Transport system in plants

• Transport


  Movement, circulation or flow of different substances within living organisms either with or without a continuous vascular system
• Vascular system


  Transport system with transport vessels like phloem and xylem in plants and blood vessels in animals
• Multicellular organisms


  • Need transport systems to supply nutrients to their cells and get rid of waste products
  • Plants transport substances through the xylem and phloem
  • Animals make use of the blood vessels
• An increase in the size of multicellular organisms leads to a decrease in the surface area to volume ratio
• Big multicellular organisms cannot depend on diffusion alone to provide their cells with materials like food, water and oxygen and remove wastes
• Big multicellular organisms therefore need specialized transport system
• Non-vascular plants


  Bryophytes (mosses and liverworts) that lack specialized xylem and phloem for transport of water, minerals salts and glucose
• Non-vascular plants


  • Small and simple plants
  • Use cell to cell diffusion for movement of water, minerals and glucose
  • Restricted to damp (wet) places
• Transport in non-vascular plants


  1. Water enters through rhizoids (root-like structures) by osmosis and moves from cell to cell up to leaf-like structures

  2. Minerals enter rhizoids by diffusion and move from cell to cell

  3. Glucose produced during photosynthesis moves in a similar way to minerals

  4. Oxygen and carbon dioxide diffuse directly into and out of cells
• Reasons why plants need water


  • For photosynthesis
  • For support (non-woody plants or herbaceous plants)
  • To transport dissolved minerals
• Transpiration


  Water loss from leaves due to evaporation
• Transpiration pull


  Suction pressure set up by transpiration
• Transpiration stream


  Movement of water from roots up the stem and to the leaves
• Transport of water in plants


  1. Water absorbed through root hairs by osmosis due to higher solute concentration of cell sap

  2. Transpiration causes a concentration gradient allowing water to move into the cell through osmosis

  3. This process continues as long as the cell sap is more concentrated with solutes than soil water
• Vascular plants


  • Tracheophytes (pteridophytes and spermatophytes) with specialized transport systems - the phloem and the xylem
  • Much bigger and taller than non-vascular plants
• Adhesion


  Attraction between molecules of different substances
• Adhesion


  • Water molecules adhering to the walls of narrow tubes like the xylem vessels in plants, helping to pull water upward
• Cohesion


  Attraction between molecules of the same substance
• Cohesion


  • Water molecules sticking together due to cohesion, forming droplets or maintaining a continuous flow in plant xylem vessels
• Transport


  Starts from a source to a sink
• Transpiration


  Water loss from leaves due to evaporation
• Transpiration pull


  Suction pressure set up due to transpiration
• Osmosis


  Movement of water into the roots
• Light is needed to split up water molecules
• Transport up stem


  Cohesion + Adhesion - Capillarity
• Transpiration stream is the overall movement of water starting from the roots to the leaves
• Transpiration pull causes water to move into the roots and then up the stem
• Root pressure from roots pushes water from roots into the stem
• Two forces help to move water up the stem: adhesion and cohesion
• Adhesion


  Water molecules clinging onto other substances like the cell wall of xylem
• Cohesion


  Water molecules clinging onto each other
• Capillary action (capillarity)


  Cohesion and adhesion allows water to travel in a long column that resist the tendency to break
• Transpiration is the water movement from roots to leaves
• Xylem vessels are dead cells that form long tubular structures called tracheids or vessel elements.
• The xylem is responsible for the transport of water, minerals, and other solutes from the roots to the leaves.
• The xylem is responsible for the transport of water, minerals, and other solutes from roots to leaves.
• The walls of these cells have thickened lignin, which makes them rigid and strong enough to withstand pressure changes as water moves through them.