| Date | November 2016 | Marks available | 1 | Reference code | 16N.3.SL.TZ0.14 |
| Level | Standard level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Outline | Question number | 14 | Adapted from | N/A |
Question
In 1997 in South Africa, a decision was made to decrease the use of mosquito-killing pesticides due to their negative effect on the environment. Mosquitoes are known to be responsible for the spread of malaria. In 2001 the decision was reversed and the use of pesticides was increased. The graph shows the estimated numbers of people with malaria in each year.
Outline the trend in the number of people with malaria during the period when the use of pesticides was decreased in South Africa.
One pesticide used in killing mosquitoes was DDT. Considering its harmful effects, discuss whether the decision to reintroduce it was justified.
Markscheme
the number of people with malaria increased
a. choice has to be made between damage to environment or increase in malaria
b. DT may lead to biomagnification/bioaccumulation in food chains
OR
taken up by species in lower trophic levels becoming more concentrated at higher trophic levels
c. causes harm to consumers at end of food chain
OR
example «eg: thin egg shells of falcons»
d. DDT is shown to be effective in reducing malaria
e. possible partial solution to be selective in areas sprayed with DDT
f. may kill insects that are not pests
Examiners report
Syllabus sections
- 17N.3.HL.TZ0.15b: State how the population of M. gallopavo may have been determined.
- 19M.3.SL.TZ1.11c: Suggest one way in which depth may act as a limiting factor for coral.
-
16N.3.HL.TZ0.17a:
State two bottom-up factors affecting algal blooms.
- 18M.3.SL.TZ1.12c: State one method that could be used to estimate the isopod population size.
-
19M.3.HL.TZ2.16a:
Explain the factors that can contribute to the exponential growth phase in a sigmoid population curve.
- 16N.3.HL.TZ0.16a: Describe one method that could have been used to estimate the population size of a given tree...
- 17N.3.HL.TZ0.15a.i: State the range of years when exponential growth of the M. gallopavo population occurred.
- 18M.3.HL.TZ1.17a.ii: Suggest one possible cause for the decrease of the number of animals after 1940.
- 17M.3.HL.TZ2.15e: Explain how an excessive growth of algae on coral reefs can be controlled by top-down factors.
- 18M.3.HL.TZ2.15c: Explain how nutrients can have a positive or negative bottom-up effect on seagrass.
- 18M.3.HL.TZ1.17a.i: State the type of growth of this population up to 1940.
- 17M.3.HL.TZ1.17: Discuss the factors affecting population growth that can result in an exponential growth curve.
-
19N.3.HL.TZ0.18:
Explain the technique used to estimate the population size of a named species of organism that is able to move.
-
19M.3.HL.TZ1.19:
The garden snail, Helix aspersa, is a herbivore.
[Source: Sinan Önder /https://www.pexels.com/photo/animal-close-up-crawling-garden-243128/]
Explain how the population of snails in an ecosystem could be estimated by capture-mark-release-recapture, identifying the limitations in the method.
- 16N.3.HL.TZ0.17b: Explain how top-down factors control algal blooms.
- 19M.3.HL.TZ2.16b: Outline the effect of carrying capacity on the growth of a population.
-
17N.3.HL.TZ0.15a.ii:
Suggest factors that could account for the growth curve of the M. gallopavo population.
-
17N.3.HL.TZ0.15c:
Hunting of M. gallopavo is currently regulated. Predict what would happen if the hunting regulations were removed.
