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Plant Morphology shoot tip (terminal bud) lateral (axillary) bud flower node internode node EPIDERMIS leaf VASCULAR TISSUES seeds (inside fruit) GROUND TISSUES withered cotyledon SHOOT SYSTEM ROOT SYSTEM primary root lateral root root hairs root tip root cap activity at meristems new cells elongate and start to differentiate into primary tissues new cells elongate and start to differentiate into primary tissues activity at meristems SHOOT APICAL MERISTEM Source of primary growth (lengthening) THREE PRIMARY MERISTEMS Protoderm epidermis Ground meristem ground tissue Procambium primary vascular tissues ROOT APICAL MERISTEM Apical meristem near all root tips gives rise to protoderm, ground meristem, and procambium These give rise to the root’s primary tissue systems: epidermis, ground tissues, and vascular tissues immature leaf shoot apical meristem procambium protoderm procambium ground meristem epidermis cortex primary phloem procambium primary xylem pith Fig. 35.19 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings cuticle upper epidermis leaf vein xylem palisade mesophyll phloem spongy mesophyll lower epidermis water, minerals products of photosynthesis oxygen and water vapor cuticle-coated cell of lower epidermis one stoma carbon dioxide pit in cell wall one vessel member cytoplasm absent (cells dead at maturity) sieve plate sieve-tube member companion cell (living) vascular cambium produced by pericycle epidermis cortex endodermis pericycle primary procambium xylem primary phloem vascular cambium produced by procambium secondary xylem secondary phloem vascular cambium pericycle derivatives vascular ray cortex, epidermis slough off crushed primary phloem Pattern of activity at vascular cambium outer surface of stem or root division One of the cells of vascular cambium at the start of secondary growth division One of the two daughter cells differentiates into a xylem cell (coded blue), and the other remains meristematic One of the two daughter cells differentiates into a phloem cell (coded pink), and the other remains meristematic The same pattern of cell division and differentiation into xylem and phloem cells continues through the growing session direction of growth secondary phloem vascular cambium cork cambium secondary xylem thickening LATERAL MERISTEMS Two lateral meristems in older stems and roots of woody plants produce secondary growth (increases in diameter): Vascular cambium Cork cambium secondary vascular tissues periderm (replaces epidermis) periderm secondary phloem BARK vascular cambium HEARTWOOD SAPWOOD Fig. 36.11 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 36.10 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Hakea gibbosa leaf, longitudinal section thick cuticle closed stoma between two guard cells (side view) palisade mesophyll cell air space Driving force of evaporation into dry air Cohesion in xylem of roots, stems, and leaves Water uptake in growth regions Water uptake from soil by roots K+ ABA signal K+ Ca+ + Ca+ + malate stoma (open) Water has moved in malate stoma (closed) Water has moved out Do not post on Internet Loading at a source upper epidermis photosynthetic cell sieve tube companion cell lower epidermis Section from a leaf Translocation along a distribution path sieve tube Section from a stem sieve tube of the phloem SOURCE Active transport moves solutes into sieve tubes Pressure pushes bulk solutes by bulk flow flow between source and sink Solutes unloaded into sink cells, lowering their water potential; water follows WATER Water moves in, increasing turgor pressure Pressure and solute concentrations decrease between source and sink SINK • In most plant tissues, two of the three cellular compartments are continuous from cell to cell. – Plasmodesmata connect the cytosolic compartments of neighboring cells. – This cytoplasmic continuum, the symplast, forms a continuous pathway for transport. – The walls of adjacent plant cells are also in contact, forming a second continuous compartment, the apoplast. Fig. 36.6b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 36.7 Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings in root cortex; water molecules pass through and between walls of cells Casparian strip vascular cylinder exodermis root hair epidermis newly forming vascular cylinder cortex Casparian strip (gold) within all the abutting walls of cells of the endodermis water and solutes Waxy, water-impervious Casparian strip in abutting walls of endodermal cells • Parenchyma cells perform most of the metabolic functions of the plant, synthesizing and storing various organic products. – For example, photosynthesis occurs within the chloroplasts of parenchyma cells in the leaf. – Some cells in the stems and roots have colorless plastids that store starch. – The fleshy tissue of most fruit is composed of parenchyma cells. Fig. 35.11a Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Collenchyma cells have thicker primary walls than parenchyma cells, though the walls are unevenly thickened. – Grouped into strands or cylinders, collenchyma cells help support young parts of the plant shoot. – Young cells and petioles often have a cylinder of collenchyma just below their surface, providing support without restraining growth. – Functioning collenchyma cells are living and flexible and elongate with the stems and leaves they support. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 35.11b Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Sclerenchyma cells also function as supporting elements of the plant, with thick secondary walls usually strengthened by lignin. – They are much more rigid than collenchyma cells. – Unlike parenchyma cells, they cannot elongate and occur in plant regions that have stopped lengthening. Fig. 35.11c Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Many sclerenchyma cells are dead at functional maturity, but they produce rigid secondary cells walls before the protoplast dies. – In parts of the plant that are still elongating, the secondary walls are deposited in a spiral or ring pattern, enabling the cell wall to stretch like a spring as the cell grows. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • Vessel elements and tracheids in the xylem are sclerenchyma cells that function for both support and transport. • Two other sclerenchyma cells, fibers and sclereids, are specialized entirely in support. – Fibers are long, slender and tapered, and usually occur in groups. • Those from hemp fibers are used for making rope and those from flax for weaving into linen. – Sclereids, shorter than fibers and irregular in shape, impart the hardness to nutshells and seed coats and the gritty texture to pear fruits. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings • A major difference between plant and most animals is that the growth and development of plants is not just limited to an embryonic or juvenile period, but occurs throughout the life of the plant. – At any given instance, a typical plant consists of embryonic organs, developing organs, and mature organs. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings