We have studied endosymbiotic hypothesis which describes the evolution of eukaryotic cells from prokaryotic cell.
According to this hypothesis, there were some small aerobic bacteria and large anaerobic bacteria. The large bacteria ingested small bacteria which stayed inside them instead of getting digested. Thus large and small both bacteria co-existed with each other in a symbiotic relationship in which small bacteria got shelter while large bacteria also got benefit. For example if they were aerobic bacteria, large bacteria got food and energy.
So with the passage of time these small bacteria got converted into organelles like Mitochondria and Chloroplast.
A student can demonstrate this theory by showing the large bacteria and the process of ingesting small one and how with the passage of time it got changed into organelle that performed special function.
Hope it help!