which substances does the cell allow in
Through these channels, some substances such as hormones or ions are allowed to pass through. They either are recognized by a receptor (a protein molecule) within the cell membrane, or they attach to a carrier molecule, which is allowed through the channels.he plasma membrane surrounding animal cells is where the exchange of substances inside and outside of cells takes place. Some substances need to move from the extracellular fluid outside cells to the inside of the cell, and some substances need to move from the inside of the cell to the extracellular fluid.