BIOL 1030 – TOPIC 5 LECTURE NOTESTopic 5: Plant Structure and Growth (Ch. 35)I. INTRODUCTIONA. Most vascular plants continue growing throughout their lives1. can achieve great size and attain great age2. genetically identical individuals have propagated for generationsB. Vascular plants have a fundamental unity of structure 1. two basic parts: root system, shoot system2. three basic organ types: roots, stems, leaves3. three basic tissue types: dermal, ground, vascularC. Vascular plants have a modular body plan (redundancy of units, general ability to replace units)II. ORGANIZATION OF THE VASCULAR PLANT BODYA. Vascular plants have a root system and a shoot system1. root system- penetrates the soil/substrate and anchors the plant- absorbs water and ions for plant to use- most vascular plants make either a taproot system (one main root with branches) or fibrous root system (many roots of similar diameter); there are several modified root types (such as prop roots, pneumatophores, storage roots)2. shoot system- stems: serve as framework and support to position leaves many modified stem types, such as rhizomes – horizontal underground stems (ferns, irises, perennial grasses), bulbs, tubers, stolons or “runners”, and cladophylls- leaves: primary location for photosynthesis many modified leaf types, such as bracts, spines, tendrils, reproductive leaves, “carnivorous” leaves- structures that serve reproductive functions (cones, flowers, fruits, seeds, etc.) – all modified stems and leavesB. meristem1. give rise to all other cells of plant2. composed of small, unspecialized cells that divide continually- after division, one cell remains meristematic- other cell becomes part of plant body; may or may not go through more mitosis before differentiatingC. primary growth1. initiated by apical meristems near tips of roots, shoots2. lengthening of primary plant body results3. produces “primary” tissues that are partially differentiated- ground meristem – produces ground tissue- protoderm – produces epidermis- procambium – produces primary vascular tissueD. secondary growth1. initiated by lateral meristems – internal meristematic cylinders2. expand girth of plant (thickening of plant body)3. produces “secondary” tissues; allows thick, woody trunk in some plants- cork cambium – cork cells in bark of woody plants (outer bark)- vascular cambium: secondary vascular tissue secondary phloem – closest to cork secondary xylem – internal; main component of wood4. appears to have evolved independently in different plant groupsIII. PLANT TISSUES AND CELL TYPESA. 3 basic tissues: dermal tissue, ground tissue, vascular tissueB. dermal tissue, or epidermis1. protective outermost cells, cover all parts of primary plant body2. usually only one cell thick3. cells usually flattened4. covered on outside by waxy cuticle layer that varies in thickness (depending on the species, plant region, and environmental conditions5. most lack chloroplasts6. includes some specialized cell types for protection or absorption: guard cells, trichomes, root hairs7. guard cells – paired cells flanking a stoma- control opening of stoma1 of 5BIOL 1030 – TOPIC 5 LECTURE NOTES- have chloroplasts- stoma openings allow passage of gases, mainly CO2, O2, H2O vapor- stomata occur on leaf epidermis, occasionally on stems and fruit- stomata usually more numerous on underside of leaves8. trichomes – hair like epidermal outgrowths- occur on stems, leaves and reproductive organs- give surface a “woolly” or “fuzzy” appearance- keep surface cool- reduce evaporation rate- help protect from predators/pathogens physical separation glandular trichomes may secrete sticky or toxic substances9. root hairs – single cells found near root tips- tubular extensions of individual epidermal cells- intimate contact with soil/substrate- responsible for all absorption in herbaceous plants (water, minerals, nutrients)C. ground tissue – primarily parenchyma cells1. parenchyma cells – most abundant cells of primary tissues- initially spherical, get compressed and flattened by neighbors- least specialized cell type (other than meristem)- usually capable of further division- typically have thin walls (usually only primary wall)- large vacuoles and usually about 14 sides at maturity- usually remain alive after maturity; some over 100 years old- function in storage, photosynthesis (chlorenchyma), secretion2. collenchyma- living at maturity (usually long-lived)- flexible, often in strands, forming support for organs (bend without breaking)- elongated cells with unevenly thickened primary cell walls- example: celery “strings”3. sclerenchyma- thick, tough secondary walls- usually lack living protoplasts at maturity- secondary walls often lignified (contain lignin); sometimes primary cell walls are lignified lignin – highly branched polymer that reinforces structure common in cells that have a supporting or mechanical function in body structure- two types: fibers and sclereids fibers – long, slender, usually grouped in strandsexample: strands of flax, woven to make linen sclereids – variable in shape; often branched; single or in groupsexample: gritty “stone cells” of pearsD. vascular tissue1. xylem- principle water conducting tissue contains various dissolved minerals and ions conducts water in unbroken stream from roots to leaves evaporation of water at leaves (transpiration) pulls water upward- provides structural support for plant body- conducting elements: tracheids and vessels both not living at maturity both are elongated cells with thick, lignified secondary walls tracheidsi. taper at ends and overlap one anotherii. water flows from tracheid to tracheid through pits in secondary cell walls vesselsi. continuous hollow tubes (linked row)ii. ends may be almost completely openiii. more efficient than tracheids (higher flow rate)iv. almost exclusively in angiosperms vessels evolved from tracheids independently in several groups2 of 5BIOL 1030 – TOPIC 5 LECTURE NOTES some fibers evolved from tracheids are specialized for support- also includes fibers and parenchyma cells- primary xylem from procambium (from apical meristem)- secondary xylem from vascular cambium (from lateral meristem) – can form wood2. phloem- principle food conducting tissue – carbohydrates (sucrose mainly); also amino acids, hormones- found in outer parts of roots and