## **Core Concept**
Dietary fiber, also known as roughage, is the indigestible part of plant-based foods that passes through the digestive system relatively intact. It is primarily composed of **carbohydrates**, specifically **polysaccharides** such as **cellulose**, **hemicellulose**, and **pectin**, which are not easily broken down by human digestive enzymes. A diet rich in fiber has numerous health benefits, including promoting regular bowel movements and supporting healthy blood sugar levels.

## **Why the Correct Answer is Right**
The correct answer, **cellulose**, is a type of dietary fiber. Cellulose is a **polysaccharide** made up of a linear chain of several hundred to many thousands of **β(1→4)** linked **D-glucose** units. It is a major component of plant cell walls and is indigestible by human enzymes due to the lack of **β-glucosidase** enzyme. This indigestibility allows cellulose to act as dietary fiber, providing bulk to stool and aiding in the movement of food through the digestive system.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While some types of fiber can be broken down by **colonic bacteria**, the term itself doesn't specify a type of dietary fiber.
- **Option B:** **Pectin** is indeed a type of dietary fiber, but it is not the correct answer provided.
- **Option D:** This option is not provided, but any other option not listed would be incorrect based on the context of the question.

## **Clinical Pearl / High-Yield Fact**
A high-fiber diet can help prevent **constipation**, **diverticulitis**, and **hemorrhoids**, and may reduce the risk of **cardiovascular disease** and **type 2 diabetes**. The **American Heart Association** recommends consuming 25 to 30 grams of fiber per day. Foods rich in fiber include fruits, vegetables, whole grains, and legumes.

## **Correct Answer:** . Cellulose