Question 19M.2.HL.TZ1.c
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.2.HL.TZ1.c |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Explain how blood solute concentrations are kept within narrow limits in the human body.
[7]
a. solute concentration of blood monitored by the brain/hypothalamus ✔
b. pituitary gland secretes ADH ✔
c. ADH secreted when solute concentration/osmolarity is too high/a person is dehydrated/OWTTE ✔
d. collecting duct more permeable to water ✔
e. «more» aquaporins/opens aquaporins «in the plasma membrane of collecting duct cells» ✔
f. «more» water reabsorbed «into the medulla» ✔
g. medulla is hypertonic/hyperosmotic «so water can be reabsorbed from filtrate» ✔
h. small volume of urine/concentrated urine produced «with ADH» ✔
i. no/little/less ADH secreted if «blood» solute concentration is too low ✔
j. collecting duct less permeable to water/less water reabsorbed/large volume of urine produced/dilute urine produced «with low/no ADH» ✔
k. insulin causes blood glucose «concentration» to be reduced ✔
l. glucose stored as glycogen in the liver ✔
m. glucagon causes blood glucose «concentration» to be increased ✔
n. negative feedback ✔
Accept hypertonic for solute concentration too high and hypotonic for too low.
This was another question where many candidates struggled. Sub-topic 11.3 of the programme is titled ‘The kidney and osmoregulation’ but perhaps the connection was not made. A significant minority wrote only about regulation of blood sugar levels Others gave an exhaustive account of kidney function, but mostly did not have time left to write enough about osmoregulation. A small proportion of candidates gave a convincing account of the negative feedback mechanisms that keep blood solute concentrations within narrow limits.
