Question 19M.2.HL.TZ1.6
| Date | May 2019 | Marks available | [Maximum mark: 15] | Reference code | 19M.2.HL.TZ1.6 |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Describe, Explain, Outline | Question number | 6 | Adapted from | N/A |
Outline the process of inspiration in humans.
[4]
a. diaphragm and external intercostal muscles contract ✔
b. diaphragm moves down/becomes flatter
OR
external intercostals raise the ribcage/move the ribcage up/out ✔
c. muscles/diaphragm/intercostals increase volume of thorax/expand the thorax
OR
muscles/diaphragm/intercostals decrease pressure in the thorax ✔
d. as volume «of thorax/lungs» increases the pressure decreases ✔
e. air enters «lungs» due to decreased pressure/higher pressure outside body ✔
f. air flows to lungs through trachea and bronchi/bronchioles ✔
Accept thoracic cavity or chest cavity in place of thorax in any part of the answer.
Do not allow “oxygen” instead of air in mpe or mpf.
The mechanisms used to cause ventilation of the lungs are poorly understood by many candidates, despite them being used throughout our lives. Cause and effect are often confused – air rushes in to cause a volume increase in the lungs for example.
Describe the functions of valves in the mammalian heart.
[4]
a. prevents backflow/ensures one-way flow/controls direction of flow ✔
b. open valves allow blood to flow through
OR
opening and closing of valves controls timing of blood flow «during cardiac cycle» ✔
c. closed «semilunar» valves allow ventricles/chambers to fill with blood
OR
closed «semilunar» valves allow pressure in ventricles to rise «rapidly» ✔
d. valves open when pressure is higher upstream/OWTTE/converse for closed valves ✔
e. AV/bicuspid/tricuspid/mitral valves prevent backflow from ventricle to atrium
OR
AV/bicuspid/tricuspid/mitral valves open when pressure in atrium is higher «than in the ventricle»/when atrium is pumping/contracting ✔
f. semilunar/aortic/pulmonary valves prevent backflow from artery to ventricle
OR
semilunar/aortic/pulmonary valves open when pressure in ventricle is higher «than in the artery»/when ventricle is pumping/contracting ✔
Allow mpa, mpb, mpc or mpd if the point is made through the example of one specific valve.
Most candidates got the general idea of valves in the heart preventing backflow, but many did not make any other valid points. A clear statement of what is achieved by valves opening and by valves closing was expected and then comments on the specific roles of the atrio-ventricular and the semi-lunar valves.
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.