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Plant Organs: Leaves

Plant Organs: Leaves. Chapter 8. LEARNING OBJECTIVE 1. Describe the major tissues of the leaf ( epidermis, mesophyll, xylem, and phloem ) Relate the structure of the leaf to its function of photosynthesis. “Typical” Leaf. Blade. Veins. Petiole. Axillary bud. Stipules. Stem.

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Plant Organs: Leaves

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  1. Plant Organs: Leaves Chapter 8

  2. LEARNING OBJECTIVE 1 • Describe the major tissues of the leaf (epidermis, mesophyll, xylem, and phloem) • Relate the structure of the leaf to its function of photosynthesis

  3. “Typical” Leaf

  4. Blade Veins Petiole Axillary bud Stipules Stem Fig. 8-1, p. 152

  5. Animation: Simple and Compound Leaves CLICKTO PLAY

  6. KEY TERMS • BLADE • Broad, flat part of a leaf • PETIOLE • Part of a leaf that attaches blade to stem

  7. Leaf Morphology

  8. Simple Pinnately compound Palmately compound California white oak (Quercus lobata) Ohio buckeye (Aesculus glabra) White ash (Fraxinus americana) (a) Leaf form: simple and compound. Opposite Alternate Whorled American beech (Fagus grandifolia) Sugar maple (Acer saccharum) Southern catalpa (Catalpa bignonioides) (b) Leaf arrangement on a stem. Palmately netted Pinnately netted Parallel Sweetgum (Liquidambar styraciflua) Bermuda grass (Cynodon dactylon) Black willow (Salix nigra) (c) Venation patterns. Stepped Art Fig. 8-2, p. 154

  9. KEY TERMS • PHOTOSYNTHESIS • The biological process that includes the capture of light energy and its transformation into chemical energy of organic molecules (such as glucose), which are manufactured from carbon dioxide and water

  10. Tissues in a Leaf Blade

  11. Animation: Leaf Organization CLICKTO PLAY

  12. Epidermis • The transparent epidermisallows light to penetrate into the mesophyll, where photosynthesis occurs

  13. KEY TERMS • CUTICLE • Waxy covering over epidermis of aerial parts (leaves and stems) of a plant • Enables the plant to survive in the dry conditions of a terrestrial environment

  14. Trichomes

  15. KEY TERMS • STOMA • Small pores in epidermis of stem or leaf • Permit gas exchange for photosynthesis and transpiration • Flanked by guard cells • GUARD CELL • Two guard cells form a pore (stoma)

  16. Stomata • Stomata typically open during the day, when photosynthesis takes place, and close at night

  17. KEY TERMS • MESOPHYLL • Photosynthetic ground tissue in the interior of a leaf • Contains air spaces for rapid diffusion of carbon dioxide and water into, and oxygen out of, mesophyll cells

  18. Vascular Bundle • Leaf veinshave • xylemto conduct water and essential minerals to the leaf • phloemto conduct sugar produced by photosynthesis to rest of plant

  19. KEY TERMS • BUNDLE SHEATH • One or more layers of nonvascular cells (parenchyma or sclerenchyma) surrounding the vascular bundle in a leaf

  20. LEARNING OBJECTIVE 2 • Contrast leaf structure in eudicots and monocots

  21. Animation: Monocot and Dicot Leaves CLICKTO PLAY

  22. Bundle Sheath Extensions

  23. Upper epidermis Bundle sheath extension Bundle sheath Midvein Bundle sheath extension Lower epidermis Fig. 8-5, p. 157

  24. Leaf Cross Sections

  25. Leaf Cross Sections

  26. Upper epidermis Palisade mesophyll Midvein Lengthwise view of vein Spongy mesophyll Privet Air space Lower epidermis Stoma Xylem Phloem (a) Privet (Ligustrum vulgare), a eudicot, has a mesophyll with distinct palisade and spongy sections. Fig. 8-6a, p. 158

  27. Bundle sheath cells Midvein Mesophyll Parallel vein Upper epidermis Lower epidermis Phloem Xylem Fig. 8-6b, p. 158

  28. Monocot and Eudicot Leaves • Monocot leaves • Usually narrow • Wrap around the stem in a sheath • Have parallel venation • Eudicot leaves • Usually have a broad, flattened blade • Have netted venation

  29. Bulliform Cells • Large, thin-walled cellson upper epidermises of leaves of certain monocots (grasses) • Located on both sides of the midvein • May help leaf roll or fold inward during drought

  30. Bulliform Cells

  31. (a) A folded leaf blade. The inconspicuous bulliform cells occur in the upper epidermis on both sides of the midvein. Bulliform cells Midvein Fig. 8-7a, p. 159

  32. Bulliform cells (b) An expanded leaf blade. A higher magnification of the midvein region shows the enlarged, turgid bulliform cells. Mesophyll cell Midvein Fig. 8-7b, p. 159

  33. LEARNING OBJECTIVE 3 • Outline the physiological changes that accompany stomatal opening and closing

  34. Variation in Guard Cells

  35. Open Closed Guard cells Subsidiary cells (a) Guard cells of eudicots and many monocots are bean shaped. Fig. 8-8a, p. 160

  36. Open Closed Guard cells Subsidiary cells (b) Some monocot guard cells (those of grasses, reeds, and sedges) are narrow in the center and thicker at each end. Fig. 8-8b, p. 160

  37. Fig. 8-8d, p. 160

  38. Animation: Stomata CLICKTO PLAY

  39. Stomatal Opening 1 1. Blue lightactivates proton pumps • in guard-cell plasma membrane • 2. Protons (H+) are pumped out of guard cells, forming a proton gradient • Charge and concentration difference on two sides of the guard-cell plasma membrane

  40. KEY TERMS • PROTON GRADIENT • Difference in concentration of protons on the two sides of a cell membrane • Contains potential energy that can be used to form ATP or do work in the cell

  41. Stomatal Opening 2 3. Gradient drives facilitated diffusionof potassium ions into guard cells 4. Chloride ions also enter guard cells through ion channels • Ions accumulate in vacuoles of guard cells • Solute concentration becomes greater than that of surrounding cells

  42. KEY TERMS • FACILITATED DIFFUSION • Diffusion of materials from a region of higher concentration to a region of lower concentration through special passageways in the membrane

  43. Stomatal Opening 3 • 5. Water enters guard cells from surrounding epidermal cells by osmosis • Increased turgidity changes the shape of guard cells, causing stoma to open

  44. Stomatal Opening

  45. Blue light activates proton pumps. Protons are pumped out of guard cells, forming proton gradient. Potassium ions enter guard cells through voltage-activated ion channels. Chloride ions also enter guard cells through ion channels. Water enters guard cells by osmosis,and stoma opens. 1 2 3 4 5 Fig. 8-9, p. 162

  46. Stomatal Closing • As evening approaches, sucrose concentration in guard cells declines • Sucrose is converted to starch (osmotically inactive) • Water leaves by osmosis, guard cells lose their turgidity, pore closes

  47. Adaptations to Environment

  48. Blade Petiole Fig. 8-10, p. 163

  49. Guard cells of sunken stoma Epidermis and cuticle Resin duct Endodermis Xylem Vascular bundle Phloem Mesophyll cell (photosynthetic parenchyma cell) Fig. 8-11, p. 164

  50. LEARNING OBJECTIVE 4 • Discuss transpiration and its effects on the plant

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