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Plant Structure Growth and Development Chapter 35 All Plants… • multicellular, eukaryotic, autotrophic, alternation of generations Alternation of Generations Sporophyte (diploid) • produces haploid spores via meiosis Gametophyte (haploid) • produce haploid gametes via mitosis Fertilization • joins two gametes to form a zygote Angiosperms Monocots vs. Dicots • named for the number of cotyledons (seed leaf) present on the embryo of the plant + monocots - orchids, corn, lilies, grasses + dicots - roses, beans, sunflowers, oaks Plant Morphology Morphology (body form) • shoot and root systems + inhabit two environments - shoot (aerial) + stems, leaves, flowers - root (subterranean) + taproot, lateral roots • vascular tissues + transport materials between roots and shoots - xylem/phloem Plant Anatomy Anatomy (internal structure) • division of labor + cells differing in structure and function - parenchyma, collenchyma, sclerenchyma (below) - water- and food-conducting cells (next slide) Parenchyma St: “typical” plant cells Fu: perform most metabolic functions Collenchyma St: unevenly thickened primary walls Fu: provide support but allow growth in young parts of plants Sclerenchyma St: hardened secondary walls (LIGNIN) Fu: specialized for support; dead Plant cell types Cell wall Parenchyma cells Collenchyma cells Sclerenchyma cells • Xylem • Phloem Plant cell types WATER-CONDUCTING CELLS OF THE XYLEM SUGAR-CONDUCTING CELLS OF THE PHLOEM Sieve-tube members: longitudinal view Vessel Tracheids Pits Companion cell Sieve-tube member Sieve plate Tracheids and vessels Nucleus Vessel element Tracheids Cytoplasm Companion cell Water- and Food-conducting Cells Xylem (water) Phloem (food) • dead at functional maturity • tracheids- tapered with pits • vessel elements- regular tubes • alive at functional maturity • sieve-tube members- arranged end to end with sieve plates & Companion cells Plant Tissues Three Tissue Systems • dermal tissue + epidermis (skin) - single layer of cells that covers entire body - waxy cuticle/root hairs • vascular tissue + xylem and phloem - transport and support • ground tissue + mostly parenchyma - occupies the space b/n dermal/vascular tissue - photosynthesis, storage, support Plant Growth Meristems • perpetually embryonic tissues located at regions of growth + divide to generate additional cells (initials and derivatives) - apical meristems (primary growth- length) + located at tips of roots and shoots - lateral meristems (secondary growth- girth) Roots • A root – Is an organ that anchors the vascular plant – Absorbs minerals and water – Often stores organic nutrients – Taproots found in dicots and gymnosperms – Lateral roots (Branch roots off of the taproot) – Fibrous root system in monocots (e.g. grass) Modified Roots • Many plants have modified roots (a) Prop roots (a) Prop roots (d) Buttress roots (b) Storage roots (b) Storage roots (c) “Strangling” aerial roots (e) Pneumatophores Primary Growth of Roots Primary Growth of Roots • apical meristem + root cap + three overlapping zones - cell division - elongation - maturation Stems • A stem is an organ consisting of – Nodes (point where leaf connects) – Internodes (stem between nodes) Modified Stems (a) Stolons Storage leaves (d) Rhizomes Stem Node Root Bulbs (c) Tubers Rhizome Root Buds • An axillary bud – Is a structure that has the potential to form a lateral shoot, or branch • A terminal bud – Is located near the shoot tip and causes elongation of a young shoot Gardening tip: Removing the terminal bud stimulates growth of axillary buds Primary Growth in Shoots Primary Growth in Shoots • apical meristem (1, 7) + cell division occurs + produces primary meristems - protoderm (4, 8) - procambium (3, 10) - ground meristem (5, 9) • axillary bud meristems + located at base of leaf primordia • leaf primordium (2, 6) + gives rise to leaves The leaf Is the main photosynthetic organ of most vascular plants Leaves generally consist of Blade Stalk Petiole Leaf Morphology • In classifying angiosperms – Taxonomists may use leaf morphology as a criterion (a) Simple leaf Petiole Axillary bud (b) Compound leaf. Leaflet Petiole Axillary bud (c) Doubly compound leaf. Leaflet Petiole Axillary bud Modified Leaves Tendrils Spines Storage leaves Bracts Reproductive leaves. The leaves of some succulents produce adventitious plantlets, which fall off the leaf and take root in the soil. Leaf Anatomy Epidermal Tissue • upper/lower epidermis • guard cells (stomata) Ground Tissue • mesophyll +palisade/spongy parenchyma Vascular Tissue • veins + xylem and phloem Leaf Anatomy Guard cells Key to labels Dermal Ground Stomatal pore Vascular Cuticle Epidermal cell Sclerenchyma fibers 50 µm (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Stoma Upper epidermis Palisade mesophyll Bundlesheath cell Spongy mesophyll Lower epidermis Guard cells Cuticle Vein Xylem Phloem (a) Cutaway drawing of leaf tissues Guard cells Vein Air spaces (c) Transverse section of a lilac (Syringa) leaf (LM) Guard cells 100 µm The Three Tissue Systems: Dermal, Vascular, and Ground Dermal tissue Ground tissue Vascular tissue Dermal Tissue – • • • Protects plant from: Physical damage Pathogens H2O loss (Cuticle) Vascular tissue – Carries out long-distance transport of materials between roots and shoots – Consists of two tissues, xylem and phloem Xylem Phloem Ground Tissue – Includes various cells specialized for functions such as storage, photosynthesis, and support – Pith = ground tissue internal to the vascular tissue – Cortex = ground tissue external to the vascular tissue Secondary Growth Lateral Meristems • vascular cambium + produces secondary xylem/phloem (vascular tissue) • cork cambium + produces tough, thick covering (replaces epidermis) • secondary growth + occurs in all gymnosperms; most dicot angiosperms The Vascular Cambium and Secondary Vascular Tissue • The vascular cambium – Is a cylinder of meristematic cells one cell thick – Develops from parenchyma cells 2° Growth • As a tree or woody shrub ages – The older layers of secondary xylem, the heartwood, no longer transport water and minerals • The outer layers, known as sapwood – Still transport materials through the xylem Cork Cambium Periderm • protective coat of secondary plant body + cork cambium and dead cork cells - bark • cork cambium produces cork cells