Explore how living sieve tubes, companion cells, active source loading and pressure gradients transport sucrose and amino acids to sinks in IB Biology HL B3.2.18.
Fluids inside unicellular and multicellular organisms allow materials to be moved.
Describe the transport of carbon compounds such as sucrose and amino acids in phloem.
transport/translocation in (phloem) sieve tubes;
flow of sap through pores in end walls/sieve plates;
sugar/amino acids are transported dissolved in water/sap;
loaded into phloem (companion cells/sieve tubes) by active transport;
protons pumped out and sucrose then enters by cotransport;
high solute concentration created in phloem/sieve tube;
water enters (sieve tube) by osmosis;
hydrostatic pressure in sieve tube increases;
unloading from sieve tubes in sink/in roots;
water leaves by osmosis lowering the hydrostatic pressure;
sap movement (in phloem) from higher to lower pressure;
movement from source/leaves to sink/roots;