Which of the following is NOT a carbohydrate? A- Cellulose B- Lipids C- Monosaccharides D- Starch
The Correct Answer and Explanation is:
The correct answer is B- Lipids.
Lipids are not a type of carbohydrate; they represent a distinct class of biological macromolecules with unique structures and functions. To understand why, it is important to first define what a carbohydrate is and then examine the other options provided.
Carbohydrates are organic compounds made of carbon, hydrogen, and oxygen atoms, typically in a ratio that can be expressed by the general formula Cm(H₂O)n. Their primary roles in living organisms are to provide and store energy and to serve as structural components. The name carbohydrate literally means “hydrated carbon.” This class of molecules includes sugars, starches, and fibers.
Let’s look at the other options. Monosaccharides (C) are the simplest form of carbohydrates. The prefix “mono” means one, and “saccharide” means sugar, so they are single sugar units. Glucose and fructose are common examples. They are the fundamental building blocks, or monomers, from which more complex carbohydrates are constructed.
Starch (D) and Cellulose (A) are both polysaccharides, meaning they are large, complex carbohydrates. The prefix “poly” means many, indicating that they are polymers made of numerous monosaccharide units linked together in long chains. Starch is the primary form of energy storage in plants, found in foods like potatoes and rice. Cellulose is a crucial structural component of the cell walls in plants, providing rigidity and support. Since monosaccharides are the basic units and both starch and cellulose are polymers of these units, they are all correctly classified as carbohydrates.
In contrast, lipids are a diverse group of molecules that include fats, oils, waxes, and steroids. While they are also composed mainly of carbon, hydrogen, and oxygen, their structure is not based on sugar monomers and they have a much lower proportion of oxygen. A key defining characteristic of lipids is that they are hydrophobic, meaning they are insoluble in water. They serve vital functions such as long term energy storage, insulation, and are the primary components of cell membranes. Because their chemical structure and properties are fundamentally different, lipids are not carbohydrates.
