PLANTS Chapters 29, 30, 35 - 39
Characteristics of Kingdom Plantae • Multicellular • Eukaryotic • Cell Walls of cellulose • Photosynthetic containing chlorophyll a & b • Contain peroxisomes (organelles with enzymes to degrade hydrogen peroxide) • Surplus carbohydrates stored as starch • Alternation of Generations Life Cycle • Gametophyte generation (1N) • Sporophyte generation (2N)
Importance to the Ecosystem • 290,000 different species of plants within very varied environments. • Most plants are terrestrial • They stabilize and build soil • Are habitats for many organisms • Release O2 and absorb CO2 • Are the Producers of food, mainly; rice, beans, soy, corn, and wheat • Moderate temperature • Are used as fiber and building material • And they are really pretty!
Geologic Time period The Earth is ~ 4.6 billion years old Cyanobacteria first colonized the earth 1.2 billion years ago. Plants do not appear until ~ 500 million years ago during Paleozoic era
Evolution of the Plants Evolved from the same branch as Charophyceans (green algae)
To adapt from an aquatic to a dry ecosystem, terrestrial plants faced a few problems: • Prevent water loss • With a waxy cuticle (cutin) – a water tight sealant that covers above ground plant structures • Stomates with guard cells & stoma that close to prevent water loss (in all but liverworts)
Defies gravity • For water transport • Rigid enough to not fall over with gravity and wind Answer Vascular tissue!! Made of lignin (6 Carbon polymer) rings to give strength to stem tissues.
Classification Bryophytes Non-vascular– No specialized conductive tissue for water & nutrients. Absorb by diffusion from air More primitive with flagellated sperm. No lignin to fortify tissue for support Found in moist areas and are small Mosses, liverworts and hornworts
Tracheophytes Vascular – possess vascular tissue Make up 93% of all land plants • Xylem and Phloem for transport • Lignified transport vessels • Roots for water absorption & anchoring plant • Leaves for photosynthesis • Life cycle dominated by Sporophyte (2N) generation
Two branches of Tracheophytes • Seedless plants produce spores Seed- “is a baby plant, inside a box, with its lunch” an embryo with stored nutrients & a protective layer Ferns,Lycopodia, Horsetails and Whisk ferns
Seed Plants - Produce seeds Gymnosperms - have naked seeds (not enclosed inside fruit) on modified leaves forming cones - needle-shaped leaves with thick cuticles Spruce, pines, fir, cedar, larch, redwoods, Sequoia
Angiosperms – Flowering plants 90% of all plants Flowers (for scent and color) to attract pollinators Have: Ovaries which will mature into fruit Ovules will develop into a seed Fruit protects dormant seeds and aids in seed dispersal Maple tree seeds
Reproduction of Land Plants A. Alternation of Generation • MulticellularSporophyte(2n) undergoes meiosis to produce 1N spores in the Sporangia • Spores undergo mitosis & develop into multicellular Gametophyte (1N) • Gametophyte (1N) produces gametes by mitosis in Gametangia • 2 (1N) gametes unit during fertilization to form a (2N) zygote • The 2N zygote undergoes mitosis to develop into a (2N) Sporophyte
Patterns in Alternation of Generations Bryophytes (Mosses)- Gametophyte is dominant generation Tracheophytes– Sporophyte generation dominates The transition from Gametophyte dominated life cycles to Sporophyte dominated life cycles is one of the most striking of all trends in the evolution of land plants!
Heterospory Evolution in 2 distinct spore producing structures Seedless vascular plants are homosporous – spores develop into bisexual Gametophytes Microsporangia – produce microspores – male gametophyte - sperm Macrosporangia – produce macrospores – female gametophyte - egg
Vascular (conductive) Tissue Necessary for the transport of water and nutrients 2 types: Xylem – conducts water and minerals from roots upward Made up of: • Tracheids – long, thin, tapered tube shaped cells dead cells, strengthened by lignin w/ pits (no secondary walls) • Vessel elements – wider and shorter w/ thin wall Perforated ends to allow free flow of water
Phloem – living cells that carry sugar around plant • Sieve tube elements – wide, short, thin w/ end sieve plates to facilitate the flow of sugar to the next cell • Companion cells – with ribosomes, nuclei & vacuoles. Non conductive but connects with sieve tube by plasmodermata (connects cells to cells)
Three types of Plant Tissues • Dermal – outer covering for gas exchange (epidermal cells, root hairs and stomates) • Ground - photosynthesis and food storage (Palisades & Mesophyll cells) • Vascular – conductive tissue & support (Xylem & Phloem)
Three types of cells • Parenchymal cells – normal living plant cells. Primary cell walls, thin & flexible w/o secondary cell walls Most abundant and least specialized 1 Central vacuole May have chloroplasts (Mesophyll cells) Plastids in roots to store starch Capable of dividing & differentiating Plants can be cloned from these Parenchymal have plastids to store food & photosynthesis
2. Collenchymal cells – unevenly thickened cells walls w/o secondary cell walls Alive & function to support growing stem “Strings of celery” Support growing parts of plant Collenchymal make up celery strings.
Sclerenchymal cells – thick primary cell walls & have a secondary cell wall with lignin Function for support of non-growing parts of plant Dead, empty cells Fibers – long, think & fibrous & in bundles Used to make ropes & flax fibers for linen Sclereids – short & irregular. Make up seed coats & pits. Gives pears their gritty texture Sclerenchymal for support Fiber
Plant Growth Plants grow continuously throughout their lives Meristematic tissue continuously divides and regenerated new cells Primary Growth – elongation into soil & up into the air Occurs at the apical meristem– tips of roots & in buds of shoots Secondary growth – increases girth Occurs in the lateral meristem& is responsible for thickening of roots and shoots. Found only in woody plants Herbaceous plants have only primary growth
Primary growth of stem • Primary growth occurs only in apical meristemswhich are located at the tips of the stems and roots. • Meristems in stems are protected by newly formed leaves within a bud.
Herbaceous stems (Nonwoody) • Herbaceous stems are produced by primary growth. • The outermost tissue is epidermis and is covered by waxy cuticle to prevent water loss. • The vascular tissue is found in bundles that are arranged in a ring (dicots) or scattered (monocots). • In dicots, the xylemis toward inside; the phloem is toward the outside. • Cortex – ground tissue for storage • In dicot stems, the cortex is located in the area between the vascular bundles and the epidermis. • In monocot stems, it occupies the area surrounding the vascular bundles. • The center of the stem is pith and functions as storage.
Vascular cambium • Initially, vascular cambium is found between the xylem and phloem in the vascular bundles of dicots. • After one years growth, it joins to form a continuous ring. • Cell division toward the inside and outside form xylem and phloem. • Seasonal climates produces growth rings because cells grow faster and are larger in the spring than later in the growing season. Epidermis Cortex Phloem Xylem Pith
Secondary Growth of Stems Secondary growth occurs in plants that live > 1 year. • Primary growth occurs for a short distance behind the apical meristem, then secondary growth occurs. • It begins with the formation of a vascular cambium and a cork cambium.
Cork cambium • Cortex cells beneath the epidermis produce the cork cambium. • The cork cambium produces cork. • Cork is waterproof because the cell walls are impregnated with of suberin. • Pockets of cells lack suberin. These are calledlenticelsand function to allow gas exchange. • Cork replaces the epidermis on woody stems and roots.
Roots: • Absorb water & minerals • Anchorage for plant • Food storage in the form of starch • Transport of water and nutrients • Stems: • Conduct water, minerals and food • Hold leaves upright • Support fruit and flowers • Photosynthesis in some cases (succulents & cacti) • Food storage in some • Leaves • Photosynthesis • Flowers & Fruits • Sexual Reproduction
Structure of Roots All have: • Epidermis (covers entire surface) with root hairs • Cortex (middle region of Parenchymal cells) for food storage with plastids • Stele– (inner vascular cylinder with xylem & phloem) surrounded by the pericycle from which lateral roots arise • Endodermis – lightly packed cells surrounding the vascular cylinder Each endodermal cell is wrapped with a Casparian strip made of suberin (waxy material) which blocks the movement of water & minerals between endodermal cells & entering vascular bundle.
Monocot vsDicot roots Dicot has the stele in the center w/ cortex cells surrounding in it Monocot has a ring of xylem & phloem w/ parenchymal (pith) cells inside of it
Longitudinal view of roots Region of maturation & Differentiation Cells differentiate into 3 primary meristem to give rise to epidermis, cortex or vascular tissue Root hairs produced – 1 cell thick to increase water absorption Region of Elongation Cells elongate to push root cap deeper into soil Apical Meristem Cells actively dividing by mitosis Root Cap Protects meristematic tissue. Secretes a polysaccharide slime to lubricate the soil
Types of roots Taproot – 1 main vertical root with lateral growth of of it. Typical of dicots Carrot & Dandelion Fibrous roots – Mat of thin roots spreading out below surface of ground Seedless & monocots Adventitous roots – roots arise from stem. Good for climbing Ivies Prop roots – Grow out from stem Corn Aerial roots – stick out of water and aerate root cells. Mangrove trees in swamps
Leaves Organized to maximize photosynthesis & sugar production Acts as a solar collector Four basic layers: • Cuticle – Waxy (cutin) • Upper epidermis – cells w/o chloroplasts • Palisades mesophyll cells – w/ chloroplasts. Thin narrow cells tightly packed together 4. Spongy mesophyll cells – w/ chloroplasts Loosely packed cells for gas exchange Vein located here with xylem & phloem cells • Lower epidermis withstomates
Functioning of the Stomates 90% of the water a plant loses escapes through the stomates Guard cells – modified epithelium w/ chloroplasts and a thickened inner wall made ofmicrofibrils. Controls the opening and closing of the stoma. When photosynthesizing, water builds up in guard cells’ central vacuole causing turgidity and opening the stoma. When not photosynthesizing, cells become flaccid and stoma closes
Control of stomates to open: • Depletion of CO2within air spaces of leaf • Increase in Potassium ions to guard cells, lower water potential, causing water to diffuse into cells • Blue light receptors in cells triggers proton pump in plasma membrane of guard cells, which promotes uptake of K+ ions causing stomates to open • Active transport of H+ out of the guard cells Control of stomates to close: • Lack of water • High temperatures – stimulates cell respiration & CO2 buildup • Abscisic acid – produced in mesophyll cells in response to dehydration. Signals guard cells to close up
Flowers Male: Stamen with anther and filament Female: Carpel (Pistil) made up of the stigma, style and ovary Ovaries contain ovules Receptacle supports carpel Sepals are flower “leaves” for protection Pedicle is flower stem
An overview of Angiosperm Reproduction Sporophyte (2N) produces haploid spores by meiosis. Spores (1N) divide by mitosis giving rise to Gametophyte (1N) within pollen grain and ovules Pollination – process of bringing pollen grain to stigma by wind, water, or animal. Gametes(1N) formed by Gametophyte – sperm and egg. Fertilization results in (2N) zygote which divides by mitosis to produce (2N)Sporophyte Sporophytedevelops into embryo and then seed, while ovary becomes the fruit.
Double Fertilization • After landing on stigma, pollen grain begins to germinate, producing a pollen tube extending down to the ovary • Pollen grain nucleus divides by mitosis to form two sperm nuclei • Tip of pollen tube enters ovary and enters ovule through the micropyle releasing the two sperm nuclei • One sperm nucleus fertilizes the egg to produce the zygote • The second sperm nucleus combines with the two polar nuclei to form a 3N nucleus at the center of the embryos sac. This will become theliquidy endosperm (nutrient for the developing seed) Great animation
From zygote to seed Each ovule develops into a seed enclosed in a fruit Embryo develops from the zygote Endosperm will be replaced by cotyledons Embryo and cotyledons are protected by seed coat Embryo structure: Hypocotyl – embryonic stem Radicle – embryonic roots Epicotyl – embryonic leaves Cotyledons are high in starch Dicots have two cotyledons like in beans Monocots have one cotyledon - corn
From Seed to Seedling – aka: Germination • Imbibitionis the uptake of water due to low water potential of dry seed. • Seed coat softens and cotyledons expand. Enzymes begin digesting starch. Energy is now available to developing embryo • Radicle is first to emerge from seed. • Hypocotyl forms a hook and when stimulated by light and phytochrome, pulls seed up through soil. • Epicotyl&cotyledonsrise up on strengthened hypocotyl • Epicotyl spreads first true leaves & begins photosynthesizing. • Cotyledons (seed leaves) shrivel and fall off
Absorption of Water & Nutrients Lateral movement of water & solutes is accomplished by apoplastic and symplastic movement Symplast –movement through interconnected cytoplasm via the plasmodermata Apoplast – movement through the network of cell walls & intercellular spaces w/i a plant – short distance extracellular movement w/i a plant. When water reaches the endodermis of the stele, it will continue to the xylem through the symplast Water in the apoplast needs to pass across the endodermis by diffusion Stele
Role of Mycorrhizae in water and nutrient absorption Mycorrhizae (“fungus roots”) are modified roots found on older plants lacking root hairs. Supply water and minerals to plant Mutualisticsymbionts: Plant roots intermingle with hyphae (filaments) of a fungus to increase surface area for absorption of water and minerals As much as three meters of fungal hyphae can extend from each centimeter of root
Transport in PlantsHow does water get up to the top of a coastal redwood that is 300ft tall? Movement of water & minerals goes against gravity 3 mechanisms for moving water & minerals: • Transport of water & minerals by individual cells like root hairs • Short distance transport from cell to cell moves the water and minerals around it • Long distance transport within xylem & phloem throughout the entire plant