Answer: By means of a carrier protein
Explanation:
There are 3 different types of ways in which molecules are transported across the cell membrane.
Diffusion (passive transport) , Active transport and facillitated transport
Since the cell membrane is semi-permeable,meaning, it only allows certain molecules to cross it so therefore some molecules can easily cross the membrane while others cant.
Small molecules such as water make use of Active and passive transport to cross the plasma membrane.
Large molecules such as glucose or ions cannot simply move across the membrane and therefore makes use of facillitated diffusion
Facillitated diffusion uses a carrier protein or channel protein which will bind to the ion or large molecule, whereby it will alter its shape in order to cross the cell membrane more easily.
