Which one of the following is a disaccharide?

December 2, 2025 •

3 min read

Disaccharides, also known as double sugars, are carbohydrates formed when two monosaccharides are joined together. Examples often encountered include sucrose, lactose, and maltose, but when presented with a choice, it is important to know the specific composition of each type of sugar.

Quick Summary

Answering which is a disaccharide requires understanding common examples like sucrose, lactose, and maltose, which are formed by combining two simpler sugar units.

Key Points

Sucrose, Lactose, and Maltose are Disaccharides: Common examples of double sugars include sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar).
Disaccharides are Made of Two Monosaccharides: These 'double sugars' are formed by linking two simpler monosaccharide units, such as glucose, fructose, or galactose.
Formation Involves Dehydration Synthesis: The chemical reaction that forms a disaccharide removes a water molecule, joining the two monosaccharide units together.
Breakdown Requires Hydrolysis: The reverse process of breaking a disaccharide back into its simple sugar components involves hydrolysis, adding a water molecule with the help of enzymes.
Disaccharides Have Different Compositions: Despite all being double sugars, sucrose (glucose+fructose), lactose (glucose+galactose), and maltose (glucose+glucose) have different monosaccharide building blocks.
Glucose, Fructose, and Galactose are Monosaccharides: These are the fundamental single sugar units that are the building blocks of all disaccharides.

Introduction to Disaccharides and Monosaccharides

Carbohydrates are a fundamental class of biomolecules essential for life, primarily serving as energy sources and structural components. They are categorized based on their size and complexity into monosaccharides, disaccharides, and polysaccharides. Monosaccharides, or 'simple sugars,' are the building blocks for more complex carbohydrates and include common examples like glucose, fructose, and galactose. A disaccharide, as its name suggests, is a 'double sugar' composed of two monosaccharide units joined by a glycosidic linkage through a condensation reaction, where a molecule of water is removed. Polysaccharides, like starch and cellulose, consist of long chains of many monosaccharides.

Identifying a Disaccharide from the Options

When presented with a question like, "Which one of the following is a disaccharide?", the key is to differentiate between simple sugars (monosaccharides) and double sugars (disaccharides). Common disaccharides include sucrose (glucose + fructose), maltose (glucose + glucose), and lactose (galactose + glucose). Monosaccharides like glucose, fructose, and galactose are single sugar units. Therefore, if these options are presented, sucrose, maltose, or lactose would be the disaccharide.

How are Disaccharides Formed and Broken Down?

The synthesis of a disaccharide from two monosaccharides is a process called dehydration synthesis, or a condensation reaction. This forms a glycosidic linkage and releases a water molecule. The reverse process, hydrolysis, breaks down a disaccharide into its monosaccharides, requiring water and specific enzymes like sucrase, lactase, or maltase.

Comparison Table: Common Mono- and Disaccharides


Feature	Glucose	Sucrose	Lactose	Starch
Classification	Monosaccharide	Disaccharide	Disaccharide	Polysaccharide
Composition	Single sugar unit	Glucose + Fructose	Galactose + Glucose	Many glucose units
Common Source	Blood sugar, corn syrup	Table sugar, cane, beets	Milk	Potatoes, rice, wheat
Reducing Sugar	Yes	No	Yes	No (ends are reducing)
Primary Function	Immediate energy for cells	Transport sugar in plants	Energy for infant mammals	Energy storage in plants

Biological Roles and Significance

Disaccharides have important biological roles. Sucrose transports carbohydrates in plants. Lactose is an energy source for infant mammals, and its digestion depends on lactase. Maltose is involved in the digestion of starches.

The Health Context of Sugars

Different sugars affect the body differently. Monosaccharides are absorbed directly, while disaccharides need to be broken down. High intake of added sugars, including disaccharides like sucrose, is linked to health issues. Moderation is important.

Conclusion: The Key to Carbohydrate Identification

To answer the question, "Which one of the following is a disaccharide?", identify the double sugar among the options. Disaccharides are composed of two linked monosaccharides, with common examples being sucrose, lactose, and maltose. Understanding the basic structure of carbohydrates allows for their proper identification.

Key Takeaways

Definition: A disaccharide is a carbohydrate molecule composed of two monosaccharide units joined by a glycosidic linkage.
Composition: Common disaccharides include sucrose (glucose + fructose), lactose (galactose + glucose), and maltose (glucose + glucose).
Formation: Disaccharides are formed via a dehydration synthesis (condensation) reaction, which releases a water molecule.
Breakdown: They are broken down into their constituent monosaccharides through hydrolysis, a process that requires water and specific enzymes.
Function: Disaccharides serve as an energy source and are important in biological functions like carbohydrate transport in plants and providing energy for infants.

Frequently Asked Questions

The simplest way to identify a disaccharide is to look for a sugar that is made of two linked monosaccharides, such as sucrose, lactose, or maltose. They are larger than single sugar units like glucose or fructose.

The three most common disaccharides are sucrose (table sugar), lactose (milk sugar), and maltose (malt sugar). Each is composed of a unique combination of two monosaccharides.

A disaccharide is made of two sugar units (monosaccharides) joined together, while a monosaccharide is a single, simple sugar unit. Examples of monosaccharides are glucose, fructose, and galactose.

The chemical formula for the common disaccharides sucrose, lactose, and maltose is C12H22O11. This is because a water molecule is lost during the condensation reaction that forms them.

During digestion, enzymes use a process called hydrolysis to break down disaccharides into their constituent monosaccharides, which can then be absorbed into the bloodstream.

Sucrose is a non-reducing sugar because its glycosidic bond involves the anomeric carbons of both the glucose and fructose units, leaving no free anomeric carbon to act as a reducing agent. Lactose and maltose, however, have one free anomeric carbon, making them reducing sugars.

No, humans cannot digest all disaccharides. For instance, many people lose the ability to produce the enzyme lactase as they age, leading to lactose intolerance and an inability to properly digest lactose. Other disaccharides like cellobiose, with a different bond, are indigestible by humans.