Electrolyte balance is NOT necessary for maintaining homeostasis in the body.

A. Microvilli: Microvilli are tiny, finger-like projections on the apical surface of some cells, especially in the small intestine. They increase the surface area of the plasma membrane, allowing the cell to absorb more nutrients efficiently.

B. Stereocilia: Stereocilia are long, non-motile projections found in certain specialized cells, such as in the epididymis, and are primarily involved in mechanosensation and absorption, but they are less widespread than microvilli.

C. Primary cilia: Primary cilia are single, non-motile organelles present on many cells that function mainly as sensory structures to detect environmental signals rather than increase nutrient absorption.

D. Flagella: Flagella are long, whip-like structures used for cell motility, such as in sperm cells. They do not contribute significantly to nutrient absorption.

Resting membrane potential arises from the uneven distribution of ions, primarily sodium (Na⁺) and potassium (K⁺), across the plasma membrane. Potassium tends to leak out of the cell while sodium remains higher outside, creating a negative charge inside relative to the outside. This separation of charges generates electrical potential energy while the cell is at rest.