Yes, all living organisms are made of at least one cell (cell theory). But, remember, viruses and prions, which cause diseases, are not technically living things, and they are NOT made of cells. Also, if asked a question similar to this on a biology test, the teacher may be trying for an answer similar to: "Organisms are made of different organ systems, which are made of various related organs, which are made of different tissues working together, which are made of cells".