Cellulose, starch and glycogen are all polysaccharides, which means long chains of sugars. All three are made of only glucose, so they are homopolymers. Cellulose builds the plant cell wall, starch stores energy in plants, and glycogen stores energy in animals. Memory hook: "CELL wall = Cellulose, plant Store = Starch, aniMal store = Glycogen."
Cellulose (straight, plant cell wall), starch (helical, plant store) and glycogen (branched, animal store) are all homopolymers of glucose joined by glycosidic bonds. Inulin is the exception, a polymer of fructose.
Your doubts, answered
What is the difference between cellulose, starch and glycogen?
All three are polysaccharides made of glucose only. The difference is their job and shape. Cellulose forms the plant cell wall and is a straight, tough fibre. Starch is the energy store in plant tissues and forms helical (coiled) chains. Glycogen is the energy store in animals and is highly branched. So the monomer is the same (glucose), but the structure and function differ.
Are cellulose, starch and glycogen homopolymers or heteropolymers?
All three are homopolymers. NCERT says a homopolymer is made of only one type of building block. Since cellulose, starch and glycogen all use only glucose, each is a homopolymer. This is a common NEET trap because starch and glycogen look complex, but complex shape does not make them heteropolymers. Proteins are heteropolymers (many different amino acids); polysaccharides here are homopolymers.
Which polysaccharide stores energy in animals?
Glycogen stores energy in animals. NCERT says starch is the store house of energy in plant tissues, and animals have another variant called glycogen. So plant store = starch, animal store = glycogen. Both are glucose polymers, but glycogen is more branched, which helps animals release glucose quickly when needed.
What is the monomer of cellulose, starch and glycogen?
The monomer (building block) of all three is glucose, a monosaccharide. The glucose units join by glycosidic bonds to form long chains. Because only glucose is used, each polymer is a homopolymer. Note: inulin is different, it is a polymer of fructose, not glucose.
Why is cellulose important for plants but humans cannot digest it?
Cellulose makes the plant cell wall, and paper and cotton fibre are cellulosic. Humans cannot digest cellulose because we lack the enzyme to break its bond type, so it passes as dietary fibre. For NEET, remember cellulose is a structural polysaccharide (support), while starch and glycogen are storage polysaccharides (energy).
⚠️ The NEET trap ✗ Students mark starch or glycogen as heteropolymers because their chains look big and branched. ✓ Cellulose, starch and glycogen are ALL homopolymers because each is made of only one sugar, glucose. Only proteins (many amino acids) are heteropolymers in this chapter. 🧠 One brick = homopolymer. Glucose is the only brick in all three, so all three are homopolymers, no matter how branched they look.
Real NEET questions
2023
Cellulose does not form blue colour with Iodine because
A · It is a disaccharide.
B · It is a helical molecule.
C · It does not contain complex helices and hence cannot hold iodine molecules. ✓
D · It breaks down when iodine reacts with it.
Solution: NCERT states that starch forms helical secondary structures and can hold I2 in the helical portion, giving the blue starch-iodine colour. Cellulose does not contain complex helices, so it cannot trap iodine molecules and stays colourless. Cellulose is a polysaccharide (not a disaccharide), so option A is wrong.
2022
Exoskeleton of arthropods is composed of:
A · Cutin
B · Cellulose
C · Chitin ✓
D · Glucosamine
Solution: NCERT says the exoskeleton of arthropods has a complex polysaccharide called chitin. Cellulose forms the plant cell wall, not the arthropod exoskeleton. This tests that different polysaccharides have different locations and jobs.
2023
Inulin is a polymer of:
A · Amino acids
B · Glucose
C · Fructose ✓
D · Galactose
Solution: NCERT clearly states inulin is a polymer of fructose. This is a trap next to cellulose, starch and glycogen, which are all polymers of glucose. Remember: inulin is the odd one out because its monomer is fructose, not glucose.
Solved Biomolecules NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Are cellulose, starch and glycogen made of the same sugar?
Yes. All three are homopolymers of glucose. Their monomer is the same glucose unit; only their shape, branching and biological role differ.
Which is the storage polysaccharide in plants and which in animals?
Starch is the storage polysaccharide in plants, and glycogen is the storage polysaccharide in animals. Cellulose is structural, forming the plant cell wall.
Why does starch give a blue colour with iodine but cellulose does not?
Starch forms helical structures that trap iodine (I2) molecules, giving a blue starch-iodine colour. Cellulose has no complex helices, so it cannot hold iodine and gives no blue colour.
Is glycogen branched or unbranched?
Glycogen is a highly branched glucose polymer with a reducing end and a non-reducing end. The branching lets animals release glucose fast for quick energy.
What bond joins the sugar units in polysaccharides?
Glucose units in polysaccharides are joined by glycosidic bonds. This is a NEET favourite: polysaccharide = glycosidic bond, protein = peptide bond, nucleic acid = phosphodiester bond.
