Biology 102Study Notes Exam 2 Chapter 24: Evolution & Diversity of Plants Evolutionary History of PlantsCharacteristics of Plants (kingdom Plantae)-       plants are multicellular photosynthetic eukaryotes adapted to life on land-       plants are believed to have evolved from a  freshwater green algal ancestor  (possibly

stoneworts) over 500 million years ago (Paleozoic era)o      both utilize chlorophylls a and b and various accessory pigments, store food as starch

& have cell walls containing cellulose-       plants, from nonvascular to vascular, nourish a multicellular embryo within the body of

the female plant; this distinguishes them from green algae-       vascular plants have vascular tissues, specialized elongated cells that conduct water and

solutes through the plant-       the cone-bearing gymnosperms and flowering angiosperms both produce seeds

o      seeds are mature ovules and stored food within protective seed coato      seeds are resistant to drought and somewhat resistant to predators

 Alternation of Generations-       plants have a two-generation life cycle called alternation of generations-       the sporophyte generation is a diploid (2n) generation producing haploid spores by

meiotic cell division-       the spores produce the gametophyte generation, a haploid

generation producing haploid gametes by mitotic division-       mitosis occurs as a spore becomes a gametophyte, and also as a zygote becomes a

sporophyte-       plants differ in which generation–gametophyte or sporophyte–is dominant

o      in nonvascular plants, the gametophyte is dominanto      in the vascular plants, the sporophyte is dominant   or more conspicuouso      the shift to sporophyte dominance is an adaptation to life on land; the gametophyte

becomes microscopic and dependent on the sporophyte 

Other Adaptations to Terrestrial Environments-       sporophyte dominance & adaptation for water transport and conservation-       vascular tissues transports water and nutrients in the body of the plant-       leaves and stems covered by a waxy cuticle that retains water & limits gas exchange-       leaves & other tissues have openings (stomata) that regulate gas and water exchange Nonvascular Plants (≥Bryophytes≤)-       nonvascular plants lack true roots, stems, and leaves, although they have rootlike,

stemlike, or leaflike structures-       the gametophyte is the dominant generation recognized in bryophytes

o      the gametophyte produces eggs in archegonia, flagellated sperm in antheridia-       nonvascular plants are quite small because of lack of vascular tissue and the need for

sperm to swim to the archegonia in watero      because sexual reproduction involves flagellated sperm, they are usually found

in moist habitatso      mosses compete well in harsh environments because the gametophyte can reproduce

asexually, allowing them to spread into stressful habitats

-       Hornworts (phylum Anthocerophyta)o      the small sporophytes look like tiny green broom handles and are attached to a filmy

gametophyte that is less than two cm in diameter-       Liverworts (phylum Hepatophyta)

o      the thallus or body appears similar to lobes of the livero      Marchantia has a flat, lobed thallus about a centimeter in lengtho      the upper surface of thallus is smooth; lower surface bears numerous rhizoids (root-

like extensions) projecting into soil (absorb water & minerals)o      asexual reproduction involves gemmae in gemmae cups on upper surface of the

thallus; gemmae can start a new planto      sexual reproduction: antheridia are on disk-headed stalks and produce flagellated

sperm; archegonia are on umbrella-headed stalks and produce eggsß       the zygote develops into a tiny sporophyte with a foot, short stalk, & capsuleß       spores produced within the gametophyte capsule are dispersed by wind

-       Mosses (phylum Bryophyta)o      mosses are found from the Arctic through the tropics to parts of the Antarctico      moss prefers damp, shaded localities but some survive in deserts, bogs & streamso      some ≥mosses≤ are not true mosses:

ß       Irish moss is a red alga; Reindeer moss is a lichen; Club mosses are vascular plants; Spanish moss is a flowering plant related to pineapple

o      most mosses can reproduce asexually by fragmentationo      the moss life cycle begins with algalike protonema developing from the germination of

a haploid sporeß       upright shoots develop covered with leafy structures & anchored by rhizoidsß       the shoots bear antheridia and archegonia at their tipsß       the antheridia produce flagellated sperm which need external water to reach eggs

in archegoniaß       the archegonium looks like a vase with a long neck; it has an outer layer of sterile

cells with a single egg at the baseß       fertilization results in a diploid zygote that undergoes mitotic division to develop a

sporophyteo      the sporophyte consists of a foot (which grows down into the gametophyte tissue

starting at the former archegonium), a stalk, and an upper capsule (sporangium) where spores are produced

-       Uses of Bryophyteso      sphagnum (bog or peat moss) has tremendous ability to absorb water and is

important in gardeningo      sphagnum does not decay in some acidic bogs; the accumulated dried peat can be

used as fuel Vascular Plants-       vascular tissue

o      xylem is vascular tissue that conducts water & minerals upward from the rootso      phloem is vascular tissue that transports sucrose & hormones throughout the planto      lignin strengthens the walls of conducting cells in xylemo      the cuticle and stomata are also characteristics of a dominant sporophyteo      seedless plants are mostly homosporous, using spores for dispersalo      all seed plants are heterosporous, using pollen grain and seeds

 Seedless Vascular Plants-       Club Mosses (division Lycopodophyta)

o      common in temperate woodlands where they are called ≥ground pine.≤o      a branching rhizome sends up aerial stems less than 30 cm tallo      tightly packed, scalelike microphylls cover stems and branches; each contains one

strand of vascular tissueo      sporangia are borne on the surface of leaves called sporophylls which are grouped in

club-shaped stroboli; spores germinate into independent gametophyteso      most club mosses live in tropics or subtropics as epiphytes, plants that live on trees

without harming themo      closely related are spike mosses (Selaginella) and quillworts (Isoetes)

-       Ferns and Allieso      Phylum Sphenophyta today contains one genus, Equisetum (horsetails)o      a rhizome produces aerial stems that stand about 1.3 meters tallo      whorls of slender side branches & small scalelike leaves encircle nodes of a stem,

resembling a horseπs tailo      the tough, rigid stems have silica in the cell walls; early Americans used them as

≥scouring brushes.≤-       Whisk Ferns (phylum Psilotophyta)

o      whisk ferns occur in the southern United States and in the tropicso      whisk ferns have no leaves or roots; a branched rhizome with rhizoids and a

mycorrhizal fungus helps gather nutrientso      other genera including Tmesipteris have true leaves that are microphylls

-       Ferns (phylum Pterophyta)o      ferns are widespread, and especially abundant in warm, moist tropical regionso      ferns range in size from low-growing mosslike forms to tall treeso      fronds are leaves that are variable in size and shapeo      ferns are the only group of seedless plants to have well-developed megaphylls;

megaphylls may have evolved by fusion or branching of stemso      life cycle of a fern: spores produced by meiotic cell division within sporangia, located

in sori on underside of leafletsß       spores are released and disperse largely by windß       a spore germinates into a prothallus which grows to develop antheridia and

archegonia underneathß       fertilization occurs if water is present; flagellated sperm swim from antheridia to

archegonium; the resulting zygote begins its development inside archegonium but embryo soon outgrows the space

ß       a sporophyte becomes visible as the first leaf grows above and as roots develop below the prothallus

ß       the young sporophyte develops a root-bearing rhizome from which fronds project. Seed Plants-       seeds are mature ovules containing embryonic sporophyte and stored food enclosed in a

protective seed coat-       seeds disperse the sporophytes-       seeds are resistant to adverse conditions (dryness and temperature extremes)-       food reserve supports the emerging seedling until it can exist on its own-       there are separate male female gametophytes-       pollen grains are drought resistant & become multicellular male gametophytes-       pollination is the transfer of pollen to the vicinity of the female gametophyte

o      the whole male gametophyte, not just the sperm, moves to the female gametophyteo      sperm is delivered to an egg through a pollen tube; no external water is required for

fertilization

-       the female gametophyte develops within an ovule which, after fertilization, becomes an embryonic plant or ≥seed.≤

-       in gymnosperms, the ovules are not completely enclosed by sporophyte tissue at pollination

-       in angiosperms, the ovules are completely enclosed within diploid sporophyte tissues which becomes a fruit

-       Gymnospermso      the Gymnosperms include the conifers, cycads, ginkgo, and gnetophyteso      all have ovules exposed on the surface of sporophylls or similar structureso      Conifers: phylum Coniferophyta (~ 575 species)

ß       conifers are cone-bearing trees and shrubs: pines, hemlocks, and sprucesß       conifers usually have evergreen needlelike leaves well adapted to withstand

extremes in climateß       pine needles have a thick cuticle and recessed stomataß       pine uses: construction wood; resin is insect & fungal deterrent (turpentine)ß       the pine life cycle:ß       the sporophyte is dominant and its sporangia are borne in conesß       two types of cones are pollen cones (small and near the tips of lower branches)

and seed conesß       each scalelike sporophyll of a pollen cone has two or more microsporangia on the

undersideß       within the sporangia, each microsporocyte undergoes meiosis and produces

four microsporesß       each microspore develops into a male gametophyte which is the pollen grainß       a megasporangium is within an ovule; a megasporocyte undergoes meiosis

producing four megasporesß       only one spore develops into a female gametophyte with 2–6 archegonia, each

containing a single large eggß       once a pollen grain is enclosed within the seed cone, it develops a pollen

tube that digests its way toward a female gametophyte and discharges twononflagellated sperm

ß       fertilization takes place one year after pollinationß       the ovule matures and becomes the seed, composed of embryo, reserve food and

seed coatß       the woody seed cone opens to release winged seeds in the fall of 2nd season

o      Cycads: phylum Cycadophyta (~100 species)ß       the trunk is stout and unbranched; the large leaves are compound giving a

palmlike appearanceß       cycads have pollen and seed cones on separate plants, pollinated by insectsß       the pollen tube bursts in the vicinity of the archegonium and multiflagellated sperm

swim to reach an eggß       today, cycads are endangered because of their very slow growth

o      Ginkgoes (maidenhair trees): phylum Ginkgophyta (1 species)ß       it is called the maidenhair trees because its forked-veined, fan-shaped leaves

resemble the maidenhair fernß       ginkgo ovules are at the end of short, paired stalks; female trees produce seeds

with a fleshy covering and foul odorß       similar to cycads, the pollen tube of Gingko bursts to release multiflagellated

sperm that swim to the egg produced by the female gametophyte in an ovuleo      Gnetophytes: phylum Gnetophyta (~70 species)

ß       gnetum consists of trees and climbing vines with broad leaves; they live mainly in the tropics (Ephedra & Welwitschia in deserts of US & Africa)

ß       the xylem and stroboli are uniform across genera, and all lack archegoniaß       angiosperms also lack archegonia, suggesting that gnetophytes are the

gymnosperms most closely related to angiospermsß       some gnetophytes produce nectar in their reproductive structures, recruiting

insects in pollination -       Angiosperms (flowering plants): phylum Anthophyta (240,000 known species)

o      unlike gymnosperms, angiosperms enclose their ovules within diploid tissueso      flowering plants became the dominant plants in the late Cretaceous and early Tertiary

periods, and probably arose ~ 200 million years agoo      Monocots and Eudicots

ß       most flowering plants belong to one of two classes: Monocotyledones (65,000 species) or the Eudicotyledones (175,000 species)

ß       the term eudicots is preferred to the earlier dicots; some former dicots are now know to have split off before the rise of these two major classes

ß       monocot produce one cotyledon (seed leaf) at germination and have flower parts mostly in threes or multiples of threes

ß       dicots produce two cotyledons (seed leaves) at germination and have flower parts mostly in fours or fives, or multiples of these numbers

o      The Flowerß       flowers have several kinds of highly modified leaves arranged in rings and

attached to a receptacleß       receptacle is a modified stem tip to which flower parts are attachedß       sepals are outer ring of modified leaves of flowers; usually green, they enclose

flower before it opensß       petals (collectively a corolla) are a ring of modified leaves inside of sepals; large

and colorful, they help attract pollinatorsß       stamens form a whorl inside the petals and around a pistil; each slender filament

has an anther at its tipß       the anther produces pollenß       the pistil contains one or more fused carpels; it consists of a stigma, style, and

ovary∑      carpels are modified sporophylls that contain ovules in which megasporangia

are located∑      a stigma is a landing platform for pollen and the site where the pollen tube

enters the style∑      the style is a slender column that holds up the stigma to receive pollen∑      pollen grains develop a pollen tube that takes sperm to the female

gametophyte in the ovule∑      glands located in the region of the ovary produce nectar, a nutrient gathered by

pollinators as they go flower to flowero      the angiosperm life cycle:

ß       a megaspore located in an ovule within an ovary of a carpal develops into an egg-bearing female gametophyte called the embryo sac

ß       usually, the embryo sac has seven cells; one is an egg and one contains two polar nuclei

ß       microspores produced in anthers become pollen grains which mature into sperm-bearing male gametophytes

ß       the mature male gametophyte consists of three cells; the tube cell and two sperm cells

ß       pollination brings the male gametophyte to the stigma where it germinatesß       during germination, the tube cell produces a pollen tube that carries the two

sperm to the micropyle opening of an ovuleß       in double fertilization, one sperm fertilizes egg and one sperm unites with

polar nuclei to form the triploid endospermß       the ovule becomes the seed and contains the embryo (the sporophyte of the next

generation) and stored food enclosed within a seed coatß       A fruit is derived from an ovary and possibly accessory parts of the flower; some

fruits are fleshy and some are dryo      Flowers and Diversification

ß       inconspicuous flowers disperse pollen by wind; colorful flowers attract specific pollinators (e.g., bees, wasps, flies, butterflies, moths, and even bats) which carry only a particular pollen

ß       flowers promote efficient cross pollination; they also aid in dispersal through production of fruits

ß       there are fruits that utilize wind, gravity, water, and animals for dispersal

Chapter 25: Structure And Organization Of Plants Plant Organs-       Diverse Flowering Plant Structure

o      structures of flowering plants are well-adapted to varied environments including watero      flowering plants usually have three  vegetative organs : root, stem and leafo      the flower itself contains a number of organs

-       Roots (root systems)o      the root system is the main root plus its lateral (side) branches; it is generally equal in

size to the shoot system, the part above groundo      roots anchor a plant in soil and give supporto      roots absorb water and minerals from soil; root hairs are central to this process

ß       root hair cells are in a zone near root tipß       root hairs are numerous to increase absorptive surface of a rootß       transplanting plants damages a plant when the root hairs are torn offß       roots produce hormones that are distributed along with water and nutrients to the

rest of the planto      perennials ≥die back≤ to regrow the next season; roots of herbaceous perennials store

food (e.g., carrots, sweet potatoes)-       Stems

o      the shoot system of a plant consists of the stem, the branches, & leaveso      the stem forms the main axis of the plant, along with lateral brancheso      upright stems produce leaves and array them to be exposed to as much sun as

possibleo      a node occurs where a leaf attaches to the stem and an internode is the region

between nodes; nodes and internodes identify a stem even if it is undergroundo      the stem has vascular tissue to transport water and minerals from roots and sugar from

leaveso      nonliving cells form a continuous pipeline through vascular tissueo      a cylindrical stem expands in girth and length; trees use woody tissue to strengthen

stemso      stems function in storage: cactus stems store water and tubers are horizontal stems

that store nutrients-       Leaves

o      a leaf is the major organ of photosynthesis in most plantso      leaves receive water from roots by way of the stemo      broad, thin leaves have a maximum surface area to absorb CO2 and collect solar

energyo      a blade is the wide portion of a leaf with most photosynthetic tissueo      petiole is a stalk that attaches a leaf blade to stemo      the leaf axil is the upper acute angle between petiole and stem where an axillary

(lateral) bud originateso      some leaves protect buds, attach to objects (tendrils), store food (bulbs), or capture

insects Monocot Versus Eudicot Plants-       cotyledons are embryonic seed leaves providing nutrition from the endosperm before the

mature leaves begin photosynthesis-       Monocots: **

o      1 cotyledon in seedo      root xylem & phloem in a ring

o      vascular bundles scattered in stemo      parallel leaf veinso      flower parts in multiples of 3o      usually one aperture in pollen graino      includes grasses, lilies, orchids, rice, wheat, corn

-       Eudicots: **o      2 cotyledons in seedo      root xylem & phloem in a cross or star-shaped patterno      vascular bundles arranged in a ring in stemo      net pattern to leaf veinso      flower parts in multiples of 4 & 5o      usually 3 aperture in pollen graino      includes dandelions to oak trees

 Plant Tissues-       Meristem Produces Tissue: plants continually grow due to meristem (embryonic tissue)

in stem and root tips (apexes)-       3 types of primary meristem continually produce three types of specialized tissue

o      protoderm is outermost primary meristem giving rise to epidermiso      ground meristem is inner meristem producing ground tissueo      procambium produces vascular tissue

-       3 specialized tissues are producedo      epidermis forms outer protective coveringo      ground tissue fills the interioro      vascular tissue transports water and nutrients and provides support

-       Epidermal Tissueo      epidermis is an outer protective covering tissue of plant roots, leaves, and stems of

nonwoody plants containing closely packed epidermal cellso      waxy cuticle covers the walls of epidermal cells, minimizing water loss and protecting

against bacteriao      in roots, certain epidermal cells are modified into root hairs that increase surface area

of the root for absorption of water and minerals and help to anchor plants in the soilo      epidermal cells are modified as glands to secrete protective substanceso      on the lower epidermis of eudicot leaves, and both   surfaces of monocot leaves, special

guard cells form microscopic pores called stomata that regulate gas exchange and water loss

o      in older woody plants, the epidermis of the stem is replaced by cork tissueß       cork is outer covering of the bark of trees; composed of dead cork cells that may

be sloughed offß       cork cambium is lateral meristem that produces new cork cellsß       mature cork cells produce the lipid suberin making them waterproof & inertß       cork protects a plant and is resistant to attack by fungi, bacteria, and animals

-       Ground Tissueo      ground tissue fills the inside of plants with parenchyma, collenchyma and

sclerenchyma cellso      parenchyma are the least specialized of all plant cell types

ß       contain plastids (e.g., chloroplasts or colorless storage plastids)ß       found in all organs of a plant & divide to form more specialized cells (e.g., roots

develop from stem cuttings in water)o      collenchyma resemble parenchyma but has thicker primary cell walls & are uneven in

the corners

ß       usually occur as bundles of cells just beneath epidermisß       give flexible support to immature regions of plants (e.g., a celery stalk is mostly

collenchyma)o      sclerenchyma cells are mostly nonliving & have thick secondary cell walls

ß       they are impregnated with lignin that makes the walls tough and hardß       provide strong support to mature regions of plantsß       form fibers (used in linen and rope) and shorter sclereids (found in seed coats, nut

shells, and gritty pears)-       Vascular Tissue

o      xylem passively conducts water and mineral solutes upward through a plant from roots to leavesß       xylem contains tracheids and vessel elementsß       both are hollow, nonliving cellsß       vessel elements form a continuous pipeline for water and mineral transportß       vascular rays conduct water and minerals across the width of the plant

o      phloem is vascular tissue that conducts the organic solutes in plants, from the leaves to the roots; it contains sieve-tube cells and companion cellsß       sieve-tube cells contain cytoplasm but no nucleus

∑      they are arranged end to end & have channels in their end walls (≥sieve-tubes≤), through which plasmodesmata extend from one cell to another

ß       companion cells are connected to sieve-tube cells by many plasmodesmata∑      they are smaller and more generalized than sieve-tube cells & have

a nucleus which may control & maintain the function of both cells∑      they are also thought to be involved in the transport function of phloem

o      vascular tissue extends from root to leaves as vascular cylinder (roots), vascular bundles (stem) and leaf veins

 Organization of Roots-       Eudicot Root Tip: the eudicot root tip, a site of primary growth, is organized into zones of

cells in various stages of differentiationo      cells are continuously added to a root cap below and zone of elongation above by

contributions from the zone of cell divisiono      the root cap is a protective cover; its cells are replaced constantly because they are

soon ground offo      the zone of elongation is above the zone of cell division where cells become longer

and more specializedo      the zone of cell division contains meristematic tissue and adds cells to root tip and

zone of elongationo      the zone of maturation is above the zone of elongation; cells are mature and

differentiated with root hairs-       Tissues of a Eudicot Root

o      epidermis is a single layer of thin-walled, rectangular cells that forms the protective outer layer of the rootß       root hairs in the region of maturation project as far as 5–8 mm into the soil

o      cortex is a layer of large, thin-walled, irregularly shaped parenchyma cellsß       these cells contain starch granules; the cortex functions in food storageß       the cells are loosely packed; water and minerals can diffuse through the cortex

o      endodermis is single layer of rectangular cells that forms the boundary between cortex and inner vascular cylinderß       it regulates the entrance of minerals into the vascular cylinder

ß       the Casparian strip is an impermeable lignin and suberin layer that excludes water and mineral ions

o      vascular cylinder is an arrangement of vascular tissues as a cylinderß       the pericycle is the first layer of cells within vascular cylinderß       its cells have retained the capacity to divide; it can start the development of branch

or secondary rootsß       vascular tissue forms main portion of a vascular cylinder

∑      it is composed of xylem, whose cells are arranged in a star-shaped pattern; and phloem, whose cells are located in regions between arms of xylem

-       Organization of Monocot Roots: monocot roots have the same zones as a eudicot root but do not undergo secondary growtho      the monocot root has a ring of vascular tissue where alternating bundles of xylem

and phloem surround pitho      monocot roots also have pericycle, endodermis, cortex, and epidermis

-       Root Diversityo      roots have adaptations to help anchor plants, absorb water and minerals, and store

carbohydrateso      there are three general root types

ß       taproot is common in eudicots; root adapted to store food (e.g., carrots, beets)ß       the fibrous root system of monocots is a mass of slender roots and lateral

branches that hold the plant secure in the soilß       adventitious roots develop from underground stems or from the base of above-

ground stems∑      prop roots (corn and mangrove plants) anchor the plant∑      ivy has holdfast roots to anchor aerial shoots

o      haustoria are rootlike projections from stems on parasitic plants (e.g., dodders and broomrapes)

o      mycorrhizae are an association between fungus and rootsß       in this mutualism, fungus receives sugars and amino acids from plant & plant

receives water and minerals from the funguso      legumes (e.g., peas and beans) have root nodules containing nitrogen-fixing bacteria

ß       bacteria extract nitrogen from air and reduce it to a form that can be used by plant tissues

 Organization of Stems-       Primary Growth

o      the stem tip is the site of primary growth where cell division extends length of stems or roots

o      shoot apical meristem produces new leaves and primary meristems, increasing stem length & is protected within a terminal bud of leaf primordia (immature leaves)

o      bud scales are scalelike coverings protecting terminal buds during winters when bud growth stops

-       Herbaceous Stemso      herbaceous stems are mature nonwoody stems that exhibit only primary growtho      the outermost tissue of herbaceous stems is epidermis covered by a waxy cuticle to

prevent water loss.o      xylem and phloem are in distinctive vascular bundles

ß       in each bundle, xylem is found to the inside of the stem; phloem is found to the outside

ß       in the eudicot herbaceous stem, vascular bundles are arranged in a ring towards outside of the stem and separating the cortex from the central pith

ß       in monocot stem, vascular bundles are scattered throughout the stem; there is no well-defined cortex or pith

ß       cortex sometimes carries on photosynthesis; pith may function as storage site-       Woody Stems

o      woody plants have both primary and secondary tissueso      primary tissues are new and form each year from primary meristem right behind the

apical meristemo      secondary tissues develop from second year onward from lateral meristem growtho      primary growth increases length of a plant; secondary growth increases its girtho      as secondary growth continues, it is not possible to distinguish individual vascular

bundleso      the woody eudicot stem has a different organization with three distinct areas: bark,

wood, and pitho      bark of a tree contains cork, cork cambium, and phloemo      cork cambium is meristem beneath the epidermis that produces new cork cells when

neededß       cork cells become impregnated with suberin, causing them to die but making

them waterproofß       consequently, cork forms an impervious barrier, even to gas exchange, except at

lenticelso      wood is secondary xylem which builds up each year; the vascular cambium is

dormant during the winterß       spring wood is composed of wide xylem vessel elements with thin walls, necessary

to conduct sufficient water and nutrients to supply abundant growth that occurs during spring

ß       summer wood forms when moisture is scarce; composed of a lower proportion of vessels, it contains thick-walled tracheids and numerous fibers

ß       an annual ring is one ring of spring wood followed by a ring of summer wood; this equals one yearπs growth

ß       sapwood is outer annual rings where transport occursß       heartwood is inner annual rings of older trees & help to support a tree

∑      vessels no longer function in transport; they become plugged with resins and gums that inhibit growth of bacteria and fungi

o      Woody Plantsß       the first flowering plants were probably woody shrubs; herbaceous plants evolved

laterß       woody plants have an advantage when there is adequate rainfall; they can grow

taller and have adequate tissue to support and service leaves-       Stem Diversity

o      stolons are stems that grow along the ground; new plants grow where the nodes contact the soil (e.g.: strawberries)

o      the succulent stems of cacti are modified for water storageo      tendrils of grapes and morning glories are stems adapted for wrapping around support

structureso      rhizomes are underground horizontal stems

ß       rhizomes are long and thin in grasses and thick and fleshy in irisesß       some rhizomes have tubers that function in food storage (e.g.: potatoes)

o      corms are bulbous underground stems that lie dormant during winter, like rhizomes (e.g.: crocus, gladiolus)

o      humans use stems: sugarcane is primary source of table sugar, cinnamon and quinine are from bark, wood is from paper, etc.

 Organization of Leaves-       Leaf Structure

o      leaves are organs of photosynthesis in plants; they have a flattened blade and a petiole

o      the leaf veins contain vascular tissues that transport water and nutrientso      leaf veins have a net pattern in eudicots and a parallel pattern in monocotso      a petiole is a stalk that attaches a leaf blade to the plant stemo      epidermis is the layer of cells that covers the top and bottom sides of a leaf

ß       epidermis often bears protective hairs or glands that irritating substancesß       epidermis is covered by a waxy cuticle that keeps the leaf from drying outß       the epidermis, particularly lower epidermis, contains stomata that allow gases to

move into and out of the leafo      mesophyll is the inner body of a leaf and the site of most of photosynthesis

ß       palisade mesophyll is the layer of mesophyll containing elongated parenchyma cells with many chloroplasts

ß       spongy mesophyll contains loosely packed parenchyma cells that increase the surface area for gas exchange

-       Leaf Diversityo      simple leaves have margins not deeply lobed or divided into smaller leafletso      compound leaves are divided into smaller leaflets, and each leaflet may have its own

stalko      leaves are variously modified

ß       shade plants have broad leaves while desert plants have reduced leaves with sunken stomata

ß       cactus spines are modified leaves; succulents have fleshy leaves to hold moistureß       onion bulbs have leaves surrounding a short stemß       the tendrils of peas and cucumbers are leavesß       the Venusπs-flytrap has leaves to trap and digest insects

 

Chapter 26: Nutrition And Transport In Plants Plant Nutrition and Soil-       Early Views

o      ancient Greeks believed plants converted soil into plant tissueso      the 17th Century Dutchman Jean-Baptiste Van Helmont conducted an experiment from

which he concluded the increase in tree weight came from water; he was unaware of substances in air

-       Essential Inorganic Nutrientso      essential inorganic nutrients (e.g., carbon, hydrogen, oxygen) comprise 96% of plant

dry weightß       carbon dioxide is the source of carbon for a plantß       water is the source of hydrogenß       oxygen can come from either atmospheric oxygen, carbon dioxide, or water

o      essential nutrients must fulfill the following criteriaß       they have an identifiable nutritional roleß       no other element can substitute and fulfill the same roleß       a deficiency of the element causes the plant to die

o      beneficial nutrients: elements required or that improve growth of a particular plant-       Determination of Essential Nutrients

o      when a plant is burned, most mineral elements (except nitrogen) remain in the asho      hydroponics is the preferred method for determining plant mineral requirements

ß       hydroponics is cultivation of plants in waterß       nutrient requirements of plants are determined by omitting a mineral and observing

the effectsß       if plant growth suffers, it can be concluded that the omitted mineral is a required

nutrient-       Soil Formation

o      soil formation begins with weathering of rock by freezing, glacier flow, stream flow, and chemicals

o      lichens and mosses grow on barren rock and trap particles and leave decaying tissueso      decayed organic matter (humus) takes time to accumulate; its acidity leaches minerals

from rockso      depending on parent material and weathering, a centimeter of soil may develop within

15 years-       The Nutritional Function of Soil

o      soil consists of soil particles, decaying organic matter, living organisms, air and watero      the best soil includes particles of different sizes; this provides critical air spaceso      soil particles include sand, silt & clay

ß       soil particles vary by size: sand particles are largest (0.05–2.0 mm in diameter); silt particles are medium sized (0.002–0.05 mm in diameter); clayparticles are smallest: below 0.002 mm in diameter

ß       sandy soils lose water too readily; clay packs tight to hold water and clumpsß       clay particles are negatively charged and attract positively charged ions (e.g.,

calcium [Ca2+] and potassium [K+])ß       in acidic soils, hydrogen ions replace positively charged nutrients and the nutrient

ions float free and are leached; this is why acid rain kills treesß       clay cannot retain negatively charged NO3

-, and the nitrogen content of clay soil is low

ß       loam (a mixture of the three soil particles) retains water and nutrients; roots take up oxygen in the air spaces

o      humus: a mixture of 10-20% humus mixed with a top layer of soil particles is best for plantsß       humus keeps soil loose and crumbly, decreases runoff and aerates soilß       humus is acidic and retains positively charged minerals for plants to use laterß       bacteria and fungi break down organic matter in humus and return inorganic

nutrients to plantso      living organisms in soil

ß       small plants play a major role in formation of soil from rock and in successionß       roots of larger plants penetrate the soil and weather rocksß       larger moles and badgers and smaller earthworms help turn over the soilß       soil animals, from mites to millipedes help break down leaves and other plant

remainsß       fungi, protozoa, algae and bacteria complete decompositionß       soil bacteria make nitrate available to plantsß       some soil organisms (roundworms and insects) are crop pests that feed on roots

o      soil erosion is caused by water or wind carrying away soilß       erosion removes 25 billion tons of topsoil worldwide annuallyß       deforestation and desertification contribute to erosion

 Uptake of Water and Minerals-       Pathways

o      minerals follow the path of water uptakeß       some mineral ions diffuse in between the cellsß       because of the impermeable Casparian strip, water must eventually enter the

cytoplasm of endodermal cellsß       water can move directly into the cytoplasm of root hair epidermal cells and is

transported across the cortex and endodermis of a rootß       in contrast to water, minerals are actively taken up by plant cells

o      mineral ions cross plasma membranes by a chemiosmotic mechanismß       plants absorb minerals in ionic form: nitrate (NO3

-), phosphate (HPO4-),

and potassium ions (K+) all have difficulty crossing a charged plasma membraneß       it has long been known plants expend energy to actively take up and concentrate

mineral ionsß       a plasma membrane pump called a proton pump hydrolyzes ATP to transport

H+ ions out of cell; this sets up an electrochemical gradient that causes positive ions to flow into cells

ß       negative ions are carried across the plasma membrane in conjunction with H+ ions as H+ ions diffuse down their concentration gradient

-       Adaptations of Roots for Mineral Uptakeo      two symbiotic relationships are known to assist roots in acquiring nutrientso      legumes have nodules infected   with the bacterium Rhizobium

ß       Rhizobium makes nitrogen compounds available to plants in exchange for carbohydrates by reducing atmospheric nitrogen (N2) to ammonium (NH4

+) (nitrogen-fixation)

o      most plants have mycorrhizae; those lacking mycorrhizae are limited in where they can growß       mycorrhizae are a mutualistic symbiotic relationship between soil fungi and

plant rootsß       the fungus increases the surface area for mineral and water uptake and breaks

down organic matterß       in return the root furnishes the fungus with sugars and amino acids

o      some plants have poorly developed roots or no roots; other mechanisms supply minerals and waterß       epiphytes take nourishment from air; their attachment to other plants gives them

supportß       parasitic plants (e.g., dodders, broomrapes, pinedrops) send

out haustoria (rootlike projections) that grow into host and tap into xylem and phloem of host

ß       venus flytrap and sundew obtains nitrogen and minerals as leaves capture and digest insects

 Transport Mechanisms in Plants-       Transport Tissues

o      vascular plants have transport tissues as an adaptation to living on lando      xylem passively conducts water and minerals from roots to leaves; it contains two

types of conducting cells: tracheids and vessel elementso      phloem conducts organic solutes in plants mainly from leaves to roots; contains sieve-

tube cells and companion cellso      these transport systems rely on the mechanical properties of water

ß       diffusion moves molecules from higher to lower concentrationsß       water potential considers both water pressure and osmotic pressure

-       The Concept of Water Potentialo      water flows from a region of higher water potential (the potential energy of water) to a

region of lower water potentialo      water potential is a measure of the capacity to release or take up water; in cells, water

potential includes the following:ß       pressure potential, the effect that pressure has on water potential; water will

move from a region of higher pressure to a region of lower pressure; andß       osmotic potential, the effect that solutes have on water potential; water tends to

move by osmosis from an area of lower solute concentration to area of higher solute concentration

o      water flows by osmosis into a plant cell with greater solute concentration than a surrounding solutionß       as water enters, pressure increases inside the cell; the strong plant cell wall allows

water pressure to build upß       pressure potential inside the cell increases and balances the osmotic potential

outside cell; water stops enteringß       turgor pressure is the pressure potential that increases due to process of

osmosis; it is critical to plants, since plants depend on it to maintain the turgidity of their bodies

ß       wilted plant cells have  insufficient turgor pressure  and the plant droops-       Water Transport

o      water entering root cells creates a positive pressure called root pressureß       root pressure (primarily at night) tends to push xylem sap upward in a plantß       guttation is the appearance of drops of water along the edge of leaves, as a result

of water being forced out of leaf vein endings; it is the result of root pressureß       root pressure is not a sufficient mechanism for water to rise to the tops of trees

-       Cohesion-Tension Model of Xylem Transporto      water and dissolved minerals must be transported upward from roots to xylem, perhaps

as high as 90 meterso      transpiration is a plantπs loss of water to atmosphere through evaporation at leaf

stomata

o      the cohesion-tension model states that transpiration creates a tension (i.e., a negative pressure) that pulls water upward in xylem

o      water molecules are cohesive with one another, adhesive with xylem wallso      cohesion is the tendency of water molecules to cling together due to their forming

hydrogen bondso      adhesion is the ability of water (a polar molecule) to interact with molecules comprising

the walls of xylem vessels; adhesion gives a water column extra strength and prevents it from slipping back down

o      at least 90% of the water taken up by roots is lost through stomata by transpirationo      with plenty of water, stomata will remain open, allowing CO2 to enter the leaf and

photosynthesis to occuro      transpiration exerts a tension that draws the water column up in vesselso      under water stress, more water is lost through a leaf than can be brought up and the

stomata closeo      photosynthesis requires CO2 to enter the leaf; there must be sufficient water so

stomata can remain open and allow CO2 to enter-       Opening and Closing of Stomata

o      each stoma has two guard cells with a pore between themo      stomata open from turgor pressure when guard cells take up water; when they lose

water, turgor pressure decreases and stomata closeo      guard cells are attached to each other at their ends; the inner walls are thicker than

outer wallso      as they take up water, they buckle out, thereby creating an opening between cellso      since 1968, it has been known that when stomata open, there is accumulation of

K+ ions in guard cellso      a proton pump run by breakdown of ATP to ADP and P transports H+ outside the cell;

this establishes an electrochemical gradient allowing K+ to enter by way of a channel protein

o      the blue-light component of sunlight is a signal that can cause stomata to openß       there is evidence that flavin pigments absorb blue lightß       this pigment sets in motion a cytoplasmic response activating the proton pump that

causes K+ ions to accumulate in guard cellso      abscisic acid (ABA) produced by cells in wilting leaves, also causes stomata to close;

photosynthesis cannot occur but water is conservedo      in plants kept in dark, stomata open and close on a 24-hour basis as if responding to

sunlight in daytime and the absence of sunlight at night; some sort of internal biological clock must keep time

-       Organic Nutrient Transporto      Marcello Malpighi (1679) suggested bark transferred sugars from leaves to roots

ß       today, we know phloem was removed but xylem remained; therefore, phloem does transport sugars

o      radioactive tracer studies using 14C confirmed phloem transports organic nutrientsß       similar studies confirm phloem transports amino acids, hormones, and mineral

ions-       Pressure-Flow Model of Phloem Transport

o      the pressure-flow model explains the transport of sap through sieve tubes by a positive pressure potential

o      the buildup of water creates a positive pressure potential within the sieve tubes that moves water and sucrose to a sink (e.g., at the roots)

o      pressure exists from the leaves to the roots; at the roots, sucrose is transported out and water also flows through due to the pressure

o      consequently, this pressure gradient causes a flow of water from leaves to rootso      the conducting cells of phloem are sieve tubes lined end to endo      cytoplasm extends through the sieve plates of adjoining cells to form a continuous tube

systemo      during the growing season, leaves produce sugaro      sucrose is actively transported into phloem by an electrochemical gradient established

by a H+ pumpo      water flows passively into sieve tubes by osmosiso      a sink can be at the roots or any other part of the plant that requires nutrientso      because phloem sap flows from source to sink, sap can move any direction along

phloem. 

Chapter 27: Control Of Growth And Responses In Plants Plant Responses-       Organisms Respond to Stimuli - a defining characteristic of life

o      adaptive organisms respond to environmental stimuli because it leads to longevity and survival of the species

o      animals have nerves and muscles; plants respond by growth patterns-       Tropisms

o      a tropism is plant growth toward or away from a directional stimuluso      positive tropism: growth toward a stimuluso      negative tropism: growth away from a stimuluso      by differential growth, one side elongates faster; the result is a curving toward or away

from a stimuluso      reception of the stimulus Æ transduction of the stimulus into a form meaningful to the

organism Æ response by the organismo      phototropism, gravitropism, & thigmotropism

-       Phototropism: growth of plants in response to lighto      stems show positive phototropismo      occurs because cells on shady side of stems elongateo      a yellow pigment related to riboflavin appears to act as a photoreceptor for lighto      following reception, the plant hormone auxin migrates from the bright side to the shady

side of a stemo      auxin is also involved in gravitropism, apical dominance, and root and seed

development-       Gravitropism: response to earthπs gravity

o      roots demonstrate positive gravitropism; stems demonstrate negative gravitropismo      an upright plant placed on its side displays negative gravitropism; it grows upward

opposite gravityo      the hormone auxin underlies both positive and negative gravitropisms

ß       auxin inhibits the growth of root cells; cells of the upper surface elongate and the root curves downward

ß       auxin stimulates the growth of stem cells; cells of the lower surface elongate and the stem curves upward

-       Thigmotropism: unequal growth due to touch (e.g., coiling of tendrils around a pole)o      the coiling of morning glory or pea tendrils around posts, etc., is a common exampleo      cells in contact with an object grow less while those on the opposite side elongateo      this process is quite rapid; tendrils can encircle an object in ten minuteso      response can be delayed; tendrils touched in the dark respond when illuminated

ß       ATP rather than light can cause the responseß       the hormones auxin and ethylene are involved; they induce curvature of tendrils

in the absence of toucho      thigmomorphogenesis is a touch response involving the whole plant

ß       an entire plant responds to presence of touch, wind or rain-       Nastic Movements: in contrast to tropisms, nastic movements are independent of the

direction of stimuluso      seismonastic movements result from touch, shaking, or thermal stimulationo      when a Mimosa pudica leaf is touched, the leaflets fold because the petiole droopso      rapid response (1-2 sec.) and is due to a loss of turgor pressure within cellso      Venusπs-flytrap has three sensitive hairs at the base of the trap

ß       when touched by an insect, an impulse-type stimulus triggers the trap to closeß       turgor pressure in leaf cells then propel the trap

-       Sleep Movements: nastic responses to the daily changes in light level; an example is the prayer plant that folds its leaves each nighto      biological clocks (maintain Circadian rhythms) are synchronized by external stimuli to

twenty-four-hour rhythmso      stomata and flowers usually open in the morning, close at night; some plants secrete

nectar at same time of day Plant Hormones: chemical messengers for communication & coordination of activities in plants; a response is influenced by several hormones and may require a specific ratio of two or more hormones-       hormones are synthesized in one part of a plant; they travel in the phloem after a plant

receives an appropriate stimulus-       auxin is produced in shoot apical meristem and found in young leaves, flowers, and fruits

o      when a terminal bud is removed, the nearest buds grow and the plant brancheso      auxin production by seeds promotes growth of fruito      if auxin is concentrated in leaves and fruits rather than stem, they do not fall offo      auxin-controlled cell elongation is involved in gravitropism and phototropismo      when gravity is perceived, auxin moves to lower surface of roots and stemso      auxin mode of action: in a plant exposed to unidirectional light, auxin moves from the

bright side to the shady side of a stemß       auxin binds to receptors and activates the ATP-driven proton (H +) pumpß       as hydrogen ions are pumped out of the cell, the cell wall becomes acidic,

breaking hydrogen bondsß       cellulose fibrils are weakened and activated enzymes further degrade cell wallß       the electrochemical gradient established causes of uptake of solutes and water

follows by osmosisß       the turgid cell presses against the cell wall, stretching it so elongation occurs

-       Gibberellins: group of 70 plant hormones that promote growth (elongate cells)o      GA3 is the most common of the natural gibberellinso      gibberellins are growth promoters that elongate cellso      mode of action: the hormone GA3 binds to a receptor; a second messenger (Ca2+)

inside cell combines with calmodulin to activate the enzyme amylase, which acts on starch to release sugars used as a source of energy by the growing embryo

-       Cytokinins: class of plant hormones derived from adenine that promote cell divisiono      a natural cytokinin zeatin is found in corn kernels; kinetin is a synthetic cytokinino      may activate oligosaccharins, chemical fragments released from cell wall, also direct

differentiation-       Senescence: aging processes; large molecules break down and are transported

elsewhere in the planto      cytokinins prevent senescence of leaves and initiate development of leaf growtho      cytokinins initiate growth of lateral buds despite apical dominance

-       Abscisic acid (ABA): sometimes called the ≥stress hormone≤; it maintains seed and bud dormancy and causes closure of stomatao      dormancy occurs when a plant organ readies itself for adverse conditions by stopping

growthß       ABA moves from leaves to vegetative buds in fall; thereafter these buds are

converted to winter buds which are covered by thick, hardened scaleso      abscisic acid brings about closing of stomata when a plant is under water stress

ß       by some unknown mechanism, ABA causes K+ ions to leave guard cells; as a result, guard cells lose water and the stomata close

o      although external application of ABA promotes abscission, the hormone ethylene is considered to have this natural function

-       Ethylene is involved in abscission, the dropping of leaves, fruits, or flowerso      lower levels of auxin in these areas (compared to stem) probably initiate abscissiono      once abscission begins, ethylene stimulates production of enzymes such

as cellulase (breaks down cellulose in cell walls) that cause leaf, fruit, or flower dropo      it was an early practice to prepare citrus fruit for market by storage in a room with a

kerosene stove; later work revealed incomplete combustion of kerosene produced ethylene which ripens fruit

o      ethylene is a gaseous plant hormone; it ripens fruit by increasing the activity of enzymes that soften fruit

 Photoperiodism: a physiological response to relative lengths of daylight and darkness-       many physiological changes in plants (e.g., seed germination, the breaking of bud

dormancy, and the onset of senescence) are related to a seasonal change in day length-       in some plants, photoperiodism also affects flowering-       plants can be divided into three groups, based on photoperiodism

o      short-day plants: flower when day length was shorter than a critical lengtho      long-day plants: flower when the day length is longer than a critical lengtho      day-neutral plants: flowering is not dependent on day length

-       a long-day and a short-day plant can have the same critical length-       Phytochrome and Plant Flowering

o      U.S.D.A. scientists discovered phytochrome, a blue-green leaf pigment that exists in two forms

o      Pr (phytochrome red) absorbs red light (wavelength 660 nm); it is converted to Pfr

o      Pfr (phytochrome far-red) absorbs far-red light (wavelength 730 nm); it is converted to Pr

o      during a 24-hour period, there is a shift in ratio of these two pigmentso      phytochrome conversion may be a first step in reception-transduction-response

pathway resulting in flowering-       Other Functions of Phytochrome: the Pr Æ Pfr conversion cycle controls other growth

functions in plantso      in addition to being involved in flowering, Pfr promotes seed germination and inhibits

stem elongation

Chapter 28: Reproduction In Plants Reproductive Strategies-       Life Cycles

o      in contrast to animals with one type of adult generation, flowering plants exhibit an alternation of generations life cycle that includes a diploid and a haploid generation

o      the sporophyte is a diploid generation in an alternation of generations life cycleß       a sporophyte produces haploid spores by meiotic divisionß       spores develop into a haploid gametophyte

o      a gametophyte is a haploid generation in an alternation of generations life cycleß       a gametophyte produces haploid gametes by mitotic division; gametes fuse to

form diploid zygoteß       the zygote undergoes mitotic cell division to develop into the sporophyte

o      a flower produces two types of spores, microspores and megasporesß       a microspore is a plant spore that develops into a microgametophyte

∑      the male gametophyte is a pollen grain; wind or animals carry it to megagametophyte

∑      when mature, its nonflagellated sperm cells travel down pollen tube to megagametophyte

ß       a megaspore is a plant spore that develops into a female gametophyte, the embryo sac which remains within a sporophyte plant

o      in flowering plants, the diploid sporophyte is dominant (longer lasting); it is what we commonly recognize

o      the sporophyte is the generation that contains vascular tissue and has other adaptations suitable to living on land, including production of flowers

o      flowers are unique to angiosperms; aside from producing the spores and protecting gametophytes, flowers attract pollinators and produce fruits to enclose the seeds

-       Flowerso      a flower is the  reproductive organ  of a flowering plant; it develops in response to

environmental signalso      the shoot apical meristem stops forming leaves to form flowers; axillary buds can

become flowers directlyo      monocot flower parts are in threes or multiples; eudicot flower parts are in fours or fives

or multipleso      sepals are leaflike, usually green; this outermost whorl protects the bud as a flower

develops withino      petals are interior to sepals; coloration accounts for attractiveness of many flowers

ß       the size, shape, and color of a flower are attractive to a specific pollinatorß       wind-pollinated flowers often have no petals at all

o      grouped about a pistil are stamens, stalked structures that have two partsß       the anther is a saclike container within which pollen grains developß       a filament is a slender stalk that supports the anther

o      the carpel is the vaselike structure located at the center of a flower (a carpel is a simple pistil or 1 element of a compound pistil); carpels usually has three partsß       the stigma is an enlarged sticky knob on end of a style; stigma serves to receive

pollen grainsß       the style is a slender stalk that connects stigma with the ovaryß       the ovary is an enlarged base of a carpel that contains a number of ovules

o      not all flowers have sepals, petals, stamens, and a pistilß       complete flowers have sepals, petals, stamens, and a pistil; incomplete

flowers do not

ß       bisexual flowers have both stamens and a pistilß       staminate flowers have only stamensß       carpellate flowers have only carpels

o      if staminate and carpellate flowers are on same plant, the plant is monoeciouso      if staminate and carpellate flowers are on different plants, the plant is dioecious

-       From Spores to Gameteso      in plants, the sporophyte produces haploid spores by meiosis; in animals, meiosis

produces gameteso      flowering plants are heterosporous, producing microspores and megaspores that

become spermbearing pollen grains and egg-bearing embryo sacs, respectivelyo      production of the male gametophyte

ß       microspores are produced in the anthers of flowersß       microspores develop into pollen grains containing a tube cell and two spermß       the pollen grain is the mature male gametophyte

o      pollination release of pollen as walls of pollen sacs within the anther break downß       self-pollination is transfer of pollen from anther to stigma of the same plantß       cross pollination is transfer of pollen from anther of one plant to stigma of

another plant; plants often have mechanisms that promote cross pollinationß       using a pollinator to carry pollen from flower to flower of only one species

increases the efficiencyß       secretion of nectar is one way to attract certain pollinators, and they may be

adapted to reach only one type of flowero      production of the female gametophyte

ß       the ovary contains one or more ovulesß       the female gametophyte (or embryo sac) consists of 7 cells: 1 egg cell, 2

synergid cells, 1 central cell with two polar nuclei, and 3 antipodal cellso      fertilization

ß       when a pollen grain lands on a stigma, it germinates, forming a pollen tubeß       as a pollen tube grows, it passes between the cells of the stigma and the style to

reach the micropyle of an ovuleß       double fertilization occurs after the release of both sperm cells into the ovuleß       one sperm nucleus unites with the egg nucleus, forming a 2n zygoteß       the other sperm nucleus migrates and unites with the polar nuclei of the central

cell, forming a 3n endosperm nucleusß       the zygote divides mitotically to become the embryo; the endosperm nucleus

divides mitotically to become the endospermß       the embryo, in most plants, is a young sporophyteß       the endosperm is tissue that will nourish the embryo and seedling as they

undergo development Seed Development-       Stages

o      development of the seed is the next evento      plant growth and development involves cell division, cell elongation, and differentiation

of cells into tissues and then organs-       Development of the Eudicot Embryo

o      immediately after double fertilization, the endosperm nucleus divides to produce a mass of endosperm surrounding the embryo

o      the single-celled zygote also divides, but asymmetrically, forming two parts: embryo and suspensor, which anchors the embryo and transfers nutrients to it from the sporophyte plant

o      globular stage: the proembryo is a ball of cellsß       the root-shoot axis is established; cells near the suspensor will become a root,

those at the opposite end will become a shootß       the outermost cells become dermal tissue that prevents dessication and also

has stomata that regulate gas exchangeo      the heart-shaped and torpedo-shaped embryos

ß       the embryo has a heart-shape when the cotyledons appear; it then grows to a torpedo shape

ß       with elongation, the root and shoot apical meristems are distinguishableß       ground meristem responsible for most of the interior of the embryo is also present

nowo      the mature embryo

ß       after differentiation into embryo and suspensor, one or two cotyledons developß       the embryo continues to differentiate into three parts:

∑      the epicotyl is between the cotyledons and first leaves; it contributes to shoot development

∑      the hypocotyl is below the cotyledon and contributes to stem development∑      the radicle is below the hypocotyl and contributes to root development

ß       the cotyledons are quite noticeable in a eudicot embryo, and may fold over-       Monocots Versus Eudicots

o      monocot embryo only has one cotyledonß       in monocots, the cotyledon rarely stores foodß       it absorbs food molecules from the endosperm and passes them to embryo

o      eudicot embryo has two cotyledonsß       during development of a eudicot embryo, cotyledons usually store the nutrients the

embryo usesß       the endosperm seemingly disappears as the nutrients are consumed

 Fruit Types and Seed Dispersal-       Fruits

o      a fruit is a mature ovary enclosing seeds; sometimes they retain other flower partso      fruits serve to protect and disperse offspringo      the fruit protects the peach seed well but makes germination difficult; the peas escape

easily but are lightly protected-       Simple Fruits

o      simple fruit develops from a single carpel or several united carpels of a compound ovary

o      legumes (pea pods), nuts and cereal grains are examples of dry fruits; such fruits are mistaken for seeds because a dry pericarp adheres to the seed within

o      hooks and spines of clover, bur, and cocklebur attach to the fur of animalso      woolly hairs, plumes, and wings disperse by windo      a fleshy fruit has a fleshy pericarp (e.g., peach, plum, olive, grape, tomato, apple, and

pear)ß       birds and mammals eat fruits, including seeds, and defecate them at a distanceß       squirrels and other animals gather seeds and fruits and bury them some distance

awayo      an apple is an example of an accessory fruit; the bulk of the fruit is not from the ovary

but from the receptacle-       Compound Fruits

o      a compound fruit develops from several individual ovarieso      an aggregate fruit develops from ovaries from a single flower (e.g., blackberry)

o      an aggregate fruit where each ovary becomes a one-seeded fruit is called an achene (e.g., strawberry)

o      a multiple fruit develops from ovaries from separate flowers fused together (e.g., pineapple)

-       Seed Germinationo      seed germination occurs when growth and metabolic activity resumeo      the embryo forms with both shoot and root apical meristem enclosed in a seed

ß       protoderm gives rise to the epidermisß       ground meristem produces the cells of the cortex and pithß       procambium produces vascular tissue

o      seeds retain their viability for varying times: maples seeds only last a week while lotus seeds are viable for hundreds of years

o      some seeds do not germinate until they have been dormant for a period of timeß       seed dormancy is a time during which no growth occurs even though conditions

are favorableß       in temperate zones, seeds may have to be exposed to cold weather before

dormancy is brokenß       in deserts, germination requires rain

o      germination has environmental requirementsß       oxygen must be available for increased metabolismß       adequate temperature allow enzymes to actß       adequate moisture hydrates cellsß       light may also be required

o      seeds that must be planted near the surface probably require light (e.g., lettuce)o      when a seedling grows in the dark, it becomes long and spindly (etiolated);

phytochrome induces normal growth in lighto      germination in eudicots and monocots

ß       prior to germination, a eudicot embryo consists of the following:∑      two cotyledons that supply nutrients to the embryo and seedling, but soon

shrivel and disappear∑      a plumule—a rudimentary plant consists of an epicotyl bearing young leaves∑      the hypocotyl, which becomes the stem∑      the radicle, which develops into roots

ß       in dicot seedling, the shoot is hook-shaped to protect the delicate plumuleß       in monocots, the endosperm is the food-storage tissue and the cotyledon does

not have a storage roleß       a monocot ≥seed≤ such as a corn kernel is actually the fruit and the outer covering

is the pericarpß       the plumule and radicle are enclosed in protective sheaths, the coleoptile and

the coleorhiza, respectivelyß       the plumule and radicle burst through these coverings when germination occurs

 Asexual Reproduction in Plants-       Means of Asexual Propagation

o      plants contain nondifferentiated meristem tissue and often reproduce asexually by vegetative propagation

o      in asexual reproduction, offspring arise from a single parent and inherit genes of that parent only

o      vegetative propagation utilizes the meristematic tissue of a parent plantß       violet plants grow from nodes of rhizomesß       the nodes of stolons will produce strawberry plants

ß       each eye of a potato plant tuber is a bud that produces a new plantß       sweet potatoes can be propagated from their modified rootsß       many trees can be started from small ≥suckers≤

o      stem cuttings have long been used to propagate a wide array of plants (e.g., sugarcane, pineapple)

o      the discovery that auxin will cause roots to develop has expanded our ability to use stem cuttings.

-       Tissue Culture of Plantso      tissue culture is the process of growing tissue artificially in a liquid or solid culture

mediumo      in 1902, German botanist Gottleib Haberlandt stated plant cells were totipotent; each

cell has full genetic potential of the organismo      when cultured cells were provided with sugars, minerals, vitamins, and cytokinin from

coconut milk, the undifferentiated cells divide and initially formed acallus, an aggregation of undifferentiated cells

o      the callus then differentiated into shoot and roots and developed into a complete planto      micropropagation is a commercial method of producing thousands to millions of

identical seedlings, by tissue culture in limited spaceo      meristem culture micropropagates many new shoots from a single shoot apex culture

in a medium with correct proportions of auxin and cytokininß       since the shoots are genetically identical, the adult plants that develop are clonal

plantsß       clonal plants have the same genome and display the same traitsß       meristem culture generates meristem & plants that are virus-free

o      entire plants can be grown from single plant cellsß       enzymes can digest cell walls & produce naked plant cells called protoplastsß       protoplasts regenerate a cell wall and begin cell divisionß       clumps of cells can be manipulated to form somatic embryosß       somatic embryos encapsulated in a hydrated gel (≥artificial seeds≤) can be

shipped anywhereo      anther culture cultures anthers in a medium of vitamins and growth regulatorso      cell suspension culture uses rapidly growing calluses cut into small pieces and

shaken in a liquid nutrient medium-       Genetic Engineering of Plants

o      traditionally hybridization (crossing different varieties or species) was used to produce new plants

o      transgenic plants carry foreign genes directly introduced into their cellso      Tissue Culture and Genetic Engineering

ß       genetic engineering alters genes of organisms so they have new and different traits; protoplasts lend themselves to genetic engineering in tissue culture

ß       high voltage electric pulses create pores in plasma membrane so new DNA can be introduced

ß       when genes for production of firefly enzyme luciferinase were inserted into tobacco protoplasts, plants glowed when sprayed with the substrate luciferin

ß       foreign DNA can be inserted into a plasmid of Agrobacterium; this bacterium infects plant cells and can deliver the recombinant DNA to target cells

ß       a gene gun is now used to bombard a callus with DNA coated metal particlesß       crops have been engineered to resist frost, fungal and viral infections, insect

predation, and herbicidesß       future crops could have more protein and require less water and fertilizer

o      Agricultural Plants with Improved Traits

ß       corn, potato, soybean, and cotton plants have been engineered to be resistant to insect predation or herbicides

ß       salt-tolerant Arabidopsis has been developed by cloning a gene for sequestering sodium ions in a vacuole

ß       genes from Vernonia and castor beans were inserted into soybeans to produce vernolic acid and ricinoleic acid used as hardeners in paints and plastics

ß       genetic engineering is attempting to improve efficiency of RuBP carboxylase and introduce C4 photosynthesis to rice

o      Commercial Productsß       corn has made antibodies to deliver radioisotopes to tumor cellsß       soybeans make an antibody to treat genital herpesß       human gene can be inserted into tobacco plants using tobacco mosaic virusß       tobacco plants produced antigens to treat non-Hodgkinπs lymphoma