Difference between sectional and public interest groups?

Sectional Interest Groups: These are the people who work in the interest of particular section or society of people. They represent only that specific section of society and work or promote the interests and demands of that section for the betterment of section. Example: Trade Unions, Business Unions. There are associations of teachers, doctors etc

Public Interest Groups: These are people of the group that do not represent just one section rather represent the entire public. Their demands are collective that is they promote the interest that would benefit everyone. Example: Backward and Minority Communities Employees Federation, they work in the direction of eliminating discrimination from the working organizations.