9.2 Transport in the phloem of plants

9.2 Transport in the phloem of plants

1. NATURE OF SCIENCE

   • Developments in scientific research follow improvements in apparatus
     • Measuring phloem transport rates
       • Aphid stylets + radioactively-labelled CO2

2. Plants transport organic compounds from sources to sinks

   • Incompressibility of water allows transport along hydrostatic pressure gradients the source
     • Active transport is used to load organic compounds into phloem sieve tubes at the source
       • High concentrations of solutes in the phloem at the source lead to water uptake by osmosis
         • Raised hydrostatic pressure causes the contents of the phloem to flow towards sinks
       • Structure-function relationships of phloem sieve tubes
   • Identification of xylem and phloem in microscope images of stem and root