That would be called a source or head water
Not always. It just depends on if the traits stay the same
Answer:
Nutrients and other materials from the environment are absorbed through mycelia. The branching mycelia have a high surface-area-to-volume ratio which allows the absorption of nutrients to be more efficient. Fungi may even digest nutrients by releasing enzymes into the environment.
Explanation:
I have a strange feeling that this isn't the answer you were looking for.