BIO203H5 Chapter Notes - Chapter 3: Electrochemical Gradient, Phloem, Soil Texture
Document Summary
Source tissue -> sink tissues release sugars for use elsewhere -> tissues using or storing sugars. Loading of sucrose by source cells into nearby phloem cells requires energy (atp) creates pressure gradient (water follows sugars) > movement of water to sinks through osmosis. Solute transport = transport of sugars = translocation. High turgor pressure near sources causes phloem sap to flow from sources to sinks. Phloem unloading - carbs out of the system. Active transport of sucrose from source leaf cells through companion cells to sieve-tube members. Water moves from the nearby xylem into the sieve-tube members. Active removal of sucrose from sieve-tube members by companion cells into sink cells (e. g. roots) Water moves from nearby sieve-tube members into the xylem. Sugar beets - they accumulate large amount of sucrose in vacuole. Water in phloem sap translocated via a steep pressure potential gradient: source -> sink tissue.
