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Biology Class 11

NEET : Doc: Carbohydrates NEET Notes | EduRev

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Carbohydrates are macronutrients and are one of the three main ways by which our body obtains its energy. They are called carbohydrates as they comprise carbon, hydrogen and oxygen at their chemical level. Carbohydrates are essential nutrients which include sugars, fibers and starches. They are found in grains, vegetables, fruits and in milk and other dairy products. They are the basic food groups which play an important role in a healthy life.
The food containing carbohydrates are converted into glucose or blood sugar during the process of digestion by the digestive system.
Our body utilizes this sugar as a source of energy for the cells, organs and tissues. The extra amount of energy or sugar is stored in our muscles and liver for further requirement. The term ‘carbohydrate’ is derived from a French term 'hydrate de carbone' meaning ‘hydrate of carbon‘. The general formula of this class of organic compounds is Cn(H2O)n.
Doc: Carbohydrates NEET Notes | EduRev

Classification of Carbohydrates

The carbohydrates are further classified into simple and complex which is mainly based on their chemical structure and degree of polymerization.

Simple Carbohydrates (Monosaccharides, Disaccharides and Oligosaccharides)

Simple carbohydrates have one or two sugar molecules. In simple carbohydrates, molecules are digested and converted quickly resulting in a rise in the blood sugar levels. They are abundantly found in milk products, beer, fruits, refined sugars, candies, etc. These carbohydrates are called empty calories, as they do not possess fiber, vitamins and minerals.
Plants, being producers, synthesize glucose (C6H12O6) using raw materials like carbon dioxide and water in the presence of sunlight. This process of photosynthesis converts solar energy to chemical energy. Consumers feed on plants and harvest energy stored in the bonds of the compounds synthesized by plants.
1. Monosaccharides
Glucose is an example of a carbohydrate monomer or monosaccharide. Other examples of monosaccharides include mannose, galactose, fructose, etc. The structural organization of monosaccharides is as follows:
Doc: Carbohydrates NEET Notes | EduRev

Monosaccharides may be further classified depending on the number of carbon atoms:
(i) Trioses (C3H6O3): These have three carbon atoms per molecule.
Example: Glyceraldehyde
(ii) Tetroses (C4H6O4): These monosaccharides have four carbon atoms per molecule.
Example: Erythrose. Similarly, we have-
(iii) Pentoses,
(iv) Hexoses, and
(v) Heptoses

2. Disaccharides
Two monosaccharides combine to form a disaccharide. Examples of carbohydrates having two monomers include- Sucrose, Lactose, Maltose, etc.
Doc: Carbohydrates NEET Notes | EduRev

3. Oligosaccharides 
Carbohydrates formed by the condensation of 2-9 monomers are called oligosaccharides. By this convention, trioses, pentoses, hexoses are all oligosaccharides.

Complex Carbohydrates (Polysaccharides)

Complex carbohydrates have two or more sugar molecules, hence they are referred to as starchy foods. In complex carbohydrates, molecules are digested and converted slowly compared to simple carbohydrates. They are abundantly found in lentils, beans, peanuts, potatoes, peas, corn, whole-grain bread, cereals, etc.
Polysaccharides are complex carbohydrates formed by the polymerization of a large number of monomers. Examples of polysaccharides include starch, glycogen, cellulose, etc. which exhibit extensive branching and are homopolymers – made up of only glucose units.
Doc: Carbohydrates NEET Notes | EduRev

  • Starch is composed of two components- amylose and amylopectin. Amylose forms the linear chain and amylopectin is a much-branched chain.
  • Glycogen is called animal starch. It has a structure similar to starch, but has more extensive branching.
  • Cellulose is a structural carbohydrate and is the main structural component of the plant cell wall. It is a fibrous polysaccharide with high tensile strength. In contrast to starch and glycogen, cellulose forms a linear polymer.

Functions of Carbohydrates

The main function of carbohydrates is to provide energy and food to the body and to the nervous system. Carbohydrates are known as one of the basic components of food, including sugars, starch, and fibre which are abundantly found in grains, fruits and milk products. Carbohydrates are also known as starch, simple sugars, complex carbohydrates and so on.
It is also involved in fat metabolism and prevents ketosis. Inhibits the breakdown of proteins for energy as they are the primary source of energy. An enzyme by name amylase assists in the breakdown of starch into glucose, finally to produce energy for metabolism.

Sources of Carbohydrates

  • Simple sugars are found in the form of fructose in many fruits.
  • Galactose is present in all dairy products.
  • Lactose is abundantly found in milk and other dairy products.
  • Maltose is present in cereal, beer, potatoes, processed cheese, pasta, etc.
  • Sucrose is naturally obtained from sugar and honey containing small amounts of vitamins and minerals.

These simple sugars that consist of minerals and vitamins exist commonly in milk, fruits, and vegetables. Many refined and other processed foods like white flour, white rice, and sugar, lack important nutrients and hence, they are labelled “enriched.” It is quite healthy to use vitamins, carbohydrates and all other organic nutrients in their normal forms.

Carbohydrate Foods

Eating too much sugar results in an abnormal increase in calories, which finally leads to obesity and in turn low calories leads to malnutrition. Therefore, a well-balanced diet needs to be maintained to have a healthy life. That is the reason a balanced diet is stressed so much by dietitians.
Let us look into the differences between the good and bad carbohydrates.
Doc: Carbohydrates NEET Notes | EduRev

Examples of Carbohydrates

Following are the important examples of carbohydrates:

  • Glucose
  • Galactose
  • Maltose
  • Fructose
  • Sucrose
  • Lactose
  • Starch
  • Cellulose
  • Chitin

Frequently Asked Questions

What are carbohydrates? 
Carbohydrates are biomolecules comprising carbon, hydrogen and oxygen atoms. They are an important source of energy. They are sugars, starch and fibres found in fruits and vegetables.

How are the carbohydrates classified?
Carbohydrates are classified into the following:

  • Simple carbohydrates
  • Complex carbohydrates

How are the carbohydrates important to our body? 
Carbohydrates provide energy to the body. It breaks down into glucose and enters our bloodstream. The body cells utilize glucose to produce ATP.

Name a few sources of carbohydrates. 
Carbohydrates are obtained from a variety of sources such as bread, milk, potatoes, cookies, corn, etc.

How are the carbohydrates digested?
Carbohydrates start being digested in the mouth by the action of salivary amylase. They are not completely broken down in the stomach, but in the intestine. 

What are simple carbohydrates? Give examples.
Simple carbohydrates are the ones that are quickly broken down by the body to be converted into energy. Fruits, milk and milk products are the main sources of simple carbohydrates. 

How are complex carbohydrates different from simple carbohydrates? 
Complex carbohydrates are the ones in which the sugar molecules are strung in long, complex chains. Peas, beans, vegetables and grains are the important sources of carbohydrates.

What are the three types of simple carbohydrates? 
Three types of simple carbohydrates include:

  • Monosaccharides
  • Disaccharides
  • Polysaccharides

Name some bad carbohydrates that are harmful to the body. 
The bad carbs include:

  • White bread
  • Sugary drinks
  • Pastries
  • Candies and chocolates
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