In leaves

• Leaf structure

  waxy cuticle

  Upper epidermis

  Palisade cells

  Spongy mesophyll

  Phloem and xylem

  stomata and guard cells
• How does CO2 enter the leaf?

  diffusion through stomata Which is opened by guard cells

  Through air spaces

  Then diffuses down the concentration gradient into cells
• Is a leaf an organ?

  Yes
• What is an organ?

  A group of tissues working together for a specific function
• Features - thin leaves

  Short diffusion distance
• Features - air spaces

  Diffusion quicker in air than cells

  Larger SA
• Features - many stomata

  To let more gas go in and out
• Open stomata

  water moves in by osmosis and becomes turgid
• Closed stomata

  Water moves out by osmosis and becomes flaccid
• When does stomata typically close?

  At night when there is low water availability