| Date | May 2015 | Marks available | 1 | Reference code | 15M.2.SL.TZ2.1 |
| Level | Standard level | Paper | Paper 2 | Time zone | Time zone 2 |
| Command term | Predict | Question number | 1 | Adapted from | N/A |
Question
Malaria is a mosquito-borne disease caused by a unicellular organism, Plasmodium. Plasmodium is a parasite that spends part of its life in a mosquito and part in a human. The mosquito transmits the Plasmodium to a human when it feeds on human blood. Mosquitoes hatch in water and are flying insects as adults. In the country of Belize, where malaria is a serious problem, studies have been made to determine what environmental factors affect the incidence of the disease. 156 villages were studied over a ten-year period.
Each of the six districts of Belize was studied from 1989 to 1999. The graph shows the mean number of people in each district to be affected by malaria per year per 1000 people.
The country of Belize has many different ecosystems. These ecosystems are shown in the bar chart. The white bars indicate the total area within each ecosystem with the lowest incidence of malaria. The dark grey bars indicate the total area within each ecosystem with the highest incidence of malaria. The total area with an intermediate incidence of malaria is not shown.
State the district where there is the highest number of villages with the highest incidence of malaria.
Analyse the data in the map to find whether there is an association between rivers and the incidence of malaria.
Compare the trends in incidence of malaria for Toledo and Corozal.
Suggest a reason for the decreases in the incidence of malaria from 1995 to 1999.
Suggest a reason why the incidence of malaria is so low in the Belize District.
Besides farmland, identify which two ecosystems have the greatest total area with a high incidence of malaria.
Predict with a reason, using the data, which district has most farmland.
Discuss whether malaria could be reduced by replacing farmland with natural ecosystems and replacing broadleaf hill forest with mixed hill forest.
Markscheme
Toledo
a. in Cayo and/or Toledo the high incidence seems to be associated with rivers;
b. however, along one river in Toledo there is no high incidence;
c. in Belize District there is low incidence along the river / high incidence away from the river;
d. Orange Walk/Stan Creek there is no clear association;
e. (consequently) association of rivers with high incidence of malaria is inconclusive OWTTE;
a. both are stable from 1989 to 1992;
b. both see upward spike in 1992;
c. Corozal reaches its peak (one year) earlier / vice versa;
d. Toledo rises after 1998 but Corozal continues to decline / Corozal at the end decreases almost to 0, while Toledo still have incidence at the end of the decade;
e. Toledo has a higher incidence (throughout the decade) / vice versa;
f. Toledo changes more rapidly than Corozal / vice versa;
Do not award numerical comparisons.
insecticides used to kill mosquitoes / more anti malarial drugs / drought/less water for mosquito breeding / increased drainage / improved education / more mosquito nets / other reasonable change in conditions
Do not accept vaccines as they do not exist.
drier climate/less rainfall / more predators / vegetation/ecology not favourable to mosquitoes / higher rainfall so faster flowing rivers/more educated inhabitants so more aware of dangers.
lowland broadleaf forest and broadleaf hill forests (both required)
Toledo because it has the highest incidence of malaria in map/graph (and farmland has highest correlation to incidence of malaria in the table).
a. if farming provides habitat for mosquitoes, then reducing it could reduce malaria / OWTTE;
b. natural habitats provide predators, but farmland does not;
c. changing native vegetation is not practical since plants are adapted to their environment/organisms have specific adaptations to their environments;
d. might work to change broadleaf forest into mixed hill forest as much of broadleaf forest has high incidence of malaria and no part of mixed hill forest has high incidence of malaria / OWTTE;
e. loss of habitat/loss of biodiversity results in less stable environment;
f. the value of maintaining natural habitat must be balanced with the value of reduced malaria;
g. farmland feeds the population, so cannot be replaced / OWTTE
Examiners report
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept. Others felt that it was too biased towards geography due to the map analysis. Really the map reading required should have been within the capabilities of all students. Perhaps a geography student may have been at some advantage, but it could be argued that sometimes a chemistry student is advantaged in other years.
Nearly all students identified Toledo correctly.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept. Others felt that it was too biased towards geography due to the map analysis. Really the map reading required should have been within the capabilities of all students. Perhaps a geography student may have been at some advantage, but it could be argued that sometimes a chemistry student is advantaged in other years.
Good candidates were able to analyse the data, quoting specific districts. Weaker ones did not mention any districts or tried to make the data fit the association.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept.
Better students were able to compare the trends correctly and easily scored all three marks. Weaker students wrote about Toledo and then Corazol, hoping that the examiner would make the comparison for them. Very weak students just quoted numbers without considering trends. There were some G2 comments that it was difficult to make out the lines. However the students seemed to have no trouble, and some well organized students drew over it to highlight the correct line.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept.
In part (i) an answer in terms of reducing the number of mosquitos or an increase in education about mosquitos was looked for. Simply "the mosquito population went down" was not deemed good enough; it needed a because… or due to…. Similarly in part (ii) "fewer mosquitoes" was too weak. Vaccines are nowadays near to becoming a reality, but certainly did not exist between 1995-1999. Similarly cures for malaria, and an increase in the number with sickle cell forest were discounted.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept.
In part (i) an answer in terms of reducing the number of mosquitos or an increase in education about mosquitos was looked for. Simply "the mosquito population went down" was not deemed good enough; it needed a because… or due to….. Similarly in part (ii) "fewer mosquitoes" was too weak. Vaccines are nowadays near to becoming a reality, but certainly did not exist between 1995-1999. Similarly cures for malaria, and an increase in the number with sickle cell forest were discounted.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept.
Nearly everyone gave broadleaf forest and broadleaf hill forest.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept.
Most correctly stated Toledo with the correct reason.
Some G2 comments seemed to think that Question 1 was too long, containing too many marks for one concept.
This proved to be a testing question, and as several pointed out, would have benefitted from a larger answer box as it was worth 4 marks. Many gained the mark for pointing out that if farming does provide the habitat for mosquitoes, then replacing would be beneficial, and that no part of mixed hill forest has high incidence, so that could work. Few got beyond these and discussed biodiversity and adaptation.
