Chapter 9: Plant structure

• Leaf stalk (Petiole)


  Part of the leaf that connects the leaf blade to the stem
• Leaf blade (Lamina)


  The flat, expanded part of the leaf
• Leaf blade


  • Has a large surface area to volume ratio, and it is thin
• Network of veins


  Consists of xylem and phloem
• Upper epidermis


  Closely packed cells that form one layer and do not contain chloroplasts
• Palisade mesophyll


  Closely packed, long and cylindrical cells that contain the most number of chloroplasts
• Spongy mesophyll


  Loosely packed and irregular-shaped cells that contain chloroplasts
• Lower epidermis


  Closely packed cells that form one layer and do not contain chloroplasts
• Stomatal pore (stoma)


  Opening in the leaf surface
• Guard cell


  Cell that contains chloroplasts and controls the opening and closing of the stomata
• Cuticle


  Waxy layer on the surface of the leaf
• Mesophyll


  Where photosynthesis occurs
• Chlorophyll absorbs light energy for photosynthesis to make glucose
• Intercellular air spaces in the leaf maximize light energy absorbed for photosynthesis
• Stomata are openings in the leaf surface that allow gas exchange
• How guard cells open and close stomata


  1. In sunlight, guard cells carry out photosynthesis and produce glucose, decreasing water potential so water enters guard cells, making them turgid and curved to open stomata

  2. On a hot sunny day, leaf loses too much water, guard cells become flaccid and stomata close
• How carbon dioxide enters leaf cells


  Carbon dioxide diffuses into intercellular air spaces through stomata, dissolves into moisture around mesophyll cells, then diffuses into mesophyll cells
• How water and mineral salts reach leaf cells


  Water and mineral salts are transported through xylem vessels from roots, then move from cell to cell by osmosis and diffusion
• Xylem


  Vascular tissue that transports water and mineral salts
• Xylem


  • Lacks protoplasm or cross walls to reduce resistance for faster conduction, has lignin in inner walls to provide mechanical support
• Phloem


  Vascular tissue that transports sucrose from leaves to other parts of the plant
• Phloem


  • A row of living cells forms a long tube, cross walls between cells have many minute pores
• Vascular bundle


  Xylem and phloem forming a unit, with cambium between them
• In stems, xylem is inner, phloem is outer
• In leaves, xylem is on top of phloem in the vascular bundles
• Photosynthesis


  Process where light energy is absorbed by chlorophyll to make glucose from carbon dioxide and water