Question 19M.2.SL.TZ2.7c
| Date | May 2019 | Marks available | [Maximum mark: 8] | Reference code | 19M.2.SL.TZ2.7c |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Explain | Question number | c | Adapted from | N/A |
Explain the cause of sickle cell anemia and how this disease affects humans.
[8]
a. caused by a single nucleotide/base substitution mutation/GAG to GTG ✔
b. «mutation of» a gene of β-globin/a subunit of hemoglobin ✔
c. mRNA copies the mutation of DNA and substitutes an amino acid in hemoglobin «subunit» ✔
d. glutamic acid is substituted by valine ✔
e. sickle cell anemia involves distorted hemoglobin protein/HbS ✔
f. «distorted HbS causes» distortion/sickling/shape change of red blood cells ✔
g. «distorted/sickled red blood cells» block capillaries/blood flow ✔
h. HbS/sickled red blood cells cannot carry enough oxygen «for the body»/leads to fatigue ✔
i. low oxygen concentration seriously affects structure of HbS ✔
j. homozygous «HbS/HbS» state causes severe anemia/death at low oxygen concentrations ✔
k. heterozygous state has less anemia/minor effects/less effect of structure of hemoglobin
OR
heterozygous state only affected at high altitude/extreme exercise/low levels of oxygen ✔
l. «heterozygous state» provides protection against malaria parasite/selective advantage in malaria areas ✔
OWTTE
This question was well answered. The mutation and its impact was well understood by most. The genetic causes were less frequently discussed.
