You know about chlorophyll. This substance can be produced by plants only in the presence of sunlight.
This is the substance that gives the green colour to the leaves.
To understand this, fix a small piece of paper on a green leaf. After some days remove this and observe the leaf. You will find that where the piece of paper was fixed, there is a pale patch. All the other exposed parts will be green due to the presence of chlorophyll.
How to Create a Mini Ecosystem?
Take an old fish tank or something similar and put some mud inside it.
Then you collect a lot of small living things from all around you from your garden, pond and trees and put them in to the tank.
Also collect some vegetation from the pond and lawn and put them also in the tank. Now cover the top of the tank with a fine net so that the insects don't escape into your house.
For the next couple of days observe the various activities of the insects and small animals. After that put they back to where you got them from.