Why are models used for understanding cells

Because when you use a model you can see the cells and understand where they are located and how they work. Also a model helps you visual because you can't see cells so a model helps.

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water