DP Biology (first assessment 2025)

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Question 23M.2.HL.TZ1.a

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Date May 2023 Marks available [Maximum mark: 4] Reference code 23M.2.HL.TZ1.a
Level HL Paper 2 Time zone TZ1
Command term Outline Question number a Adapted from N/A
a.
[Maximum mark: 4]
23M.2.HL.TZ1.a

Outline the role of ADH in osmoregulation.

[4]

Markscheme
  1. ADH (secreted by pituitary) if body/blood is dehydrated/hypertonic/has high solute concentration;
  2. more aquaporins / aquaporins open (in collecting duct);
  3. collecting duct more permeable to water/reabsorbs more water (from filtrate/urine);
  4. water reabsorbed by osmosis/water reabsorbed because medulla is hypertonic;
  5. (reabsorbed) water passes (from filtrate) to blood / blood solute concentration reduced;
  6. less water lost in urine / smaller volume of (more concentrated) urine;
  7. negative feedback / less/no ADH secreted when blood solute concentration returns to normal;

Do not accept answers suggesting that ADH has a different effect when body fluids are hypotonic.

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