Date | May 2019 | Marks available | 2 | Reference code | 19M.3.SL.TZ1.15 |
Level | Standard level | Paper | Paper 3 | Time zone | Time zone 1 |
Command term | Suggest | Question number | 15 | Adapted from | N/A |
Question
Vitamin D is converted from an inactive form to an active form by exposure to sunlight. The graph shows the mortality (death rate) from falls in women over 75 as a function of latitude (distance from the equator).
[Source: Food and Agriculture Organization of the United Nations, 1997, B E C Nordin,
Calcium in Health and Disease, www.fao.org/3/W7336T/w7336t04.htm#calcium%20in%20health%20
and%20disease. Reproduced with permission]
Vitamin D deficiency can cause low blood calcium concentrations (hypocalcemia). Very low blood calcium can have an impact on heart function. The first ECG is for a patient with normal blood calcium concentrations. The second ECG is for a patient who has very low blood calcium concentrations.
[Source: © International Baccalaureate Organization 2019]
Osteomalacia is a condition that can be caused by Vitamin D deficiency. Outline one effect of osteomalacia.
Outline the relationship shown in the graph.
Suggest reasons for this relationship.
Compare and contrast the two ECG traces.
Outline one event that occurs in the heart during the T wave.
Markscheme
softened/weakened bones/bone pain/increased fractures/difficulty walking/stunted growth ✔
a. direct relationship/positive correlation ✔
b. increased latitude, higher mortality from falls ✔
Or vice versa
a. higher latitude, lower levels of sunlight ✔
b. less uptake of calcium
OR
less vitamin D ✔
c. higher incidence of osteomalacia leads to higher risk of broken bones/mortality ✔
compare:
a. no difference in the P wave/QRS wave
OR
both traces have all 4 waves/PQRST ✔
contrast:
b. delayed T wave
OR
T wave is shorter/higher in hypocalcemia ✔
Allow reference to events in the cardiac cycle for mpa or mpb
Allow converse statements for mpb.
a. repolarization of ventricles ✔
b. ventricles are in diastole/relaxation ✔
Examiners report
Osteomalacia producing weak bones was a common answer. Low calcium levels were also mentioned but this is a cause not an effect of osteomalacia.
Nearly all candidates recognized a positive correlation.
Lack of sunlight leading to less Vitamin D was the most common answer here. Calcium was rarely mentioned.
A difference between the traces was more often seen than a similarity, although many candidates gained the two marks.
Many candidates did not know that ventricular diastole occurs during the T wave.