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Cell Walls

Cell Walls. Cell walls are: Structural Provide defense against invading pathogens Provide signaling pathways for cells. Cell Wall Chemistry. Cell walls contain cellulose , pectin and lignin Cellulose is the major component Most abundant polymer in the world

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Cell Walls

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  1. Cell Walls Cell walls are: • Structural • Provide defense against invading pathogens • Provide signaling pathways for cells

  2. Cell Wall Chemistry • Cell walls contain cellulose, pectin and lignin • Cellulose is the major component • Most abundant polymer in the world ~40-60% of dry weight of plants • Form strong strands of parallel chains called Cellulose Microfibrils • Cellulose strands are cemented together by pectins

  3. TEM photograph

  4. Pectin and Lignin • Pectins are polymers of a-galacturonic acid • Flexible, long molecules that link Microfibrils together…like ‘glue’ • Lignin is very hard, tough, rigid • Chemistry is not fully elucidated • Polymer of complex, amino-acid derived monomers • Creates strong cell walls

  5. And don’t forget the 5 colors !

  6. Plant Tissues • Tissues are groups of cells that form a structural and functional unit • Vascular plants have three tissue systems: • Dermal tissue Outer covering for the plant body • Ground tissue Photosynthesis, storage and support • Vascular tissue Water and nutrient conduction system

  7. Functions for Plant Epidermis • Prevent water loss in • shoot (waxy surface • and bark) • 2) Controlling exchange • of gases in shoot (stomates) • 3) Absorption by roots (root hairs) • 4) Produce hairs, called trichomes, that shade • the leaf or protect from • herbivores (physically • or chemically)

  8. A Gymnosperm

  9. B Dicot

  10. C Monocot

  11. Yam D Monocot

  12. E Monocot

  13. Do Animals have epidermis? What is animal epidermis called? What does this have to do with Safe Sex? Cheek cells

  14. Jicama -- Pachyrhizus erosus (L.)

  15. Jicama -- Pachyrhizus erosus (L.) Eaten in celebration of Day of the Dead November 1st Mexico

  16. Plant Tissues • Tissues are groups of cells that form a structural and functional unit • Vascular plants have three tissue systems: • Dermal tissue Outer covering for the plant body • Ground tissue Photosynthesis, storage and support • Vascular tissue Water and nutrient conduction system

  17. Vascular Tissues - Xylem • Xylem conducts water and nutrients from roots to the rest of the plant • Two types • Tracheids • Dead at maturity • Main water-conducting cells of fern and gymnosperms • Relatively few plasmodesmata in end of cell in pit fields, thin areas w/only primary cell wall • Vessel elements • Dead at maturity – stacked on top of each other • Broader than tracheids, large holes in ends of cell • Much more efficient at water transport

  18. End wall with perforations Xylem carries water & soil nutrients Pits Cell wall Lumen Tracheids Vessels (a) (b)

  19. Xylem Vessel Xylem Tracheid

  20. Vascular Tissues - Phloem • Transports food materials • Provides structural support • Two types: - Sieve tube cells • Alive at maturity • Extensive holes via sieve plate at cell ends, with shared cytoplasm between cells • Reduced cellular organelle volume – some lose nucleus • Companion cells • Nucleated, support cells for sieve tubes • Connected by many plasmodesmata to sieve tube cell • Involved in sugar transport to sieve tube cell

  21. Sieve plate Sieve tube member Phloem parenchyma cells Lateral sieve area Plasmodesma Companion cell (c) (d) Fig. 31.05cd

  22. Companion Cell Sieve Tube Cell

  23. Xylem and Phloem Cells

  24. Fiber Cells

  25. Fibers Xylem & Phloem: (in Squash) Phloem Xylem Xylem

  26. Vascular Cambium

  27. Epidermis Phloem Vascular Cambium Xylem

  28. Notice that the vascular cambium circles all the way around Fibers Dicot stem

  29. Jute for burlap Hemp Examples of plant fibers from stem vascular bundles Sisal = fiber from monocot stem

  30. Epidermis Vascular Bundles (scattered) Monocot Stem

  31. Monocot Stem Air Space Xylem (big cells & smaller ones in circle Phloem (all cells within box

  32. Secondary Growth

  33. Secondary Growth……Why? * Plant is getting bigger so needs more materials * Old vascular tissue gets “clogged up”

  34. 1, 2, 3 years Of age Pith

  35. Rays in wood

  36. Tree Borer For assessing tree rings

  37. Bristlecone Pine How old are these trees?

  38. Oldest one is 4,800 years old The oldest living trees on earth.

  39. The Curly Redwood Lodge is one of northern California’s most unique lodges. It was built from one curly redwood tree that produced 57,000 board feet of lumber. The tree (cut down in 1952) was 18 feet wide at the trunk. Curly redwood is unique because of the curly grain of the wood, unlike typical straight grained redwood. http://www.curlyredwoodlodge.com/rooms.htm

  40. 1952

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