In a(n) structure, which usually is based on interpersonal relationships, some people have more influence or knowledge than appears on an organization chart.

Informal.

Explanation:

As the exercise explains, an informal structure is usually based on interpersonal relationships, and people have more influence or knowledge than appears on an organization chart. This structure is the interlocking social structure that governs how people work together in practice. It's the sum of all behavior, norms, laws, interactions and connections, attitudes, etc., through which people build their interpersonal relationships.