Answer;
The substance that can enter a cell by diffusion without having to be digested is water.
Step-by-step explanation;
Diffusion involves the movement of molecules from a region of high concentration to a region of low concentration, down a concentration gradient.
Water is able to diffuse through the cell membrane without being digested since it has small molecules.
One property of cell membrane is semi-permeability; it selectively allows material to enter or leave the cell. Large molecules such as starch , fat and proteins, can not enter the cell due to their size and will need to be digested to small molecules for the to gain access to the cell.