MCQ Detailed View

Carbohydrates are one of the four major classes of biological macromolecules, along with proteins, lipids, and nucleic acids. They are organic compounds composed of three main elements: carbon (C), hydrogen (H), and oxygen (O), usually in the ratio of 1:2:1. The two most common groups of compounds classified as carbohydrates are sugars and starch.

Sugars, also known as simple carbohydrates, include monosaccharides such as glucose, fructose, and galactose, and disaccharides such as sucrose, maltose, and lactose. These are small, soluble molecules that can be quickly absorbed and used by living cells for energy. Glucose, in particular, is the primary fuel for cellular respiration and plays a central role in energy metabolism.

Starch, on the other hand, is a complex carbohydrate. It is a polysaccharide made of many glucose units linked together. Plants store energy in the form of starch, which is found in seeds, grains, and tubers such as rice, wheat, maize, and potatoes. When humans or animals consume starchy foods, digestive enzymes break starch down into glucose molecules, providing long-term energy.

Carbohydrates are not classified with proteins. Proteins are made of amino acids and serve different biological functions such as building tissues, enzymes, and hormones. Similarly, lipids (fats and oils) are another distinct category of biomolecules that primarily store energy and make up cell membranes. Thus, only starch and sugar fall under carbohydrates.

The main biological functions of carbohydrates include:

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  Providing immediate and stored energy.

  
  


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  Serving as structural components (e.g., cellulose in plant cell walls, chitin in insect exoskeletons).

  
  


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  Acting as recognition molecules on cell surfaces.

  
  

In summary, the correct group of compounds classified as carbohydrates is starch and sugar, since both represent the simple and complex forms of this essential biomolecule.