As far as I know you are allowed to use questions as chapter headings (i did last year and got band 6).
However, I would tend to only use a question as a chapter heading when there is no set answer to the question you are asking (eg. in a chapter where you are discussing several different possible answers to the posed question).
In most other circumstances, I think it would be better to rephrase your question into a statement.
eg.
What is the defintion of cyberbulling and what are the effects? could become:
The effects of cyberbulling on (whatever your subject matter eg. young people, society etc.)
Also, instead of putting "what is the definition" etc. in the title, I think it would seem more academic to include the definiton somewhere at the beginning of the chapter eg.
Cyberbulling can be defined as.... , or,
It is difficult to define cyberbulling because.... I don't think it needs to be in the chapter heading as well.
Hope that helps. Talk about it with your teacher too, see what he/she thinks. Good Luck finishing your PIP.