Transport of Pholem and structure

The vascular tissue in charge of transport and distribution of the organic nutrients

Xylem is a one way transport upwards of water and minerals while Phloem is a upwards and downwards transport of organic molecules. Xylems outer cells are non living while the phloem cells are living but need support. Xylem has no end walls while phloem has sieve plates which are end walls.

Phloem are composed of sieve tubes, which are columns of specialized cells. Individual sieve tube cells

transpiration is the loss of water vapour from the leaves and stems of plants while translocation is the transport of organic solutes in the phloem tissue as it is a transport system to give solutes to parts of plants that require solutes

Translocation is a process carried out by the phloem which links parts of the plant that need a supply of sugars and other solutes (i.e. amino acids) to other parts of the plant that have a surplus

 both have a fluid flowing inside of tubes which moves due to pressure gradients  generating these pressure gradients requires energy, so flow of blood and phloem sap are both active processes  there are no valves or central pump in phloem

its not readily available so it will not be metabolized immediately making it a good transport carb

H+ ions are actively transported out of the companion cells using ATP. The build-up of H+ then flows down the conc. gradient through a co-transport protein Energy is released, and used to carry sucrose into the companion cell-sieve tube complex.

Once the sucrose reaches the companion cell it is converted to oligosaccharides to maintain the sucrose concentration gradient.

 Build-up of sucrose and other draws water into the companion cell through osmosis  This causes a build-up of pressure in the phloem  loss of solute causes a reduction in osmotic pressure then water that carried the solute to the sink is then moved into the xylem.

leaf cell (the source)

 areas where sugars and amino acids are loaded into the phloem are called sources  areas where sugars and amino acids are unloaded and used are called sinks.  Sometimes, sinks can turn into sources and vice versa. This means that phloem must be able to transport biochemical in either direction yes

Sources mature green leaves green stems storage tissues in germinating seeds tap roots or tubers at the start of growth season sinks Roots that are growing or absoribng mineral ions Developing fruits developing seeds developing leaves developing tap roots or tubers

Sieve tube cells are closely associated with companion cells that carry out cellular functions. Sieve cells are living and maintain sucrose and organic molecules concentrations within the phloem

Sieve tube cells are closely associated with companion cells that carry out cellular functions.

Sucrose travels between cells through connections between cells called plasmodesmata Once the sucrose reaches the companion cells it is converted to oligosaccharides to maintain the sucrose concentration gradientPHLOEM LOADING: SYMPLAST ROUTE

 To achieve this, H + ions are actively transported out of the companion cells and then they move back into the companion cell through a co-transport protein that also moves a molecule of sugar with the H + into the companion cell-sieve tube complex.