Simulation · Biology · Class 11
The iodine test for starch
From the lesson Polysaccharides in Biomolecules. Change the values and watch what happens.
The iodine test for starchBiology · Class 11
The idea behind it
NCERT §9.5
- Polysaccharides (carbohydrates) are another class of macromolecule in the acid-insoluble pellet. They are long chains, or threads, of monosaccharide units.
- Cellulose is made of one type of monosaccharide only, glucose, so it is a homopolymer. Starch is a variant that stores energy in plant tissues; glycogen is the animal variant. Inulin is a polymer of fructose.
- In a polysaccharide chain such as glycogen, the right end is the reducing end and the left end the non-reducing end. Glycogen is branched.
- Starch forms helical secondary structures and can hold I2 molecules inside the helix; the starch-iodine complex is blue. Cellulose has no complex helices, so it cannot hold iodine.
- Plant cell walls are made of cellulose, and paper from plant pulp and cotton fibre is cellulosic.
- More complex polysaccharides are built from amino-sugars and chemically modified sugars such as glucosamine and N-acetyl galactosamine. Chitin, in the exoskeleton of arthropods, is one; these complex polysaccharides are mostly homopolymers.