The United State's International Trade Commission and the United State's Treasury are in charge of the United State's imports. They have the ability to apply tariffs (through congress), remove tariffs, limit the importation of certain goods (sheltering the US private sector), or even outright import bans.
Arne Duncan is the United States Secretary of Education. It is this role that is defined as the person in charge of the United States Department of Education.
The attorney general is the head of the United States Department of Justice.
USDA - the United States Department of Agriculture.
In the United States, the Attorney General is a cabinet level position. The Attorney General is in charge of the US Justice Department.
The United States Department of Defense is part of the executive branch of the United States government. The head of the Department of Defense is the Secretary of Defense, who is a member of the President's cabinet. Other countries have their own equivalents, which are usually presided over by a Minister of Defense.
The person that is in charge of the United States of America is the President of the United States.
The weather bureau is typically under the jurisdiction of the country's meteorological department or agency, such as the National Weather Service in the United States or the Met Office in the United Kingdom.
The Secretary of State is in charge of encouraging trade with other countries and the United States. The Department of Commerce deals with trade among states.
Federal prisons are jurisdiction of the Bureau of Prisons, and is subordinate to the United States Department of Justice. At state level, they're usually maintained by the Department of Corrections, which will normally be subordinate to the state Department of Justice or Department of Public Safety.
The Vice President of the United States is in charge of the U.S. Senate.
The United States Department of the Treasury is in charge of proposing new currency. It is part of the Executive Branch.
The IRS is the Internal Revenue Service. It is an agency inside the United States Department of the Treasury that is in charge of administering the tax laws of the United States. Since the IRS is in charge of collecting federal taxes, some people refer to federal taxes as IRS taxes. While this is not strictly wrong, it sounds ignorant.