Here's why:

* Cell Theory: A fundamental principle in biology states that all living organisms are made up of cells. This applies to plants, animals, fungi, bacteria, and even some viruses.

* Exceptions: The only exceptions to this rule are some very simple, non-cellular life forms, like viruses and prions. These are not considered "true" organisms because they lack the ability to reproduce independently and rely on host cells for their survival.

So, while some primitive plants do exist (like algae), the statement is generally true.