The part of the ear where sound is transduced is the cochlea.

The cochlea is a spiral-shaped structure located in the inner ear. It is responsible for converting sound vibrations into electrical signals that can be interpreted by the brain. This process, known as transduction, allows us to perceive and understand sounds.

Function of the cochlea:
The cochlea plays a vital role in the auditory system. It contains thousands of tiny hair cells that are responsible for transducing sound waves into electrical signals. These hair cells are arranged along the length of the cochlea and are connected to the auditory nerve.

Anatomy of the cochlea:
The cochlea is divided into three fluid-filled chambers: the scala vestibuli, the scala media, and the scala tympani. These chambers are separated by two membranes called the basilar membrane and the Reissner's membrane.

- The scala vestibuli and the scala tympani are filled with a fluid called perilymph, while the scala media is filled with a fluid called endolymph.
- The basilar membrane runs along the length of the cochlea and supports the hair cells.
- The Reissner's membrane separates the scala vestibuli from the scala media.

Transduction of sound:
When sound waves enter the ear, they cause vibrations in the tympanic membrane (eardrum). These vibrations are transmitted through the middle ear by the ear ossicles (bones) - the malleus, incus, and stapes.

The stapes, the last ossicle, is connected to the oval window, which leads to the scala vestibuli. When the oval window vibrates, it creates pressure waves in the perilymph of the scala vestibuli. These pressure waves travel through the cochlea, causing the basilar membrane to vibrate.

As the basilar membrane vibrates, the hair cells attached to it are also stimulated. The hair cells have tiny hair-like projections called stereocilia on their surface. When the basilar membrane moves, it causes the stereocilia to bend.

This bending of stereocilia opens ion channels on the hair cells, allowing ions to enter and generate electrical signals. These electrical signals are then transmitted to the auditory nerve fibers, which carry the information to the brain for interpretation.

In conclusion, the cochlea is the part of the ear where sound is transduced. Its complex structure and specialized hair cells allow for the conversion of sound vibrations into electrical signals, enabling us to perceive and understand the sounds around us.

Option D is correct answer