The circulatory system of a whale is considered an organ system because it is composed of different a. cells. b. tissues. c. organs. d. molecules. e. heart.

organs

Explanation:the body of multicellular organisms are organised into levels of organization.these levels increases in complexity.

The macromolecules makes up the organelles . organelles in turn makes up the cell.A group of similar cells at a certain location makes up an organ.for example the heart consists of a number of cells.

A group of organs which work together to achieve a specific function in the body , makes up the organs system.

For example the circulatory system of a while is made up of different connected organs - heart, blood vessels,to perform the function of transporting blood around it's body.this makes it an organ system.