Question

Mammals usually have an external ear or pinnae, but one of the following has no pinnae. Which one is that?
A.Echidna
B.Erinaceaus
C.Pteropus
D.Funambulus

Answer 1

Hint: We know that ear is the sense organ in our body that helps with auditory perception. Know that it also helps with body balancing. Most mammals possess pinnae that help in collecting sound from the external environment.

Complete step by step answer: We know that there are mainly three sections in the human ear. They are the outer ear, middle ear, and inner ear. The outer ear contains pinnae which are like a trumpet that helps to collect sound waves from the surroundings. Sound waves absorbed then pass through the external auditory meatus and vibrate the eardrum which is also called a tympanum. The middle ear consists of three small bones called malleus, incus, and stapes. These bony ossicles then transmit vibrations to the cochlea present in the inner ear and it helps for auditory perception by creating waves in the fluid inside the inner ear.
The external ear consists of the pinnae, ear canal, and eardrum. The ear canal is also known as the external auditory meatus that terminates in the eardrum which is also called tympanum. In the ear canal, there are several waxes secreting glands present called ceruminous glands. Pinnae absorb sound from the surroundings and its size varies in organisms. It is absent in some mammals.
Echidna that is also called spiny anteaters lacks pinnae. Instead, they have two openings that lead to the ear canal.
Hence the correct option is A.

Note:According to the size of pinnae, the ability to pick up the sound waves from the surroundings also varies.
Know that the human ear can perceive a maximum of 120 dB of intensity, although it damages our ear. It can also pick up intensities that are close to 0 dB. Know that a soft whisper has an intensity of around 30 dB.