Bio 101 Day 18

Bio 101 Day 18 - Stems and Transport in Vascular Plants...

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Stems and Transport in Vascular Plants Stem Function --Stems perform three main functions in plants: --Support leaves and reproductive structures --Provide internal transport of water, mineral ions and dissolved sugars (source and sink) --Produce new living tissue --Vascular system is continuous from roots to stems, through leaves to reproductive system Herbaceous Stems 1 --Epidermis: protective layer covered by a water-conserving cuticle --Stomata: permit gas exchange (via guard cells) --Xylem: conducts water and dissolved minerals --Phloem: conducts dissolved sugar --Cortex, Pith: ground tissue function primarily for storage Herbaceous Monocot Stem --Corn Stem: vascular bundles scattered in ground tissue --No lateral meristems (secondary growth) --Vascular bundle: air space is where first xylem elements form and then later disintegrate --Bundle Sheath—sclerenchyma covering entire bundle for support Herbaceous Eudicot Stem --Sunflower: vascular bundles arranged in circle around central core: pith consists of thin-walled parenchymal cells (storage) -Vascular bundle: xylem is located toward the stem’s interior; phloem toward exterior; vascular cambium between. Vascular bundle is “capped” by batch of fibers for support Stem Growth and Structure --Primary growth=increase in length of a plant (apiral meristems)
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--In tips of roots, shoots, and buds --Produces primary tissue --Secondary growth=increase in girth of plant (lateral meristems) --Located in stems and roots --Produces secondary tissue Secondary Growth --Production of secondary tissues: wood (secondary xylem) and bark (secondary phloem—inner bark; periderm—outer bark) --occurs in some flowering plants (woody eudicots) and all cone-bearing gymnosperms --Vascular cambium divides in two directions --Secondary xylem (to the inside) --Secondary phloem (to the outside) Development of Secondary Growth --Once secondary growth begins, the internal structure of a stem changes considerably
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Bio 101 Day 18 - Stems and Transport in Vascular Plants...

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