| Date | November 2010 | Marks available | 1 | Reference code | 10N.3.HL.TZ0.10 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | State | Question number | 10 | Adapted from | N/A |
Question
Many factors affect the distribution of animal species including weather patterns. The mosquito Anopheles is a carrier of malaria, a disease that kills one to two million people annually. The eggs of the mosquito are laid in water and they hatch out as larvae before turning into adult mosquitoes. A study was undertaken to look at the influence of weather patterns on the incidence of bites on children. Being bitten increases the risk of catching malaria.
The graphs show human biting rates (HBR) by Anopheles gambiae and Anopheles funestus and precipitation over the study period.
State the week number when the highest human biting rate (HBR) is found for A. gambiae.
Calculate the difference in peak HBR for A. gambiae and A. funestus for week 6.
Evaluate the effect of increased precipitation on HBR for both species.
Suggest how predictions of global climate changes, such as predictions of precipitation patterns, could be used to help control malaria.
Suggest another factor which might affect the ecological distribution of mosquitoes.
Suggest a biological control that might be introduced to reduce HBR.
Markscheme
(highest HBR for Anopheles gambiae/A. gambiae week) 107/108
35 (accept answers in the range of 34 to 37)
a. both species show relationship between elevated precipitation and higher HBR (e.g. between week 0 and week 8 / week 100 and week 108);
b. there is a lag between the period of precipitation and the increase in HBR;
c. sometimes elevated precipitation does not lead to peaks of HBR (e.g. week 27);
d. precipitation has a greater effect on Anopheles gambiae/A. gambiae;
a. spraying insecticides just before rainy seasons;
b. draining swamps before (and after) rain;
c. providing (endangered) population with repellents/mosquito nets before rainy season;
temperature / breeding site / food supply / predators / other reasonable answer
Do not accept global warming.
a. using natural predators of mosquitoes;
b. using natural pathogens of mosquitoes;
c. introduction of sterile males;
d. setting traps baited with mosquito pheromones/hormones;
Examiners report
About half of the candidates could relate the peaks at different times. Most read the week well and calculated the difference in peaks well, but the evaluation of the effect of increased precipitation was poor.
About half of the candidates could relate the peaks at different times. Most read the week well and calculated the difference in peaks well, but the evaluation of the effect of increased precipitation was poor.
About half of the candidates could relate the peaks at different times. Most read the week well and calculated the difference in peaks well, but the evaluation of the effect of increased precipitation was poor.
About half of the candidates could relate the peaks at different times. Most read the week well and calculated the difference in peaks well, but the evaluation of the effect of increased precipitation was poor.
About half of the candidates could relate the peaks at different times. Most read the week well and calculated the difference in peaks well, but the evaluation of the effect of increased precipitation was poor.
About half of the candidates could relate the peaks at different times. Most read the week well and calculated the difference in peaks well, but the evaluation of the effect of increased precipitation was poor.
