Mechanical investigations of biological materials are becoming increasingly important in the study of organismic and evolutionary ecology. Such studies help to explain how and why organisms evolve and exist today, and address some questions of scale (e.g., how big can a tree or mammal grow?). These ideas and questions often intrigue biology students, but rarely are they exposed to the measurements and principles underlying the mechanics of biological structures. We present a simple technique to measure an important biomechanical feature of tissues, namely tissue stiffness or elastic modulus, that is used to determine the strength and durability of biological structures. Using this technique on tubers of Russet Burbank potatoes (Solanum tuberosum), the elastic (or Young's) modulus (E) ranged from 1.08 to 14.15 MPa. This was well within the range reported for this plant material. We suggest several experimental manipulations and provide results for one of these which can be easily conducted in an A-level or early university 3-hour teaching practical (or laboratory).