Acknowledging sources means providing written recognition* of any ideas that are used or adapted for students' work. WAB uses MLA citation style, which means:
The only exception is "common knowledge." Most people know, for example, that Columbus "discovered" America, that Paris is the capital of France, and that China is a communist country. Those facts are considered common knowledge, and would not need to be cited.
*'Referencing', 'citing' and 'attribution' are terms often used to refer to the acknowledgement of sources.
excerpt from: HSC: All My Own Work
http://amow.boardofstudies.nsw.edu.au/module2/module2s1.html
Ethical or not?
You have just completed a research paper for one of your science classes. On your final check, you realise that you forgot to acknowledge the source of one of the key ideas used in your paper. Worse still, you have lost the details of the source and really can't be bothered spending additional time searching for details of the source. You decide to submit the work as it is, assuming everything will be OK, because your teacher will never know.