NCERT & CBSE Biology Class 11 Digestive Enzymes notes

CBSE Biology 1 online notes & NCERT Solutions 11th science,

NCERT & CBSE Biology Class 11 Digestive Enzymes notes

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In this article, the following topic “Role of Digestive Enzymes” from the unit 5 named ‘Human Physiology’ of class 11 Biology syllabus is discussed.


Role of Digestive Enzymes – NCERT & CBSE Biology Class 11 Digestive Enzymes notes

Food acts as a source of energy for all creatures in this world including human beings.

Proper & complete digestion of food is necessary to harness energy out of it and to maintain good health. Complex components of food like Proteins, Carbohydrates, and Fats are converted into simpler molecules by the process called Digestion. In digestion, different types of digestive enzymes and gastrointestinal hormones play an important role in converting the complex substances of food into simpler substances which can be absorbed by the body. In this article, we will learn more about digestive enzymes, gastrointestinal hormones and their role in digestion.

Enzyme can be understood as any of a group of complex proteins or conjugated proteins that are produced by living cells and act as catalysts in specific biochemical reactions

The enzyme is a substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction. Enzymes are proteins that act as catalysts within living cells. Catalysts increase the rate at which chemical reactions occur without being consumed or permanently altered themselves. A chemical reaction is a process that converts one or more substances (known as reagents, reactants, or substrates) to another type of substance (the product).

As a catalyst, an enzyme can facilitate the same chemical reaction over and over again.

As we eat food, the food enters and travels through a long tube so called gastrointestinal tract or the alimentary canal.This alimentary canal starts at the mouth cavity and continues through the pharynx, oesophagus (food pipe), stomach, small and large intestines, rectum and finally stops at the anus. The food particles get digested gradually as they travel through various compartments of the alimentary canal. The process of digestion begins from the mouth cavity and ends in the anus.


Digestive Enzymes involved in the process of digestion can be classified into four broad categories:

  1. Lipolytic Enzymes: These enzymes break down fats into glycerol and fatty acids.
  2. Proteolytic Enzymes: These enzymes breakdown proteins into amino acids.
  3. Amylolytic Enzymes: These enzymes breakdown carbohydrates into simple sugars.
  4. Nucleolytic Enzyme:This enzyme breaks down nucleic acids into


  • The enzymes present in the mouth/saliva are:

Amylase: This is the enzyme that breaks down carbohydrates. When you chew carbohydrates/bread, it becomes sweeter as you chew because the mechanical action of your teeth and amylase in the saliva are breaking the carbohydrates down into their component sugars.

Bromelain: It is an anti-inflammatory compound, and tenderizes meat.

Ptyalin: This enzyme also breaks down carbohydrates into simple and single molecules of sugars.


  • Enzymes present in the stomach are:


Gastric amylase: It breaks down carbohydrates into simple sugar.

Gastric lipase: It breaks down fat into fatty acids and glycerol.

Gelatinase: This enzyme breaks down gelatine and collagen present in meat.

Pepsin: It breaks down proteins into smaller peptides.


  • Enzymes present in the pancreas are:


Chymotrypsin: It acts on proteins and breaks it down into aromatic amino acids

Elastase: It breaks down elastin

Nuclease: converts nucleic acids into nucleotides

Pancreatic amylase: It converts carbohydrates into simple sugar.

Trypsin: It breaks down peptides into amino acids.


  • Enzymes present in the small intestine are:


Lactase: Itconverts lactose to glucose and galactose.

Maltase: It converts maltose to glucose.

Sucrase: It breaks down sucrose to monosaccharides.

Watch animated video on ‘Role of Digestive enzymes’ by clicking at biology notes for class 11

In the stomach, the food resides about 60 to 90 minutes or more as it is further digested by the stomach acid and pepsin. Pepsin is a proteolytic enzyme released into the stomach. There is more mechanical breakdown too by the stomach muscles. If we consume plant enzymes, most of them are quite stable in the stomach environment and go to work. This gives the plant enzymes an edge on digestion over animal/pancreatic enzymes. Plant enzymes can be working on food for at least an hour before the food proceeds to the small intestine.

Once the food enters the small intestine, plant enzymes continue to work. At this point, any pancreatic or animal enzymes kick in. It is at this point that the naturally produced pancreatic enzymes are released by the pancreas. Some enzymes are released by the small intestine lining as well.

In the small intestine, three major digestive juices comprising various other enzymes are secreted. These are as follows:

  1. Bile juice
  2. Pancreatic juice
  3. Intestinal juice

Bile juice

Bile juice is secreted by the liver. It is a yellowish color fluid. The main function of bile juice is to digest the lipid molecules and to activate the lipase enzymes. Bile juice consists of the following components:

  1. Bilirubin and biliverdin
  2. Bile salts
  3. Cholesterol

Bile juice helps to break down the lipid molecules into di-and monoglycerides by the lipase enzymes.

Pancreatic Juice

Pancreatic juice contains digestive enzymes such as amylase for the hydrolysis of polysaccharides, lipase for the breakdown of fats, and trypsin and chymotrypsin for the digestion of proteins. These enzymes catalyze the breakdown of their substrates in an alkaline medium. But the catalysis does not completely break all the substrates into their simplest units.

Intestinal Juice

The complete digestion of the remaining food material takes place in the ileum (small intestine). There are numerous small glands in the walls of the small intestine. These glands secrete intestinal juice. The digestive enzymes in the intestinal juice break small peptides further into amino acids, disaccharides into monosaccharide’s, lipids into fatty acids and glycerol, and nucleic acids into nucleotides.

Anything that disrupts the small intestine may also disrupt the production and release of these enzymes. If we have a leaky gut, inflammation, yeast, or something else which hampers the small intestine, then we are likely to have trouble digesting the components of food on which these enzymes work on.

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