plant leaf

• Guard cells regulate the opening and closing of stomata to maintain water balance within the leaf.
• leaf - overgrowth of the stem, usually flat and thin, needlelike o scalelike. It is green or some other color (such as red).

  •Leaves are the powerhouse of plants
• Function

  1. Photosynthesis
  2. For storage of water and food
  3. source of food by humans
  4. used as medicines and flavoring
  5. protection of the plant by capturing insects
  6. provide support for climbing
• leaf parts:

  •Petiole - cylindrical part; attaches blade to the stem

  •Lamina or blade - flattened green part
• monocot leaf

  • support by leaf sheath

  •ligule and auricles

  function: protection from dirt water
• stipule - two leaflike flaps of the petiole; protect from flower bud; dicot leaves
• stipulate - with stipule

  exstipulate - without
• midrib - central vein
• veins - conducting tissue of the leaf
• veinlets - secondary veins
• margin - edge of the leaf
• phyllotaxy - arrangement of leaves on a stem
• phyllotaxy

  1. alternate - one leaf at each node
  2. opposite - two leaves opposite each other at each node
  3. whorled/verticillate - several leaves at equal distance around the node
  4. spiral - leaves arise succeedingly around the stem
  5. decussate - two opposite leaves at right angles to the one below or above it
• epidermis

  • upper and lower
  • single layer of cells
  • derived from protoderm

  Function:

  a., protects leaf from dessication - (cuticle)

  b. Abrasion

  c. prevents entry of fungi and bacteria

  d. regulates exchange of gasses (oxygen and carbon dioxide)
• trichomes - protection against water loss
• stomata - more stomata in lower epidermis

  -, high concentration of CO2, close stomata
• mesophyll - located between upper and lower epidermis

  -. dicotss (2distinct layers)

  • palisade mesophyll - arranged in compact columnar fashion; most photosynthetic activity takes place
  • spongy mesophyll - irregularly shaped; prominent intercellular air spaces; diffusion of carbon dioxide to other parts of leaf
• upper epidermis - covered with cuticle; bulliform cells; stomata present in upper and lower epidermis
• guard cells monocot - dumbbell in shape
• guard cells dicot - kidney shaped
• mesophyll - not differentiated into palisade and spongy mesophyll; monocot leaf
• cuticle - much thicker; monocot
• epidermis - multilayered; monocot
• Netted venation - one or a few prominent midveins from which smalller minor veins branch into a meshed network, common to dicots and some nonflowering plants.
• Pinnately veined leaves - main vein called midrib with secondary veins branching from it
• Palmately veined leaves - veins radiate out of base of blade
• Parallel venation - characteristics off many monocots (eg, grasses, cereall grains); veins are parallel to one another.
• Dichotomous venation - no midrib or large veins, rather individual veins have a tendency to fork evenly from the base of the the blade to the opposite margin, creating a fan-shaped leaf (gingko)
• Venation - arrangement of veins in a leaf
• xylem - part that faces upper surface of the leaf
• phloem - part that faces the lower surface of the leaf
• bundle sheath cells - for added strength and protection
• reticulated - main vein branches
• pinnately netted - vein and veinlets arise from midrib
• palmately netted - vein arise at the base of the leaf
• radiately netted - veins spread at the tip of petiole
• parallel venation - veins parallel with midrib; common in monocot

  1. radial parallel - form right angles to midrib