Based on the additional tests, it appears that the function f(x) is more selective for words related to physical processes, particularly those that involve some form of change (like "folding", "melting") or biological concepts (like "biology", "bacteria", "apple", "carrot", "cucumber").

[DESCRIPTION]: The function f(x) is more selective for words that are related to physical processes, involving change or biological concepts, assigning higher values to these words.