Biology Class 11 NCERT Solutions: Chapter 16 Digestion and Absorption Part 2

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Q: 4. State the role of pancreatic juice in digestion of proteins.


Pancreatic juice contains a variety of inactive enzymes such as trypsinogen, chymotrypsinogen, and carboxypeptidases. These enzymes play an important role in the digestion of proteins. Physiology of protein-digestion

The enzyme enterokinase is secreted by the intestinal mucosa. It activates trypsinogen into trypsin.


Trypsin then activates the other enzymes of pancreatic juice such as chymotrypsinogen and Carboxypeptidase.

Chymotrypsinogen is a milk-coagulating enzyme that converts proteins into peptides.

Carboxypeptidase acts on the carboxyl end of the peptide chain and helps release the last amino acids. Hence, it helps in the digestion of proteins. Peptides Smaller peptide chain + Amino acids

Thus, in short, we can say that the partially hydrolysed proteins present in the chyme are acted upon by various proteolytic enzymes of the pancreatic juice for their complete digestion.

Proteins, peptones Dipeptides and proteases

Image shows the pancreatic juice

Image Shows the Pancreatic Juice

Q: 5. Describe the process of digestion of protein in stomach.


The digestion of proteins begins in the stomach and is completed in the small intestine. The digestive juice secreted in the gastric glands present on the stomach walls is called gastric juice. The food that enters the stomach becomes acidic on mixing with this gastric juice.

The main components of gastric juice are hydrochloric acid, pepsinogen, mucus, and rennin. Hydrochloric acid dissolves the bits of food and creates an acidic medium so that pepsinogen is converted into pepsin. Pepsin is a protein- digesting enzyme. It is secreted in its inactive form called pepsinogen, which then gets activated by hydrochloric acid. The activated pepsin then converts proteins into proteases and peptides.

Rennin is a proteolytic enzyme, released in an inactive form called prorennin. Rennin plays an important role in the coagulation of milk.

Image shows the digestion of protein

Image Shows the Digestion of Protein

Q: 6. Given the dental formula of human beings


The dental formula expresses the arrangement of teeth in each half of the upper jaw and the lower jaw. The entire formula is multiplied by two to express the total number of teeth.

Image shows the tooth formulas

Image Shows the Tooth Formulas

The dental formula for milk teeth in humans is

Each half of the upper jaw and the lower jaw has 2 incisors, canine, and molars. Premolars are absent in milk teeth.

The dental formula for permanent teeth in humans is:

Each half of the upper jaw and the lower jaw has incisors, canine, premolars, and molars. An adult human has permanent teeth.

Image shows the dental formula

Image Shows the Dental Formula

Q: 7. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?


Bile is a digestive juice secreted by the liver. Although it does not contain any digestive enzymes, it plays an important role in the digestion of fats. Bile juice has bile salts such as bilirubin and biliverdin. These break down large fat globules into smaller globules so that the pancreatic enzymes can easily act on them. This process is known as emulsification of fats. Bile juice also makes the medium alkaline and activates lipase.

Q: 8. Describe the digestive role of chymotrypsin. What two other digestive enzymes of the same category are secreted by its source gland?


The enzyme trypsin (present in the pancreatic juice) activates the inactive enzyme chymotrypsinogen into chymotrypsin.

Image of the digestive role of chymotrypsin

Image of the Digestive Role of Chymotrypsin

The activated chymotrypsin plays an important role in the further breakdown of the partially hydrolysed proteins.

The other digestive enzymes of the same category are trypsinogen and Carboxypeptidase. These are secreted by the same source-gland, pancreas. Trypsinogen is present in an inactive form in the pancreatic juice. The enzyme enterokinase - secreted by the intestinal mucosa - activates trypsinogen into trypsin.


The activated trypsin then further hydrolyses the remaining trypsinogen and activates other pancreatic enzymes such as chymotrypsinogen and Carboxypeptidase. Trypsin also helps in breaking down proteins into peptides.

Carboxypeptidases act on the carboxyl end of the peptide chain and help in releasing the last amino acids.

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