transport-translocation Flashcards
what does the mass flow theory suggest
suggests there is a passive mass flow of sugars from source to sink
name 7 features of a sieve tube
-alive
-end walls of eavh cell is perforated forming a sieve plate.
-have enlarged plasmodesmata.
-produces a tube.
-walls also have perforations
-as they mature they lose their nucleus, vacuole mitochondria and ribosomes for space.
what is the role of the companion cell
are very active and control metabolism of sieve tube elements via plasmodesmata.
name 4 bits of evidence for metabolic activity in companion cells.
-large nucleus.
-dense cytoplasm.
-large quantities of rough ER
-many mitochondria.
what evidence is there to suggest translocation is an active process.
translocation is slowed by low temperatures and respiratory inhibitors.
what is cytoplasmic streaming-
cytoplasm movement means solutes can be moved in different directions at the same time
whta is the role of protein filaments in solute transport.
pass through pores in sieve plates transporting different solutes through the same sieve plates.
what are the problems with mass flow.
rate of transport in phloem is 10000x faster than diffusion.
-does not take into account sieve plates.
-sucrose and amino acids move at different rates and directions at the same time.
-phloem has high 02consuption and translocation is slowed or stopped at low tamps or with cyanide.
in ringing experiments to provide evidence for phloem transport- what is below the ring.
no sucrose
-suggesting it has been used by plant tissues and had not been replaced as ring blocks movement.
how is radioactive tracers and autoradiography used as evidence?
plant photosynthesises in presence of c02.
-stem section placed on photoautographic film which is exposed if there is radiation producing an autoradiograph.
-position of exposure and radioactivity coincides with the position of the phloem . indicating that it is the phloem that translocated sucrose made from the radioactive carbon.
