1. Chemical Basis of Life

The bodies of all organisms are composed of variety of chemical compounds.

There are only about 25 elements in the living body out of the 92 elements present in nature.

The most common 4 elements in the living body are 

Other than above Sulphur, Phosphorous, Sodium, Potassium, Calcium, Magnesium, Iron and Chlorine are essential for the survival of organisms. 

Chemical compounds that build up living matter can be divided into two categories as organic compounds and inorganic compounds.

Those organic compounds that build up the living body or living matter are known as bio molecules.

Carbohydrates

This is the most abundant organic compound on earth. 

They are produced during the photosynthesis of green plants. 

Potato, sweet potato, grains, sugar, flour are some of the examples for foods which contain carbohydrates. 

The main elemental composition of carbohydrates is Carbon (C), Hydrogen (H) and Oxygen (O).

Hydrogen and oxygen combine in 2:1 ratio in carbohydrates.

Significance of Carbohydrates

• As an energy Source - The main source to obtain energy for the activities of organisms is the carbohydrate. The Monosaccharides (Glucose) produced due to hydrolysis of those compounds release energy. 

• As a storage compound 

• As a structural component in plant cell wall 

• As a constituent of Nucleic acid

Tests to identify Carbohydrates

Starch test 

Small amount of food is obtained and grind well with water. 

A drop of Iodine solution is added to the above solution. 

Purplish blue colour appears

Test for Glucose

A solution of Glucose is obtained into a test tube. 

Few drops of Benedict solution to the above solution is added.

The above solution is immersed in a water bath and heated.

Can observe colour changes as below.

Blue --> Green --> Green yellow --> Orange --> Brick red precipitate

Test for (Sucrose) 

A sucrose solution is obtained into a test tube. 

Few drops of Benedict solution is added to it. 

The test tube is immersed in a water bath and heated. 

No colour change. 

Few drops of diluted Sulphuric acid (H2SO4) is added to a freshly prepared sugar solution and heated.

Neutralize the excess acids by adding NaHCO3 until red litmus change to blue

Next few drops of Benedict solution is added to it. 

Can observe colour changes as below. 

Blue --> Green --> Green yellow --> Orange --> Brick red precipitate 

Proteins

Protein is an essential constituent in all living cells. 

Carbon(C) Hydrogen (H), Oxygen (O) and Nitrogen (N) are always present in proteins. Sometimes Sulphur can also be present. 

17% of the mature human body is composed of proteins. 

Protein is a complex molecule made up of polymerized amino acid molecules. 

Meat, fish, egg white cereals are some of the foods rich with proteins

Amino acids 

Due to the change in R group, 20 different amino acids are present. 

All proteins present in organisms from bacteria to human are made up of these 20 different amino acids combined in different sequences

Significance of Proteins 

• As an energy source 

When energy supply from Lipids and Carbohydrates is not sufficient protein is used in energy generation. 

• To make structural components 

Proteins are important components in making cell membrane. Hairs and feathers also contain keratin protein. 

• As enzymes 

All the bio-chemical reactions take place in organisms are catalyzed by enzymes. The enzymes are proteins.

• As hormones 

Some hormones are proteins which involve in homeostasis and coordination of organisms. 

• As antibodies 

The antibodies that are produced in the body to protect the body against microorganisms that enter into the body are proteins.

Test to identify proteins 

Biuret test 

A solution made by grinding dhal or an egg white is obtained into a test tube. 

An extra amount of Sodium hydroxide (NaOH) and then few drops of Copper Sulphate is added into it.

(CuSO4) Solution turn to purple colour  

Enzymes 

The special proteins (organic catalysts) that are produced within the organism to increase the rate of bio-chemical reactions are known as enzymes. 

For example, to convert Sucrose into Glucose, Sucrose has to be heated with a dilute acid. 

But the enzymes present in the digestive system do the same reaction at a low temperature. 

Therefore, the activity of enzyme is to catalyze the bio-chemical reactions. 

Activity of Amylase on Starch 

Materials required 

Flour, Amylase, Test tube, white porcelain tile, Iodine solution, Water, A stop watch 

Method 

• Put 2ml of Starch solution into a test tube. 
• Add 2ml of Amylase (Filter a solution of ground germinating green gram (Mung) seedlings) into it and mix well.
• Get a drop from the solution after 2 minutes and place it on a white porcelain tile.
• Add a drop of Iodine onto the drop of mixture.
• Continue same procedure for about 20 minutes in 2 minute intervals. 

Observation 

The blue colour of the drop obtained from the mixture gradually reduces with time and finally obtains the colour of Iodine (yellow /brown colour) 

Conclusion

Starch gives black blue colour with Iodine but it does not give colour change with Iodine after 20 minutes as there is no Starch there.

That is because Starch is converted to Maltose by Amylase enzyme