Final answer:
The long, straight-chain type of starch found in plants is called amylose, which is a polysaccharide composed of D-glucose units. It makes up 10%-30% of the natural starches in plants and is distinct from the branched molecule amylopectin.
Step-by-step explanation:
The long, straight-chain type of starch found in plants is called amylose. Amylose is a type of polysaccharide made up of hundreds of D-glucose monomers linked by alpha-1,4-glycosidic bonds. It is a component of the starch that plants use as a storage form of sugar.
The straight-chain structure of amylose is different from that of amylopectin, which is the other component of starch and is highly branched. Amylose accounts for about 10%-30% of natural starches, whereas amylopectin makes up the remaining 70%-90%. The characteristic blue-violet color reaction of starch with iodine mainly involves the amylose portion due to its coiled structure that can trap iodine molecules.