Which of the following is not a physical force involved during cell adhesion?

In the context of cell adhesion, various physical forces play critical roles in the interactions between cells and their surrounding environment. Among these forces, Van der Waals forces, steric stabilization forces, and electrostatic forces are fundamental in facilitating the adhesion of cells to surfaces or to each other.

Van der Waals forces are weak attractions that occur between molecules, which contribute to the overall adhesion through close-range interactions. Steric stabilization refers to the repulsive forces that arise from the physical presence of bulky groups or structures, which can influence how cells adhere or interact with surfaces. Electrostatic forces involve the attraction or repulsion between charged groups, making them significant in cell adhesion since many cellular components are charged.

Gravity, on the other hand, is not a direct physical force involved in the microscopic process of cell adhesion. Although gravity affects the macroscopic behavior of biological systems, it does not contribute to the molecular or cellular interactions that dictate how cells adhere to substrates or each other. It operates on a larger scale and does not play a role in the specific forces that mediate cell adhesion. Therefore, gravity is correctly identified as the force that is not involved in the adhesive interactions at the cellular level.