Periodic changes and examples : 2 Marks
Non-periodic changes and examples : 2 Marks
Type of change : 1 Mark
Apart from irreversible and reversible changes, there are periodic and non-periodic changes. 
Periodic changes are the changes that repeat themselves after a fixed interval of time. Example - Change of season, day and night cycle, heart beat.
Non-periodic changes are the changes that do not repeat themselves after a fixed interval of time. Example - Tornado, volcanic eruption, tsunami, etc. (most natural disasters).
A forest fire is a non-periodic change.