Which among the following substances build up in the muscles during sudden physical activities  may cause cramps?

Lactic acid + Energy

The correct answer is Option (4) –Lactic acid + Energy

The food material taken in during the process of nutrition is used in cells to provide energy for various life processes. Diverse organisms do this in different ways – some use oxygen to break-down glucose completely into carbon dioxide and water, some use other pathways that do not involve oxygen.

In all cases, the first step is the break-down of glucose, a six-carbon molecule, into a three-carbon molecule called pyruvate.  Breakdown of pyruvate using oxygen takes place in the mitochondria. This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide. The other product is water. Since this process takes place in the presence of air (oxygen), it is called aerobic respiration. 

Sometimes, when there is a lack of oxygen in our muscle cells, another pathway for the break-down of pyruvate is taken .Here the pyruvate is converted into lactic acid which is also a three-carbon molecule. This build-up of lactic acid in our muscles during sudden activity causes cramps.