What is a Scientific Fact?

Facts must not be believed for what they are, but for what they explain.

It is said that half of the information in a science textbook is outdated within a few decades. So what then constitutes a scientific fact? From the point of view of outdated science textbooks, it can be concluded that biology is a historical science, i.e., a scientific fact has a history and could not be understood without understanding its history. The changing knowledge in science is the result of refutations or the falsification of a theory (see Karl Popper).

What has not been refuted can be considered a scientific fact. This is a functional definition and pays tribute to the 'fact' that knowledge changes with time, and it is exactly this historical starting point that will be adhered to most rigorously here. When looking beyond the physical sciences, theories often lack mathematical formalism. So how do we get hold of a fact? What is there that defines the relationship between hypothesis, experiment and theory? 

One example from the biological sciences shall shed light on the process of acquiring scientific knowledge as we will gain hold on the concept of a 'scientific fact' in the process. The example offered here is about the currently accepted model of the structure of biological cell membranes. 

The cell membrane as a scientific fact