Which of the following senses relies primarily on the shape and properties of molecules?

The sense that relies primarily on the shape and properties of molecules is smell. This sense, also known as olfaction, detects airborne chemical molecules that bind to olfactory receptors in the nasal cavity. Each type of receptor is tuned to specific molecular shapes, allowing the brain to identify various odors based on the shape of the interacting molecules.

When molecules enter the nasal passages, they activate these receptors, which send signals to the olfactory bulb in the brain. The unique configuration of molecules thus plays a crucial role in how we perceive different scents. This mechanism is fundamental to distinguishing a wide range of smells, making molecular structure key to olfaction.

Other senses, such as taste, do involve chemical interactions, but they rely on different mechanisms that encompass the interaction between molecules and taste receptors on the tongue rather than the direct shape of molecules. Vision depends on light waves and their interactions with the photoreceptors in the eyes, whereas hearing is based on the vibration of air particles and sound waves, which are unrelated to molecular shape.