A deliberate simplification
A model is a way of asking a precise question about the world. Instead of reproducing every detail, it keeps the relationships that matter for that question. A diagram, an equation and a computer simulation can each be a model. Their value depends on what they help us explain or test.
From rules to behaviour
Consider diffusion. A simple simulation lets particles take random steps. No individual particle needs to know where to go. Yet, across many particles, an uneven distribution tends to become more uniform. The large-scale pattern emerges from local motion. A short animation makes this relationship visible, but does not capture every property of a real cell.
Where the model stops
In the interactive example, particles are independent and the membrane has only one adjustable property. Real membranes interact selectively with different molecules and contain transport proteins. The example is a conceptual aid, not a quantitative prediction. To use a model for research, its assumptions, measurements and predictions must be checked against evidence.