Question

prepare a model based on any natural cycle and present it in science exhibition

Answer 1

At attachment you can see the pictures describing about the water cycle from ground to environment and then environment to ground . I hope this will help you alot in preparing the model and at least in getting the idea how to make a model .So you can take the idea for this. 
Also , exhibiting model is a good way to spread messages about natural thins to different kinds of people.

Answer 2

prepare a modal based on any natural cycle and present it in a science exhibition