Question

state one reason that food must digest before they can enter a cell

Answer 1

Well the food has to be broken up so the proteins/vitamins/glucose whatever can enter the cell. It just won't be accepted/absorbed if it's not in the right form.
Hope this helps, and happy studying~!
~{Dunsforhands}

Answer 2

The particals are too large and must be broken down into smaller parts before entering the cell