Question 19M.2.HL.TZ1.6b
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.2.HL.TZ1.6b |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Describe | Question number | b | Adapted from | N/A |
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.
