Sort the phrases based on whether they describe or give an example of facilitated diffusion, active transport, or both.
- movement assisted by proteins
- movement to area of lower concentration
- sodium ion transport out of cell
- movement across a membrane
- glucose transport into muscle cell
- requires energy

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.