A closed-loop aquaponics system is designed to grow tilapia fish and lettuce plants together. The system recirculates water from the fish tank, through a biofilter and a bed of plants, before returning it to the fish.
State the main form in which nitrogenous waste is excreted by freshwater fish into the water.
Explain why allowing high levels of organic fish waste to accumulate in the tank would rapidly reduce the concentration of dissolved oxygen in the water.
In many commercial systems, ultraviolet (UV) sterilisers are installed in the water filtration loop. Explain how this treatment helps to maintain healthy fish populations.
Describe how decomposers and nitrifying bacteria in the filter bed convert fish waste into accessible nutrients that promote plant growth.
Suggest how fish farmers can prevent intraspecific predation within a fish tank.
74 exam-style questions on Edexcel IGCSE Biology Food production. Each one has a worked solution and a mark scheme showing where the marks go.