Chapter 23.2, Problem 9SSC

Interpretation Introduction

Interpretation:

The structure of starch and cellulose should be compared and contrast. The reasons due to which structural differences affect our ability to digest both should be determined.

Concept introduction:

A biological molecule which consists of carbon, hydrogen and oxygen is known as saccharide or carbohydrate. The general formula of saccharide is ${{\text{(CH}}_{\text{2}}\text{O)}}_{\text{n}}$.

Saccharides (sugar) are classified as: monosaccharides, disaccharides and polysaccharides.

Monosaccharides are defined as a simpler carbohydrate which contains one sugar molecule and can’t be hydrolysed into smaller carbohydrate.

Disaccharides are defined as a saccharide which contains two sugar molecules that is when two monosaccharides are linked by glycosidic bonds. It is a double ring structure.

Polysaccharides are defined as a saccharide which contains many units of sugar molecules that is more than two monosaccharides are linked by glycosidic bonds.

Explanation of Solution

Starch consists of many units of monosaccharide as it is a polymeric carbohydrate which consists of glucose units linked with glycosidic bonds.

Cellulose consists of many units of monosaccharide or sugar as it is a polymeric carbohydrate which consists of various sugar units linked with glycosidic bonds.

The structures of both cellulose and starch are similar as both contains similar ring structures consist of carbon atoms, hydrogen atoms and oxygen atoms. Both starch and cellulose consist of ether bond.

According to the above structures, cellulose is an unbranched structure or a linear molecule whereas the starch is not a linear molecule or branched structure.

Now, the linear structure of cellulose results in the strong and rigid structure as linear structure allows the chain (molecule) to stick with each other whereas the starch consist of glucose units which makes them insoluble in water results in the storage reservoir for energy.

Thus, cellulose is insoluble polymer in water which forms plant cell walls whereas the starch is insoluble molecule in water that is used to store energy.

One can eat starch but one can’t able to digest cellulose. Our body consist of enzymes which has ability to break down the starch molecule into glucose units.