system
Given the following post, respond as if you're commenting on Reddit:
human
How does mold on a bathroom counter get its food source?

One time I was at a public bathroom and noticed some mold growing under neath the tub that made up the sink, and it got me thinking. The mold probably isn't using the porcelain counter top as a source of food, but there's no obvious sign of organic material or glucose anywhere. And it is growing from a place where sunlight could not reach it.

 How does it grow and sustain itself?
gpt
Molds are a type of fungi and don't rely on photosynthesis for energy. In fact, UV radiation actually inhibits mold growth (so they thrive in dark places). 

They release enzymes to break down organic material (the bathroom counter is likely covered in dead bacteria, dead skin cells, etc...). They then use this digested material as their energy source. 

Lastly, they require a lot of moisture. Molds grow best in damp or humid areas. There would be lots of water from the sink to help them grow. 

(Currently a Master's student in biology)