many food particles are polar. how do these get into the cell?
When we talk about polar objects in the cell, they are not big enough to be considered food. Food particles and particles that are transported in and out of the cell are not the same. Polar particles in the are transported through the membrane gates and receptors. These gates and receptors are located on the membrane of the protein, but they are very selective. Only certain types of particles are allowed into the cell. The gates need to recognize the particle. This process is analogous to lock and key. This occurs by the particle (key) fitting into a pocket on the receptor (lock). Once the cell recognizes the key, the cell allows the polar particle to travel through the membrane. Sometimes these particles need to transported with more than one molecule. This is called cotransport. There many other kinds of transport that occurs in the cell membrane that allows for the transport of polar molecules. For the most part, the cell has specific gates that allow these particles into the cell.