1. The property of a cell, tissue, or organism of being structurally and/or functionally different at opposite ends of its long axis. For example, plants consist of roots, which grow in the direction of the force of gravity, and stems, which grow away from the gravitational force (see geotropism). In developing insect embryos, the anterior-posterior polarity of larval body segments is determined by segment polarity genes. (see segmentation genes). See also animal pole.

2. The property of molecules of having an uneven distribution of electrons, so that one part has a positive charge and the other a negative charge. Such polar molecules include water.