Carbohydrates are an essential macromolecule in living organisms and play an important role in our diets. They are the main source of energy for our bodies and provide fuel for our cells. Carbohydrates are found in many of the foods we eat, such as pasta, bread, and biscuits. They are also essential for cell structure and recognition. [^3]

Glucose is the main form of energy that carbohydrates provide. It is important for the normal functioning of living organisms and helps to keep us energized. Eating the right amount of carbohydrates can help to prevent digestive problems, like constipation and indigestion. [^6] Fiber is a type of carbohydrate that is especially beneficial for digestion and can help to keep cholesterol levels in check.

The chemical structure of carbohydrates

Carbohydrates are organic compounds made of the elements carbon, hydrogen, and oxygen. The ratio of hydrogen atoms to oxygen atoms in carbohydrate molecules is 2:1 . Carbohydrates serve as energy sources and as essential structural components in organisms; in addition, part of the structure of nucleic acids, which contain genetic information, consists of carbohydrate. There are thousands of different carbohydrates, but they all consist of one or more smaller units called monosaccharides. Every carbon atom is attached to one oxygen atom. Carbohydrates contain a chain of carbons, an aldehyde or a ketone, and hydroxyl groups.

The molecular structure of carbohydrates

Carbohydrates are made up of simple sugar molecules called saccharides. A single unit of carbohydrate is called a monosaccharide. The prefix "mono-" means one and "sacchar" means sugar. Examples of monosaccharides include glucose, fructose, and galactose. These simple sugars are the building blocks of more complex carbohydrates, such as disaccharides and polysaccharides.

Types of carbohydrates

Carbohydrates can be classified into simple and complex types. Simple carbohydrates are small molecules composed of one or two sugar molecules, also known as monosaccharides and disaccharides, respectively. Monosaccharides are single sugar molecules, such as glucose, galactose, fructose, deoxyribose, and ribose. They are soluble in water and serve as the building blocks for larger carbohydrate molecules called polysaccharides. Disaccharides, such as sucrose, lactose, and maltose, are formed by linking two monosaccharides together and are also soluble in water.

Complex carbohydrates are larger molecules composed of long chains of sugar molecules, or polysaccharides. Polysaccharides are not sugars, even though they are made up of glucose units. They are insoluble in water and have many important functions in the body, including energy storage and structural support. Three important polysaccharides are starch, glycogen, and cellulose. Starch is a polysaccharide found in plants and is an important source of dietary carbohydrates. Glycogen is a highly branched polysaccharide found in animals and serves as a storage form of glucose. Cellulose is a complex polysaccharide found in plant cell walls and provides structural support to the plant. 

The main function of carbohydrates

Carbohydrates play a crucial role in providing and storing energy for important cellular processes, such as respiration. They are stored as starch in plants and glycogen in animals. However, beyond their role in energy metabolism, carbohydrates also have other important functions. For example, carbohydrates play a structural role in cells, with cellulose serving as a key component of cell walls. Carbohydrates are also essential building blocks for biological macromolecules, including nucleic acids such as DNA and RNA, which contain simple carbohydrates such as deoxyribose and ribose as part of their structure. In addition, carbohydrates can attach to proteins and lipids to form glycoproteins and glycolipids. These carbohydrate-containing molecules play important roles in cell recognition, which is crucial for the formation of tissues and organs. Overall, carbohydrates are essential molecules that play many important roles in biological processes.

How do you test for the presence of carbohydrates?

You can use two tests to test the presence of different carbohydrates: Benedict's test and the iodine test.

Benedict's test

Benedict's test is used to test for simple carbohydrates: reducing and non-reducing sugars. It is called Benedict's test because Benedict's reagent (or solution) is used. To perform the test, you need a test sample (liquid or solid, dissolved in water if it is solid), a test tube, and Benedict's reagent (which is blue in colour).

For reducing sugars, the test is performed by adding 2cm3 (2 ml) of the test sample into a test tube, adding the same amount of Benedict's reagent, and heating the solution in a gently boiling water bath for five minutes. The change in colour of the solution is then observed and recorded.

For non-reducing sugars, the test is performed by adding 2cm3 (2 ml) of the test sample into a test tube, adding the same amount of dilute hydrochloric acid, heating the solution in a gently boiling water bath for five minutes, adding sodium hydrogen carbonate to neutralize the solution, checking the pH of the solution with a pH tester, and then adding Benedict's reagent to the solution. The solution is then heated in a gently boiling water bath for five minutes and the change in colour is observed and recorded. If there is any, it means reducing sugars are present. Therefore, you can conclude that a non-reducing sugar is present in the sample, as it was successfully broken down into reducing sugars.

Iodine test

The iodine test is a simple and widely used test to detect the presence of starch, which is a complex carbohydrate made up of many glucose units. The test is performed using a solution called potassium iodide, which is yellow in color.

To perform the test, 2 cm3 (2 ml) of the test sample (liquid or solid) is added to a test tube, and a few drops of the potassium iodide solution are added. The solution is then shaken or stirred, and the change in color is observed. If the solution turns blue-black, it indicates the presence of starch. If there is no change and the solution remains yellow, it means that there is no starch present.

This test can also be performed on solid test samples, such as peeled potatoes or grains of rice. In this case, a few drops of the potassium iodide solution are added to the solid sample, and if the color changes to blue-black, it indicates the presence of starch.

Overall, the iodine test is a simple and effective way to detect the presence of starch in various test samples, and it is widely used in many fields, including food science, biology, and chemistry.


What exactly are carbohydrates?

Carbohydrates are organic biological molecules and one of the four most important biological macromolecules in living organisms.

What is the function of carbohydrates?

The main function of carbohydrates is to provide and store energy. Other functions include structural components of cells, building macromolecules, and cell recognition.

What are examples of carbohydrates?

 Examples of carbohydrates are glucose, fructose, sucrose (simple carbohydrates) and starch, glycogen, and cellulose (complex carbohydrates).

What are complex carbohydrates?

Complex carbohydrates are large molecules - polysaccharides. They consist of hundreds and thousands of covalently bonded glucose molecules. Complex carbohydrates are starch, glycogen, and cellulose.

What elements make up carbohydrates?

Elements that make up carbohydrates are carbon, hydrogen, and oxygen.

How does the structure of carbohydrates relate to their function?

The structure of carbohydrates relate to their function in that it makes complex carbohydrates compact, allowing for them to be stored easily and in great amounts. Also, branched complex carbohydrates are easily hydrolysed so that small glucose molecules are transported to and absorbed by cells as an energy source.

Join Shiken For FREE

Gumbo Study Buddy

Try Shiken Premium
for Free

14-day free trial. Cancel anytime.
Get Started
The first 14 days are on us
96% of learners report x2 faster learning
Free hands-on onboarding & support
Cancel Anytime