The concentration of DDT at different trophic levels of the food chain.
Figure 1: Levels of concentration of DDT in food chain
State the main source of energy for the food chain in Figure 1.
Sun/sunlight/insolation/solar energy
State the trophic level labelled X in Figure 1.
(primary) producer / autotrophs / phototrophs / phytoplankton / green plants
The command term “State” requires a “specific name” so do not credit “trophic level 1”.
Identify one use of DDT that has led to its presence in the environment.
insecticide/pesticide / kill pests/insects / control malarial mosquitoes / plague / OWTTE
With reference to the concepts of bioaccumulation and biomagnification, outline how the concentration of DDT has changed along the food chain.
-
bioaccumulation: DDT absorbed by a given trophic level is not broken down/excreted / is non-biodegradable so accumulates in tissues
1 mark -
biomagnification: the concentration of DDT will increase as it’s passed along/up food chain (because other biomass is lost)
1 mark
Do not allow simply “organisms at higher levels eat/consume more”. Higher trophic levels do not consume more biomass in a given time than lower trophic levels.
State the relationship between large and small fish in Figure 1.
Outline how this relationship may be of benefit to the populations of both species.
- the predator benefits by gaining food from prey / its population is limited/stabilized by amount of prey available
1 mark - they prey benefits by predators limiting/stabilizing its population / selecting out weaker/diseased individuals / maintaining healthy gene pool in prey / reducing competition in prey for available food/resources
1 mark
Award full marks is response describes negative feedback between both populations, or indicates that each group regulates population of the other.
