Translocation

The movement of dissolved products from photosynthesis from a source to a sink (Active process)

Sucrose Amino acids Hormones

Organs that perform photosynthesis ( Pallisade mesophyll) Storage organs that contain starch that can be readily hydrolysed Roots which absorb minerals

Cells in parts of a plant actively growing Roots (High mitotic index)

Vague references to sugar being transported to “the sink” can lose marks in exams. Always aim to describe the movement of assimilates from or to specific groups of cells, e.g.: photosynthetic cells in a leaf are a source dividing cells in a growing root tip would be a sink

Tube of elongated LIVING cells - sieve tube No nucleus / organelle only thin layer of cytoplasm to reduce flow resistance Companion cells help as they contain lots of mitochondria to produce ATP for active transport Sieve plates allow passage of dissolved substances between cells

1) Companion cells use ATP to actively transport to pump H+ ions out source cell and then H+ ions are co-transported back in down their concentration gradient with sucrose molecules. 2) Sucrose molecules diffuse through companion cell and diffuse into sieve tubes through carrier proteins both by facilitated diffusion 3) Sucrose in the phloem decreases water potential so water from xylem or neighbouring tissue moves into phloem near source cell by omosis 4) This increase hydrostatic pressure and generates a hydrostatic pressure gradient between source cell and sink cells so sucrose moves towards sink cell down pressure gradient 5) Sucrose moves into sink cell by facilitated diffusion down concentration gradient while this is happening water potential increases again and moves back into xylem by osmosis 6) DONE :D

End walls between cells have sieve plates - Allow solutes through

Removal of phloem prevents passage of sugar Puncture problem - Sap comes out due to positive pressure Water in by osmosis at source and out by osmosis at sink Metabolic inhibitors stop translocation - ATP needed for mass flow

Sieve plates act as a slight barrier - No reason to have evolved them Amino acids travel more slowly than sucrose at the phloem when they should travel at the same rate Substances flow in opposite directions but should only be flowing in one direction (Source to sink)

Remove ring of bark and phloem leaving only the xylem Tree swells above the ring and everything continues to grow Roots begin to die Proves evidence for translocation

Also provides evidence for translocation Plants are given radioactive substance which is absorbed - tracer e.g c14 Given to plants to form CO2 Absorbed during photosynthesis Follow path of sucrose whilst glowing