12.3 Stems - PowerPoint PPT Presentation

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12.3 Stems

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  1. 12.3 Stems Pages 552-557

  2. Canadian Economy • The forest sector’s contribution to the Canadian economy (GDP) was $23.5 billion, or 1.9 percent, in 2010. • In 2010, Canada was the world’s second-largest forest product exporter (10.2 percent).

  3. Functions of Stems • Connect roots to leaves • Raise leaves to the sun and flowers to pollinators • Store water or carbohydrates • Photosynthesis • Protection

  4. Types of stems • Herbaceous-do not contain wood

  5. Vascular bundle • Long continuous strand of vascular tissue (xylem and phloem)

  6. Herbaceous Stems • Eudicot Monocot

  7. Difference • In monocots the vascular bundles are found throughout the ground tissue of the stem. • In eudicots the vascular bundles are found in a ring around the stem.

  8. Eudicot-herbaceous • Xylem is closer to the centre and phloem is closer to the outside of the stem

  9. Woody stems • Contain wood and bark • All gymnosperms • Most woody angiosperms are eudicots • Monocots do not produce wood

  10. Cross-section of woody stem

  11. Vascular cambium • Woody stems contain vascular cambium meristematic tissue. • Divides to form new xylem tissue on the inside and new phloem tissue on the outside.

  12. Wood • Sapwood-young xylem transports water and minerals • Heartwood-cells fill up with resins and oils -provide rigidity and support

  13. Typical Woody Stem

  14. Bark • Tissues found outside the vascular cambium (phloem, cork cambium, and cork) • Cork cambium-meristematic tissue produces cork

  15. Bark • Protects the tree from predators and fires

  16. Growth rings • Spring…rapid growth, large xylem cells, thin walls, lighter in colour • Summer…slow growth, smaller xylem cells, thick walls, darker in colour

  17. Xylem cells • Thick-walled • Dead at maturity • Cell walls with lignin for strength

  18. Tracheids • Tracheids-long cylindrical cell with tapered ends with pits, holes that allow water to move to adjoining cells

  19. Vessel Elements • Shorter, wider, less tapered • Sides have pits • Ends have perforation plates

  20. Phloem • -living at maturity • -contain cytoplasm

  21. Types of phloem • Sieve cells • Sieve tube elements • Companion cells

  22. Phloem • Sieve cells- pores, organelles • Sieve tube elements have cytoplasm but lack a nucleus, ends are called sieve plates • Companion cells have nucleus and organelles associated with sieve tube element

  23. Pictures

  24. Table 1. Xylem and phloem in gymnosperms and angiosperms

  25. Underground Stems • Tubers Corms Rhizomes

  26. Stolons • Grow along the soil • For example: strawberries, mint