Bullet points instead of paragraph

You can - in fact many have. However, I certainly wouldn't advise it. What's the problem with writing a plan using bullets and then expanding those into proper sentences?

How can you use bullets to "Define and explain"

As a general principle, bullets are NOT acceptable to the ACCA, their examiners nor their markers.

What's the difficulty with using full sentences.

But make your sentences short and to the point!