Life would not exist if the molecules involved did not interact in a very dynamical way. An equilibrium situation must not be reached and evolution has to be continual. This implies that life originates from interactions and bonds that are weak and have a short lifetime (1 µsec to several days) because of thermal fluctuations. Living systems endure a constant competition among these molecules that bind to each other. These molecular bonds, called ligand-receptor bonds or keylock bonds, define what is known as specific interactions. All molecules interact with each other, but, if possible, will form the strongest possible bond. It can be considered that two molecules that tend to bind in many situations are able to recognize each other. This can be observed in cell adhesion when two cells adhere because of specific molecules that they express at their surfaces. In real cells, this adhesion is usually difficult to quantify because of their complex physical properties and the high number of molecules that are present at their surfaces. However, for model cells, it is possible to quantify the adhesion and to deduce molecular properties of the bonds, even for very weak bonds. Here such a model of a cell adhering to a substrate will be presented. This model will be experimentally checked by the vesicle micromanipulation technique and applied to a bond involved in embryogenesis.