Class 11 Biology

Digestion Absorption

NCERT Solution

Question 1: Gastric juice contains

  1. Pepsin, lipase and rennin
  2. Trypsin, lipase and rennin
  3. Trypsin, pepsin and lipase
  4. Trypsin, pepsin and rennin

Answer: (a) Pepsin, lipase and rennin

Question 2: Succus entericus is the name given to

  1. A junction between ileum and large intestine
  2. Intestinal juice
  3. Swelling in the gut
  4. Appendix

Answer: (b) Intestinal juice

Question 3: Match column I with column II

Column IColumn II
(a) Bilirubin and biliverdin(1) Parotid
(b) Hydrolysis of starch(2) Bile
(c) Digestion of fat(3) Lipases
(d) Salivary gland(4) Amylases

Answer: (a) 2, (b) 4, (c) 3, (d) 1

Question 4: Why are villi present in the intestine and not in the stomach?

Answer: Major portion of absorption of food takes place in small intestine. Absorption in small intestine is also important because digestion is almost complete by the time food reaches ileum. Presence of villi in the stomach is not relevant because digestion is only partial in the stomach.

Question 5: How does pepsinogen change into its active form?

Answer: Pepsinogen changes into its active form by the action of hydrochloric acid.

Pepsinogen + HCl → Pepsin

Question 6: What are the basic layers of the wall of alimentary canal?

Answer: The wall of the alimentary canal is made of four layers, viz. serosa muscularis, sub-mucosa and mucosa. Serosa is the outermost layer and is made up of a thin mesothelium with some connective tissues. The epithelium of visceral organs is called mesothelium. Muscularis is formed by smooth muscles which are usually arranged into an inner circular and outer longitudinal layer. An oblique muscle layer may be present in some regions. The sub-mucosal layer is formed of loose connective tissues.

Question 7: How does bile help in the digestion of fats?

Answer: Bile helps in emulsification of fats and also activates lipases. Thus, bile helps in digestion of fats.

Question 8: State the role of pancreatic juice in digestion of proteins.

Answer: Proteins, proteoses and peptones are acted upon by the proteolytic enzymes of pancreatic juices; as given below:

Proteins/Peptones/Proteoses + Trypsin/Chymotrypsin/Carboxypeptidases → Dipeptides

Question 9: Describe the process of digestion of protein in stomach.

Answer: The proenzyme pepsinogen gets converted into the active enzyme pepsin; on exposure to hydrochloric acid. Pepsin converts proteins into proteoses and peptones (peptides).

Pepsinogen + HCl → Pepsin + Protein → Proteose + Peptone

Question 10: Give the dental formula of human beings.

Answer: In human beings, each half of the upper and lower jaw has teeth in the order I, C, PM, M as represented by following dental formula:


Question 11: Bile juice contains no digestive enzymes, yet it is important for digestion. Why?

Answer: Bile juice plays two important roles, i.e. of changing the medium of food from acidic to alkaline and of emulsifying the fat. Alkaline medium is necessary for action of enzymes in the succus entericus. Thus, bile is important for digestion.

Question 12: Describe the digestive role of chymotrypsin. Which two other digestive enzymes of the same category are secreted by its source gland?

Answer: Chymotrypsin completes the digestion of protein. Trypsin and carboxypeptidases are the two other enzymes of the same category secreted by its source gland.

Question 13: How are polysaccharides and disaccharides digested?

Answer: Polysaccharides are hydrolysed by pancreatic amylase into disaccharides.

Polysaccharides + Amylase → Disachharides

Disaccharides are then digested by the enzymes in succus entericus into various monosachharides.

Maltose + Maltase → Glucose + Glucose

Lactose + Lactase → Glucose + Galactose

Sucrose + Sucrase → Glucose + Fructose

Question 14: What would happen if HCl were not secreted in the stomach?

Answer: Acidic medium is necessary for the action of gastric enzymes. Moreover, it also kills various microbes which may be present in food. These actions would not be possible in the absence of hydrochloric acid.

Question 15: How does butter in your food get digested and absorbed in the body?

Answer: Butter is mainly composed of fat. Fat is digested by lipases.

Fats + Lipase → Diglycerides → Monoglycerides

Di and monoglycerides are then digested into fatty acids and glycerol.

Di and monoglycerides + Lipases → Fatty acids + Glycerol

Question 16: Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.

Answer: The proenzyme pepsinogen; in stomach; gets converted into the active enzyme pepsin; on exposure to hydrochloric acid. Pepsin converts proteins into proteoses and peptones (peptides).

Pepsinogen + HCl → Pepsin + Protein → Proteose + Peptone

Proteins, proteoses and peptones are acted upon by the proteolytic enzymes of pancreatic juices (in small intestine); as given below:

Proteins/Peptonse/Proteoses + Trypsin/Chymotrypsin/Carboxypeptidases → Dipeptides

The enzymes in the intestinal juice act on dipeptides to make amino acids.

Dipeptides + Dipeptidases → Amino acids

Question 17: Explain the term thecodont and diphyodont.

Answer: Thecodont: Each tooth is embedded in a socket of jaw bone. This type of attachment is called thecodont.

Diphyodont: The type of dentition in which an animal gets two sets of teeth during its lifetime is called diphyodont. This type of dentition is present in most of the mammals.

Question 18: Name different types of teeth and their number in an adult human.

Answer: Different types of teeth and their number in an adult human are as follows:

Incisors: 8
Canine: 4
Premolars: 8
Molars: 12

Question 19: What are the functions of liver?

Answer: Function of liver can be broadly categorized into two types, viz. synthesis and breakdown.



Breakdown of insulin and other hormones, haemogloin, some toxic substances and conversion of ammonia into urea takes place in liver.