Transport in flowering plants

• Xylem vessels are dead cells that form long tubular structures called tracheids or vessel elements.
• upper epidermis


  single layer of closely packed

  cells (epidermal cells) covered

  by a waxy and transparent

  cuticle on the outside

  • waterproof to reduce water loss through

  evaporation

  • transparent to allows light to enter the

  leaf
• Palisade mesophyll


  one or two layers of closely

  packed long, cylindrical cells

  containing numerous

  chloroplasts

  • chlorophyll in chloroplasts traps light

  and converts light energy to chemical

  energy by photosynthesis

  • more light is trapped on the surface of

  leaf, hence has most chloroplasts
• Spongy mesophyll

  irregular shaped cells with

  large intercellular air spaces

  • rapid diffusion of carbon dioxide and

  oxygen into and out of mesophyll cells

  cells contain fewer

  chloroplasts than palisade

  mesophyll layer

  • more light trapped on surface of leaf

  cells covered by thin film of

  moisture

  • allow carbon dioxide to dissolve and diffuse

  into cells

  contains vascular bundle transports water and mineral salts to cells;

  manufactured food away from cells
• Lower epidermis


  single layer of closely packed

  cells covered by a waxy

  cuticle

  • reduces water loss through evaporation
• Stomata


  pores/ openings on the

  epidermis which are regulated

  by guard cells

  • opens in the presence of light allowing

  carbon dioxide to diffuse in and oxygen

  to diffuse out for photosynthesis

  • guard cells can photosynthesise

  (contains chloroplasts)
• Xylem 


  dead empty vessel with

  lumen without protoplasm

  and cross-walls

  • conducts water and dissolved

  mineral salts from roots to

  stems and leaves rapidly as

  resistance to water flow is

  reduced

  inner walls are lined with

  lignin

  • provides mechanical support

  for plant
• Phloem

  1. sieve tubes

  • consist of elongated, thin-

  walled living sieve tube

  cells

  • cross walls present (sieve

  plates)

  • cytoplasm of sieve tube

  cells are interconnected

  holes in sieve plates allow

  rapid transport of sucrose

  (produced as glucose during

  photosynthesis) and amino

  acids from the source (leaves)

  to the sink companion cells

  ▪ metabolic processes and

  contains many

  mitochondria, cytoplasm

  and nucleus

  provides energy to load

  sugars from mesophyll cells

  into sieve tubes by active

  transport
• Water molecules continuously move out of mesophyll cells to form a thin film of moisture over their surfaces
• Water evaporates from the thin film of moisture and moves into intercellular air spaces
• Water vapor accumulates in the air cavities near stomata
• Water vapor molecules diffuse through stomata into drier air in the atmospheric surroundings by transpiration
• As water evaporates from mesophyll cells, the water potential of cell sap decreases
• Mesophyll cells absorb water molecules by osmosis from cells deeper inside the leaf and, in turn, remove water from xylem
• Transpiration pull results in pulling the column of water up xylem vessels
• transpiration pull draws water and mineral salts from roots to stems and leaves

  • evaporation of water from cells in leaves removes latent heat of vapourisation and

  cools the plant

  • water is essential for photosynthesis, maintaining turgidity of cells and replacing water Lost