How do plants and animals adapt in the freshwater biome?
The simple answer is, by a process of natural selection.
According to modern biological theory, species change over time (evolve, or adapt) by a process of selection, meaning the best adapted individuals survive and reproduce more successfully.
In a sense, whether we are talking about freshwater biomes or any other biome, is irrelevant as the underlying process is the same everywhere.
The question becomes, what challenges do plants, and animals face in a freshwater biome? These include, for plants-
obtaining water in drought
obtaining sufficient minerals and light
(typically) avoiding being washed away in rivers
For animals the answers include obtaining food, avoiding being predated on and finding a mate