Cells have organelles to promote their cellular function and keep the cell active. For instance the mitochondria is responsible for producing ATP/energy and the lysosome is responsible for digesting materials. If there were no organelles in the cell, there will be no maintainance of homeostasis. But the organelles are able to work together to utilize food particles or other materials (oxygen, water etc) that come into the cell membrane. The way I like to think of it is that a cell works like a human body. The human body needs organs to stay alive and those organs work as a unit while having various functions. The same concept applies for the cell which has several organelles.