Question 19M.3.SL.TZ1.15
| Date | May 2019 | Marks available | [Maximum mark: 7] | Reference code | 19M.3.SL.TZ1.15 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Compare and contrast, Outline, Suggest | Question number | 15 | Adapted from | N/A |
Osteomalacia is a condition that can be caused by Vitamin D deficiency. Outline one effect of osteomalacia.
[1]
softened/weakened bones/bone pain/increased fractures/difficulty walking/stunted growth ✔
Osteomalacia producing weak bones was a common answer. Low calcium levels were also mentioned but this is a cause not an effect of osteomalacia.
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]
Outline the relationship shown in the graph.
[1]
a. direct relationship/positive correlation ✔
b. increased latitude, higher mortality from falls ✔
Or vice versa
Nearly all candidates recognized a positive correlation.
Suggest reasons for this relationship.
[2]
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 ✔
Lack of sunlight leading to less Vitamin D was the most common answer here. Calcium was rarely mentioned.
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]
Compare and contrast the two ECG traces.
[2]
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 difference between the traces was more often seen than a similarity, although many candidates gained the two marks.
Outline one event that occurs in the heart during the T wave.
[1]
a. repolarization of ventricles ✔
b. ventricles are in diastole/relaxation ✔
Many candidates did not know that ventricular diastole occurs during the T wave.