Epidermis

1
Leaves - vocabulary

• Epidermis
• Covers top and bottom of leaf
• Tough cells that help form waterproof barrier to
  limit H2O loss
• Cuticle
• Covers the epidermis forming a waterproof barrier
  to limit H2O loss
• Vascular tissue
• Transports H2O and nutrients throughout the plant
• In plants, consists of xylem and phloem

2

• Xylem   
• Carries H2O from roots through the stem to the
  leaf (spongy mesophyll) to replaces H2O lost
  through stomata in transpiration
• Phloem    
• Carries carbohydrates from mesophyll to the rest
  of the plant
• Vein    
• In plants, consists of xylem and phloem
• Transports H2O and nutrients
•   
• Photosynthesis
• Production of sugars (glucose) using sunlight,
  CO2 and H2O (O2 is a byproduct of photosynthesis)

3

• Mesophyll
• Takes up the majority of leaves
• Mesophyll cells are packed with chloroplasts
•  
• Palisade mesophyll
• Just under the upper epidermis
• Cells are closely packed together
• Absorbs most of sunlight that enters leaf
• Spongy mesophyll
• Just under the palisade mesophyll
• Cells are loosely packed together
• Spaces in between cells are moist, which
  increases gas exchange

4

• Stomata (stoma) 
• Connects exterior with air spaces
• Openings on underside of leaf that allow CO2, O2,
  and H2O to diffuse in and out of cells. 
•   
• Guard cells
• Cells in lower epidermis that control opening and
  closing of stomata
• Respond to
• High water pressure open
• Low water pressure closed
•   
• Transpiration
• The loss of H2O from a plant through its leaves
  (stomata)
• In general, stomata are open during day
  (photosynthesis rate is high) and closed at night