transport

• Unicellular organisms


  Organisms that are single-celled
• Unicellular organisms


  • Need to exchange substances such as food molecules and waste products between itself and its environment
  • Exchange of substances occurs across the cell membrane
• Transport processes used by living organisms


  1. Diffusion

  2. Osmosis

  3. Active transport
• Unicellular organisms (e.g. amoeba)


  • Have very large surface areas (SA) in comparison to their volumes
  • The distance between the surface of the organism to its centre is very small
• Unicellular organisms do not need to have specialist exchange surfaces or transport systems as diffusion, osmosis and active transport through the cell membrane occur at a sufficient rate to meet the organisms needs
• Phloem


  Vascular tissue that transports food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem
• Phloem


  • Movement can be in any direction around the plant
  • Cells are living and not hollow
  • Substances move from cell to cell through pores in the end walls of each cell
• Phloem


  Has structural features different to the xylem
• Xylem


  One of the two specialist transport vessels in plants
• Xylem


  • Transports water and minerals from the roots to the stem and leaves
  • Composed of dead cells which form hollow tubes
  • Xylem cells are strengthened by lignin and so are adapted for the transport of water in the transpiration stream
• Plant organ system for the transport of substances around the plant

  1. Roots

  2. Stem

  3. Leaves
• Plants possess two specialist transport vessels called the xylem and phloem
• The xylem and phloem are arranged throughout the root, stem and leaves in groups called vascular bundles