The diagram shows a fish farm using floating cages in a lake. Pellets are added as food for trout. Some uneaten pellets and fish waste sink beneath the cage...
Question 1 Report
The diagram shows a fish farm using floating cages in a lake. Pellets are added as food for trout. Some uneaten pellets and fish waste sink beneath the cages, where bacteria use them as food. The farm manager monitors oxygen concentration because low oxygen can kill fish and other aquatic organisms.
(a) State the source of food energy for the trout. [1]
(b) Describe what bacteria do to uneaten pellets and fish waste. [2]
(c) Explain why a large increase in bacteria can lower the oxygen concentration of the water. [2]
(d) Suggest one action the manager could take to reduce this problem. [2]
Answer Details
(a) The source of food energy for trout is the food pellets. [1]
(b) Bacteria decompose or break down the uneaten pellets and fish waste. They release enzymes onto the material and absorb the soluble digestion products. [2]
(c) Bacteria respire as they break down the waste. Respiration uses oxygen dissolved in the water, so a large bacterial population can lower oxygen concentration. [2]
(d) The manager could add less food and avoid overfeeding, so less waste reaches the lake bed. Another suitable action is to remove waste, reduce fish numbers, or improve water flow or aeration. [2]
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