Cambridge O Level Biology · Syllabus 5090 · Biological Molecules
Cellulose
What is Cellulose?
A carbohydrate built from glucose that forms the cell walls of plants. Its role is structural rather than nutritional: the cell wall supports the cell and prevents it bursting when water enters. Cellulose contains carbon, hydrogen and oxygen only.
This definition is part of the Biological Molecules chapter in Cambridge O Level Biology.
Cellulose in context
Biological molecules are the large molecules that cells build from smaller units. Cambridge O Level Biology (5090) Chapter 4 asks three separate questions about each family. Which elements? Carbohydrates and lipids contain carbon, hydrogen and oxygen; proteins also contain nitrogen; DNA also contains nitrogen and phosphorus. Which building blocks? Glucose builds starch, cellulose and glycogen; amino acids build proteins; fatty acids and glycerol build lipids; nucleotides build DNA. Which role? Starch and glycogen store energy, cellulose forms plant cell walls, proteins work as enzymes and as structural material, lipids store energy, insulate and build membranes, and DNA carries genetic information.
Questions students ask about Cellulose
What is the difference between an element and a building block?
Elements are the atoms a molecule contains; building blocks are the whole small molecules from which the large molecule is assembled. Glucose is the building block of starch, cellulose and glycogen; amino acids build proteins; fatty acids and glycerol build lipids; nucleotides build DNA. If a question asks for the smaller units, answering "carbon, hydrogen and oxygen" scores nothing, and answering "glucose" to a question about elements scores nothing either. Never swap the two answers.
What is the difference between starch, glycogen and cellulose?
All three are carbohydrates built from glucose and contain only carbon, hydrogen and oxygen; the difference is their role. Starch is the storage carbohydrate of plants and glycogen is the storage carbohydrate of animals, and both can be broken back down to release glucose when the organism needs it. Cellulose is structural rather than nutritional: it forms plant cell walls, which support the cell and prevent it bursting when water enters.