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Plant Structure and Growth Chapter 35 Monocots vs. dicots Page 595 Monocot or Dicot? Monocot or Dicot? Monocot or Dicot? Monocot or Dicot? Annuals vs. perennials Annuals live for a year Examples?? Perennials live for several years Examples?? PLANT BODY PARTS Roots Fibrous Root systems Monocots Anchor plants Prevent erosion Increases surface area for absorption of water and nutrients Taproot Systems Dicots Anchor plants Stores food Carrots, turnips, sugar beets Can go far below ground Desert plants Root Hairs Epidermal extensions Increase surface area Symbiosis with fungi Most plants have mutualistic partnership with fungi forming a root/fungus structure called mycorrhizae Fungi absorb water and select minerals for host plant (HUGE surface area) Host plant nourishes fungus Stems Support transport Leaves Typical leaves Flattened blades Petioles – join leaf to the stem node Specialized leaves to reduce water loss? Specialized leaves to store water? CELL TYPES Parenchyma Most abundant type “typical” plant cell Thin cell walls Most photosynthetic and storage tissue, phloem, fruit tissue Starch grains from potato tuber, stained with I2KI. Cross section of Phormium (New Zeland flax) leaf. Note large areas of supporting fibers and thin-walled parenchyma cells that function in water storage. Collenchyma Thicker cell walls Provides support for young shoot, petioles Sclerenchyma Supports Thickest cell walls May be dead at maturity (xylem) Plant fibers (Hemp, flax) Cross section of Phaseolus (bean) seed showing two layers of sclereids the seed coat. The outer layer (actually the epidermis) is composed of macrosclereids. Cross section of Cannabis stem. Note thick-walled fibers. TISSUE SYSTEMS Dermal tissue Protects Secretes waxy cuticle Ground Tissue Photosynthetic Storage Vascular Tissue Xylem – water transport toward leaves Phloem – sugar transport Found in “bundles” in all plant body parts Vascular tissue organization Monocot Stem – vascular bundles (combo of xylem and phloem) scattered Dicot stem – vascular bundles arranged in a ring around the periphery Cross section of Helianthus (sunflower) stem with major tissues labeled Micrograph by Biodisc Meristems def: perpetually embryonic tissues Indeterminate growth Primary growth lengthens roots and shoots Secondary growth thickens roots and shoots Secondary Growth Growth in girth Two lateral meristems (dicots): Vascular cambium Forms secondary xylem and phloem Secondary xylem accumulates (“wood”) while secondary phloem is sloughed off Cork cambium Forms cork Bark=cork, cork cambium, and secondary phloem TRANSPORT IN PLANTS Vascular Tissue Xylem (review) Transports water and nutrients up from the roots Dead at maturity Has thick secondary walls (often hardened with lignin), supports the plant (this is wood…) Phloem (review) Transports food from leaves to other parts of the plant Absorption by Roots (review) Root hairs increase surface area Mycorrhizae (mutualistic fungi) enhance absorption Long Distance Transport in the Xylem Root Pressure: Pushing Transpiration: Pulling Transpiration =pull of water toward leaves as water molecules evaporate through stomata Major mechanism of movement Water is adhesive and cohesive As one water droplet moves, the next also moves (water in continuous column in xylem) As water evaporates out of the stomata, water below moves upward Stomata What adaptations are seen for arid climates? thick leaves (low SA/vol) Thick cuticle Stomata on lower leaf surface Stomata in pores to shield wind Shed leaves in hot dry season Cacti have no leaves (adapt to spines) Phloem Transport Sugar moves from “sugar source to sugar sink” Sugar loaded into phloem by active transport Water follows by osmosis (increases pressure) At sink, sugar leaves phloem (by diffusion or active transport) Water follows (decreases pressure) Water is recycled by xylem Oleander: stomata in “cypts” Old Man cactus For what purposes do humans use plants?