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Introduction to Plants Kingdom: Plantae Plants: Cell wall Autotroph (photosynthesis) Multi-cellular 12 Divisions (Phyla) Anthophyta = Angiosperms (flowering plants) Largest # of species (~250,000 - 90% plants) Seed plants: product seed w/in a fruit Key adaptations: flowers & fruits Sporophytes are trees, shrubs, herbs that flower 2 main groups: Monocots & Dicots Monocots vs. Dicots Monocot Dicot • One cotyledon (seed leaf) •Two cotyledon • Parallel veins in leaves •Netted veins in leaves • Fibrous root system •Taproot • Floral parts in multiples of 3 •Floral parts in multiple layers of 4 or 5 • Complex vascular arrangement •Ring vascular arrangement • Eg. grass, corn, palm, onion, tulip, bamboo •Eg. bean, pea, rose, sunflower Concept 35.1 The plant body has a heirarchy of organs, tissues, and cells Basic Organs • Roots • Stems • Leaves Types of Tissue • Dermal • Vascular • Ground Cell Types • • • • • Parenchyma Collenchyma Sclerenchyma Xylem Phloem Shoot system •Above ground •Stems, leaves Root system •Underground (usually) •Roots A. Roots Anchors plant, absorbs H2O & minerals, stores sugars/starches Root hairs – tiny extensions of epidermal cells, increase surface area for H2O and mineral absorption Mycorrhizae: symbiosis with fungi Root hairs Fibrous Roots Taproots •Mat of thin roots spread just below surface •One thick, vertical root •Shallow •Many lateral (branch) roots •Increased surface area •Firmly anchors •Monocots •Stores food in root •Dicots Fibrous Root (scallion) Taproot (carrot) Roots B. Stems Alternating system of nodes (leaf attachment) and internodes Function: display leaves Terminal bud – growth concentrated at apex (tip) Apical dominance: terminal bud prevents growth of axillary buds; growth directed upward, toward light Axillary buds – located in V between leaf and stem; forms branches (lateral shoots) Pinching/pruning – removing terminal bud Stems Modified stems Runner or stolin ◦ Aspen, strawberries, grass ◦ Grow on surface ◦ For asexual reproduction Rhizome ◦ Iris, ginger, potato, onion ◦ Grow underground ◦ Store food & DNA for new plant ◦ Tuber: end of rhizome Bulb – underground shoot ◦ Onion ◦ storage leaves C. Leaves ◦ ◦ ◦ ◦ epidermis of underside interrupted by stomata (pores) Mesophyll: ground tissue between upper/lower epidermis Parenchyma: sites of photosynthesis Cuticle: waxy layer Three Tissue Systems A. Dermal Tissue Single layer, closely packed cells that cover entire plant Protect against water loss & invasion by pathogens Cuticle: waxy layer Epidermis, periderm B. Vascular Tissue Continuous throughout plant Transports materials between roots & shoots stele 1. Xylem: transport H2O and minerals up from root 2. Phloem: transports food from leaves to other parts of plant C. Ground Tissue Anything that isn’t dermal or vascular Function: storage, photosynthesis, support Pith: inside vascular tissue Cortex: outside vascular tissue III. Cell Types Parenchyma: most abundant Perform metabolism, synthesizes & stores organic products B. Collenchyma: grouped in cylinders, support growing parts of plant C. Sclerenchyma: rigid support cell D. Xylem: water conduction Tracheids, vessel elements – dead, tubular, elongated cells E. Phloem: sugar, organic cmpd. conduction Sieve tubes, plates, companion cells – alive cells which aid movement of sugar A. WATER-CONDUCTING CELLS OF THE XYLEM PARENCHYMA CELLS Vessel Parenchyma cells in Elodea leaf, with chloroplasts (LM) Tracheids 100 µm 60 µm Pits COLLENCHYMA CELLS 80 µm Cortical parenchyma cells Tracheids and vessels (colorized SEM) Vessel element Vessel elements with perforated end walls Tracheids SUGAR-CONDUCTING CELLS OF THE PHLOEM Collenchyma cells (in cortex of Sambucus, elderberry; cell walls stained red) (LM) Sieve-tube members: longitudinal view (LM) SCLERENCHYMA CELLS 5 µm Companion cell Sclereid cells in pear (LM) Sieve-tube member Plasmodesma 25 µm Sieve plate Cell wall Nucleus Cytoplasm Companion cell 30 µm 15 µm Fiber cells (transverse section from ash tree) (LM) Sieve-tube members: longitudinal view Sieve plate with pores (LM) Primary and Secondary Growth (apical vs. lateral meristems) Concept 35.3 Primary growth lengthens roots and shoots Root Hairs Zone of Maturation: growth & differentiation complete; fully mature cells Zone of Elongation: cells elongate; push root tip ahead Zone of Cell Division: apical meristem; new cells produced Root cap: protects meristem as it pushes through soil; also secretes polysaccharide lubricant Concept 35.4 Secondary growth adds girth to stems and roots in woody plants Involves lateral meristems ◦ Vascular cambium: produces secondary xylem (wood) ◦ Cork cambium: produces tough covering that replaces epidermis Bark = all tissues outside vascular cambium What does a plant need? Solute transport across plant cell plasma membranes Osmosis **Water potential (ψ): H2O moves from high ψ low ψ potential, solute conc. & pressure ◦ Pure water: ψ = 0 MPa ◦ Plant cells: ψ = 1 MPa Water potential equation: ψ = ψS + ψP ◦ Solute potential (ψS) – osmotic potential ◦ Pressure potential (ψP) – physical pressure on solution; turgor pressure Bulk flow: move H2O in plant from regions of high low pressure ** Review AP Lab 1 Flaccid: limp (wilting) Plasmolyze: shrink, pull away from cell wall (kills most plant cells) due to H2O loss Turgid: firm (healthy plant) Turgid Plant Cell Plasmolysis Vascular Tissues: conduct molecules Xylem Phloem Nonliving functional Living functional Xylem sap = H2O & minerals Phloem sap = sucrose, minerals, amino acids, hormones Source to sink (sugar made) to (sugar consumed/stored) Apoplast = continuum of cell walls/extracellular spaces Symplast = continuum of cytosol Absorption of H2O and minerals Root hairs: increase surface area of absorption at root tips Mycorrhizae: symbiotic relationship between fungus + roots ◦ Increase H2O/mineral absorption The white mycelium of the fungus ensheathes these roots of a pine tree. Transport of H2O and minerals from root hairs xylem Guttation: exudation of water droplets seen in morning (not dew), caused by root pressure Stomata regulate rate of transpiration Stomata – pores in epidermis of leaves/stems, allow gas exchange and transpiration Guard cells – open/close stoma by changing shape ◦ Take up K+ lower ψ take up H2O pore opens ◦ Lose K+ lose H2O cells less bowed pore closes Cells stimulated open by: light, loss of CO2 in leaf, circadian rhythms Stomata closure: drought, high temperature, wind Sugar Transport Translocation: transport of sugars to phloem by pressure flow Source Sink ◦ Source = produce sugar (photosynthesis) ◦ Sink = consume/store sugar Via sieve-tube elements Active transport of sucrose Nutritional Requirements Essential element: required for plant to complete life cycle and produce another generation Macronutrients (large amounts): CHNOPS + K, Ca, Mg ◦ Nitrogen = most important! Micronutrients (small amounts): Fe, Mn, Zn, Cu, etc. Mutualistic Relationships: Rhizobium bacteria supply nitrogen at roots (fix atmospheric N2 to usable N) • Plant supplies sugar & amino acids 2. Mycorrhizae (plant + fungus) 1. Unusual nutritional adaptations: epiphytes, parasitic plants, canivorous plants Epiphyte: grow on another plant, absorb H2O from rain through leaves Parasitic Plants: not photosynthetic; absorb sugar and minerals from living hosts Carnivorous Plants: photosynthetic, but obtain some nitrogen and minerals by digesting small animals Angiosperms have 3 unique Features: 1. 2. 3. Flowers Fruits double Fertilization Alternation of Generations: Sporophyte (2n) (meiosis) Spores (mitosis) gametophytes (mitosis) gametes (n) (fertilization) Male Gametophyte Female Gametophyte = Pollen Sac = Embryo Sac Produced in anther Produced in ovule (in ovary) Has 2 haploid nuclei: 1.Tube nucleus (forms pollen tube) 2.Generative nucleus (divides to form 2 sperm cells) Has 3 important haploid nuclei: 1.Egg (fuses with sperm) 2.2 polar nuclei (fuses with 2nd sperm to make 3n endosperm) Pollination: transfer pollen from anther to stigma Pollen tube grows down into ovary Double Fertilization Union of 2 sperm cells with different cells of embryo sac 1. One sperm + egg zygote (2n) 2. One sperm + 2 polar bodies endosperm (triploid 3n) ◦ Endosperm = nutrition for embryo plant 3. Ovule develops into seed; ovary develops into fruit ◦ Seed = embryo + endosperm Self-incompatibility: prevent reject own pollen or closely related individual Stigma Stigma Anther with pollen Pin flower Thrum flower “Pin” and “thrum” flower types reduce self-fertilization The development of a eudicot plant embryo Fruit Protects enclosed seed(s) Aids in dispersal by water, wind, or animals Simple Single ovary of one flower Cherry Aggregate Multiple Many ovaries of Many ovaries of one flower many flowers Raspberry Pineapple Seeds Adaptations: 1. Dormancy = “resting” Low metabolic rate, not growing or developing Increases chances of germination in most advantageous time & place 2. Dispersal: variety of methods 3. Protection: well protected by fruit Seed Structure Germination Imbibition: uptake of H2O ◦ Seed expands and seed coat ruptures ◦ Trigger metabolic changes to begin growth ◦ Enzymes digest storage materials of endosperm (cotyledons) ◦ Nutrients transferred to growth regions of embryo Germination Radicle Root Shoot tip emerges above ground 1. 2. Stimulated by light 3. Foliage leaves expand & turn green photosynthesis Very hazardous for plants due to vulnerability ◦ Predators, parasites, wind Dicot and Monocot Seed Germination Plant Reproduction Sexual Asexual Both ways to reproduce Flower seeds Runners, bulb, root, graft, vegetative (grass), fragmentation Genetic diversity Clone More complex & hazardous for plant Simpler & safer for plant • Monoculture - cultivate w/ 1 plant • Reduces competition • Benefits farmers Tip of coleoptile senses light Cells on darker side elongate faster than cells on brighter side AUXIN = chemical messenger that stimulates cell elongation Excised tip placed on agar block Growth-promoting chemical diffuses into agar block Control (agar block lacking chemical) has no effect Control Agar block with chemical stimulates growth Offset blocks cause curvature Hormones: chemical messengers that coordinate different parts of a multicellular organism Important plant hormones: 1. Auxin – stimulate cell elongation; fruit development; apical dominance; phototropism & gravitropism 2. Cytokinins – stim. cell division & growth; germination; delay senescence (aging) 3. Gibberellins – promotes seed & bud germ.; stem elong. & leaf growth; stim. flowering & fruit development 4. Abscisic Acid – inhibit growth; closes stomata during H2O stress; encourage dormancy 5. Ethylene – promote fruit ripening; inhibit/promote growth & dev. depending on species The effects of gibberellin on stem elongation and fruit growth Ethylene gas: fruit ripening Plant Movement 1. Tropisms: growth responses SLOW Phototropism – light Gravitropism – gravity Thigmotropism – touch 2. Turgor movement: allow plant to make relatively rapid & reversible responses Venus fly trap, mimosa leaves, “sleep” movement Plant Responses to Light Plants can detect direction, intensity, & wavelenth of light Phytochromes: light receptors, absorbs mostly red light ◦ Two forms: Pr (red light) and Pfr (far-red light) ◦ Pr Pfr: switches depending on light in greatest supply ◦ Pfr aids in detection of sunlight ◦ Regulate seed germination, shade avoidance Photoperiodism: physiological response to the relative length of night & day (i.e. flowering) Short-day plants: flower when nights are long (mums, poinsettia) Long-day plant: flower when nights are short (spinach, iris, veggies) Day-neutral plant: unaffected by photoperiod (tomatoes, rice, dandelions) Night length is a critical factor! How does interrupting the dark period with a brief exposure to light affect flowering? Plant Response to Stress Causes of stress: 1. 2. 3. 4. 5. 6. 7. Drought (H2O deficit) Flooding (O2 deprivation) Salt excess Heat Cold Herbivores Pathogens 1. H2O deficit: close stoma release abscisic acid to keep stoma closed Inhibit growth roll leaves reduce SA & transpiration deeper roots 2. Flooding (O2 deprivation): release ethylene root cell death air tubes formed to provide O2 to submerged roots 3. Salt: cell membrane – impede salt uptake produce solutes to ↓ψ - retain H2O 4. Heat: evap. cooling via transpiration heat shock proteins – prevent denaturation 5. Cold: alter lipid composition of membrane (↑unsat. fatty acids, ↑fluidity) increase cytoplasmic solutes antifreeze proteins 6. Herbivores: physical (thorns) chemicals (garlic, mint) recruit predatory animals (parasitoid wasps) 7. Pathogens: 1st line of defense = epidermis 2nd line = pathogen recognition, host-specific