Stems and Transport in Vascular Plants

Stems and Transport in Vascular Plants - Stems and...

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Stems and Transport in Vascular Plants (Chapter 34) Transport o Stems perform three main functions in plants Support leaves and reproductive structures Provide internal transport (inorganic nutrient) from roots , where materials are absorbed from the soil to leaves and other parts of the plants Produce new living tissue o Stems are not the only plant organs that conduct materials: Vascular system in continuous in roots, stems, leaves and reproductive structures Herbaceous Stems 1 o Epidermis Protective layer covered by water conserving cuticle o Stomata Permit gas exchange (via guard cells) o Xylem Conducts water and dissolved minerals o Phloem Conducts dissolved sugar o Cortex, pith both ground tissue Function primarily for storage Basic Tissues in Herbaceous Stems o Eudicot stem Vascular bindles arranges in a circle (in cross section) Distinct cortex and pith sunflower o Monocot stems Vascular bundles scattered in ground tissue No distinct areas of cortex and pith No lateral meristems and therefore no secondary growth (vascular cambrium or cork cambrium) Palms are massive primary growth; and can contain sclerenchyma tissue – hard and woody Corn Stem Primary tissues of stems develop from shoot apical meristems Stem Growth and Structure o Primary growth = increase in length of plant (apical mersitems) In tips od roots, shoots and buds Produces primary tissue o Secondary growth = increase in girth of plant (lateral meristems) Located in stems and roots Produces secondary tissue o Some plants have both primary and secondary growth Those with just primary are herbaceous Those with both primary and secondary are woody Increases in length by primary and increases in girth by added wood and bark Learning Objective 4
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Secondary Growth o Production of secondary tissues, wood , ark Occurs in some flowering plants (woody eudicots) and all cone-bearing gymnosperm o Vascular cambium divides in two directions Secondary xylem (to the inside) Secondary phloem (to the outside) Secondary Growth 2 o Primary xylem and phloem in the original vascular bundles become separated as secondary growth proceeds The primary tissues located outside the cylinder of secondary growth (phloem, cortex, epidermis) succumb to pressure of 2 nd growth Gradually crushed or torn apart and sloughed off o Once secondary growth begins, the internal structure of a stem changes considerably
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Stems and Transport in Vascular Plants - Stems and...

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