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Vascular Plants with Seeds

Vascular Plants with Seeds. C9L3P5 Leaves. External Structures of Leaves. Blade : the flat portion of a leaf. Petiole : the stalk of a leaf; attaches leaf to stem. Margin : the edge of a leaf’s blade. Veins : the pipelines that carry food & water. Margin.

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Vascular Plants with Seeds

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  1. Vascular Plants with Seeds C9L3P5 Leaves

  2. External Structures of Leaves Blade: the flat portion of a leaf Petiole: the stalk of a leaf; attaches leaf to stem Margin: the edge of a leaf’s blade Veins: the pipelines that carry food & water Margin Node: place on stem where leaves are attached

  3. External Structures of Leaves Stipule: a small leaf like or scale like structure on a plant that helps to cover a leaf while it is developing

  4. Leaf Venation Two basic patterns of leaf venation: • Parallel Venation • Netted Venation

  5. Parallel Venation A series of veins which originate at the stem and proceeds to the tip of the leaf Occurs in monocots – corn, grass, irises, orchids

  6. Netted Venation Palmate: two or more main veins coming from a single point Examples: maple, ivy, geraniums Pinnate: if the veins branch off one large central vein called a midrib Examples: oaks, apple trees, African violets

  7. Classification of Leaves • Simple leaves • Compound leaves

  8. Simple or Compound? Simple Leaves: one blade on each petiole

  9. Simple or Compound? Compound: more than one blade on each petiole Each small blade on a compound leaf is referred to as a leaflet

  10. Sessile Leaves Sessile leaves lack petioles

  11. Sessile Leaves Grasses and certain other monocots have sessile leaves that attach to the stem by way of a sheath that seems to wrap around the stem

  12. Leaf Mosaic Alternate Opposite Whored Leaf mosaic: the arrangement of leaves on a stem

  13. Leaf Mosaic Alternate Mosaic: leaves alternate from opposite sides of the stem (one petiole per node)

  14. Opposite Mosaic: two leaves grow from the same point on the stem (two petioles per node) Leaf Mosaic

  15. Leaf Mosaic Whorled Mosaic: three or more leaves grow from a single point on a stem (3 or more petioles per node)

  16. Leaf Mosaic

  17. Leaf Shapes Linear Lobed Cordate Deltoid Circular

  18. Linear Leaf Shape long and narrow 

  19. Lobed Leaf Shape

  20. Cordate Leaf Shape kidney or heart-shaped

  21. Deltoid Leaf Shape deltoid-shaped

  22. Circular Leaf Shape

  23. Leaf Margins Entire Serrate Undulate Dentate

  24. Entire Leaf Margin smooth margin with no teeth

  25. Serrate Leaf Margin toothed margins

  26. Undulate Leaf Margin wavy margins

  27. Dentate Leaf Margin teeth point out

  28. The internal structures of leaves.

  29. Leaves • Most leaves are the major site of photosynthesis for the plant. • The top and bottom layers of a leaf are made of epidermal tissue.

  30. The Covering of a LeafThe Epidermis

  31. The Epidermis • the top and bottom layer • one cell layer in thickness • lacks chlorophyll • serves as protection • often secrets a waxy substance that forms a cuticle • usually transparent

  32. The Cuticle Cuticle Epidermis waxy substance made by some epidermal cells for protection

  33. The Lower Epidermis • tiny openings called stomata (stoma, sing.)(or leaf pores) permit the exchange of gases between atmosphere and spaces in leaf • main purpose - to allow air to move in and out of the leaves

  34. Dr. Gerald Van Dyke/Visuals Unlimited/Getty Images Most leaves have a small opening in the epidermis called stomata.

  35. Stomata When the stomata open, carbon dioxide, oxygen, and water vapor can pass through them. Dr. Gerald Van Dyke/Visuals Unlimited/Getty Images

  36. The Lower Epidermis • may be very abundant (apple tree leaf - 47,000 stomata per square inch; oak tree – • 100,000) • guard cells - two crescent-shaped cells around each stomata; open and close the stomata

  37. The Lower Epidermis Stoma Guard Cells

  38. The Lower EpidermisStomata & Guard Cells Guard Cells Stomata

  39. The Lower EpidermisStomata & Guard Cells

  40. The Lower EpidermisGuard Cells Guard Cells

  41. Stomata & Guard Cells

  42. Internal Leaf Structures Between the upper and lower epidermis is the mesophyll. It is in the mesophyll where most of the photosynthesis takes place. It is structural tissue called parenchyma. Mesophyll is divided into two layers: Palisade Mesophyll Spongy Mesophyll

  43. Internal Leaf Structures

  44. Palisade Mesophyll Below the upper epidermis are rows of tightly packed cells called palisade mesophyll cells where photosynthesis mainly occurs.

  45. Palisade Mesophyll • located toward the upper side of the leaf • consists of elongated, column like cells • there may be several layers • abundance of chloroplasts move in a circle

  46. Spongy Mesophyll • located toward the lower side of the leaf • sometimes sandwiched in the middle • consists of large, irregularly shaped cells • separated by large air spaces • form a system of passages throughout the leaf that permits air to come in contact with the individual cells

  47. Veins (Fibrovascular Bundles) • run through the mesophyll • contain the vascular tissue xylem and phloem • contain thick-walled strengthening collenchyma tissue

  48. Scanning Electron Microscopic Picture of a Freeze-Dried Cross-Section Through a Bean Leaf E: Upper and lower epidermis, Sz: Guard cell, P: Cells of the palisade parenchyma, S: Cells of the spongy parenchyma, I: Intercellular space.

  49. Cross Section of a Leaf

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