Starch makes up the nutritive reserves of many plants. During the growing season, the green leaves collect solar energy. In plants with tuberous roots this energy is transported as a sugar solution down to the tubers and it is down there, that the sugar is converted to starch in the form of tiny granules occupying most of the cell interior.
The conversion of sugar to starch takes place by means of enzymes. Then the following spring enzymes are also responsible for the re-conversion of starch to sugar which is transported upwards as energy for the growing plant.

STARCH for HUMANS
Cassava / Tapioca starch is used in the manufacture of sweeteners, sizing of paper and textile and is in particular an excellent food starch used as a thickener and stabilizer. The pulp is used as cattle feed. Juice and spent process water are valuable fertilizers disposed of by land spreading.
Being a pure renewable natural polymer starch has a multitude of applications. Starch can be further processed to manufacture Ethanol / Alcohol, Pharmaceuticals, Snack Foods, fast food, sweets, sausages, tablets, paper, corrugated board etc.
Starch once produced can be stored for long periods to match demand and products. The period of the storage will depend on the form it is stored in, Slurry or Chips or Flour

Cassava starch is the most sought after as it needs less process to convert to Sugar, Alcohol etc.