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Plants - General it contains the “Big Baobab Pub” built inside it the plant and animal kingdoms are the best known of all the kingdoms of life on earth !tallest life form: coastal redwood = 385’ tall[117M] taller trees have been reported but not verified: they show a much more complex level of organization -a Douglas fir exceeding 400’ !both are comprised of many cells (there are NO unicellular plants OR animals) -a Australian mountain ash at 436’ !in most plants and animals the cells have specialized into various tissues and the tissues into organs for greater efficiency !plants are some of oldest organisms on earth: eg. sacred fig (Ficus religiosa) 2293 yrs old plants are very diverse in size, shape and complexity eg. Sequoias are 2000-3000 years old; oldest known is 3,200 years today, range in size from microscopic pondweeds to giant sequoias: eg. oldest bristlecone pine was 4844 years old when felled in 1964 !one of world’s most massive organism: “general Sherman’ (giant sequoia in California) 272’ tall [81-5M] eg. a baobab tree has been carbon dated to 6000 yrs old (doesn’t produce growth rings) eg. new record holder is a Norway Spruce discovered in Sweden that had a relatively young trunk; but its roots were dated to 9,550 years - it apparently began growing as soon as land appeared after the last ice age 79’ girth (>25’ dia) volume: 52508 ft3 (148 trillion m3 ) weight: 2,100,000 kg (~2000 tons) (>10x’s heaver than blue whale=180,000kg (~200 tons)) many plants grow in clonal colonies and while individuals of the clone have relatively short lifespans some clones appear to be much older (but no hard evidence yet): estimated to contain over 600,000 board feet of timber; enough to build 120 average size homes also, Baobab Tree in South Africa is 72 ft tall but 155’ in circumference Plants: Introduction; Ziser Lecture Notes, 2010.8 eg. some creosote bush colonies may live up to 1 Plants: Introduction; Ziser Lecture Notes, 2010.8 2 Major Characteristics of Plants 11,700 yrs eg. Eucalyptus (Eucalyptus recurva) groves may live 13,000 yrs Members of the Plant Kingdom (Metaphyta) share the following characteristics: eg. Kings lomatia (Lomatia tasmanica) an Australian tree that produces colonies is claimed to be 43,600 years old 1. All plants are multicellular eg. quaking aspen ( Pando sp.). one grove may contain 47,000 trees, cover 43 ha and weighs 6,500 tons (6,000,000 kg) typical plant cells: are eukaryotic eg. some Aspen clones may be as old as 80,000 yrs surrounded by cell wall eg. large underwater meadows of Posidonia oceanica, a seagrass in the Mediterranean may be up to 100,000 years old many have chloroplasts for photosynthesis 2. plants are nonmotile !subjects plants to dictates of nature ! primary influence on most of a plants characteristic adaptations !must be able to withstand fluctuations in light, temperature, water availability, space & nutrients 3. most plants are autotrophs (photosynthesis) while diverse in form, almost all plants are similar in function: use the sun’s energy to make organic food from simple inorganic nutrients; nitrogen, phosphorus, CO2, etc. Plants: Introduction; Ziser Lecture Notes, 2010.8 3 Plants: Introduction; Ziser Lecture Notes, 2010.8 4 photosynthesis to make food but some store oils instead or in addition to starch CO2 + H2 O + sunlight ! sugars + O2 a few are parasitic or saprophytic and some of these cannot do photosynthesis and must “eat” organic food eg. a few plants are parasitic on other plants or on fungi and do not do photosynthesis; they get all their nutrition from their host cellulose is found in the cell walls of all plants cellulose comprises ~70% of land biomass ! saprobe, no photosynthesis b. lignin is also one of the 4 most common natural polymer ! pollinated by tiny flies that gain access via mud cracks in dry season ligning is found in cell walls of some plants and in the wood of perennial plants as well as in many seeds a few plants, while autotrophs, are carnivorous ! they eat insects and other animals comprises ~25% of land biomass they usually grow in nitrogen poor soil very difficult to degrade, mainly only by certain species of fungi ! use nitrogen in proteins of animals they catch presence of lignin helps to make cellulose difficult to digest or extract for commercial uses 4. plants use aerobic respiration to extract energy from that food c. plants also produce a variety of chemicals such as alkaloids, tannins, volatile oils, resins that are used for defense, communication, coordination of plant activities, waste disposal sugars + O2 ! CO2 + H2 O + energy can’t do anaerobic respiration like bacteria ! have to have O2 7. most plants have true tissues and true organs 5. most plants store excess foods as starch tissues = groups of specialized cells performing common function (a complex carbohydrate) 5 6 Plants: Introduction; Ziser Lecture Notes, 2010.8 all plants begin with primary growth organs = groups of tissues working together to perform a common function herbaceous plants have only primary growth Animals are the only other kingdom with true tissues and true organs annuals: live 1 year only eg. beans, grasses, many wildflowers 8. Plants have simple responses to environmental stimuli biennials: require two growing seasons to complete their life cycle a. plants are nonmotile but do show some simple movements: eg carrots, cabbage, beets, etc b. secondary growth (woody) !sunflowers and others turn leaves or flowers to track sun during day wood and bark replace the softer herbaceous tissues of the stem and main roots !sensitive plants close their leaves when touched !vines and tendrils wrap around supports perennials (=plants that grow for more than 2 years) produce secondary growth in the stem and roots !insectivorous plants close leaves to trap insects ! sleep movements b. many plants also can make slower, more permanent, changes in orientations =tropisms eg. all trees & shrubs sometimes just the roots are perennial !above ground parts dies back each winter eg. phototrophism (light) some plants may be annual in one climate and perennial in another climate eg. geotropism (gravity) 10.Many plants show a distinctive alternation of generations between sexual and asexual stages eg. thigmotropism (touch) 9. plants have two different kinds of growth related to the length of their life cycle: plants (& some algae, fungi, and animals) have a life cycle which consists of two completely different forms a. primary growth (herbaceous) Plants: Introduction; Ziser Lecture Notes, 2010.8 a. cellulose & lignin are the primary chemicals used by plants for support and protection. cellulose is the most abundant natural polymer in the world eg. one species of orchid is known to be the only “underground” plant Plants: Introduction; Ziser Lecture Notes, 2010.8 6. plants produce several distinctive or unusual chemicals: 7 Plants: Introduction; Ziser Lecture Notes, 2010.8 8 Most Fundamental Values of Plants: both forms reproduce, 1 sexually and the other asexually human live is tightly interwoven, directly & indirectly, into the activities of plants: the stage that reproduces asexually is called the sporophyte 1. all land based animal life is dependent on plants as beginning of food chains (primary producers) !it produces asexual spores the stage that reproduces sexually is called the gametophyte 2. plants also produce & maintain about 30% of all oxygen (O2) in our atmosphere. (gametes are the sex cells; egg & sperm) the other 70% is produced by marine algae and photosynthetic bacteria In some plant groups they exist as completely separate entities 3. plants play a vital role in the carbon cycle gametophyte male eg. 1 acre of corn (.4ha) ~10,000 plants ! accumulates >5000 lbs of Carbon from CO2 during the growing season female [Haploid] egg asexual spores ………………………………… [Diploid] sperm ! equiv to >11 tons of Carbon Dioxide fertilization absorption by plants is balanced by production of CO2 from decomposition zygote 4. from earliest times human distributions have been inextricably tied to plants (embryo) sporophyte our preliminary knowledge about plants arose from trial & error experiences eg. hunter/gatherers: roots, berries, seeds ~8000BC agriculture – cereals !greater yields and growth 9 Plants: Introduction; Ziser Lecture Notes, 2010.8 only plants and fungi are primarily terrestrial organisms 300-400BC: greeks –identification by 200AD: Romans – crop rotation, manure, grafting, plant varieties eg. heart shaped leaves ! for heart ailments today the science of plants continues as botany with many specialties: physiology genetics agriculture !true plants probably arose ~465 MY (ordovician) ago as green algae moved from water to land [photosynthetic bacteria began to colonize the land long before algae or plants ~1.2 BY ago] humans use plants for: shelter, furniture, chemicals, lubricant latexes, etc ! only a few are truly aquatic ! these two kingdoms have a long history of symbiosis by 1700’s: larger “herbals” folklore, medicinal properties of plants food, heat, antibiotics, oils, rubber, poisons, 10 Origins of Plants our formal study of plants: morphology systematics horticulture Plants: Introduction; Ziser Lecture Notes, 2010.8 Advantages of moving from water to land: clothing, paper, dyes, waxes resins, 1. plenty of light 2. CO2 more easily available than in water 3. no competition for minerals or growing space (at first at least) esthetic benefits recreation (camping, backpacking, hiking) house plants flowers Disadvantages of moving from water to land: 1. obtaining & holding onto water water now becomes a limiting factor need to find ways to get it and to store it also outer surface must become more water tight 2. gas exchange Plants: Introduction; Ziser Lecture Notes, 2010.8 11 Plants: Introduction; Ziser, Lecture Notes, 2010.3 12 as outer surface becomes less permeable still need a way to get gasses in and out 3. need effective support to counteract counteract gravity eg. resistant seeds, dormancy, evaporative cooling to withstand environmental extremes eg. specialized structures to get egg and sperm together and to disperse offspring most organisms in water are naturally buoyant or have floats or gas sacs to lift them to the surface all plants appear to have arisen from green algae 4. must be able to withstand greater extremes in temperature, weather, etc [probably charophytes are closest algal relative] !must develop ways survive freezing, drought, extreme heat, etc Evidence for green algal ancestor to plants: 1. most green algae are found in freshwaters and damp terrestrial habitats 5. reproduction and dispersal on land requires some way to get sex cells together and some way to disperse offspring in water gametes and zygotes are released directly into the water many of the distinctive characteristics of plants evolved to solve the problems for living on land: including swamps and marshes where some of the earliest plant fossils first appear primitive plants are still tied to water 2. many green algae today can live on land: some are found in moist soil, forest floor and tree trunks eg. cellulose cell walls offered enough support for living on land 3. some green algae produce larger multicellular forms such as “seaweeds” eg. plants developed vascular tissue to move water and nutrients around and for added support some of the earliest plant fossils resemble some of these multicellular green algae eg. plants developed roots to find water and minerals 4. the cells of both green algae and plants: eg. plants developed waxy cuticle to prevent water loss Plants: Introduction; Ziser, Lecture Notes, 2010.3 eg. plants can store food in specialized structures such as rhizomes, tubers, storage roots, etc ! main pigment is chlorophyll a ! store starch in plastids rather than free in cytoplasm 13 Plants: Introduction; Ziser, Lecture Notes, 2010.3 14 Plant Cells ! have cellulose in cell wall ! have peroxisomes (contain protective enzymes) ! cytoplasm divides by cell plate animals have 100’s of different kinds of cells plants have relatively few kinds plant cells share many features with most eukaryotic cells: nucleus cell membrane mitochondria for aerobic respiration ribosomes for protein synthesis; but much fewer compared to bacteria and animals additional structures typical of most plant cells a. cellulose cell wall – protection, support, porous for moving things into and out of cell b. plastids: chloroplasts – contain chlorophyll for photosynthesis chromoplasts – contain other pigments: fruits, flowers amyloplasts – colorless, store starch c. large central vacuole other eukaryotes have various kinds of smaller vacuoles but a larger vacuole is characteristic of plant cells for storage & simple support Plants: Introduction; Ziser, Lecture Notes, 2010.3 15 Plants: Introduction; Ziser, Lecture Notes, 2010.3 16 Plant Tissues wilting indicates that this vacuole requires addition water the cell is the basic structural and functional unit of plants (all all life) watering plant restores the ability of the vacuole to support the plant cells only one kind of plant cell, the sperm, is able to move using a flagellum each cell in plant requires a continuous supply of water, oxygen, nutrients in large plants it would be impossible for each cell to “fend for itself”: -light cannot penetrate to interior cells -light cannot penetrate below ground -water, nutrients and gasses are not easily accessible to interior cells or those below ground therefore, in multicelled organisms groups of cells become specialized to perform a specific function eg. protection, photosynthesis, support, etc !more efficient !division of labor !but all become dependent on each other can no longer survive alone tissues are groups of similar cells that have become specialized for specific functions There are 3 main kinds of plant tissues: Plants: Introduction; Ziser, Lecture Notes, 2010.3 17 18 b. periderm 1. Dermal Tissue 2. Vascular Tissue 3. Ground Tissue !covers the stems and roots of perennial plants a. epidermis each plant organ (roots, stem, leaf) contains all three tissues usually a single layer of tightly packed cells covers and protects the young plant 1. Dermal Tissues generally no chloroplasts; cells are transparent dermal tissue covers the entire outside of the plant allows light to penetrate into interior photosynthetic cells on leaves and herbaceous stems, the epidermis: is the “skin” of a plant -secretes waxy protective cuticle to restrict water loss main functions of dermal tissue: ! physical protection ! thicker in drier habitats; thinner in wet habitats ! water conservation and protect from pathogens and disease ! repairs damaged area -contains pores (=stomata) for gas exchange ! absorbs water and minerals ! contains pores for gas exchange -epidermis of leaves & stems may contain leaf hairs (= trichomes) with a variety of functions two kinds of dermal tissue in plants: a. epidermis ! covers the leaves in all plants ! covers stems and roots in herbaceous plants (eg. annuals and biennials) Plants: Introduction; Ziser, Lecture Notes, 2010.3 Plants: Introduction; Ziser, Lecture Notes, 2010.3 19 on roots, cells of the epidermis produce root hairs Plants: Introduction; Ziser, Lecture Notes, 2010.3 20 !greatly increase the surface area of the roots for absorption of water and mineral !move water and minerals from roots to leaves !move organic chemicals such as sugars and hormones throughout the plant b. periderm ! provide support for plant periderm replaces epidermis in stems and roots of woody plants !provide cooling for plants in hot weather two main kinds of vascular tissue: forms the outer layer of “bark” much thicker for better protection since plants live many years periderm consists mostly of dead cork cells always found together in each plant organ =vascular bundles a. xylem: cells contain suberin made up of dead cells that are joined together to form long hollow tubes that branch throughout the plant –a fatty material for waterproofing instead of stomata, periderm often with lenticels for gas exchange generally larger cells with thicker cell walls 2. Vascular Tissue moves water and minerals from roots, up the stem to the leaves the plumbing of vascular plants consists of a series of interconnected tubes that extend throughout the plant form tips of roots to all leaves main functions of vascular tissue: Plants: Introduction; Ziser, Lecture Notes, 2010.3 xylem & phloem b. phloem: made up of living cells connected end on end that branch throughout the plant cells generally smaller with thinner cell walls 21 Plants: Introduction; Ziser, Lecture Notes, 2010.3 22 b. pith moves sugars, hormones and organic materials throughout plant for use or storage or signaling ground tissue in the center of some stems and roots; interior to the vascular bundles c. mesophyll 3. Ground Tissues ground tissue in the leaves that does photosynthesis and gas exchange this tissue forms the bulk of young plants, annual plants and most leaves Meristem Tissue fills most of ‘space’ between dermal and vascular tissues in addition to the three basic kinds of tissues plants also contain clumps of undifferentiated, embryonic cells that can give rise to any of the other tissue types does most of the plants’ metabolic work functions of ground tissue: all plant cells arise from these embryonic plant cells =actively dividing cells ! photosynthesis ! food storage meristem is located wherever growth is occuring ! some support in herbaceous plants or organs ! gas exchange !in buds along the stems of plants ! secretion; some cells secrete: nectar, oils, mucilage, resin !in woody plants, as a layer of tissue called the cambium that forms new vascular tissue and periderm referred to by different names in different locations in plant: a. cortex the ground tissue in roots and stems between epidermis and vascular bundles Plants: Introduction; Ziser, Lecture Notes, 2010.3 23 Plants: Introduction; Ziser, Lecture Notes, 2010.3 24 Plant Organs Reproductive Organs probably the most recognizable feature of plants are their simple organs unlike in most animals, plant reproductive organs are always temporary structures organ = groups of tissues arranged in clearly defined structures or parts some plants produce asexual reproductive organs plant organs are much simpler than animal organs all plants produce sexual reproductive organs eg. capsule, sori eg. antheridia, archegonia, sporangia, cones, flowers, fruits. each plant organ contains all three plant tissues dermal, vascular & ground tissue plants are classified based mainly on the kinds of reproductive organs that they produce so these organs will be discussed when we describe the major kinds of plants two basic categories of plant organs !vegetative & reproductive organs a. Vegetative Organs almost all plants have developed three major vegetative organs: a. an underground portion that anchors the plant and in some absorbs water and nutrients = root b. some kind of supporting structure for the leaves =stem c. a flat structure used for most photosynthesis =leaf 25 Plants: Introduction; Ziser, Lecture Notes, 2010.3 Plants: Introduction; Ziser, Lecture Notes, 2010.3 26 [like hyphae of fungi] Vegetative Plant Organs taproots extend deep to water tables Roots shallow fibrous roots are better at collecting rainwater normally found below ground 3. food or water storage they are nonphotosynthetic and therefore not green surplus carbohydrates produced by leaves are sent to roots for storage usually highly branched some desert plants can store water in taproots often more extensive than above ground part of plant whatever conditions the above ground part of plant is subjected to the roots most often survive eg. corn roots: 8 ft deep, extends 4 ft in diameter even in winter when whole above ground plant dies back, roots live and resprout the next spring eg. tamarisk (desert shrub): roots are up to 165’ deep Root Structures: eg. 4 month old ryegrass plant in one gallon of soil!had 310 miles of roots A. patterns of root growth: roots grow rapidly 1. taproots up to 2” per day 1 main root with many smaller lateral branches soil conditions greatly affect extent of root growth Root Functions: eg. dandelion 1. Anchor plant most mature trees begin with a taproot but at maturity have large, shallow, lateral roots instead extend into soil may be thick strong taproot or extensive spreading roots but hickory retains its taproot 2. Gather water & minerals Plants: Introduction; Ziser, Lecture Notes, 2010.3 27 Plants: Introduction; Ziser, Lecture Notes, 2010.3 28 2. fibrous roots epidermal cells behind root cap and growing zone produce long threadlike extensions =root hairs several to many roots of same size that develop from bottom end of stem greatly increase surface area for absorption ! up to 90% of root absorption occurs through root hairs smaller lateral roots branch from them eg. onions, crabgrass, monocots 3. adventitious roots removing plant from soil destroys most of these root hairs ! decreases plants ability to absorb water any roots that arise from other places on stems or directly from leaves ! need to keep transplants moist often modified for various additional functions eg attachment, reproduction, etc B. Parts of the Root since plants lack any kind of respiratory system each organ must be able to carry out gas exchange on its own like all plant organs roots need O2 1. root cap good soil normally has lots of air spaces to allow gas exchange with roots tip of each growing root is protected by a root cap eg. wont grow well if covered by concrete ! covers and protects rapidly dividing cells of root (apical meristem) eg. soil with too much clay (Austin) must be aerated with compost and sand for most plants to grow well !also directs tip of growing root downward eg. soil aerators sold at home stores when cap is removed ! roots grow randomly until they grow new root cap a few plants that grow in stagnant water or waterlogged soil produce pneumatophores that act as siphons to draw air into the root 2. root hairs 29 Plants: Introduction; Ziser, Lecture Notes, 2010.3 Stems 30 Plants: Introduction; Ziser, Lecture Notes, 2010.3 at nodes are leaves, buds or branches arrangement of buds and leaves on stem: in plants with true stems, there is no sharp line of demarcation between roots and stems opposite alternate whorled basal the stem is typically above ground and the roots, below ground ! ! ! ! 2/node 1/node 3 or more/ node only around base of stem new stems, leaves or reproductive organs develop from buds but many variations exist. terminal bud = tip of stem axillary bud = at nodes General Stem Functions: 2. Stems can be herbaceous or woody: 1. Support leaves and reproductive organs for maximum efficiency a. herbaceous 2. Internal transport: annual or biennial - grow 1 or 2 years then die stems connect the nutrient and water gathering organs (=roots) with the food synthesizing organs (=leaves) dermal tissue is epidermis Conducting water and minerals from the root to other parts of the plant. Conducting food, which is manufactured in the leaves by photosynthesis, to all other parts of the plant stem is usually green b. woody stems: the first land plants (465MY) were small herbaceous plants that grew low to the ground External Features of Stems 80 MY later (385 MY) we find the first fossils of trees; ie woody plants indicating that plants had developed vascular tissue and true roots, stems and leaves and the strong supportive secondary growth that allows trees and shrubs today to grow many feet high 1. leaves and buds branch off at specific locations on the stem= nodes distances between nodes = internodes the first tree’s also led to a revolution in terrestrial ecology: Plants: Introduction; Ziser, Lecture Notes, 2010.3 31 Plants: Introduction; Ziser, Lecture Notes, 2010.3 32 -the roots dug into cracks and crevases speeding up the weathering of rock and soil -as trees decomposed they began to build rich humus soil -the leaves removed large amounts of CO2 from the air and replaced it with large amounts of O2 hard, thick, long lived; stem is not green may also have trichomes 2. Vascular Tissue arranged as bundles of xylem and phloem just inside of the epidermis dermal tissue is periderm with cork 3. Ground Tissue outer surface of periderm often contains raised areas = lenticels for gas exchange fills in the spaces between vascular tissue and epidermis Anatomy of Woody Stems bulk of stem consists of tough woody xylem tissue Plants that live more than one year, ie. perennials, produce secondary growth each year. !lots of cellulose and lignin the stem grows in width from embryonic cells (meristem) in a layer of cambium within each vascular bundle woody plants are either: trees = branching relatively high above ground each year this cambium produces new layers of xylem and phloem cells. shrubs = branches at or near ground since woody stems are perennial: they maintain some embryonic tissues that can grow into new plant tissues and organs xylem grows much faster than phloem Anatomy of Herbaceous Stems ! virtually all of the “wood” of a tree is 33 dead xylem cells Plants: Introduction; Ziser, Lecture Notes, 2010.3 34 vs lighter sapwood (still used for transport) the layers of phloem are much thinner and become part of the bark Dendrochronology The phloem, on the “outer-side” of the cambium, the cortex and the periderm make up the bark of a tree. growth rings can also retain info on yearly climate and other factors that affect growth ! can date back to ~9000 yrs Differences in the size of the xylem cells produced throughout the growing season produce the familiar “growth rings” in the wood. eg. Mesa verde !Cliff Palace constructed in 1073 !Pueblo Bonito 919-1130 spring: fastest growth, plenty of water and nutrients !cells are larger with thinner walls =springwood late summer: less water fewer nutrients available !cells are small and thicker walled = summerwood wood is typically produced in the stem (=trunk) but major roots of trees also usually have wood, bark and annual rings the arrangement of different cell types in the secondary tissue results in the distinctive characteristics of each kind of wood: the oldest cells are closer to the center of the trunk eg oak, maple, pine, etc the amount of old wood closest to the center expands as new cells are laid down in the vascular cambium variations in wood structure: 1. in moist humid tropics trees do not produce annual growth rings !environmental conditions determine the presence or absence of rings these older cells are often darker and are called heartwood. xylem becomes plugged with pigments, tannins, gums and resins ! heartwood no longer functions in transport Plants: Introduction; Ziser, Lecture Notes, 2010.3 1. Epidermis on outside outer surface has stomata in thin epidermis for gas exchange woody stems are mainly the secondary growth of perennial plants (grow >2 yrs) Plants: Introduction; Ziser, Lecture Notes, 2010.3 soft and green little or no woody tissue usually short lived: characteristic of annual plants little or no growth in diameter eg. those growing in areas with pronounced wet and dry seasons show rings 35 Plants: Introduction; Ziser, Lecture Notes, 2010.3 36 but may be more than one ring per year Leaves 2. in Panama canal zone is “the valley of square trees” leaves are the most variable part of a plant a species of cottonwood can be round, needle-like, scale-like, cylindrical, heart-shaped, fan shaped trunks are roughly square in cs; an entire set of terminology is used to describe growth rings are also square shape margins vein patterns ways of attaching to stem believed to be due to local growing conditions 3. softwood vs hardwood vary in size: raffia palm ! 20 M (65’) long duckweed ! 1/32nd of an inch Victoria water lily pads up to 12’ circumference pines and other conifers typically have wood that lacks fibers and vessel elements have only tracheids for conduction Function of Leaves: ! conifer woods are generally softer than wood of flowering plants 1. Carry out most photosynthesis for most plants herbaceous stems also do photosynthesis 2. Gas Exchange hardwoods are mostly flowering plants (dicots, except Balsa Ochroma leaves have pores (=stomata) that pyramidale)) !take in CO2 for photosynthesis today >4500 products are made from wood !release water vapor and O2 3. Absorption 37 Plants: Introduction; Ziser, Lecture Notes, 2010.3 all leaves can absorb some water and minerals Plants: Introduction; Ziser, Lecture Notes, 2010.3 eg. most conifers, live oaks, privets, etc deciduous ! tree loses all its leaves at the same time eg. miracle grow fertilizer is sprayed on leaves of many yard plants, eg roses in some plants leaves absorb most of the nutrients and water eg. in temperate areas – before winter eg. epiphytes helps them survive low temperatures of winter eg. pond plants metabolism and photosynthesis slow saves water Leaf Structure eg. in tropical areas – before dry periods A. leaf arrangement on stem opposite alternate whorled basal 38 ! ! ! ! eg. maples, most oaks, sumac, pecan, etc 2/node 1/node 3 or more/ node only around base of stem C. leaf anatomy 1. most leaves consist of two parts: B. leaf permanence petiole & blade all trees (and other perennial plants) shed leaves but not eg. grasses and other monocots in perennial plants the leaves can be deciduous or evergreen petiole ! thin flexible stalk that allows blade to move freely in the wind in some plants the petiole can change orientation of leaf to make photosynthesis more efficient evergreen ! tree loses leaves year round but always has some leaves on the tree base of petiole often with 1 or 2 stipules and/or an axillary bud can be an advantage in areas with short growing seasons blade ! does most of the photosynthesis usually thin, greatest exposure to the sun Plants: Introduction; Ziser, Lecture Notes, 2010.3 39 Plants: Introduction; Ziser, Lecture Notes, 2010.3 40 leaves tend to be arranged on tree and among trees to provide greatest access to sunlight vascular tissue can be seen as leaf veins also help support the blade ! a single blade on a petiole compound !1 blade on a single petiole b. leaf hairs (=trichomes) outgrowths of epidermal cells 2. leaves can be simple or compound simple but some floating plants have them on the upper surface eg. some have protective function eg. stinging nettle – contain poisons that inhibit herbivory eg. in some mountain wildflowers (eg. Edelweiss) leaf hairs protect plants from intense UV radiation 3. other parts of leaves a. stomata leaf epidermis contains pores (=stomata) for gas exchange stomata are protected by two guard cells stomata generally open during day, closed at night to conserve water in many desert plants, stomata are closed during day and open at night eg. many desert plants have a thick “furry” layer of trichomes to reduce windspeed and reduce water loss from pores eg. in plants in salty environment often have trichomes on leaves that remove excess salt (excretion) eg. may produce various volatile chemicals with distinctive scents to ward off herbivores unlike flower scents, leaft trichomes produce aromatic products that are not released until leaf is touched 4 main plant leaf scents (mainly terpenoids): turpentine (pine needles) camphoraceous (wormwood, yarrow, sage) mint miscellaneous (parsley,onions, watercress, celery) during drought, stomata may remain closed during day evaporation of water from stomata also helps to cool plant in summer usually more stomata on lower surface of leaf Plants: Introduction; Ziser, Lecture Notes, 2010.3 c. 41 also, leaves of many grasses accumulate silica Plants: Introduction; Ziser, Lecture Notes, 2010.3 42 Reproductive Plant Organs sometimes forms teeth at edge of leaf that can easily cut flesh in addition to vegetative organs plants typically produce reproductive organs 4. Leaf variations due to environmental factors: unlike most animals: sexual organs are usually temporary structures eg. plants in arid environments often have thick leathery leaves with fewer pores to reduce water loss appear as plant reaches maturity eg. and may have dense hairs to reflect light and keep plant cooler in perennials, may form each year eg. leaves that develop in shade are usually thinner with fewer leaf hairs eg. leaves that float on the surface of ponds have stomata on top of leaf rather than on the bottom as in most plants reproductive organs can be produced for asexual reproduction or sexual reproduction organs for asexual reproduction !produce asexual spores capsule sori strobili (asexual cones) organs for sexual reproduction !produce egg and sperm antheridium and archegonium cones (sexual cones) flowers and fruits specific kinds of reproductive organs are characteristic of each major plant group and will be discussed with each group Plants: Introduction; Ziser, Lecture Notes, 2010.3 43 Plants: Introduction; Ziser, Lecture Notes, 2010.3 44 Plant Diversity General Plants are classified into 4 major groups: !from simplest to most complex !from oldest to most recently evolved Mosses (~15,000 species) small, simple, in moist habitats, oldest fossils eg mosses, liverworts, hornworts Ferns (11,000 species) more complex tissues and organs eg horsetails, whisk ferns, club mosses Seed Ferns (>>>1000; extinct) Conifers (760 species) mostly trees and shrubs, reproduction by producing pollen, and seeds in “cones” eg pines, spruce, fir, cedar, cypress Flowering Plants (235,000 species, 90% all plants) most complex in terms of structure reproduce by producing pollen, and seeds in fruits eg. lilies, irises, grasses, wildflowers, crop plants, oaks, willows, maples, etc Plants: Introduction; Ziser, Lecture Notes, 2010.3 45