Why are starch and cellulose considered different compounds even though they are built from the same monomer?

Answer 1

Starch and cellulose are both polymers built from glucose, but the glucose molecules are arranged differently in each case. Having different arrangements means that starch and cellulose are different compounds. They serve different functions in the plants that make them. Your body also uses starch very differently from the way it uses cellulose.

Answer 2

The glucose molecules form different, larger molecules. The difference between starch and cellulose is how the constituent glucose molecules are arranged.

In starch each glucose molecule is oriented in the same direction.

In cellulose each glucose molecule is "upside down" as compared to its neighboring molecules, meaning each molecule is oriented in the opposite way as the previous molecule in the polymer chain, creating an alternating pattern.

Answer 3

They are both made of chains of glucose molecules.

However, for one or the other (I can't remember which), the glucose molecules alternate sides (flip over) in the chain, and on the other, the glucose molecules don't flip over or alternate sides in the chain.

In other words, there are alpha and beta connection points on each glucose molecule, and the connection points of glucose in starch vs cellulose is like this:

AABBAABBAABB

as opposed to

ABABABABABAB

Answer 4

The molecular arrangement is different ...

besides, all you have to do is to rearrange an atom or two to get a different compound. What its main components are is a minor factor.

Answer 5

Starch and Cellulose have different molecular compositions where starch can be broken down by humans and cellulose cannot.