The answer is diffusion.
Facilitated diffusion is a process by which molecules are transported across the plasma membrane with the help of membrane proteins.
Answer:
a. A hypothesis that does not generate a testable prediction is not useful.
Explanation:
In the scientific method, we generate a hypothesis to explain a phenomenon. After this, it is necessary to create a method to test the hypothesis and make predictions. Moving forward, we test this methodology, generating results and reject or not reject the hypothesis. If the hypothesis can't be tested, the scientific method can't be applied.
To control,maintain a rate or speed