How does a biologist decide when she has enough results to publish a paper?
When you do science you start with a question or a hypothesis. How is Gene A regulated? Or "does hormone B have an effect on the immune system". Or whatever.

Then you start by thinking how you can prove or disprove your question/hypothesis with experiments. You then do your experiments and see if they are enough to prove your question. It often happens that you have to do additional experiments to cover side-questions which appear during the work or to exclude some side-effects which may also be important. If you have done all this (with replicates) and looked from different angles on your problem, then you can start writing an article.

This includes some introduction from the literature and a classification of your results into the things already known. If you make strong claims, then you will need a lot of arguments (=results) to prove your point. It is quite hard to argue against "common knowledge".

The question of how much research is enough is quite philosophical, since you usually don't "finish" a topic. You look only at certain aspects from a certain angle. This can be quite different for other researchers.