EduNinjaThe diagram shows levels of DDT, a pesticide, in an aquatic food web in Lake Kariba, Africa. Numbers represent ppm (parts per million) of DDT in fat tissue.
Justify the observation that the crocodile has a higher mean DDT level than the cormorant or tigerfish.
Discuss the impact of overfishing in Lake Kariba and how sustainable harvesting of resources can be assessed.
Laboratory-scale mesocosms were built to investigate the effect of very small contaminants (nanoparticles) on ramshorn snails (Planorbarius corneus).
Suggest one advantage of using a mesocosm in this type of research.
Outline the requirements for sustainability within a sealed mesocosm.
Mean annual chlorophyll concentration was measured in surface water of Narragansett Bay along the Atlantic coast of the USA, from 1971 to 2006. Field data of chlorophyll concentrations are shown below.
Mesocosm experiments using water from Narragansett Bay were completed in the laboratory during a six month period. Discuss advantages and limitations of carrying out mesocosm investigations. be marked.
The gut of a healthy human contains more than 1000 species of bacteria. Some of these species are shown in the cladogram.
Scientists have found that B. fragilis and B. stercosis are keystone species in the human gut ecosystem.
Define keystone species.
In fruit flies (Drosophila melanogaster), the allele for brown body (B) is dominant to black body (b) and the allele for long wings (L) is dominant to short wings (I). A dihybrid cross was made between a fruit fly heterozygous for both traits and a black, short-winged fruit fly, as shown in the image.
The expected and observed ratios of offspring of the cross are given.
Fruit flies are sometimes kept in enclosed glass mesocosms to study their population dynamics, genetics and interactions with the abiotic environment.
Explain the advantages of using mesocosms in these studies.
Indigenous human populations living along riverbanks in the Amazon basin often rely heavily on fish as a major part of their diet. The data shown below come from a study that was carried out to investigate levels of mercury contamination in the Rio Negro basin in Brazil. Mercury concentration was measured in fish belonging to four different trophic levels and is shown in parts per billion (ppb).
State the trophic level of the fish that presents the least risk of mercury contamination for human consumers.
Discuss how an understanding of biomagnification could help these human populations reduce their risk of mercury poisoning while maintaining their traditional diet.
Outline the features of ecosystems that make them sustainable.
Surtsey, a volcanic island approximately 32 km from the south coast of Iceland, is a new island formed by volcanic eruptions that took place from 1963 to 1967. It has been legally protected since its formation and is free from human interference.
What changes are likely to have been observed since the formation of Surtsey?
Cyclical succession as the climax community changes
Secondary succession when animal species arrived
Arrested succession due to the drainage of wetlands
Primary succession including an increase in size of plants
What occurs during primary succession?
Saprotrophs are the first to colonize bare rock.
The amount of primary production remains stable.
There is a decrease in species diversity.
There is an increase in the complexity of food webs.
Increased leaching of nitrogen fertilizers disrupts the stability of aquatic ecosystems such as lakes. What change is expected if nitrogen leaches into a lake over time?
Wilting of surface plants
Increased biochemical oxygen demand (BOD)
Weakened mollusc shells
Bioaccumulation of pollutants at higher trophic levels