Phloem Flashcards
What is translocation?
is the movement of phloem sap from source to sink or from one place to another
What does the phloem do?
transports assimilates(compounds produced by the plants metabolism)
What do sieve tube elements have?
cell membranes that retain sucrose and other assimilates within the cells
little cell contents to reduce resistance flow of phloem sap
sieve plates to hold sieve tubes together and resist internal pressures
sieve pores to allow ease of flow between sieve tube elements
What do companion cells have?
mitochondria- to provide energy to move solutions into the sieve tubes
plasmodesmata- to allow easy movement of phloem sap into and out of the sieve tubes
pump proteins and co transporter proteins in the cell surface membranes for absorption of sucrose
plasmodesmata shared w mesophyll cells for transport of sucrose via symplast
Where does the phloem sap and xylem sap move?
phloem- move in either direction in a plant
xylem- moves in only one direction as it is pulled upwards by transpiration
What are 3 main principles involved with transport in the phloem?
sucrose and other assimilates are loaded at the source where there is a build up of hydrostatic pressure
a pressure gradient is responsible for movement of phloem sap through sieve tubes from source to sink
sucrose and other assimilates are unloaded at the sink forming a low hydrostatic pressure
What is the source and sink in phloem?
The photosynthetically active parts of the plants are referred to as the sources. The areas of active growth and the areas of storage are referred to as the sinks
How are sieve elements of the phloem loaded with solutes against a concentrated gradient?
At the source, sugar and other organic molecules are loaded into the sieve tube members thus increasing solute concentration within the sieve tube cells (decreases water potential). Water from surrounding tissues, enters the sieve tube members by osmosis following a concentration gradient
