What are the characteristics of a semipermeable membrane ?
A semi-permeable membrane is one which allows only a few substances to pass through it while preventing the others. The cell membrane found in the cell is a semi-permeable membrane which allows only certain substances to pass throught it.
Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.