Problem 100 - A Complete Resource Book in Chemistry for JEE Main

Question

The carbohydrate which cannot be hydrolyzed by the human digestive system is (a) starch (b) cellulose (c) glycogen (d) all of these

Step-by-Step Solution

Answer

The correct answer is (b) cellulose.

Step 1: Understand the Question

The question is asking us to identify which carbohydrate cannot be broken down, or hydrolyzed, by the human digestive system.

Step 2: Consider Each Option

Let's evaluate each carbohydrate: - **Starch**: This is a polysaccharide that can be broken down into glucose by enzymes like amylase. - **Cellulose**: This is a polysaccharide that the human digestive system cannot break down due to the lack of the enzyme cellulase. - **Glycogen**: This is a branched polysaccharide similar to starch but in animals, and it is readily mobilized as glucose. - **All of these**: This option suggests that none of these can be hydrolyzed.

Step 3: Identify Which Carbohydrate Cannot Be Hydrolyzed

From step 2, only cellulose cannot be digested by humans because we lack the necessary enzyme to break down its specific beta-glycosidic linkages.

Step 4: Choose the Correct Answer

Based on the evaluation, cellulose is the carbohydrate that cannot be hydrolyzed by the human digestive system. Therefore, the correct choice is (b) cellulose.

Key Concepts

Digestive Enzymes

Digestive enzymes are special proteins in our body that help break down food into smaller, usable substances. When we eat carbohydrates, these enzymes are at work to ensure we absorb the nutrients. Each enzyme is specific to a certain type of molecule; that's why we need a variety of enzymes in our digestive system.

• For carbohydrates like starch and glycogen, enzymes such as amylase are crucial. They break down these polysaccharides into simpler sugars like glucose, making them easier for the body to absorb.
• However, we lack cellulase, the enzyme needed to break down cellulose in plants. This is why cellulose passes through our system undigested.

Without these enzymes, our bodies wouldn't be able to harness the energy from the foods we eat effectively.

Polysaccharides

Polysaccharides are long chains of sugar molecules linked together. They're a type of carbohydrate, and their complex structure makes them a great source of energy. The most common polysaccharides include starch, glycogen, and cellulose, each having unique roles in nature and nutrition.

• Starch: Found in plants, it's a major energy source for animals and humans. It's easily broken down by enzymes like amylase.
• Glycogen: It's similar to starch but is stored in animals, especially in the liver and muscles, and is readily converted into glucose when needed.
• Cellulose: This is found in plant cell walls and gives them structural support. Unlike starch and glycogen, humans cannot digest cellulose.

Understanding polysaccharides helps us recognize what our diets provide and what's ultimately available as energy.

Human Digestive System

The human digestive system is a complex network responsible for breaking down food and absorbing nutrients. It starts from the mouth and ends at the anus, involving several organs along the way. Each part of the digestive system plays a vital role in ensuring our body receives the energy and nutrition it needs.

• The mouth: Chewing breaks down food physically, while enzymes in saliva begin chemical digestion.
• The stomach: It uses acids and enzymes to further break down food into a usable form.
• The intestines: Here, digestion continues, and absorption of nutrients like sugars, fats, and proteins occurs.

Despite this complexity, some substances, like cellulose, cannot be broken down because our digestive system lacks the necessary enzymes. This illustrates how our bodies are specialized in utilizing specific nutrients while letting others pass through undigested.