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STEMS PowerPoint Presentation

STEMS

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STEMS

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Presentation Transcript

  1. STEMS And you thought roots were fun...

  2. Purpose of Stems • Support leaves • Transport water and nutrients • Store water and food

  3. WHY?!? • Growth in height only occurs at tip of roots and branches

  4. Specialized Stems • Cactus • is a stem that stores food and water for the plant • spines are leaves of a cactus

  5. Specialized Stems • Rhizomes • underground stem which grows horizontally through soil • Ex. Iris

  6. Specialized Stems • Bulbs • specialized stems that store food • Ex. onions, tulips, daffodils

  7. Specialized Stems • Corms • Short, swollen underground plant stem used as food storage • Ex. crocuses, gladiolas • Stolons • slender stem that grows above ground • “touch, root-and-shoot” • Ex. strawberries

  8. Where do Stems Grow? • Apical Meristems • cell division occurs at tip of stem • Lateral Meristems • cell division occurs • stems grow in diameter

  9. Structure of stems • Nodes • region on stem where 1 or more new leaves form • Internode • distance between segments • Lenticels • pores in surface of stem • allow gas exchange

  10. Structure of stems • Buds • Terminal - bud at the end of stem • Lateral - buds on side of stem • Bud scales- protective covering over embryonic shoots (present in winter) Lateral Bud

  11. Primary Growth in Stems • Epidermis • outer layer • protection • prevents H20 loss • contains lenticels • allow for O2 and CO2 exchange • Cortex • lies inside epidermis • storage of food for stem

  12. Primary Growth in Stems • Pith • located in center of stem • stores food • Vascular Bundles • Xylem : transfers H2O • Phloem : transfers food

  13. Type of stems • Monocot Stem • **V.B. are scattered** • xylem in center • phloem on outside

  14. Types of Stems • Dicot Stem • **V.B. make a circle** • xylem closer to center • phloem behind xylem

  15. Secondary Growth in Stems • Occurs mainly in dicots b/c monocots lack lateral meristems • Stems increase in diameter due to lateral meristems • 2 types : vascular cambium, cork cambium

  16. Secondary Growth in Stems • Vascular cambium • makes new xylem, phloem through cell division • this becomes secondary xylem & secondary phloem

  17. Secondary Growth in Stems • Wood • is secondary xylem • Heartwood (pith) • is older primary xylem • stopped transporting H20

  18. Secondary Growth in Stems • Sapwood • new secondary xylem • lighter in color (still transports H20) • Bark • protection for woody stems • made up of cork, cork cambium, phloem

  19. Why does bark appear to be rough or crack? • Cells aren’t living • cork cambium produces cork, but dies before maturity • as tree grows, cork ruptures and forms cracks

  20. Annual rings • Springwood • xylem produced in spring • rain is plentiful • cells are larger than summer wood • Summerwood • xylem still produced • limited amt. of water • cells are smaller than springwood

  21. Annual rings • Annual rings • during hibernation xylem isn’t produced • difference from 1 year to the next • can tell app. age of tree • tell environmental conditions • lg.= moist • sm. = drought