Question 21N.2.SL.TZ0.c.i
| Date | November 2021 | Marks available | [Maximum mark: 2] | Reference code | 21N.2.SL.TZ0.c.i |
| Level | SL | Paper | 2 | Time zone | TZ0 |
| Command term | Compare and contrast | Question number | c.i | Adapted from | N/A |
The incidence of white syndrome, an infectious disease of coral, was investigated in a six-year study on Australia’s Great Barrier Reef. The map shows disease conditions on coral reefs at six study sites.
[Source: adapted from Bruno, J.F., Selig, E.R., Casey, K.S., Page, C.A., Willis, B.L., Harvell, C.D., Sweatman,
H. and Melendy, A.M., 2007. PLOS Biology, [e-journal] 5(6), e124. https://doi.org/10.1371/journal.pbio.0050124.]
Satellites were used to record sea surface temperatures. The temperatures each week above a reef were compared with mean temperatures for that week between 1985 and 2004. If the sea surface temperature was 1 °C or more above the mean, this was recorded as a weekly sea surface temperature anomaly (WSSTA). The number of WSSTAs was calculated for the twelve months preceding the date on which a reef was surveyed for white syndrome.
On each reef, the number of cases of white syndrome in a 1500 m2 sample area was surveyed once per year. The table shows these cases in relation to numbers of WSSTAs and coral cover on the reef. Low coral cover was 0–24 % and high coral cover was 50–75 %.
[Source: adapted from Bruno, J.F., Selig, E.R., Casey, K.S., Page, C.A., Willis, B.L., Harvell, C.D., Sweatman,
H. and Melendy, A.M., 2007. PLOS Biology, [e-journal] 5(6), e124. https://doi.org/10.1371/journal.pbio.0050124.]
The graphs show the relationship between the weekly sea surface temperature anomalies (WSSTA) and coral cover during two twelve-month periods (1998–99 and 2002–03), which were the warmest in the six-year study. Each dot represents one studied reef.
[Source: adapted from Bruno, J.F., Selig, E.R., Casey, K.S., Page, C.A., Willis, B.L., Harvell, C.D., Sweatman,
H. and Melendy, A.M., 2007. PLOS Biology, [e-journal] 5(6), e124. https://doi.org/10.1371/journal.pbio.0050124.]
Compare and contrast the data for 1998–1999 and 2002–2003.
[2]
Similarities
a. similar range of cover in both periods
OR
weak correlation/no correlation in either;
Differences
b. higher WSSTA range/more WSSTA in 1998–1999 than 2002–2003
OR
positive (2002–2003) versus negative correlation (98–99)
OR
more coral reefs with very low % of coral cover (0–20 %) in 2002–2003;
Must respond with one similarity and one difference for full marks.
In 1c contrasts were common, but few gained the comparison mark as well.
