What describes molecules moving down to a concentration gradient

A molecule diffuses down its concentration gradient by moving from one region of higher concentration to a region of lower concentration. No energy is needed because the molecules move down a concentration gradient.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]