Question 19M.2.HL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.2.HL.TZ1.b |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Outline | Question number | b | Adapted from | N/A |
Outline the causes of sickle cell anemia.
[2]
a. genetic disease/caused by a gene
OR
inherited «from parents»
OR
caused by mutation «of a gene» ✔
b. base substitution
OR
GAG → GTG ✔
c. hemoglobin gene mutated / different allele/form/version of hemoglobin gene
OR
HbA → HbS ✔
d. leads to change in amino acid sequence «in hemoglobin»
OR
glutamic acid → valine ✔
e. only homozygotes have full disease/sickled cells / heterozygote has milder form
OR
hemoglobin crystallizes at low oxygen concentration ✔
f. «selected for/spreads in population» as it gives resistance to malaria ✔
This question also elicited a wide range of answers. Some were accurate and detailed but some showed no knowledge of this genetic disease. There was lack of clarity in many answers, for example the disease was described as the mutation and sickling of cells was known but not linked to haemoglobin. The weakest answers tended to describe anemia in general, with iron deficiency sometimes given as the cause.
