Transport In Plants

• Vascular Bundles


  Tissues that transport substances in plants
• Substances transported


  • Water
  • Mineral ions
  • Manufactured food (sucrose, amino acids)
• Xylem tissue


  Transports water and mineral ions
• Phloem tissue


  Transports manufactured food (sucrose, amino acids)
• Roots


  • Organs consisting of tissues
  • Tissues consisting of cells
• Absorption of water and mineral ions in roots

  1. Osmosis

  2. Active transport
• Vascular bundle in a root

  • Xylem
  • Phloem
• Root hair cells


  Modified epidermal cells

  
• Root hair cell


  • Elongated extension (root hair)
  • Concentrated cell sap
  • Large numbers of mitochondria

  
• Absorption of water into root hair cell

  Osmosis - water molecules move from higher water potential (dilute solution in soil) to lower water potential (concentrated cell sap) across partially permeable cell membrane
• Absorption of mineral ions into root hair cell

  Active transport - mineral ions moved against concentration gradient from dilute soil solution into concentrated cell sap
• Movement of water from root hair cell to xylem vessel

  Cell to cell route - water potential difference allows movement of water molecules from cell to cell
• Each root hair is a fine tubular outgrowth of an epidermal cell, growing between soil particles and in close contact with the water surrounding them

  
• The sap in the root hair cell has a lower water potential than the soil solution, so water enters the root hair by osmosis
• Movement of water from root hair cell to inner cells

  Osmosis - water passes from root hair cell with lower water potential to next cell with higher water potential, continuing until water enters xylem vessels
• Endodermis


  • Layer of cells located just outside the vascular bundle
• Stem


  • Organs consisting of tissues
  • Tissues consisting of cells
• Vascular bundle in stem

  • Xylem
  • Phloem
  • Cambium (actively dividing cells)
  • Thick-walled fibres
• Why water from roots needs to reach leaves

  • Water is the raw material of photosynthesis
  • Leaves cannot absorb water directly from surroundings
• Leaf


  • Vascular bundle (xylem and phloem)
  • Epidermis
  • Intercellular air spaces
• Leaves are the site of photosynthesis, where glucose is one of the end products
• Xylem


  Tissue that transports water and mineral ions
• Phloem


  Tissue that transports manufactured food (sucrose and amino acids)
• Xylem


  • Lignified walls
  • Transports water and mineral ions
  • Provides mechanical support to the plant
• Xylem function


  1. Transport of water and mineral ions (dissolved mineral salts)

  2. Provides plant with mechanical support
• Xylem adaptation


  • Hollow and dead (no cell organelles)
  • Continuous (from roots to stem to leaves)
  • Lignified cell walls
• Phloem


  • Consists of sieve tube element (hollow) and companion cell
  • Transports manufactured food (sucrose and amino acids) via translocation
• Phloem sap


  Sucrose and amino acids dissolved in water
• The cytoplasm of photosynthesising cells converts glucose into sucrose for transport

  
• Sucrose is less reactive than glucose, and more likely to "survive the journey" in the phloem (not converted to other products)
• Sucrose has low viscosity at high concentrations
• Transpiration


  Loss of water vapour from the aerial parts of the plant, mainly the stomata of leaves
• Phloem adaptation


  • Companion cell is connected to sieve tube element and keeps it alive
  • Sieve tube element is hollow (lacks nucleus, ribosomes, vacuole and various cytoplasmic elements)

  
• Movement of water inside a leaf

  1. Osmosis: cell to cell movement of water molecules, from xylem to spongy mesophyll cells

  2. Evaporation: thin layer of moisture on spongy mesophyll cells to intercellular air spaces

  3. Transpiration: movement (diffusion) of water vapour from intercellular air space to surroundings

  
• Guard cells


  Open and close stomata; control gaseous exchange
• Guard cells are turgid


  Stomata are open
• Guard cells are flaccid


  Stomata are closed
• Transpiration is a consequence of gaseous exchange
• Transpiration pull is the suction force that brings water (and mineral ions) up the xylem from roots to leaves
• Transpiration pull


  • It extends all the way from the xylem in the leaves to the xylem of the roots
  • The adhesion force where water molecules are attracted to the walls of the xylem helps to fight the force of gravity