Growing plant roots can exert stress or pressure on rock. Although the process is physical, the pressure is exerted by a biological process (i.e., growing roots). Burrowing animals can also move rocks which hit against each other; hence leading to weathering
Biological processes can produce chemical weathering, for example where plant roots or microorganisms produce organic acids which help to dissolve minerals. Microbial activity breaks down rock minerals by altering the rock's chemical composition, thus making it more susceptible to weathering.
