Question

This section contains multiple choice questions. Each question has 4 choices (a), (b), (c) and (d), out of which ONLY ONE is correct. Which of the following carbohydrates is a non-sugar? (a) Galactose (b) Glycogen (c) Fructose (d) Lactose

Short answer

a) Galactose b) Glycogen c) Fructose d) Lactose Answer: b) Glycogen

Step-by-step solution

Understanding Carbohydrate Types

Carbohydrates can be classified into two main types: sugars and non-sugars (polysaccharides). Sugars are sweet-tasting, simple carbohydrates, while non-sugars are complex carbohydrates that do not have a sweet taste.

Evaluating Choice (a): Galactose

Galactose is a monosaccharide, which means it is a simple sugar. It is also a component of lactose, which is a disaccharide.

Evaluating Choice (b): Glycogen

Glycogen is a polysaccharide that is used as a storage form of glucose in the body. It is a large and complex molecule and it is not sweet-tasting. Glycogen is a non-sugar.

Evaluating Choice (c): Fructose

Fructose is a simple sugar and it is one of the main components of sucrose, which is common table sugar. It is a sweet-tasting carbohydrate.

Evaluating Choice (d): Lactose

Lactose is a disaccharide, meaning it is made up of two simple sugars, glucose and galactose. It is a sugar found in milk and dairy products.

Conclusion

Out of the given choices, (b) Glycogen is the only non-sugar carbohydrate. The correct answer is (b) Glycogen.

Key concepts

Carbohydrates

Carbohydrates are essential biomolecules that serve as a primary source of energy for all living organisms. They consist of carbon, hydrogen, and oxygen atoms and are classified based on their complexity and digestibility.

• Simple Carbohydrates: Known as sugars, they can be monosaccharides like glucose and fructose, or disaccharides like sucrose and lactose.
• Complex Carbohydrates: These are polysaccharides and include starch, cellulose, and glycogen, which are made up of long chains of monosaccharide units.

Our bodies break down these carbohydrates to release energy, with simple carbohydrates providing quick energy due to their rapid digestion, while complex carbohydrates offer sustained energy release as they require more time to be broken down. An in-depth understanding of carbohydrate types aids in choosing healthy foods and managing energy levels effectively.

Monosaccharides and Disaccharides

Monosaccharides are the simplest form of carbohydrates, consisting of a single sugar molecule. They serve as building blocks for more complex carbohydrates and are found naturally in fruits and honey. Common examples include glucose, fructose, and galactose, each with distinct structural formulas but a general formula of \(C_6H_{12}O_6\).

Disaccharides

Disaccharides are formed when two monosaccharide molecules undergo a dehydration reaction to form a glycosidic bond. This process results in sugars like sucrose (common table sugar), lactose (found in milk), and maltose. These sugars are slightly more complex and provide sweetness to a variety of foods. Understanding the structure and function of these molecules is crucial for students tackling exercises on carbohydrate identification and properties.

Polysaccharides

Polysaccharides represent a higher level of carbohydrate complexity. These are long chains of monosaccharide units linked by glycosidic bonds, which can be linear or branched in structure. Polysaccharides are not sweet-tasting and are typically non-soluble in water.

• Starch: A storage polysaccharide in plants, made up of amylose and amylopectin. It's a major food source for humans.
• Glycogen: Often referred to as the 'animal starch', glycogen is the primary storage form of glucose in animals and is found in the liver and muscles.
• Cellulose: This is a structural polysaccharide present in the cell wall of plants, providing rigidity and strength. Unlike starch and glycogen, cellulose can not be digested by humans.

Recognizing the differences between these polysaccharides is essential for understanding their biological roles and nutritional value. For example, knowing that glycogen is a non-sugar can help students eliminate choices in multiple-choice questions related to carbohydrate classification as demonstrated in the textbook exercise.