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leaf structure - external/internal 

  • external form - initiated by primordial in apical meristems
    • main sites of photosynthesis on land
    • cell enlargement/division >> leaves expand
    • microphyll - leaf w/ 1 vein
    • megaphyll - has several veins, leaves gap in cylinder once it branches off
    • veins - collection of xylem/phloem, parallel in monocots, networked in dicots
    • simple leaves - undivided blades
    • compound leaves - blades divided into leaflets
    • pinnately compound - leaflets arranged in pairs
    • palmately compound - leaflets radiate from a center
    • leaves alternately/oppositely arranged, or in whorls (leaf circle)
  • internal form - transparent epidermis covers each leaf
    • no chloroplasts in epidermal cells
    • mesophyll - tissue between upper/lower epidermis, contains vascular bundles and majority of photosynthesis
    • palisade mesophyll - closer to upper epidermis, contains chlorenchyma
    • spongy mesophyll - closer to lower epidermis, contains many air spaces for gas exchange
  • stomata - surrounded by guard cells, regulates water mov’t/gas exchange
    • K+ controls guard cells
    • water enters osmotically >> guard cells swell >> stomata closes
    • opens in the day, closes at night
Subject X2: 

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