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Leaf structure

  2. 2. Role of leaves: Trap light for photosynthesis Exchange gases
  3. 3. Leaves do not shade each other To trap as much light as possible
  4. 4. External structure of a leaf margin petiole [leaf stalk] midrib vein lamina [blade]
  5. 5. Monocot & Dicot leaves Long & slender leaf Parallel veins Broad leaf Branching veins
  6. 6. Veins contain xylem & phloem
  7. 7. Xylem & Phloem transport materials in plants Xylem transports: Water + mineral salts Phloem transports: Food [sucrose, amino acids]
  8. 8. Internal structure of a leaf margin guard cells Stoma [plural: stomata] palisade layer spongy layer xylem phloem
  9. 9. Internal structure of a leaf
  10. 10. Function of the waxy cuticle:  prevents loss of water
  11. 11. Why are epidermal cells transparent?  to allow a lot of light to pas through
  12. 12. Vertical section through a leaf 8. Guard cell 7. stoma 1. Waxy cuticle 2. Upper epidermis 3. Palisade mesophyll cell 4. Air space 5. Spongy mesophyll cell 6. Lower epidermis
  13. 13. QUESTION: [MAY, 2010] Give a biological explanation for the following statement: Leaves are well adapted for efficient diffusion of carbon dioxide. (4)
  14. 14. QUESTION: [MAY, 2010] The flattened shape of leaves increases the surface area for diffusion. 1 mark Most plants have thin leaves – this means that the distance for the carbon dioxide to diffuse from the outside air to the photosynthesising cells is kept as short as possible. 2 marks The many air spaces inside the leaf allow carbon dioxide to come into contact with lots of cells – this provides lots of surface area for diffusion. 1 mark Stomata allow carbon dioxide into the leaf. 1mark
  15. 15. Why is the upper leaf surface darker green than the lower surface? More chloroplasts in palisade layer than in spongy layer.
  16. 16. Vascular tissue is present throughout the plant
  17. 17. What is the function of the: Stoma: allows exchange of gases Guard cells: to adjust the opening and closing of the stoma
  18. 18. When are stomata open and when are they closed? DAY NIGHT
  19. 19. open their stomata during the NIGHT
  20. 20. How do stomata open during the day? potassium ions enter the guard cells & water follows.
  21. 21. Where are stomata located in:
  22. 22. Stomata are located: mostly on the lower leaf surface  each leaf surface has an equal number of stomata
  23. 23. NO stomata in submerged leaves  Stomata only on upper leaf surface in floating leaves
  24. 24. Why are stomata located like this? Lower leaf surface is more protected from the sun Each leaf surface is equally exposed to the sun
  25. 25. Stomata are useless: they are not in contact with air Stomata allow gas exchange with the air
  26. 26. Differences between guard cells and the surrounding epidermal cells. Guard cells Epidermal cells 1) have chloroplasts Chloroplasts absent 2) are bean-shaped Cuboidal in shape 3) cell walls are not evenly thick Cell walls evenly thick
  27. 27. Structure of a dicot plant
  28. 28. Structure of a dicot plant Internode Node Main/tap root Veins Terminal/apical bud Leaf Petiole Lateral/axillary bud Stem Lateral roots