Lecture # 16 Date _____ 8Chapter #35~ Plant Structure and Growth

Angiosperm structure 8Three basic organs: 8Roots (root system) 8fibrous: mat of thin roots 8taproot: one large, vertical root 8Stems (shoot system) 8nodes: leave attachment 8internodes: stem segments 8axillary bud: dormant, vegetative potential 8terminal bud: apex of young shoot 8apical dominance: inhibits axillary buds 8Leaves (shoot system) 8blade 8petiole

Plant Organ Systems 8Dermal (epidermis): single layer of cells for protection 8cuticle 8Vascular (material transport) 8xylem: water and dissolved minerals roots to shoots 8tracheids & vessel elements: xylem elongated cells dead at maturity 8phloem: food from leaves to roots and fruits 8sieve-tube members: phloem tubes alive at maturity capped by sieve plates; companion cells (nonconducting) connected by plasmodesmata 8Ground (photosynthesis, storage, support): pith and cortex

Plant Tissue Cell Types 8Parenchyma primary walls thin and flexible; no secondary walls; large central vacuole; most metabolic functions of plant (chloroplasts) 8Collenchyma unevenly thick primary walls used for plant support (no secondary walls ; no lignin) 8Sclerenchyma support element strengthened by secondary cell walls with lignin (may be dead; xylem cells); fibers and sclereids for support

Plant Growth 8Life Cycles 8annuals: 1 year (wildflowers; food crops) 8biennials: 2 years (beets; carrots) 8perennials: many years (trees; shrubs) 8Meristems 8apical: tips of roots and buds; primary growth 8lateral: cylinders of dividing cells along length of roots and stems; secondary growth (wood)

Primary growth 8Roots 8root cap~ protection of meristem 8zone of cell division~ primary (apical) meristem 8zone of elongation~ cells elongate; pushes root tip 8zone of maturation~ differentiation of cells (formation of 3 tissue systems)

Primary Tissues of Roots 8Stele~ the vascular bundle where both xylem and phloem develop 8Pith~ central core of stele in monocot; parenchyma cells 8Cortex~ region of the root between the stele and epidermis (innermost layer: endodermis) 8Lateral roots~ arise from pericycle (outermost layer of stele); just inside endodermis, cells that may become meristematic

Primary Tissues of Stems 8Vascular bundles (xylem and phloem) 8Surrounded by ground tissue (xylem faces pith and phloem faces cortex) 8Mostly parenchyma; some collenchyma and sclerenchyma for support

Primary Tissues of Leaves 8Epidermis/cuticle (protection; desiccation) 8Stomata (tiny pores for gas exchange and transpiration)/guard cells 8Mesophyll: ground tissue between upper and lower epidermis (parenchyma with chloroplasts); palisade (most photosynthesis) and spongy (gas circulation)

Secondary Growth 8Two lateral meristems 8vascular cambium ~ produces secondary xylem (wood) and secondary phloem (diameter increase; annual growth rings) 8cork cambium ~ produces thick covering that replaces the epidermis; produces cork cells; cork plus cork cambium make up the periderm; lenticels (split regions of periderm) allow for gas exchange; bark~ all tissues external to vascular cambium (phloem plus periderm)

Summary of primary & secondary growth in a woody a stem Apical meristem of stem PRIMARY PRIMARY LATERAL SECONDARY MERISTEMSTISSUES MERISTEM TISSUES ProtodermEpidermis Secondary phloem Primary phloem Vascular Procambiumcambium Secondary Primary xylem xylem Ground meristemGroundPith & tissue:CortexCork cambium Cork Periderm

Lecture #16 Date ______ 8Chapter 36~ Transport in Plants

Transport Overview 81- uptake and loss of water and solutes by individual cells (root cells) 82- short-distance transport from cell to cell (sugar loading from leaves to phloem) 83- long-distance transport of sap within xylem and phloem in whole plant

Whole Plant Transport 81- Roots absorb water and dissolved minerals from soil 82- Water and minerals are transported upward from roots to shoots as xylem sap 83- Transpiration, the loss of water from leaves, creates a force that pulls xylem sap upwards 84- Leaves exchange CO2 and O2 through stomata 85- Sugar is produced by photosynthesis in leaves 86- Sugar is transported as phloem sap to roots and other parts of plant 87- Roots exchange gases with air spaces of soil (supports cellular respiration in roots)

Cellular Transport 8Water transport √ Osmosis; hyper-; hypo-; iso- 8Cell wall creates physical pressure: √water potential solutes decrease; pressure increase 8Water moves from high to low water potential 8Flaccid (limp, iostonic); 8Plasmolysis (cell loses water in a hypertonic environment; plasma membrane pulls away); 8Turgor pressure (influx of water due to osmosis; hypotonic environment)

Transport within tissues/organs 8Tonoplast vacuole membrane 8Plasmodesmata (components) cytosolic connection 8Symplast route (lateral) cytoplasmic continuum 8Apoplast route (lateral) continuum of cell walls 8Bulk flow (long distance) movement of a fluid by pressure (xylem)

Transport of Xylem Sap 8Transpiration: loss of water vapor from leaves pulls water from roots (transpirational pull); cohesion and adhesion of water 8Root pressure: at night (low transpiration), roots cells continue to pump minerals into xylem; this generates pressure, pushing sap upwards; guttation

Cohesion of Water

Transpirational Control 8Photosynthesis-Transpiration compromise…. 8Guard cells control the size of the stomata 8Xerophytes (plants adapted to arid environments)~ thick cuticle; small spines for leaves

Translocation of Phloem Sap 8Translocation: food/phloem transport 8Sugar source: sugar production organ (mature leaves) 8Sugar sink: sugar storage organ (growing roots, tips, stems, fruit) 81- loading of sugar into sieve tube at source reduces water potential inside; this causes tube to take up water from surroundings by osmosis 82- this absorption of water generates pressure that forces sap to flow alon tube 83- pressure gradient in tube is reinforced by unloading of sugar and consequent loss of water from tube at the sink 84- xylem then recycles water from sink to source