The inability to maintain proper balance of the body in humans may be due to a defect in the

Analyze the question: It asks which part of the ear is responsible for balance (equilibrium). A defect there would make a person unable to keep the body balanced.

Explain the concept: The human ear has three main parts, and each has its own job.

• Outer ear: collects sound waves.
• Middle ear: transmits and amplifies vibrations. It contains the ear ossicles (malleus, incus, stapes), the oval window, and the Eustachian tube.
• Inner ear: contains the cochlea (hearing) and the semi-circular canals with the utricle and saccule (balance).

Check each option:

• A. Cochlea: a coiled tube containing sound receptors. It is for hearing, not balance.
• B. Eustachian tube: connects the middle ear to the pharynx. It equalizes air pressure on both sides of the eardrum.
• C. Semi-circular canals: three fluid-filled canals set at right angles to each other. They detect head rotation and movement, and send signals to the brain to help keep balance and posture.
• D. Oval window: a membrane that passes vibrations from the stapes to the fluid in the inner ear. It is part of hearing.

Answer: The semi-circular canals are the organs of balance, so a defect in them would cause loss of balance.

Exam tip: Remember "Cochlea = Catching sound" and "Semi-circular = Stability". When a question mentions balance, equilibrium, or dizziness, think semi-circular canals (and the utricle and saccule).