Practise IB Biology HL 3.2.18 by explaining how phloem loads organic compounds at sources and moves them to sinks through pressure-driven translocation.
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.
a. transport/translocation in (phloem) sieve tubes;
b. flow of sap through pores in end walls/sieve plates;
c. sugar/amino acids are transported dissolved in water/sap;
d. loaded into phloem (companion cells/sieve tubes) by active transport;
e. protons pumped out and sucrose then enters by cotransport;
f. high solute concentration created in phloem/sieve tube;
g. water enters (sieve tube) by osmosis;
h. hydrostatic pressure in sieve tube increases;
i. unloading from sieve tubes in sink/in roots;
j. water leaves by osmosis lowering the hydrostatic pressure;
k. sap movement (in phloem) from higher to lower pressure;
I. movement from source/leaves to sink/roots;
Marking guidance:
[7 max]