Study Notes Exam 2
Characteristics 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 coat
o seeds are resistant to drought and somewhat resistant to predators
- 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 dominant
o in the vascular plants, the sporophyte is dominant or more conspicuous
o the shift to sporophyte dominance is an adaptation to life on land; the gametophyte becomes microscopic and dependent on the sporophyte
- 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 (³Bryophytes²)
- 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 water
o because sexual reproduction involves flagellated sperm, they are usually found in moist habitats
o 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 liver
o Marchantia has a flat, lobed thallus about a centimeter in length
o 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 plant
o sexual reproduction: antheridia are on disk-headed stalks and produce flagellated sperm; archegonia are on umbrella-headed stalks and produce eggs
§ the zygote develops into a tiny sporophyte with a foot, short stalk, & capsule
§ 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 Antarctic
o moss prefers damp, shaded localities but some survive in deserts, bogs & streams
o some ³mosses² are not true mosses:
§ 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 fragmentation
o the moss life cycle begins with algalike protonema developing from the germination of a haploid spore
§ upright shoots develop covered with leafy structures & anchored by rhizoids
§ the shoots bear antheridia and archegonia at their tips
§ the antheridia produce flagellated sperm which need external water to reach eggs in archegonia
§ the archegonium looks like a vase with a long neck; it has an outer layer of sterile cells with a single egg at the base
§ fertilization results in a diploid zygote that undergoes mitotic division to develop a sporophyte
o 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 Bryophytes
o sphagnum (bog or peat moss) has tremendous ability to absorb water and is important in gardening
o 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 roots
o phloem is vascular tissue that transports sucrose & hormones throughout the plant
o lignin strengthens the walls of conducting cells in xylem
o the cuticle and stomata are also characteristics of a dominant sporophyte
o seedless plants are mostly homosporous, using spores for dispersal
o 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 ³ground pine.²
o a branching rhizome sends up aerial stems less than 30 cm tall
o tightly packed, scalelike microphylls cover stems and branches; each contains one strand of vascular tissue
o sporangia are borne on the surface of leaves called sporophylls which are grouped in club-shaped stroboli; spores germinate into independent gametophytes
o most club mosses live in tropics or subtropics as epiphytes, plants that live on trees without harming them
o closely related are spike mosses (Selaginella) and quillworts (Isoetes)
- Ferns and Allies
o Phylum Sphenophyta today contains one genus, Equisetum (horsetails)
o a rhizome produces aerial stems that stand about 1.3 meters tall
o whorls of slender side branches & small scalelike leaves encircle nodes of a stem, resembling a horseıs tail
o the tough, rigid stems have silica in the cell walls; early Americans used them as ³scouring brushes.²
- Whisk Ferns (phylum Psilotophyta)
o whisk ferns occur in the southern United States and in the tropics
o whisk ferns have no leaves or roots; a branched rhizome with rhizoids and a mycorrhizal fungus helps gather nutrients
o other genera including Tmesipteris have true leaves that are microphylls
- Ferns (phylum Pterophyta)
o ferns are widespread, and especially abundant in warm, moist tropical regions
o ferns range in size from low-growing mosslike forms to tall trees
o fronds are leaves that are variable in size and shape
o ferns are the only group of seedless plants to have well-developed megaphylls; megaphylls may have evolved by fusion or branching of stems
o life cycle of a fern: spores produced by meiotic cell division within sporangia, located in sori on underside of leaflets
§ spores are released and disperse largely by wind
§ a spore germinates into a prothallus which grows to develop antheridia and archegonia underneath
§ 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
§ a sporophyte becomes visible as the first leaf grows above and as roots develop below the prothallus
§ 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 gametophyte
o 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 ³seed.²
- 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
- Gymnosperms
o the Gymnosperms include the conifers, cycads, ginkgo, and gnetophytes
o all have ovules exposed on the surface of sporophylls or similar structures
o Conifers: phylum Coniferophyta (~ 575 species)
§ conifers are cone-bearing trees and shrubs: pines, hemlocks, and spruces
§ conifers usually have evergreen needlelike leaves well adapted to withstand extremes in climate
§ pine needles have a thick cuticle and recessed stomata
§ pine uses: construction wood; resin is insect & fungal deterrent (turpentine)
§ the pine life cycle:
§ the sporophyte is dominant and its sporangia are borne in cones
§ two types of cones are pollen cones (small and near the tips of lower branches) and seed cones
§ each scalelike sporophyll of a pollen cone has two or more microsporangia on the underside
§ within the sporangia, each microsporocyte undergoes meiosis and produces four microspores
§ each microspore develops into a male gametophyte which is the pollen grain
§ a megasporangium is within an ovule; a megasporocyte undergoes meiosis producing four megaspores
§ only one spore develops into a female gametophyte with 2–6 archegonia, each containing a single large egg
§ 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 two nonflagellated sperm
§ fertilization takes place one year after pollination
§ the ovule matures and becomes the seed, composed of embryo, reserve food and seed coat
§ the woody seed cone opens to release winged seeds in the fall of 2nd season
o Cycads: phylum Cycadophyta (~100 species)
§ the trunk is stout and unbranched; the large leaves are compound giving a palmlike appearance
§ cycads have pollen and seed cones on separate plants, pollinated by insects
§ the pollen tube bursts in the vicinity of the archegonium and multiflagellated sperm swim to reach an egg
§ today, cycads are endangered because of their very slow growth
o Ginkgoes (maidenhair trees): phylum Ginkgophyta (1 species)
§ it is called the maidenhair trees because its forked-veined, fan-shaped leaves resemble the maidenhair fern
§ ginkgo ovules are at the end of short, paired stalks; female trees produce seeds with a fleshy covering and foul odor
§ 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 ovule
o Gnetophytes: phylum Gnetophyta (~70 species)
§ gnetum consists of trees and climbing vines with broad leaves; they live mainly in the tropics (Ephedra & Welwitschia in deserts of US & Africa)
§ the xylem and stroboli are uniform across genera, and all lack archegonia
§ angiosperms also lack archegonia, suggesting that gnetophytes are the gymnosperms most closely related to angiosperms
§ 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 tissues
o flowering plants became the dominant plants in the late Cretaceous and early Tertiary periods, and probably arose ~ 200 million years ago
o Monocots and Eudicots
§ most flowering plants belong to one of two classes: Monocotyledones (65,000 species) or the Eudicotyledones (175,000 species)
§ 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
§ monocot produce one cotyledon (seed leaf) at germination and have flower parts mostly in threes or multiples of threes
§ dicots produce two cotyledons (seed leaves) at germination and have flower parts mostly in fours or fives, or multiples of these numbers
o The Flower
§ flowers have several kinds of highly modified leaves arranged in rings and attached to a receptacle
§ receptacle is a modified stem tip to which flower parts are attached
§ sepals are outer ring of modified leaves of flowers; usually green, they enclose flower before it opens
§ petals (collectively a corolla) are a ring of modified leaves inside of sepals; large and colorful, they help attract pollinators
§ stamens form a whorl inside the petals and around a pistil; each slender filament has an anther at its tip
§ the anther produces pollen
§ 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 flower
o the angiosperm life cycle:
§ a megaspore located in an ovule within an ovary of a carpal develops into an egg-bearing female gametophyte called the embryo sac
§ usually, the embryo sac has seven cells; one is an egg and one contains two polar nuclei
§ microspores produced in anthers become pollen grains which mature into sperm-bearing male gametophytes
§ the mature male gametophyte consists of three cells; the tube cell and two sperm cells
§ pollination brings the male gametophyte to the stigma where it germinates
§ during germination, the tube cell produces a pollen tube that carries the two sperm to the micropyle opening of an ovule
§ in double fertilization, one sperm fertilizes egg and one sperm unites with polar nuclei to form the triploid endosperm
§ the ovule becomes the seed and contains the embryo (the sporophyte of the next generation) and stored food enclosed within a seed coat
§ A fruit is derived from an ovary and possibly accessory parts of the flower; some fruits are fleshy and some are dry
o Flowers and Diversification
§ 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
§ flowers promote efficient cross pollination; they also aid in dispersal through production of fruits
§ 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 water
o flowering plants usually have three vegetative organs: root, stem and leaf
o 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 ground
o roots anchor a plant in soil and give support
o roots absorb water and minerals from soil; root hairs are central to this process
§ root hair cells are in a zone near root tip
§ root hairs are numerous to increase absorptive surface of a root
§ transplanting plants damages a plant when the root hairs are torn off
§ roots produce hormones that are distributed along with water and nutrients to the rest of the plant
o perennials ³die back² 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, & leaves
o the stem forms the main axis of the plant, along with lateral branches
o upright stems produce leaves and array them to be exposed to as much sun as possible
o 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 underground
o the stem has vascular tissue to transport water and minerals from roots and sugar from leaves
o nonliving cells form a continuous pipeline through vascular tissue
o a cylindrical stem expands in girth and length; trees use woody tissue to strengthen stems
o 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 plants
o leaves receive water from roots by way of the stem
o broad, thin leaves have a maximum surface area to absorb CO2 and collect solar energy
o a blade is the wide portion of a leaf with most photosynthetic tissue
o petiole is a stalk that attaches a leaf blade to stem
o the leaf axil is the upper acute angle between petiole and stem where an axillary (lateral) bud originates
o 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 seed
o root xylem & phloem in a ring
o vascular bundles scattered in stem
o parallel leaf veins
o flower parts in multiples of 3
o usually one aperture in pollen grain
o includes grasses, lilies, orchids, rice, wheat, corn
- Eudicots: **
o 2 cotyledons in seed
o root xylem & phloem in a cross or star-shaped pattern
o vascular bundles arranged in a ring in stem
o net pattern to leaf veins
o flower parts in multiples of 4 & 5
o usually 3 aperture in pollen grain
o 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 epidermis
o ground meristem is inner meristem producing ground tissue
o procambium produces vascular tissue
- 3 specialized tissues are produced
o epidermis forms outer protective covering
o ground tissue fills the interior
o vascular tissue transports water and nutrients and provides support
- Epidermal Tissue
o epidermis is an outer protective covering tissue of plant roots, leaves, and stems of nonwoody plants containing closely packed epidermal cells
o waxy cuticle covers the walls of epidermal cells, minimizing water loss and protecting against bacteria
o 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 soil
o epidermal cells are modified as glands to secrete protective substances
o 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 tissue
§ cork is outer covering of the bark of trees; composed of dead cork cells that may be sloughed off
§ cork cambium is lateral meristem that produces new cork cells
§ mature cork cells produce the lipid suberin making them waterproof & inert
§ cork protects a plant and is resistant to attack by fungi, bacteria, and animals
- Ground Tissue
o ground tissue fills the inside of plants with parenchyma, collenchyma and sclerenchyma cells
o parenchyma are the least specialized of all plant cell types
§ contain plastids (e.g., chloroplasts or colorless storage plastids)
§ 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
§ usually occur as bundles of cells just beneath epidermis
§ 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
§ they are impregnated with lignin that makes the walls tough and hard
§ provide strong support to mature regions of plants
§ 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 leaves
§ xylem contains tracheids and vessel elements
§ both are hollow, nonliving cells
§ vessel elements form a continuous pipeline for water and mineral transport
§ 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 cells
§ sieve-tube cells contain cytoplasm but no nucleus
· they are arranged end to end & have channels in their end walls (³sieve-tubes²), through which plasmodesmata extend from one cell to another
§ 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 differentiation
o cells are continuously added to a root cap below and zone of elongation above by contributions from the zone of cell division
o the root cap is a protective cover; its cells are replaced constantly because they are soon ground off
o the zone of elongation is above the zone of cell division where cells become longer and more specialized
o the zone of cell division contains meristematic tissue and adds cells to root tip and zone of elongation
o 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 root
§ 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 cells
§ these cells contain starch granules; the cortex functions in food storage
§ 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 cylinder
§ it regulates the entrance of minerals into the vascular cylinder
§ 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 cylinder
§ the pericycle is the first layer of cells within vascular cylinder
§ its cells have retained the capacity to divide; it can start the development of branch or secondary roots
§ 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 growth
o the monocot root has a ring of vascular tissue where alternating bundles of xylem and phloem surround pith
o monocot roots also have pericycle, endodermis, cortex, and epidermis
- Root Diversity
o roots have adaptations to help anchor plants, absorb water and minerals, and store carbohydrates
o there are three general root types
§ taproot is common in eudicots; root adapted to store food (e.g., carrots, beets)
§ the fibrous root system of monocots is a mass of slender roots and lateral branches that hold the plant secure in the soil
§ 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 roots
§ in this mutualism, fungus receives sugars and amino acids from plant & plant receives water and minerals from the fungus
o legumes (e.g., peas and beans) have root nodules containing nitrogen-fixing bacteria
§ 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 Stems
o herbaceous stems are mature nonwoody stems that exhibit only primary growth
o 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
§ in each bundle, xylem is found to the inside of the stem; phloem is found to the outside
§ 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
§ in monocot stem, vascular bundles are scattered throughout the stem; there is no well-defined cortex or pith
§ cortex sometimes carries on photosynthesis; pith may function as storage site
- Woody Stems
o woody plants have both primary and secondary tissues
o primary tissues are new and form each year from primary meristem right behind the apical meristem
o secondary tissues develop from second year onward from lateral meristem growth
o primary growth increases length of a plant; secondary growth increases its girth
o as secondary growth continues, it is not possible to distinguish individual vascular bundles
o the woody eudicot stem has a different organization with three distinct areas: bark, wood, and pith
o bark of a tree contains cork, cork cambium, and phloem
o cork cambium is meristem beneath the epidermis that produces new cork cells when needed
§ cork cells become impregnated with suberin, causing them to die but making them waterproof
§ consequently, cork forms an impervious barrier, even to gas exchange, except at lenticels
o wood is secondary xylem which builds up each year; the vascular cambium is dormant during the winter
§ 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
§ summer wood forms when moisture is scarce; composed of a lower proportion of vessels, it contains thick-walled tracheids and numerous fibers
§ an annual ring is one ring of spring wood followed by a ring of summer wood; this equals one yearıs growth
§ sapwood is outer annual rings where transport occurs
§ 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 Plants
§ the first flowering plants were probably woody shrubs; herbaceous plants evolved later
§ 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 storage
o tendrils of grapes and morning glories are stems adapted for wrapping around support structures
o rhizomes are underground horizontal stems
§ rhizomes are long and thin in grasses and thick and fleshy in irises
§ 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 nutrients
o leaf veins have a net pattern in eudicots and a parallel pattern in monocots
o a petiole is a stalk that attaches a leaf blade to the plant stem
o epidermis is the layer of cells that covers the top and bottom sides of a leaf
§ epidermis often bears protective hairs or glands that irritating substances
§ epidermis is covered by a waxy cuticle that keeps the leaf from drying out
§ the epidermis, particularly lower epidermis, contains stomata that allow gases to move into and out of the leaf
o mesophyll is the inner body of a leaf and the site of most of photosynthesis
§ palisade mesophyll is the layer of mesophyll containing elongated parenchyma cells with many chloroplasts
§ spongy mesophyll contains loosely packed parenchyma cells that increase the surface area for gas exchange
- Leaf Diversity
o simple leaves have margins not deeply lobed or divided into smaller leaflets
o compound leaves are divided into smaller leaflets, and each leaflet may have its own stalk
o leaves are variously modified
§ shade plants have broad leaves while desert plants have reduced leaves with sunken stomata
§ cactus spines are modified leaves; succulents have fleshy leaves to hold moisture
§ onion bulbs have leaves surrounding a short stem
§ the tendrils of peas and cucumbers are leaves
§ the Venusıs-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 tissues
o 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 Nutrients
o essential inorganic nutrients (e.g., carbon, hydrogen, oxygen) comprise 96% of plant dry weight
§ carbon dioxide is the source of carbon for a plant
§ water is the source of hydrogen
§ oxygen can come from either atmospheric oxygen, carbon dioxide, or water
o essential nutrients must fulfill the following criteria
§ they have an identifiable nutritional role
§ no other element can substitute and fulfill the same role
§ 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 ash
o hydroponics is the preferred method for determining plant mineral requirements
§ hydroponics