female gametophyte→eggs microspore→ male gametophyte→ sperm

Liverworts

Liverworts don't have stomata→likely diverged first; hornworts, mosses can't close theirs on hot days like other plants can

Which of the following is NOT a possible function of roots?

Photosynthesis

placental transfer cells

enhances the transfer of nutrients from parent to embryo (multicellular embryo retained within tissues of female gametophyte, nourished by placental transfer cells)

Seed Composition

fertilized ovule →embryo + food + seed coat(formerly integument)

Multicellular gametangia

tissues in gametophyte which produce gametes; archegoniumin females, antheridium in males (lost in seed plants) •Many plants have flagellated sperm that swim to eggs via water droplets

Walled spores produced in sporangia

tissues in sporophytes contain sporangia which protect spores, AND contain sporocytes:cells which produce haploid spores by meiosis •sporopollenin protects spores (prevents zygotes of charophytes from drying out)

Plant Growth: lateral meristems

vascular cambrium adds secondary xylem, phloem; cork cambrium adds secondary dermal tissue •cause secondary growth:increase in width→makes stems woody

Seedless Vascular Plants

• Dominated 359-299 mya giant trees > 40m great swamp forests • Removed significant CO2 during this period cooling climate glacial event; most plant species became extinct, climate too dry and cold • These forests eventually, through heat and pressure rich coal deposits

Alternation of Generations

•Alternation of multicellular haploid, diploid stages •Haploid spores (usually formed via meiosis) →develop into new organism The gametophyte generation begins with a spore produced by meiosis. The spore is haploid, and all the cells derived from it (by mitosis) are also haploid. In due course, this multicellular structure produces gametes — by mitosis — and sexual reproduction then produces the diploid sporophyte generation. The sporophyte generation thus starts with a zygote. Its cells contain the diploid number of chromosomes. Eventually, though, certain cells will undergo meiosis, forming spores and starting a new gametophyte generation.

Shared Derived Characters of Plants

•Apical meristems •Alternation of generations with multicellular, dependent embryos •Multicellular gametangia •Walled spores produced in sporangia:

To Branch or Not To Branch

•Branching→more efficient light gathering, but branched stems aren't as tall (can't maximize both) •Tall stems→less light competition,must be thicker (uses resources that aren't available for reproduction→vines are notable exception) •Branching roots →effective anchors, facilitate growth, acquire water, nutrients from the soil •plants can adjust growth, physiology of roots to respond to changing environmental conditions, such as increased nitrogen availability

Importance of Seed Plants

•Domestication of seed plants→humans from hunter/gatherer to agricultural •Six crops yield 80% of our calories: corn, potatoes, wheat, rice, cassava, sweet potatoes •Provide: tea, coffee, spices, paper, medicines like digitalin, pain relievers like morphine

Seedless Vascular Plants

•Dominated 359-299 mya→giant trees > 40m→great swamp forests •Removed significant CO2 during this period→cooling climate →glacial event; most plant species became extinct, climate too dry and cold •These forests eventually, through heat and pressure→rich coal deposits

Key Adaptations for Land

•Drying out (dessication) real danger→cuticle= waxy coating that prevents water loss=key adaptation •Nutrients, minerals available in soil, early plants had no roots →mycorrhizae= symbiotic fungi help plants absorb more water, nutrients than they can alone •475 mya ancestors of modern plants colonized land along with symbiotic mycorrhizae →fossil evidence

Bryophytes (Non-vascular Plants)

•Earliest plant lineages to diverge: earliest spores of land plants (470-450 mya) have structural features found only in liverworts; spores similar to hornworts,mosses appear 430 mya •Spores germinate →form one-cell-thick filaments= protonema(acquires nutrients by diffusion) →each protonema can form multiple gametophores →these + protonema = gametophyte(dominant stage)

Seedless Vascular Plants: Leaves

•Fern sporophylls produce clusters of sporangia (sori) on undersides of sporophylls •Most lycophytes, gymnosperms groups of sporohylls form cone-like structures(strobili, Greek for cone)

Angiosperms (Flowering Plants)

•First appear ~ 140 mya →rapid adaptive radiation •Flowers:specialized structure for sexual reproduction; pollinated by wind or animals (e.g. bees, bats); contain up to 4 rings of modified leaves: -sepals, petals, stamens, carpels

Evolution of Seed Plants

•First seed plants (gymnosperm ancestors) evolved ~ 305 mya in giant lycophyte, monilophyte forests •Drier environment:•thick cuticles, needle-shaped leaves •tender, moist gametophyte moved inside sporophylls •Gametophytes develop from spores retained in parental sporophyte→ keeps them from drying out •Microspores produce pollen→ male gametophyte inside

Angiosperm

•Fruit: mature ovary, can include other flower parts; seeds develop from ovules, ovary wall thickens •Can be fleshy(e.g. tomatoes, apples), or dry (e.g. walnuts, grains) •Seeds pass unharmed through animal digestive tracts→dispersed with fertilizer •Some fruits split to release seeds into wind (e.g. milkweed) •Some have parachutes or propellers to aid dispersal (e.g. maple, dandelion), some sticky to cling to fur •Seeds in angiosperms develop inside ovary, not on top of modified leaf

Evolution of Seed Plants

•Integument:layers of sporophyte tissue(1 gymnosperm, 2 angiosperm) →envelops megasporangium →produces megaspore •Megaspore + megasporangium + integument = ovule; megaspore develops into female gametophyte

Bryophytes

•Lack of vascular tissue (used to move water, nutrients against gravity), limits of diffusion prevent bryophytes from becoming large, tall •Some mosses have simple vascular tissue (via convergent evolution) →can get up to 2m

Structure of Plants: Leaves

•Leaves: light-gathering organs, site of photosynthesis •Stomata→openings in epidermis allow CO2 into cell for photosynthesis(controlled by guard cells); high surface area to volume ratio→efficient gas exchange but also water loss

Seedless Vascular Plants: Leaves

•Leaves→increased surface area for photosynthesis; first microphylls ~ 410 mya (megaphylls 370 mya) •microphylls: spine-shaped leaves supported by single strand of vascular tissue; lycophytes only 9one single, unbranched leaf vein) •megaphylls: leaves with multiple branches of vascular tissue (veins);nearly all vascular plants

Ecological Roles of Bryophytes

•Mosses form important symbiotic relationships with nitrogen-fixing cyanobacteria •Many can survive losing most of their water→deadly to most vascular plants •Species living at high altitudes have compounds which absorb damaging UV radiation •Sphagnum (peat moss) decays very slowly →low temp, pH, O2 level of peat bogs →decreased decomposition (carbon sinks, storing ~ 30% global carbon) •Peat can absorb 20X its weight in water→dead bodies become mummified

Gymnosperms

•Naked seeds exposed on clusters of sporophylls (cones) •First evolved ~ 305 mya →dominated until ~ 65 mya (dinosaur food) •Some retain flagellated sperm (ginkgos, cycads) •Pollen spread by wind; pollination occurs when pollen lands at sticky base of sporophyll →forms papery seed on top of it

Kingdom Plantae

•Nearly 300,000 known species; 6,500 in CA •Important producers (50% global photosynthesis), supply oxygen as result of photosynthesis •Most terrestrial→some returned to aquatic environments

Key Adaptations for Land

•No true leaves or roots →anchored by rhizoids, no nutrient absorption •Algae get CO2 by diffusion from water →plants get it through air via microscopic pores in leaves= stomata •High surface area/volume = lots of water lost on hot days (up to 95% of plant's total water loss)

Structure of Plants

•Organized into tissues and organs (several tissues working together to perform particular functions) -Two main systems in plants: roots and shoots •sugars produced in leaves→get to root cells •leaves need water, minerals from roots→to produce sugars •vegetative growth(non-reproductive growth of stems, leaves, roots) takes up majority of plant's energy budget

Challenges: Moving to Land

•Photosynthetic prokaryotes (cyanobacteria) already there, confined to damp surfaces •First eukaryotes colonize land ~ 500 mya, first plants ~ 475 mya •Colonizing land 475 mya presented some clear challenges:

Gymnosperm: Species

•Phylum Cycadophyta: palm-like leaves, large cones; most endangered •Phylum Ginkgophyta: one surviving member, G. biloba; deciduous, fleshy seeds smell like rotting cheese, turns gold in fall •Phylum Coniferophyta: pines, firs; ancient bristle-cone pines (among oldest living things); giant sequoias (among tallest, oldest) •Includes junipers →berries actually fleshy sporophylls

Structure of Plants: Leaves (specialized functions)

•Plantlets by asexual reproduction •Water storage (e.g. aloe) •Defense (e.g. cactus spines) •Clinging or climbing like vines

Kingdom Plantae

•Plants are multicellular photosynthetic autotrophic eukaryotes →cellulose in cell walls like dinoflagellates, brown and green algae (result of convergent evolution)

Structure of Plants: Roots

•Root:organ that anchors plant, absorbs water, minerals, can store excess sugars •taproot long, main vertical root; best for soils with deep groundwater, tall plants •root hairs:thin tubes extending from root epidermis;main site of water, nutrient absorption -Adventitious roots:roots that arise in unusual place→form fibrous networks near soil surface •Help grasses hold topsoil, prevent erosion

Angiosperms

•Some self-pollinate; most have mechanisms to prevent (avoid inbreeding) •Pollen contains two cells: one develops intopollen tube; other divides into two haploid sperm cells -one sperm fertilizes egg, other fuses with gametophyte →triploid cell = double fertilization(unique to angiosperms) →endosperm, tissue that nourishes developing embryo •Ovule matures into seed; zygote →embryo with rudimentary root, one or two seed leaves(cotyledons)

Bryophytes

•Sperm must swim to egg→bryophytes generally restricted to moist habitats •Sporophyte much smaller, dependent on gametophyte for nutrients •Sporangium releases spores when conditions are favorable →single sporophyte can produce 50 million spores •Gametophytes can reproduce asexually →brood bodies, small plantlets that detach from parent, grow into new plants

Structure of Plants: Stems

•Stem: organ that supports light-gathering organs, conduit for water, minerals •contain nodes:points for leaf attachment, axillary buds→these can form lateral shoots, branches, particularly if apical bud is damaged or lost

Nutrient Transport: Phloem

•Translocation:transport of sugars from photosynthesis in phloem •Phloem moves sugar from sources (production) to sinks (storage) •Storage organs can be sources or sinks •Mature leaves are sources; growing leaves, fruit, buds, roots, stems are usually sinks

Nutrient Transport: Xylem

•Transpiration:loss of water vapor from leaves, stomata→creates pressure gradient, pulling water from xylem into leaf by surface tension •Water pulled up tracheids (primitive element) by cohesion, adhesion, surface tension (result of hydrogen bonding) •Living cells generally under positive osmotic pressure→water flows into cells to equalize solute concentration across membrane, causing cell contents to press against cell wall= turgor pressure •Turgor pressure responsible for stiffness of plant tissues, drives cell elongation in meristems

Structure of Plants: Stems

•Vegetative propagation(asexual reproduction); e.g. stolons, plantlets form at nodes -Can store sugars as well: •bulbs→underground shoots (e.g. onions) •Rhizomes, tubers →enlarged horizontal stems (e.g. potatoes)

Alternation of generations with multicellular, dependent embryos

•haploid gametophyte(gamete-producing plant)→gametes by mitosis which fuse →diploid zygote→sporophyte(spore-producing plant)•meiosis in mature sporophytes→haploid spores →develop into new haploid organism

Flower Components

•sepals:enclose flower before it opens •petals:help in attracting pollinators •stamens:produce microspores →pollen, contain male gametophytes; filament with terminal anther •carpels:produce megaspores →female gametophytes(may be one or several fused together); stigma receives pollen, style leads to ovary at base; each ovary may contain multiple ovules

Function of Roots

•storage of carbohydrates •extra support •acquiring oxygen in waterlogged environments →pneumatophores project above water surface

Vascular System

•tracheids :tube-shaped cells that carry water, minerals up from roots(lost in aquatic species) •one-way transport of water, minerals by xylem(cell walls reinforced with polymer lignin) •two-way transport of sugars, proteins by phloem •vascular tissue allowed first plants to grow tall against gravity → increased light competition→ first forests

Lycophytes and Monilophytes

•~ 1,200 species of club mosses, spike mosses, quillworts (lycophytes) today •Ferns (monilophytes) diverse in tropics, thrive in temperate forests (~ 12,000 species left)

Monocot and Eudicot

•~90% of plant species are angiosperms; basal taxa include magnolias, water lilies •25% of plant species are monocots (grasses, palms, orchids); ~ 1/3 are eudicots (legumes, flowering trees, roses)