DP Biology (first assessment 2025)

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Question 23M.2.HL.TZ1.8b

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Date May 2023 Marks available [Maximum mark: 7] Reference code 23M.2.HL.TZ1.8b
Level HL Paper 2 Time zone TZ1
Command term Describe Question number b Adapted from N/A
b.
[Maximum mark: 7]
23M.2.HL.TZ1.8b
(b)

Describe the transport of carbon compounds such as sucrose and amino acids in phloem.

[7]

Markscheme
  1. transport/translocation in (phloem) sieve tubes;
  2. flow of sap through pores in end walls/sieve plates;
  3. sugar/amino acids are transported dissolved in water/sap;
  4. loaded into phloem (companion cells/sieve tubes) by active transport;
  5. protons pumped out and sucrose then enters by cotransport;
  6. high solute concentration created in phloem/sieve tube;
  7. water enters (sieve tube) by osmosis;
  8. hydrostatic pressure in sieve tube increases;
  9. unloading from sieve tubes in sink/in roots;
  10. water leaves by osmosis lowering the hydrostatic pressure;
  11. sap movement (in phloem) from higher to lower pressure;
  12. movement from source/leaves to sink/roots;

Syllabus sections