4/7 lecture Flashcards
What is the rate of sucrose movement?
~1 m/hr
What is the rate of sucrose movement by diffusion?
~1 m/32 years
What happens because of sucrose loading into sieve cells?
makes the water potential more negative than the xylem
What happens when water moves into the sieve cell?
creates positive pressure
What happens when sucrose is unloaded into sieve cells
makes their water potential less negative than the xylem
What happens when water moves out of sieve cells?
pressure decreases
Is the process of translocation active or passive?
Passive!
Apoplastic loading
mesophyll cells export sucrose to the apoplast by active transport, then loading into companion cells is accomplished by secondary active transport
_______ concentration is higher in the phloem than in the rest of the leaf
Sugar
What does hydrogen ion gradients power?
the unfavorable uptake of sucrose into companion cells
What is symplastic loading?
sucrose is exported symplastically from mesophyll cells to companion cells; loading relies completely on diffusion
Sugar concentration must be kept higher in the _____ than in the ______ to drive loading
leaf; phloem
What is the result of cellular respiration in sink tissues?
results in low sucrose concentrations (like in roots); promotes diffusion
High sucrose sink need
active transport
(sink size) x (rate of uptake) =
sink strength
