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  Structure of Carbohydrates:  
  Sources of Carbohydrates:  
  Functions of Carbohydrates:  
  Carbohydrates Work Sheet:  

Carbohydrates: are the cheapest and most plentiful of all nutrients and are an important part of our daily diet. Carbohydrates are fromed by plants through the process of photosynthesis. Foods, which contain carbohydrates are called energy foods.

Structure of Carbohydrates
  Structure of carbohydrates: Pure carbohydrates consist of just three elements: carbon, hydrogen, and oxygen in the ratio of 1:2:1. The traditional general structure of carbohydrates is: Cx H2x Ox, but many important carbohydrates, like deoxyribose have more hydrogen. Carbohydrates are classified into monosaccharides, disaccharides, and polysaccharides.


Monosaccharides (simple sugars): Monosaccharides are the simplest of all sugars and are a base for all other carbohydrates. Monosaccharides include Glucose, Fructose and Galactose, and share the chemical formula C6 H12 O6. Even though they are chemically similar, different sugars are formed because the elements are arranged differently.

The basic structure is of a ring structure containing carbon atoms and one oxygen atom. Glucose is the most common monosaccharide, and it plays a major role in nutrition because it is a readily available source of energy. Fructose is only found in fruits and honey. Galactose idoes not occur naturally in foods, but results from digestion of a disaccharide.


* Chemical formula for the three monosaccharides:


Disaccharides (sugars): Disaccharides are commonly referred to as sugars. Disaccharides are composed of two monosaccharides joined together. When the two molecules join together a molecule of water is released. The disaccharide sugars include Sucrose, Lactose,and Maltose.

Glucose + Fructose = Sucrose

Glucose + Galactose = Lactose

Glucose + Glucose = Maltose

These different disaccharides contribute to various levels of sweetness in foods. Sugars are found naturally in fruit and vegetables, and are also found in many processed foods. Processed foods usually contain much more sugar than natural foods. Sugars act as sweeteners in food but they are also very high in energy. This is a concern because sugars make up a large part of the diet and if the energy isn't expended, the body stores the enrgy as fat. Excessive sugar in the diet can lead to nutritional disorders such as obesity and dental caries.


Polysaccharides: are very large moleculeswhich are formed from many monosaccharides joined together. The four most important polysaccharides are Starch, Glycogen, Pectin, and Cellulose.


Starch: is a complex carbohydrate and is a polymer of glucose produced by plants. there are two forms of starch, they are Amylose and Amylopectin. Amylose is linear in structure and contains between 50 and 500 glucose units. Amylopectin is in a branching structure and can contain upto 100 000 glucose units. Some sources of starch include wheat, rice, potatoes and oats. Starch is stored in granules of plants and is broken down to glucose for use as energy.

Glycogen is the body's equivalent to starch. It is stored in the liver and muscles, and is broken down into glucose when energy is required. The structure of glycogen is very similar to amylopectin but has more branching occuring every 10 - 15 glucose units.

Pectin: and pectic substances are compounds which are found in the cells of fruits and some root vegetables. Pectin isn't significant to human nutrition but are important in the gelling of certain foods eg. jams.

Cellulose: is dietary fibre found in plants and it is the undigestible part of plant foods. Cellulose is similar to starch but is structurally and nutritionally different because of the way the glucose molecules are joined together. The human body is incapable of digesting cellulose because it lacks the necessary enzymes. Cellulose is only broken down by the action of chewing.

Sources of Carbohydrates

Food sources of carbohydrates include grain products, potatoes, table sugar, syrups, fruit, cereals, pasta, flour, bread, soft drinks and vegetables.

Functions of Carbohydrates

The function of carbohydrates includes the glucose and the fibre in the carbohydrate foods.

Glucose: has a major role in nutrition because it is a readily available source of energy. Glucose supplies the body with heat and energy it needs, providing 16 kilojules of energy per gram. Glucose is obtained from food, through the digestion and absorption of sugars and starches. It is also obtained from glycogen which is stored in the liver and muscles, and is broken down into glucose when energy is required. Glucose can also be obtained from amino acids only when other sources fail, the glucose is transported to the cells of the body via the bloodstream.

Dietary fibre: isnt a actual nutrient since the body can't actually digest it. It provides no energy and no involvment in the growth and repair of the body, and doesn't regulate any metabolic processes. The dietary fibre passes through the digestive system and is then excreted. However the fibre has important functions in the digestive system. It slows the process of food passing through the stomach which contributes to the feeling of satiation (fullness). It also slows the passing of food through the small intestine which aids in the absorption of many nutrients. Dietary fibre also absorbs moisture which softens and increases the bulk of the wastes. This bulk then stimulates the muscles of the colon to contract which promotes excretion and avoids constipation.

Carbohydrates Worksheet

Click on the link below to go to the carbohydrates worksheet.

Carbohydrates Worksheet:

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