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NCERT Class 11 Biology Chapter 16 Digestion and Absorption
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Digestion and Absorption
Chapter: 16
BIOLOGY
TEXTUAL QUESTIONS ANSWERS
Q.1. Choose the correct answer among the following:
(a) Gastric juice contains-
(i) pepsin, lipase and rennin.
(ii) trypsin lipase and rennin.
(iii) trypsin, pepsin and lipase.
(iv) trypsin, pepsin and renin.
Ans. (i) Pepsin, lipase, and rennin.
(b) Succus entericus is the name given to-
(i) a junction between ileum and large intestine.
(ii) intestinal juice.
(iii) swelling in the gut.
(iv) appendix.
Ans. (ii) Intestinal juice.
Q.2. Match column I with column II
| Column I | Column II |
| (a) Bilirubin and biliverdin. | (i) Parotid |
| (b) Hydrolysis of starch. | (ii) Bile |
| (c) Digestion of fat. | (iii) Lipases |
| (d) Salivary gland. | (iv) Amylases |
Ans.
| Column I | Column II |
| (a) Bilirubin and biliverdin. | (ii) Bile |
| (b) Hydrolysis of starch. | (iv) Amylases |
| (c) Digestion of fat. | (iii) Lipases |
| (d) Salivary gland. | (i) Parotid |
Q.3. Answer briefly:
(a) Why are villi present in the intestine and not in the stomach?
Ans. Small intestine has villi which increase the surface area for food absorption.
(b) How does pepsinogen change into its active form?
Ans. Pepsinogen is a precursor of pepsin and is converted into pepsin by hydrochloric acid.
(c) What are the basic layers of the wall of alimentary canal?
Ans. The walls of the alimentary canal are made up of four layers:
(i) Serosa.
(ii) Muscularis.
(iii) Sub-mucosa.
(iv) Mucosa.
(d) How does bile help in the digestion of fats?
Ans. Functions of Bile:
(i) Neutralization of HCI that comes from the stomach.
(ii) Emulsification of fats – Bile breaks large fat droplets into smaller ones.
(iii) Activation of Lipase.
Q.4. State the role of pancreatic juice in digestion of proteins.
Ans. Action of Pancreatic Juice in digestion of proteins-
(i) Pancreatic juice contains proenzymes – trypsinogen, chymotrypsinogen and procarboxypeptidase.
(ii) Trypsinogen is activated by enterokinase into active trypsin.
(iii) Trypsin activates chymotrypsinogen and procarboxypeptidase into chymotrypsin and carboxypeptidase.
(iv) The bile provides alkaline medium for enzymatic reactions.
(v) Trypsin, chymotrypsin and carboxypeptidase hydrolyse proteins, peptones and proteose into Dipeptides.
Q.5. Describe the process of digestion of protein in stomach.
Ans. Digestion of protein in stomach is with the help of Gastric Juice.
(i) Gastric juice contains hydrochloric acid, proenzymes – pepsinogen and prorennin.
(ii) Hydrochloric acid maintains acidic pH of 1.5 to 2.5 in the stomach.
(iii) HCI converts pepsinogen and prorennin into pepsin and rennin respectively.
(iv) Pepsin converts proteins into Peptones and Proteoses (Peptides).
(v) Rennin converts Casein (milk protein) into paracasein.
Q.6. Give the dental formula of human beings.
Ans. Dental formula of Milk Teeth –
2102/2102 X 2 = 20
Dental formula of Permanent Teeth –
2123/2123 X 2 = 32
Q.7. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?
Ans. Functions of Bile-
(i) Neutralization of HCI that comes from the stomach.
(ii) Emulsification of fats – Bile breaks large fat droplets into smaller ones.
(iii) Activation of Lipase.
Q.8. Describe the digestive chymotrypsin. What two role of other digestive enzymes of the same category are secreted by its source gland?
Ans. Chymotrypsin hydrolyse proteins, peptones and proteoses into Dipeptides.
The pancreatic juice contains-
(i) sodium bicarbonate.
(ii) three proenzymes – trypsinogen, chymotrypsinogen and procarboxypeptidase.
(iii) Enzymes – elastase, pancreatic amylase, nucleases and pancreatic lipase.
Q.9. How are polysaccharides and disaccharides digested?
Ans. DIGESTION OF CARBOHYDRATES
1. Oral cavity –
(i) The saliva contains salivary amylase which converts starch into maltose at optimum pH = 6.8.
(ii) Bicarbonate ions in saliva neutralize the acids in food.
[The gastric juice contains gastric amylase but its action is inhibited by the highly acidic condition.]
2. Small intestine-
(a) Action of Pancreatic Juice –
(i) The pancreatic juice has pancreatic amylase which converts starch into Maltose.
(ii) Bicarbonate of the pancreatic juice neutralizes hydrochloric acid of the chyme (semi fluid mass) that enters the duodenum.
(b) Action of Intestinal Juice-
(i) The intestinal juice contains maltase, sucrase and lactase which act as follows-
Q.10. What would happen if HCI were not secreted in the stomach?
Ans. Protein digestion is disturbed because pepsinogen is not activated to pepsin and acidic pH for gastric enzymes is not provided.
Q.11. How does butter in your food gets digested and absorbed in the body?
Ans. DIGESTION OF FATS
1. Stomach-
(i) Gastric juice contains gastric lipase which converts fats into monoglycerides and fatty acids.
2. Small Intestine-
(i) Fat is largely digested in small intestine.
(ii) Bile salts break down fat droplets into many small ones. This process is called emulsification.
(iii) Lipase is present in the pancreatic juice and intestinal juice.
(iv) Pancreatic lipase is the principal enzyme for the digestion of fat.
(v) Lipase is activated by the bile.
Absorption of Fatty acids and Glycerol-
(i) They are absorbed via diffusion.
(ii) Fatty acids and glycerol are converted into small water soluble droplets called micelles with help of bile salts.
(iii) Micelles are absorbed into intestinal mucosa by diffusion.
(iv) Micelles are converted into very small protein coated fat molecules called chylomicrons.
(v) Chylomicrons are transported into lymphatic vessels called lacteals in the villi.
Q.12. Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.
Ans. DIGESTION OF PROTEINS
(i) Stomach.
Action of Gastric Juice-
(i) Gastric juice contains hydrochloric acid, proenzymes – pepsinogen and prorennin.
(ii) Hydrochloric acid maintains acidic pH of 1.5 to 2.5 in the stomach.
(iii) HCI converts pepsinogen and prorennin into pepsin and rennin respectively.
(iv) Pepsin converts proteins into Peptones and Proteoses (Peptides).
(v) Rennin converts Casein (milk protein) into paravasein.
2. Small intestine-
Action of Pancreatic Juice-
(i) Pancreatic juice contains proenzymes – trypsinogen, chymotrypsinogen and procarboxypeptidase.
(ii) Trypsinogen is activated by enterokinase into active trypsin.
(iii) Trypsin activates chymotrypsinogen and procarboxypeptidase into chymotrypsin and carboxypeptidase.
(iv) The bile provides alkaline medium for enzymatic reactions.
(v) Trypsin, chymotrypsin and carboxypeptidase hydrolyse proteins, peptones and proteoses into Dipeptides.
Action of Intestinal Juice-
(i) Intestinal juice contains enterokinase, aminopeptidase and dipeptidases.
(i) Enterokinase juice converts trypsinogen of pancreatic juice into trypsin.
Q.13. Explain the term thecodont and diphyodont.
Ans. Diphyodont Teeth: Two sets of teeth – temporary and permanent.
Thecodont: Teeth are embedded in sockets of the jaw bones.
Q.14. Name different types of teeth and their number in an adult human.
Ans. Temporary teeth or Milk/Deciduous teeth: are 20 in number; 10 in each jaw.
Milk teeth include 8 incisors, 4 canines and 8 molars.
Permanent teeth: replace the milk teeth and are 32 in number; 16 in each jaw.
Permanent teeth include 8 incisors, 4 canines, 8 premolars and 12 molars.
Q.15. What are the functions of liver?
Ans. Liver has Kupffer cells that are phagocytic cells. Liver cells (hepatocytes) secrete bile which is stored in Gall Bladder.
