Two Major Plant Polysaccharides: Starch and Cellulose

December 7, 2025 •

3 min read

Cellulose is the most abundant organic macromolecule on Earth, a fact that highlights the critical importance of plant polysaccharides. Two of the most significant plant polysaccharides are starch and cellulose, each playing a vital yet distinct role in the life of a plant.

Quick Summary

Starch and cellulose are two primary plant polysaccharides with different functions. Starch stores energy, while cellulose provides structural support. Despite being polymers of glucose, their different glycosidic bonds give them unique properties and roles in nature.

Key Points

Two key polysaccharides: Starch is the primary energy storage molecule, while cellulose is the main structural component of plants.
Different molecular structures: Starch uses α-glycosidic bonds, which result in a coiled or branched structure, whereas cellulose uses β-glycosidic bonds, leading to a straight, rigid, and linear structure.
Impact of bonding: The β-linkages in cellulose allow for extensive hydrogen bonding between chains, forming strong microfibrils that provide tensile strength to cell walls.
Digestibility differences: Humans can digest starch for energy using amylase enzymes, but they cannot digest cellulose, which functions as insoluble dietary fiber.
Source of raw materials: Cellulose from wood and cotton is a vital raw material for the paper and textile industries.

Starch: The Plant's Energy Reserve

Starch is a carbohydrate that serves as the primary energy storage for plants. It is crucial for a plant's survival, providing a reserve of glucose that can be mobilized when photosynthesis is limited, such as at night or during winter.

The Composition of Starch

Starch is a homopolymer, meaning it is made from repeating units of the same monosaccharide, which in this case is glucose. It exists in two primary forms:

Amylose: A linear polysaccharide consisting of glucose units linked by α-(1,4) glycosidic bonds. This structure causes the molecule to coil into a helical shape.
Amylopectin: A highly branched polysaccharide. It is also made of α-(1,4) glycosidic bonds but has additional α-(1,6) glycosidic bonds at the branch points. This branching allows for rapid access to glucose when the plant needs a burst of energy.

Starch is typically stored as granules within the plant, especially in roots, seeds, and tubers like potatoes and corn. When these granules are heated, the starch gelatinizes, forming the basis for many food applications.

Cellulose: The Structural Backbone of Plants

Unlike starch, cellulose serves a structural purpose in plants, forming the strong and rigid cell walls that encase each plant cell. This structural role allows plants to grow tall, resist gravity, and withstand environmental stress.

The Indigestible Fibers of Cellulose

Cellulose is also a homopolymer of glucose, but a crucial difference in its chemical structure sets it apart from starch. In cellulose, the glucose units are joined by β-(1,4) glycosidic bonds, which cause each successive glucose unit to be rotated 180 degrees. This arrangement leads to:

Linear Chains: Cellulose forms long, unbranched chains that lie parallel to one another.
Microfibrils: These parallel chains are held together by extensive hydrogen bonds, forming strong, cable-like bundles called microfibrils.
High Tensile Strength: The microfibrils are woven into a resilient network within the plant cell wall, giving it a tensile strength comparable to steel.

Humans cannot digest cellulose because our bodies lack the necessary enzyme, cellulase, to break down the β-(1,4) linkages. This is why cellulose is considered insoluble dietary fiber, which is important for digestive health by adding bulk and promoting regular bowel movements. Grazing animals like cows and termites, however, harbor symbiotic bacteria that produce cellulase, allowing them to digest cellulose.

Comparison of Starch and Cellulose


Feature	Starch	Cellulose
Function	Energy storage in plants	Structural support in plant cell walls
Glucose Linkage	α-1,4 and α-1,6 glycosidic bonds	β-1,4 glycosidic bonds
Structure	Coiled and branched (amylopectin) or linear (amylose)	Linear, extended chains that form microfibrils
Digestibility	Easily digested by humans and most animals	Not digestible by humans; requires specialized gut microorganisms in some animals
Solubility	Can dissolve in warm water	Insoluble in water and most organic solvents
Location	Roots, seeds, tubers (e.g., potatoes, corn)	Plant cell walls, wood, cotton
Strength	Weaker; designed for energy release	Very strong due to extensive hydrogen bonding

The Broader Role of Plant Polysaccharides

Plant polysaccharides are far more diverse than just starch and cellulose and have numerous applications beyond basic plant biology. Other examples include pectins, which are used as gelling agents in food, and hemicellulose, which cross-links with cellulose in the cell wall. The pharmaceutical industry also makes extensive use of plant polysaccharides in drug delivery systems, binders, and excipients due to their biocompatibility and versatility. From providing nutrition to serving as a raw material for paper and textiles, plant polysaccharides have an immense impact on both natural ecosystems and human society. For more in-depth information on the chemical properties and applications of plant-derived polysaccharides, consult scientific resources like ScienceDirect, which features detailed reviews on the topic.

Conclusion: A Tale of Two Polysaccharides

In summary, starch and cellulose are two critical polysaccharides found in plants that perfectly illustrate how a minor chemical difference can lead to dramatically different functions. Starch, with its alpha linkages, is the plant's energy depot, while cellulose, with its beta linkages and fibrous structure, is the plant's essential scaffolding. Understanding these two molecules is fundamental to comprehending plant biology and their far-reaching influence on agriculture, nutrition, and industrial applications.

Frequently Asked Questions

The primary function of starch in plants is to serve as an energy reserve. Excess glucose produced during photosynthesis is converted into starch and stored in parts of the plant like seeds, roots, and tubers for later use when energy is needed.

Cellulose's main function is to provide structural support for plants. It is the main component of plant cell walls, giving the plant its rigidity, strength, and protection against mechanical stress.

Yes, both starch and cellulose are homopolymers, meaning they are both made from repeating units of the same simple sugar, which is glucose.

Humans cannot digest cellulose because they lack the specific enzymes, called cellulases, needed to break the β-1,4 glycosidic bonds that link the glucose units in cellulose.

Dietary fiber refers to the indigestible parts of plant food. Since humans cannot digest cellulose, it passes through the digestive system largely intact and is considered a type of insoluble fiber. It aids digestion by adding bulk to stool.

Yes, their structures are significantly different. Starch's α-glycosidic bonds result in a coiled, sometimes branched structure. In contrast, cellulose's β-glycosidic bonds create straight, linear chains that align to form strong fibers.

Starch is typically stored in the energy-storing parts of a plant, such as seeds (e.g., grains), fruits, and underground tubers (e.g., potatoes) and roots.