| Date | November 2011 | Marks available | 6 | Reference code | 11N.3.HL.TZ0.15 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Describe | Question number | 15 | Adapted from | N/A |
Question
Describe the control of ADH secretion.
Markscheme
receptors in hypothalamus detect decrease in blood solute potential/increase in blood concentration;
occurs when excessive sweating/too little water intake/excessive salt intake;
nerve impulses pass to posterior pituitary gland where ADH is released;
ADH secreted by neurosecretory cells;
ADH makes epithelium of convoluted tubule /collecting duct more permeable to water;
water reabsorption results in more concentrated urine;
when high intake of water/solute potential of blood increases/blood more dilute ADH release is inhibited;
walls of convoluted tubule and collecting duct become less permeable to water;
less water is reabsorbed creating dilute urine;
is example of negative feedback;
Examiners report
Many quality answers with marks being lost due to insufficient or erroneous details or incomplete accounts, lacking details of the type of urine produced.
