Starch and Cellulose

Starch and cellulose are two very similar polymers. In fact, they are both made from the same monomer, glucose, and have the same glucose-based repeat units.

There is only one difference. In starch, all the glucose repeat units are oriented in the same direction. But in cellulose, each succesive glucose unit is rotated 180 degrees around the axis of the polymer backbone chain, relative to the last repeat unit.

When material scientists are talking material science talk they say that the glucose units in starch are connected by alpha linkages, and that the glucose units in cellulose are connected by beta linkages.

Does this make any difference? It makes a lot of difference! The most important difference in the way the two polymers behave is this: You can eat starch, but you can't digest cellulose. Your body contains enzymes that break starch down into glucose to fuel your body. But we humans don't have enzymes that can break down cellulose. Some animals do, like termites who eat wood, or cattle who eat grass and break down cellulose in their four-chambered stomachs. So unless you're a termite or a cow, don't try to nourish yourself on woodchips. It's not even good as "fiber" in your diet, sorry to say.

Cellulose is also a lot stronger than starch. Starch is practically useless as a material to make things, but celluose is strong enough to make fibers, and hence rope, clothing and paper products. Cellulose doesn't dissolve in water the way starch does, and certainly doesn't break down as easily. Breaking down or dissolving in water just would be a little too inconvenient for something we use to make clothes and buildings with. It would certainly be embarrassing if a good soaking rain washed away all the wooden houses, park benches, and playground equipment. And what about trees? The forests that we depend on for so many important contributions to our world would melt away in a good downpour. Glad that doesn't happen.

Go to the Starch Page

Go to the Cellulose Page

Return to Macrogalleria Directory