Write a short note on metabolism.

Hint: All living cells are undergoing metabolism. This is the basic process of life and is composed of several biochemical pathways and reactions. Metabolism starts with the digestion of food substances into smaller molecules which are used to produce energy.

Complete answer:
The two main components of metabolism are catabolism and anabolism.
Catabolism is the breakdown system. We use many catabolic pathways to break down food substances and convert them into energy that can be used by our cells. For example, glycolysis is the process by which a molecule of glucose is broken down to release energy in the form of ATP, and an intermediate molecule which then goes further into the citric acid cycle to produce even more molecules of ATP.

The ATP produced is then used to provide energy for other processes. These include making our muscles move, transporting substances across membranes, providing energy to our neurons so that we can process and store information. The ATP generated is also important for carrying out anabolic pathways like amino acid synthesis, the building blocks of proteins.
Anabolic pathways, on the other hand, are processes that build molecules. Gluconeogenesis is therefore the synthesis of glucose from non-carbohydrate precursors like Acetyl CoA. Plants use photosynthesis to produce carbohydrates starting with only carbon dioxide and water. All our macromolecules like proteins are built via anabolic processes.

Note: Metabolic pathways are regulated in more than one way. The simplest being the feedback mechanisms where the decrease in an end product would stimulate certain enzymes to become more active, and increase production.