DP Biology (first assessment 2025)

Test builder »

Question 22M.2.SL.TZ2.b

Select a Test
Date May 2022 Marks available [Maximum mark: 7] Reference code 22M.2.SL.TZ2.b
Level SL Paper 2 Time zone TZ2
Command term Explain Question number b Adapted from N/A
b.
[Maximum mark: 7]
22M.2.SL.TZ2.b

Humans need to balance water and solute concentrations and also excrete nitrogenous wastes. Explain how the different parts of the kidney carry out these processes.

[7]

Markscheme
  1. humans are osmoregulators/maintain the internal concentrations of the blood/osmolarity within specific/ limited range / OWTTE;
  2. glomerulus / Bowman’s capsule (in the nephron) carry out ultrafiltration;
  3. proximal convoluted tubule selectively reabsorbs glucose/solute/salts/amino acids;
  4. loop of Henle maintains hypertonic conditions in the medulla/absorbs salts (by active transport);
  5. loop of Henle reabsorbs water (by osmosis);
  6. (osmoreceptors in the hypothalamus) cause production of ADH if the blood is too concentrated / person is dehydrated / OWTTE;
  7. ADH causes more uptake of water/increases permeability in the collecting duct;
  8. resulting in a more concentrated urine / lower volume of urine;
  9. excess amino acids are broken down producing nitrogenous waste / ammonia / urea as a result;
  10. ammonia is toxic and is converted into non-toxic urea;
  11. urea is eliminated in the urine;

Marks can be awarded to clearly annotated diagrams.

Examiners report

Generally, there were good accounts of the functioning of the nephron, but some elements were missing such as which substances are reabsorbed in the proximal tubule and which are absorbed in the loop of Henle, although permeability was mentioned. Discussion about the role of ADH was well done. The discussion of the management of nitrogenous wastes was least well done in this question.

Syllabus sections