Question

Endolymph contains white crystals of CaCO$_3$, called as
A. Otoconia
B. Otoliths
C. Ear dust
D. Both A and B

Answer 1

Hint: The membranous labyrinth of the inner ear is filled with a fluid called endolymph. Potassium is the major cation present in the endolymph along with sodium. a membranous labyrinth refers to the inner portion of the ear that consists of fluid-filled tubes and chambers.

Complete answer: Human ear consists of three parts called external ear or pinna, middle ear, and inner ear. The inner ear is made up of two parts: the membranous labyrinth and the bony labyrinth. The membranous labyrinth of the inner ear is filled with a fluid called endolymph. A fluid called perilymph is present in the space between the wall of the bony labyrinth and the outer wall of the membranous labyrinth. Endolymph contains white crystals of CaCO$_3$ called otoconia or otoliths. Otolith is a structure made up of calcium carbonate present in the saccule of the utricle of the inner ear. The utricle and saccule together make the otolith organ. Otoliths are tiny particles that are made up of calcium carbonate and gelatinous matrix in the viscous fluid endolymph of the utricle and saccule. The hair cells are stimulated by the inertia of these small particles when the head moves. Otoliths are used as movement, balance, gravity, and directional indicators in all vertebrates. The secondary function of otoliths is to detect the sound in higher aquatic and terrestrial vertebrates.

So, option D is the correct option.

Note: An otolith is also known as otoconium or statconium or statolith. This organ is responsible to perceive the linear acceleration, both vertically and horizontally in all organisms including humans. In invertebrates, the same analogous structure called statocysts is found to perceive the linear acceleration.