When studying a complex biological phenomenon, it is required to look at the workings of the various systems associated with it. The research is a top-down approach of getting down to the very detail of the cells and molecules taking part in it. Example, a person finds it difficult to digest milk and vomits it on ingestion. As we go a level down, we identify the systems getting affected by the milk. Then, further down, the cells that take in digesting the milk are identified. The enzymes that break down the substances in the milk are identified. The gene regulation of this enzyme (lactase) is studied to check its regulation. This work of doing a top-down approach to find the signalling pathway within the cells to identify the problem with the working of lactase to digest milk, is a necessary approach.
By which organisms that contain the pigment chlorophyll convert light energy into chemical energy which can be stored in the molecular bonds of organic molecules.
