Final answer:
Receptors close to the apex of the cochlea will respond to a tone of 20 Hz, as they are sensitive to low-frequency sounds within the human hearing range of 20 Hz to 20,000 Hz.
Step-by-step explanation:
The human tonotopic map illustrates how different parts of the cochlea respond to different frequencies of sound. The receptors close to the apex of the cochlea, which are tuned to low frequencies, will respond to a tone of 20 Hz. This is due to the cochlea's ability to encode auditory stimuli across a spectrum of frequencies, ranging from 20 Hz to 20,000 Hz. Hair cells at the apex of the cochlea are responsible for detecting these low-frequency sounds. As the frequency rises, hair cells positioned closer to the base, near the round and oval windows of the cochlea, detect these sounds. This separation of frequencies by the cochlea functions much like a prism separates light into a spectrum of colors. It's important to note that the lowest frequencies humans can hear, starting at 20 Hz, are detected at the apex of the cochlea.