Leaf

• Leaf structures affecting the rate of transpiration:

  • Leaf surface area
  • Thickness of epidermis and cuticle
  • Stomatal frequency
  • Stomatal size
  • Stomatal position
• Palisade Mesophyll Cells: Well adapted to photosynthesis: long, cylindrical and packed close together with only a small gap for carbon dioxide, and a huge vacuole so chloroplasts are pushed to the peripheral of the cell, reducing diffusion distance; contain many chloroplasts and a cytoskeleton moves chloroplasts closer to leaf surface when light intensity is low and further away when it is high
• Guard Cells: Two cells surrounding a hole called the stoma; light energy used to produce ATP, which is used to transport potassium ions from epidermal cells into guard cells, lowering water potential so water enters causing them to swell
• Root Hair Cells: Epidermal cells on outer layer of plant roots; hair-like projections increase surface area for absorption of water and minerals (e.g. nitrates) from soil, carrier proteins in the membrane actively transport (produces ATP for this) mineral ions into the cell
• Leaf cross-section

  A) cuticle

  B) upper epidermis

  C) chloroplast

  D) palisade cell

  E) xylem

  F) water

  G) phloem

  H) food

  I) vein

  J) lower epidermis

  K) spongy cells

  L) stoma

  M) guard cell

  N) cuticle

  
• Guard Cell

  A) chloroplast

  B) thickened inner wall

  C) stoma

  D) guard cell

  
• Root Hair Cell

  A) root

  B) soil

  C) cell wall

  D) nucleus

  E) vacuole

  F) cytoplasm

  
• Guard Cell: Thick inner wall remains rigid and the gap enlarges, so gaseous exchange can occur (CO_2 can diffuse into palisade cells down a steep concentration gradient and O_2 made in photosynthesis diffuses out)