Problem 155 - Advanced Problems in Organic Chemistry for Competitive Examinations

Question

Which of the following is a polysaccharide? (a) Cellobiose (b) Polyethene (c) Cellulose (d) Nylon

Step-by-Step Solution

Answer

Cellulose is the polysaccharide.

Step 1: Understanding Polysaccharides

Polysaccharides are large molecules composed of long chains of monosaccharide units. These carbohydrates play various roles, including energy storage and providing structural support.

Step 2: Analyze Option (a) Cellobiose

Cellobiose is a disaccharide, meaning it is composed of two monosaccharides linked together. It does not qualify as a polysaccharide as it lacks long chains of more than two sugar units.

Step 3: Analyze Option (b) Polyethene

Polyethene is a type of plastic polymer and is not a carbohydrate. It forms from ethene monomers and contains no sugar units, eliminating it from being a polysaccharide.

Step 4: Analyze Option (c) Cellulose

Cellulose is a polysaccharide composed of a long chain of glucose units. It is known for providing structural support in plant cells and is a classic example of a polysaccharide.

Step 5: Analyze Option (d) Nylon

Nylon is a synthetic polymer made from repeating units of chemical monomers different from sugar units. It is a material used in fabrics and textiles, not a carbohydrate.

Step 6: Identify the Polysaccharide

Among the given options, cellulose is the only option that is a polysaccharide. It comprises long chains of glucose, making it suitable for the polysaccharide category.

Key Concepts

Understanding Carbohydrates

Carbohydrates are a vital class of macronutrients essential for energy. They are composed of carbon, hydrogen, and oxygen atoms. Often found in foods like bread, fruits, and vegetables, carbohydrates come in different forms:

• Monosaccharides: Simple sugars, such as glucose and fructose.
• Disaccharides: Comprising two monosaccharides, like sucrose (table sugar) and lactose (milk sugar).
• Polysaccharides: Complex carbs made of long chains of sugar molecules, including starch and cellulose.

Carbohydrates serve multiple functions in organisms, providing energy and structural integrity. For instance, the body breaks down carbohydrates to release glucose, a primary energy source. In plants, carbohydrates like cellulose offer structural support.

Role of Glucose

Glucose is a simple sugar and a critical energy source for both plants and animals. It's a monosaccharide and plays a crucial role in cellular respiration, where it's broken down to produce energy.

• Photosynthesis in plants creates glucose, converting sunlight into chemical energy stored in the form of this sugar.
• In humans, glucose circulates in the bloodstream, providing immediate energy or being stored as glycogen in liver and muscles for later use.

Its structure and properties make glucose a vital building block for larger carbohydrates like starch and cellulose. Understanding glucose and its functions helps in learning how the body and other organisms utilize carbohydrates for energy and growth.

Exploring Cellulose

Cellulose is a complex carbohydrate classified as a polysaccharide, consisting of numerous glucose units joined together.

• It forms an essential structural component in plant cell walls, offering rigidity and strength.
• Unlike starch, another glucose-based polysaccharide meant for energy storage, cellulose's bonds are not easily broken by human digestive enzymes.
• This makes cellulose a key fiber source in human nutrition, aiding digestion by promoting bowel movements.

Interestingly, while humans can't digest cellulose, some animals have specialized stomachs or symbiotic bacteria in their guts to help break it down. Thus, cellulose is not just vital for plant structure, but also for dietary purposes.

Understanding Disaccharides

Disaccharides are carbohydrates formed by the combination of two monosaccharides. This bond forms through a dehydration synthesis reaction, meaning a water molecule is removed to link the sugars.

• Sucrose, the common table sugar, consists of glucose and fructose.
• Lactose, found in milk, comprises glucose and galactose.
• Maltose is formed from two glucose units and is found in malted foods and beverages.

Disaccharides must be broken down into monosaccharides by specific enzymes in the digestive system before absorption into the bloodstream. This process ensures that the body can use the sugars from disaccharides efficiently as an energy source.