North Africa includes Egypt so do the conquest of Egypt and the rest of North Africa (Central and Western) separately.

There are two kinds of questions related to NA in past papers. 1 Conquests and 2 Material prosperity. The former would include the conquests beginning in the reign of Hazrat Umar up to Abdul Malik, no mention of Fatimids is required. But the latter question will include the Fatimids, establishment of Qayrowan and the Murabitun of North Africa (plz check the Murabitun part because I dont have access to my books right now so can't say for sure).

Causes mentioned by sfmascot are absolutely spot on, though, specific to Egypt include a)"Umar's policy of systematic conquest and b) the Plague of Amwas" in them.

Causes for NA include:
Muawiya's Expansionist policy.
Amr's ambition
Solidifying hold on acquired territory
Byzantine's reduced naval supremacy.