1st PUC Biology Question Bank Chapter 16 Digestion and Absorption

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Karnataka 1st PUC Biology Question Bank Chapter 16 Digestion and Absorption

1st PUC Biology Digestion and Absorption NCERT Text Book Questions and Answers

Question 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
Answer:
(i) Pepsin, lipase and rennin

(b) Succus entericus is the name given to
(i) A junction between the ileum and large intestine
(ii) Intestinal juice
(iii) Swelling in the gut
(iv) Appendix
Answer:
(ii) Intestinal juice

KSEEB Solutions

Question 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
Answer:
(a) – ii
(b) – iv
(c) – iii
(d) – i

Question 3.
Answer briefly:
(1) Why are villi present in the intestine and not in the stomach?
Answer:
Because villi are supplied with a network of capillaries and a large lymph vessel called a lacteal. The mucosal epithelium has goblet cells which secrete mucus that help in lubrication. Mucosa also forms glands in the stomach (gastric glands) and crypts in between the bases of villi in the intestine (crypts of lieberkuhn).

(2) How does pepsinogen change into its active form?
Answer:
The proenzyme pepsinogen, on exposure to hydrochloric acid, gets converted into the active enzyme pepsin, the proteolytic enzyme of the stomach. Pepsin converts proteins into proteases and peptones (peptides).

(3) What are the basic layers of the wall of the alimentary canal?
Answer:
The wall of the alimentary from the esophagus to the rectum possesses four layers namely serosa, muscularity, submucosa, and mucosa. The serosa is the outermost layer and is made up of a thin mesothelium (epithelium of visceral organs) with some connective tissues. Muscularity is formed by smooth muscles usually arranged into an inner circular and an outer longitudinal layer. An oblique muscle layer may be present in some regions. The submucosal layer is formed of loose connective tissue containing nerves, blood, and lymph vessels. In the duodenum, glands are also present in the submucosa. The innermost layer lining the lumen of the alimentary canal is the mucosa.

(4) How does bile help in the digestion of fats?
Answer:
The bile released into the duodenum contains bile pigments (bilirubin and biliverdin), bile salts, cholesterol and phospholipids but no enzymes. Bile helps in the emulsification of fats i.e. break down the fats into very small micelles. Bile also activates lipases. Fats are broken down by lipases with the help of bile into di-and monoglycerides.

Question 4.
State the role of pancreatic juice in the digestion of proteins.
Answer:
The pancreatic juice contains inactive enzymes trypsinogen, chymotrypsinogen, procarboxy¬peptidases, amylases, lipases, and nucleases. Trypsinogen is activated by an enzyme enterokinase secreted by intestinal mucosa into active trypsin, which in turn activates the other enzymes in the pancreatic juice. These enzymes are concerned with protein, carbohydrate, fats, and nucleic acid digestion.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 1

Question 5.
Describe the process of digestion of protein in the stomach.
Answer:
The proenzyme pepsinogen present in the stomach gets converted to proteolytic enzyme pepsin in presence of Hydrochloric acid. Pepsin converts proteins into proteases and peptones. Rennin is another proteolytic enzyme present in the gastric juice of infants which helps in the digestion of milk proteins.

Question 6.
Give the dental formula of human beings.
Answer:
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 2

Question 7.
Bile juice contains no digestive enzymes, yet it is important for digestion. Why?
Answer:
Bile is a watery greenish fluid mixture containing bile pigments, bile salts, cholesterol, and phospholipids. Bile helps in the emulsification of fats i.e. breaking down of the fats into smaller micelles, it also activates lipases. Thus, it is important for digestion.

Question 8.
Describe the digestive role of chymotrypsin. Which two other digestive enzymes of the same category are secreted by its source gland?
Answer:
Chymotrypsin is a protein digestive enzyme that breaks down proteins, peptones, and proteoses into dipeptides. The other two proteolytic enzymes are trypsin and carboxyl peptidase.

KSEEB Solutions

Question 9.
How are polysaccharides and disaccharides digested?
Answer:
About 30% of starch is hydrolysed by the enzyme salivary amylase into disaccharide maltose in oral cavity.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 3
Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides. Polysaccharides (starch)
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 4
Maltase present in the intestinal juice converts maltose into glucose. Lactase converts lactose into glucose and galactose. Sucrase converts sucrose into glucose and fructose
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 5

Question 10.
What would happen if HCl were not secreted in the stomach?
Answer:
Importance of HCl secreted by stomach:
HCl provides the acidic pH (pH 1.8) optimal for pepsins. It converts proenzyme pepsinogen into active enzyme pepsin, the proteolytic enzyme of the stomach.
HCl is also necessary to kill harmful bacteria which may be present in the food.

Question 11.
How does butter In your food get digested and absorbed in the body?
Answer:
Butter is rich in lipids. Digestion of fat starts in the stomach. The gastric lipase hydrolyses a small amount of lipids. Bile helps in the emulsification of fats and activates lipases which break down fats into diglycerides and then to monoglycerides. Monoglycerides and Diglycerides are further broken down to fatty acids and glycerol in presence of a lipase.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 6
Fatty acids and glycerol being insoluble is converted to small droplets called micelles which are reformed to very small protein-coated fat globules called the chylomicrons which are absorbed by the intestine villi.

Question 12.
Discuss the main steps in the digestion of proteins as the food passes through different parts of the alimentary canal.
Answer:
There is no protein digestion in the oral cavity as there are no proteases present.
Stomach: The proenzyme pepsinogen, on exposure to hydrochloric acid gets converted to active enzyme pepsin. Which converts proteins into proteases and peptones.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 7

Intestine: Pancreatic juice contains inactive enzymes like trypsinogen, chymotrypsinogen, and procarboxy peptidases. Trypsinogen is converted to active trypsin with the help of the enzyme enterokinase. Trypsin, in turn, activates other proteolytic enzymes in the pancreatic juice. Proteins, proteoses, and peptones in the intestine are now converted to dipeptides in presence of trypsin, chymotrypsin, and carboxypeptidase.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 8

The aminopeptidase hydrolyses the peptide bond that attaches the terminal amino acid to the amino end of the peptide. Dipeptidase acts on dipeptides and converts them to amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 9
Amino acids are the end products of protein digestion.

Question 13.
Explain the terms thecodont and diphyodont.
Answer:
The alimentary canal begins with an anterior opening-the mouth, and it opens out posteriorly through the anus. The mouth leads to the buccal cavity or oral cavity. The oral cavity has a number of teeth and a muscular tongue. Each tooth is embedded in a socket of the jaw bone. This type of attachment is called thecodont. The majority of mammals including humans forms two sets of teeth during their life, a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. This type of dentition is called diphyodont.

Question 14.
Name different types of teeth and their number in an adult human.
Answer:
Incisors – 8, canine – 4, premolars – 8, molars – 12.

Question 15.
What are the functions of the liver?
Answer:
Functions of Liver:

  1. The liver performs several roles in carbohydrate, lipid, and protein metabolism.
  2. The liver is responsible for the mainstay of protein metabolism, synthesis as well as degradation.
  3. The liver produces and excretes bile (a greenish liquid) required for emulsifying fats.
  4. The breakdown of insulin and other hormones
  5. The liver breaks down hemoglobin, creating metabolites that are added to bile as a pigment (bilirubin and biliverdin).
  6. The liver converts ammonia to urea.

1st PUC Biology Digestion and Absorption Additional Questions and Answers

1st PUC Biology Digestion and Absorption One Mark Questions

Question 1.
What type of medium is required for the activity of trypsin?
Answer:
Alkaline medium.

Question 2.
Which cells secrete HCI?
Answer:
Parietal cells.

Question 3.
What is the other name for Pancreatic amylase?
Answer:
Amylopsin

Question 4.
What is chylomicron?
Answer:
The reconstructed triglycerides combine with phospholipids and cholesterol are released into the lymph in the form of protein-coated water-soluble fat globules or droplets. These are called chylomicron.

Question 5.
Which glands secrete HCI?
Answer:
Gastric glands.

Question 6.
Which digestive Juice is non-enzymatic?
Answer:
BWe.

Question 7.
Which gland secretes Bile?
Answer:
Liver.

Question 8.
Where is caecum located in the alimentary canals?
Answer:
The caecum is located at the junction of the small intestine and colon (large intestine).

Question 9.
What type of muscles present on the wall stomach?
Answer:
Smooth muscles.

Question 10.
Which part of small intestine is the longest?
Answer:
Ileum

Question 11.
Give an example of a vestigial organ.
Answer:
Vermiform appendix. (Oct. 83)

Question 12.
How is the tongue attached to the floor of the buccal cavity?
Answer:
The tongue is attached to the floor of the buccal cavity by the frenulum.

KSEEB Solutions

Question 13.
Mention the function of villi. (Oct. 84)
Answer:
The Villi are structures of the intestinal wall that increase the surface of absorption i.e. their chief function is absorption

Question 14.
What is ‘Bile’? (Oct. 85)
Answer:
Bile is the juice secreted by the liver.

Question 15.
What is the mechanical action taking place in the mouth called? (Oct. 90)
Answer:
The mechanical action taking place in the mouth is known as ‘Mastication’.

Question 16.
Name a proteolytic enzyme
Answer:
Pepsin (or trypsin, chymotrypsin, carboxypeptidase Aminopeptidase, tripeptidase, dipeptidase – anyone can be named)

Question 17.
Name the gland which is both exo and endocrine? (April 93)
Answer:
Pancreas.

Question 18.
What is the sphincter of Oddi?
Answer:
The sphincter of Oddi is the muscular structure, that guards the opening of the hepato-pancreatic duct into the duodenum.

Question 19.
Name the Enzyme that hydrolyses lipids.
Answer:
‘Lipases’ hydrolyze lipids. (Oct. 94)

Question 20.
Name the enzyme which does not act on the food materials in the small intestine.
Answer:
The “Enterokinase” enzyme.

Question 21.
What prevents the entry of food into the larynx during swallowing? (April 96)
Answer:
Epiglottis.

Question 22.
Which hormone causes Diabetes mellitus? (April 1996)
Answer:
The deficiency of ‘Insulin’ causes Diabetes mellitus.

Question 23.
Name the pancreatic hormone which acts as a hypoglycemic factor.(April 97, M.Q.P.)
Answer:
Insulin acts as a hypoglycemic factor.

Question 24.
Name the Carbohydrate digesting enzyme present in saliva. (Oct. 97)
Answer:
Salivary amylase or Ptyalin.

Question 25.
What is the basic mechanism of digestion in the intestine? (Oct. 88)
Answer:
‘Hydrolysis’.

Question 26.
The catalytic activity of which enzyme produces Fructose as one of the end products? (Oct. 88)
Answer:
Sucrase acts on the disaccharide sucrose resulting in a molecule of Fructose and a molecule of glucose.

Question 27.
What type of enzyme is pepsin? (Oct. 89)
Answer:
Proteolytic enzyme.

Question 28.
What Is emulsification? (Oct. 98)
Answer:
Emulsification is a process by which fats are converted to small water-soluble muscles by Bile salts making them easily accessible to the action of Fats digesting enzymes called lipases.

KSEEB Solutions

Question 29.
Mention the function of microvilli. (April 99)
Answer:
The chief function of the microvilli is absorption (i.e., it increases the surface of absorption).

Question 30.
What Is Chyme? (April 2000, July 2010)
Answer:
The liquified and acidified food present in the stomach is called as chyme.

Question 31.
What are the end products of protein digestion? (April 2001)
Answer:
Amino acids.

Question 32.
What is Peristalsis? (Oct. 2003)
Answer:
The powerful, rhythmic waves of muscular contraction and relaxation in the walls of hollow tubular organs like the digestive tract is called peristalsis.

Question 33.
Name an enzyme present in saliva meant for killing bacteria. (July 2006)
Answer:
Lysozyme.

Question 34.
What Is succus entericus? (April 2007)
Answer:
Succus entericus is the intestinal juice made of water, mucin and 7 digestive enzymes.

Question 35.
Give reason: (July 2008)
In the absence of Enterokinase, protein digestion is incomplete.
Answer:
Enterokinase activates trypsinogen to trypsin which breaks down proteins. Hence the absence of enterokinase results in indigestion of proteins.

Question 36.
Mention two characteristics of mammalian teeth.
Answer:
Heterodont and thecodont.

Question 37.
Why are proteases generally released In – inactive form? (All India 2003)
Answer:
proteases are inactive form, they would hydrolyse the cellular and extracellular proteins of the gut wall in the absence of food.

Question 38.
What are micelles? (All India 1998)
Answer:
The products of fat digestion are incorporated with the help of bile salts and phospholipids, into small spherical, water-soluble droplets called micelles.

Question 39.
Name the passage that leads bile from the liver Into gall bladder. (Delhi 1998)
Answer:
Cystic duct.

Question 40.
Name the different parts of large intestine in humans in their natural sequence. (Delhi 1998C)
Answer:
Caecum, colon and rectum.

Question 41.
What is the number of permanent teeth in an adult human being?
Answer:
32. (Thirty-two).

KSEEB Solutions

Question 42.
Name the two sets of teeth a human gets In his life.
Answer:
Milk teeth (deciduous teeth) and permanent teeth.

Question 43.
Name the substance that makes up the chewing surface of teeth.
Answer:
Ename

Question 44.
What are the four different types of teeth present in humans?
Answer:
lncisdrs, canine, premolars, and molars.

Question 45.
How many (I) molar and (II) premolar teeth are there in an adult human?
Answer:

  • 12 molars
  • 8 premolars.

Question 46.
Where are the taste buds located?
Answer:
Taste buds are located in the papillae on the upper surface of the tongue.

Question 47.
How is the tongue attached to the floor of the buccal cavity?
Answer:
The tongue is attached to the floor of the buccal cavity by the frenulum.

Question 48.
What is the function of epiglottis?
Answer:
Epiglottis prevents the entry of food into the trachea during swallowing.

Question 49.
Name the muscular structure that regulates the movement of food from the esophagus into the stomach.
Answer:
Gastro-Oesophageal sphincter.

Question 50.
Where is the stomach located?
Answer:
Stomach is located in the upper part of the abdominal cavity on the left side, just below the diaphragm.

Question 51.
Name the three regions of the stomach in proper sequence.
Answer:
Cardiac, fundic and pyloric regions.

Question 52.
Which part of the stomach does the oesophagus enter into?
Answer:
Cardiac region.

Question 53.
Which part of the stomach continues into the duodenum?
Answer:
Pyloric region.

Question 54.
Name the three regions of the human small intestine in the proper sequence.
Answer:
Duodenum, jejunum and ileum.

KSEEB Solutions

Question 55.
Name the muscular structure that guards the opening of the stomach Into the duodenum.
Answer:
Mr.-Pyloric sphincter.

Question 56.
Name the part of the alimentary canal where symbiotic microbes live.
Answer:
Caecum.

Question 57.
Name the three parts of the colon.
Answer:
Ascending, transverse and descending part.

Question 58.
Name any two structural features of the small intestine, which helps in absorption.
Answer:

  • Presence of villi
  • Projections called microvilli giving brush border appearance.

Question 59.
What is the name of the major lymph vessel present in the intestinal villi?
Answer:
Lacteal.

Question 60.
Where are the crypts of leiberkuhn located?
Answer:
They are located in between the bases of the villi in the intestine.

Question 61.
Name any two major glands associated with the human alimentary canal.
Answer:
Pancreas, liver, and the salivary glands.

Question 62.
Name the largest gland in our body.
Answer:
Liver.

Question 63.
Name the structural and functional unit of liver.
Answer:
Hepatic lobules.

Question 64.
Name the connective tissue sheath of liver lobules.
Answer:
Glisson’s capsule.

Question 65.
What are the constituents of the common bile duct?
Answer:
Hepatic duct and cystic duct.

Question 66.
How does bile reach the gall bladder?
Answer:
The bile secreted by the hepatic cells passes through the hepatic ducts and enters the gall bladder through the cystic duct.

Question 67.
What is sphincter of Oddi?
Answer:
Sphincter of Oddi is the muscular structure, that guards the opening of the hepato-pancreatic duct into the duodenum.

KSEEB Solutions

Question 68.
Name one gland in human body, that secretes both digestive enzymes as well as hormones.
Answer:
Pancreas.

Question 69.
What are the two major functions of buccal cavity?
Answer:
Buccal cavity helps in the mastication of food and facilitates in swallowing.

Question 70.
What is a bolus?
Answer:
When thoroughly masticated food mixes with saliva, the food particles stick together with the help of mucus into what is known as bolus.

Question 71.
Define deglutition.
Answer:
Deglutition is the process of swallowing in which bolus is conveyed into the pharynx and then into the oesophagus.

Question 72.
In humans, starch digestion begins in the buccal cavity, but stops in the stomach. Why?
Answer:
Hydrochloric acid in the gastric juice (acidic pH) inactivates salivary amylase. Hence starch digestion stops in the stomach.

Question 73.
What is the role of the intrinsic factor?
Answer:
lntrinsic factor helps in the absorption of vitamin B12 from the intestine.

Question 74.
Name two enzymes which take part in the digestion of proteins in our body.
Answer:
Pepsin, trypsin, chymotrypsin and carboxypeptidase.

Question 75.
What type of medium (pH) is required for the activity of trypsin?
Answer:
Trypsin requires an alkaline pH.

Question 76.
What is the role of intrinsic factor?
Answer:
Intrinsic factor helps in absorption of vitamin B12from the intestine.

Question 77.
Name two enzymes which take part in the digestion of proteins in our body.
Answer:
Pepsin, Trypsin, Chymotrypsin and carboxypeptidase.

Question 78.
What type of medium (pH) is required for the activity of trypsin?
Answer:
Trypsin requires an alkaline pH.

KSEEB Solutions

Question 79.
What provides the alkaline medium for the action of trypsin in small Intestine?
Answer:
Alkaline medium is provided by bile from the liver and bicarbonates from the pancreas and Brunner’s glands.

Question 80.
What are peptones?
Answer:
Peptones are partially hydrolysed proteins.

Question 81.
Which is the food constituent which bile helps to digest and absorb?
Answer:
Fats.

Question 82.
Name the bile pigments?
Answer:
Bilirubin and biliverdin.

Question 83.
Name the end products of digestion of fats.
Answer:
Glycerol, fatty acids, and monoglycerides.

Question 84.
Define absorption.
Answer:
Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph.

Question 85.
Name the form in which fats enter lymph.
Answer:
Chylomicrons.

Question 86.
What are chylomicrons?
Answer:
Chylomicrons are the protein-coated, water-soluble globules of the newly synthesized fats that is combined with phospholipids and liberated into the lymph for circulation.

Question 87.
What is defaecation?
Answer:
The egestion of faeces through the anal opening is called defaecation.

Question 88.
Name the most common disorder of the alimentary system.
Answer:
Inflammation of the intestinal tract.

Question 89.
Which of the body is affected by jaundice?
Answer:
Liver.

Question 90.
What is Constipation?
Answer:
Constipation is the condition where the faeces are retained within the rectum, as the bowel movement occurs irregularly.

KSEEB Solutions

Question 91.
What is facilitated transport?
Answer:
Some of the substances like fructose and few amino acids are absorbed by the blood with the help of carrier ions like Na+. This mechanism is called facilitated transport.

1st PUC Biology Digestion and Absorption Two Marks Questions

Question 1.
If the pancreatic duct of a person is blocked, how would it affect the digestion of fat in the duodenum?
Answer:
If the pancreatic duct is blocked, the pancreatic juice cannot reach the duodenum. As a result, the enzymes like trypsin, chymotrypsin, carboxypeptidase, aminopeptidase (help in the digestion of protein); amylase (help in carbohydrate digestion), lipase (help in fat digestion) could not reach the duodenum. Digestion of carbohydrates, proteins, and fats will remain incomplete.

Question 2.
Mention any four proteolytic enzymes Involved in human digestion. (April 90)
Answer:

  • Pepsin
  • Trypsin
  • Chymotrypsin
  • Carboxypeptidase.

Question 3.
Name the watery fluid secreted from Brunner’s gland in the duodenum. Mention its any two characteristics. What role does it play inside the duodenum?
Answer:
The watery fluid secreted by Brunner’s gland is called mucoid fluid or mucus.
Characteristics:
(i) It is viscous.
(ii) It is enzyme-free
(iii) It is alkaline in nature.
Functions:
It enables the duodenum to withstand the acidic chyme entering from the stomach.

Question 4.
Write the role of Trypsin and Chymotrypsin in protein digestion. (April 2002)
Answer:
Trypsin is secreted as trypsinogen. It is activated by the enterokinase of the intestinal juice.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 10
Trypsin breaks down proteins into proteases, peptones & polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 11
polypeptides.Chymotrypsin is secreted as chymotrypsinogen. It is activated by trypsin. It too converts proteins into protein fragments, Chymotrypsinogen
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 12

Question 5.
Mention the three types of salivary glands in man and name the carbohydrate present in the saliva. (Oct. 2002)
Answer:
In man there are 3 pairs of salivary glands, they are are the parotid, Sublingual and Submaxillary glands. Saliva contains the starch splitting enzyme salivary amylase or Ptyalin.

Question 6.
Name the non-digestive enzyme found in intestinal juice. Mention its significance. (Oct. 2004)
Answer:
The non-digestive enzyme in intestinal juice is ‘E-‘nterokinase’ and helps to activate trypsinogen into trypsin which digests proteins.

KSEEB Solutions

Question 7.
What are microvilli? State their functions.
Answer:
Microvilli are bristle-like extensions of the free surface of epithelial cells that line the surface of villi. They increase the surface area of epithelium for the absorption of nutrients.

Question 8.
Write any two roles of HCI In human digestion. (July 2010)
Answer:
The major roles played by HCI in human digestion are;

  • It activates pepsinogen to pepsin which is required for protein digestion.
  • It prevents decay of food in the stomach.

Question 9.
How is our gut lining protected from its own secretion?
Answer:

  • Proteases are secreted in an inactive form and pose no threat to the gut lining.
  • The mucus and bicarbonates present in the gastric juice play an important role in the protection of the mucosal epithelium from excoriation by the highly concentrated Hydrochloric acid.

Question 10.
What would happen if hydrochloric acid is not secreted in our stomach?
Answer:
If hydrochloric acid is not secreted in the stomach, the following will happen:

  • Pepsinogen will not be converted into pepsin.
  • An acidic medium needed for the action of proteases will not be created.
  • Salivary amylase may continue to function.

Question 11.
Amylase is secreted by two different glands. Name them what is its action on food? (Foreign 2002)
Answer:
Amylase is secreted by the salivary glands into the buccal cavity and also by the pancreas.
Amylase acts on starch and breaks it into two molecules of glucose.

Question 12.
What is the site of fat digestion In humans? Name the enzymes responsible for it and mention its end products.
Answer:
Fat is mainly digested in the small intestine and very little in the stomach.
Lipase is the enzyme responsible for fat digestion. The final products of fat digestion in humans are glycerol, fatty acids and some monoglycerides.

Question 13.
Enumerate the contents of saliva.
Answer:
The saliva secreted into the oral cavity contains electrolytes like Na+, K+, Cl, \({ HCO }_{ 3 }^{ – }\) and enzymes like salivary amylase and lysozyme. Salivary amylase helps in digesting starch and lysozyme acts as an antibacterial agent that prevents infections.

Question 14.
What is rennin? What is its function?
Answer:

  • Rennin is the proteolytic enzyme found in the gastric juice of infants.
  • It hydrolyses milk proteins and helps in its digestion.

Question 15.
How would it affect the digestion of proteins and carbohydrates, if there is a blockage in the pancreatic duct?
Answer:
If the pancreatic duct is blocked:

  • Digestion of proteins will be impaired, as pancreatic juice contains the proteolytic enzymes trypsin, chymotrypsin and carboxypeptidase.
  • Digestion of carbohydrates will stop as there will be no enzyme amylase.
  • Since the bicarbonates provide an alkaline pH for the action of enzymes in the duodenum, the whole process of digestion in the intestine will be affected.

Question 16.
Give two protein-digesting enzymes of pancreatic Juice with their action.
Answer:
Pancreatic juice contains enzymes like trypsin, chymotrypsin and carboxyptidase which help in digestion of proteins.

  • Trypsin acts on the proteins, proteoses and peptones and convert them into small peptides/ dipeptides
  • Carboxypeptidase release the last amino acid from the peptide chain and shorten the peptide chain.

Question 17.
What are the basic layers of the wall of the alimentary canal?
Answer:
The wall of the alimentary canal consists of four main concentric layers. Beginning from outside, these layers are

  • visceral peritoneum
  • muscular layer
  • sub-mucosa
  • mucosa.

Question 18.
Mention the Important functions of the large intestine.
Answer:

  • It helps in the absorption of water, minerals, and certain drugs.
  • Secretion of mucus helps in adhering the waste particles together and lubricating it for an easy passage.

Question 19.
Where is the ileocaecal valve present? What are its functions?
Answer:

  • The ileo-caecal valve is present at the junction of ileum of small intestine and the caecum of the large intestine.
  • It prevents the backflow of the matter from the caecum into the ileum.

Question 20.
What Is diarrhea? What is its consequence In nutrition?
Answer:
The abnormal frequency of bowel movement and increased liquidity of the faecal discharge is known as diarrhea. It reduces the absorption of food.

Question 21.
Briefly explain the structure and regions of the stomach.
Answer:
Stomach is a ‘J’ shaped bag-like structure. A muscular sphincter called ‘gastro-oesophageal sphincter regulates the opening of oesophagus into the stomach. The stomach is located in the upper-left portion of the abdominal cavity and has three major parts a cadiac portion into which the oesophagus opens, a fun dic region and a pyloric region which opens into the small intestine.

Question 22.
How Is saliva produced?
Answer:
Saliva is mainly produced by three pairs of salivary glands, the parotids (cheek), the sub-maxillary/sub-mandibular and the sub linguals. These glands are situated just outside the buccal cavity and secrete salivary juice into the buccal cavity.

Question 23.
Where is the pancreas situated? Name the secretions of the pancreas.
Answer:
The pancreas is a compound (both exocrine and endocrine) elongated organ situated between the limbs of the U shaped duodenum. The exocrine portion of the pancreas secretes an alkaline pancreatic juice containing enzymes liketrypsinogen, chymotrypsinogen, procarboxy peptidases, amylases, lipases and nucleases. The endocrine portion secretes hormones, insulin and glucagon.

KSEEB Solutions

Question 24.
What constitutes the juice? What does it .contain?
Answer:
The secretions of the brush border cells of the mucosa along with the secretions of the gobletcells constitute the intestinal juice or succus entericus. This juice contains a variety of enzymes like disaccharidases (e.g. maltase) dipeptidases, lipases and nucleosidase.

Question 25.
How are fatty acids and glycerol absorbed into the blood?
Answer:
Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first incorporated into small droplets called micelles which move into the intestinal mucosa. They are re-formed into very small protein-coated fat globules called the chylomicrons which are transported into the lymph vessels in the villi. These lymph vessels ultimately release the absorbed substances into the bloodstream.

Question 26.
Draw a labelled diagram of anatomical regions of the human stomach.
Answer:
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 13

1st PUC Biology Digestion and Absorption Three Marks Questions

Question 1.
Draw a neat labelled diagram representing the duct system of liver, gall bladder and pancreas.
Answer
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 14

Question 2.
Name any three enzymes secreted by the pancreas Specify the substrate and product of each.
Answer:

  • Amylase: It acts on starch and converts it into maltose.
  • Trypsin: It acts on proteins, proteases and peptones and converts them into shorter peptides or dipeptides.
  • Lipase: It acts on triglycerides and converts them into triglycerides and monoglycerides along with the release of fatty acids.

Question 3.
Draw a neat labelled diagram representing transverse section of gut.
Answer:
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 15

Question 4.
What is protein-energy malnutrition? How it is responsible to cause marasmus and kwashiorkor in infants and children?
Answer:
Protein-energy malnutrition (PEM) may affect large sections of the population during drought and famine.
This happened in Ethiopia during the severe drought in the mid-eighties. PEM affects infants and children to produce Marasmus and Kwashiorkor diseases.

  • Marasmus is produced by a simultaneous deficiency of proteins and calories. It is found in infants less than a year in age if mother’s milk is replaced too early by other foods which are poor in both proteins and caloric value.
  • This often happens if the mother has second pregnancy or childbirth when the older infant is still too young.
  • In Marasmus, protein deficiency impairs growth and replacement of tissue proteins; extreme emaciation of the body and thinning of limbs results, the skin becomes dry, thin, and wrinkled.
  • Growth rate and bodyweight decline considerably. Even growth and development of the brain and mental abilities are impaired.
  • Kwashiorkor is proceeded by protein deficiency unaccompanied by calorie deficiency.
  • It resubs from the replacement of mother’s milk by a high calorie-low protein diet in a child more than one year in age. Like marasmus, kwashiorkor shows wasting of muscles, thinning of limbs, failure of growth, and brain development.
  • But unlike, marasmus, some fat is still left under the skin; moreover, extensive oedema and swelling of body parts are seen.

KSEEB Solutions

Question 5.
Draw a neat labelled diagram of a section of small intestinate mucosa showing villi.
Answer:
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 16

Question 6.
Which layer of the stomach contains gastric glands? Name the three types of cells present in gastric glands with their functions.
Answer:
The mucosa of the stomach has gastric glands.
Three major types of cells in gastric glands are:

  • Mucus neck cells which secrete mucus
  • Peptic or chief cells secrete the proenzyme pepsinogen.
  • parietal or oxyntic cells which secrete HCL and intrinsic factors essential for the absorption of vitamin B12.

Question 7.
How are the nucleic acid fraction of our food digested?
Answer:
Nucleases present in the pancreatic juice convert the nucleic acids to nucleotides.

  • Nucleotidases present in the pancreatic juice convert the nucleotides into nucleosides and phosphates.
  • Nucleosides present in the intestinal juice convert the nucleosides into nitrogen bases and sugar.

1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 17

Question 8.
Write a note on hormonal control and co-ordination of digestive parts.
Answer:
The activities of the gastrointestinal tract are under neural and hormonal control for proper co-ordination of different parts. The sight, smell, or the presence of food in the oral cavity can stimulate the secretion of saliva. Gastric and intestinal secretions are also, similarly, stimulated by neural signals. The muscular activities of different parts of the alimentary canal can also be moderated by neural mechanisms, both local and through CNS. Hormonal control of the secretion of digestive juices is carried out by the local hormones produced by the gastric and intestinal mucosa.

Question 9.
Write a note on absorption in different parts of the digestive system
Answer:
Mouth: Certain drugs coming in contact with the mucosa of the mouth and lower side of the tongue are absorbed into the blood capillaries lining them.

Stomach: Absorption of water, simple sugars, and alcohol, etc. takes place in the stomach. Small intestine: Principle organ for the absorption of nutrients. The digestion is completed here and the final products of digestion such as glucose, fructose, fatty acids, glycerol, and amino acids are absorbed through the mucosa into all bloodstream and lymph.

Large Intestine: Absorption of water, some minerals, and drugs take place in the large intestine.

KSEEB Solutions

1st PUC Biology Digestion and Absorption Five Marks Questions

Question 1.
Mention the components of human saliva. Give the function. (M.Q.P.)
Answer:
The salivary glands produce a secretion called salivary juice or saliva. It is composed
Nucleosidases of water; mucin; ions like sodium, chlorides, HCO3 etc; a bactericidal enzyme and a digestive enzyme called ptyalin or salivary amylase.
Functions of Saliva

  • Moistens dry food and helps in swallowing
  • Keeps mouth and teeth clean.
  • Helps in tasting food
  • The Salivary amylase helps in digesting the polysaccharides, starch & glycogen to maltose, a disaccharide.
  • The bactericidal enzyme kills microbes and checks their load in food.
  • Many substances like Iodides, lead etc are excreted through saliva.

Question 2.
Describe the digestion of carbohydrates in the small intestine. (Apr. 83, Oct. 04)
Answer:
The undigested food in terms of polysaccharides, starch and glycogen and disaccharides, sucrose & lactose (got from diet), maltose (produced from digestive action of salivary amylase on polysaccharides or those got directly as a food source) are acted upon by the carbohydrates of the pancreas and intestinal juice in the lumen of the intestine.

(i) The polysaccharides starch (plant source) and glycogen (animal source) are acted upon by the pancreatic amylase (or amylopsin) splitting them into a pool of maltose, a disaccharide.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 18

(ii) The final pool of disaccharides produced by the action of polysaccharides (Pancreatic and salivary amylases) or those obtained directly through diet are acted upon by the di- saccharases Sucrase, Lactase, and Maltase

(disaccharide splitting enzymes) of the intestinal juice in the intestinal lumen as follows, (a) Sucrose (s) are acted upon by sucrase enzyme and split into a molecule of glucose and a molecule of Fructose each.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 19

(b) Maltose (s) are acted upon by Maltase -enzyme and split into two glucose molecules each.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 20

(c) Lactose (s) are acted upon by Lactase enzyme and split into a molecule of glucose and galactose
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 21

Finally resulting in an absorbable pool of monosaccharides in the intestinal lumen.

Question 3.
Explain protein digestion In small Intestine? (M.Q.P., Apr. 83, Oct. 99, Mar. 2010, July 2011)
Answer:
The acid chyme released from the stomach into the intestinal lumen may contain digested protein (by pepsin) or native protein (untouched by pepsin if any) apart from carbohydrates and fats. The acid chyme is first neutralised by bicarbonates of pancreatic juice and then acted upon by various enzymes. The proteins in the chyme are acted upon by the proteolytic enzymes of the

  • Pancreatic juice – namely trypsin, chymotryr.in and carboxypeptidase.
  • ‘Intestinal juice – aminopeptidase, tripeptidase and dipeptidases.

Among these trypsin and chymotrypsin are endopeptidases (attacking internal peptide bonds) acting on native protein and the carboxypeptidases, aminopeptidases, tri and dipeptidases are exopeptidases (attacking superficial peptide bonds at the carbxyl end or amino end respectively) acting on protein fragments produced from whole or native proteins.

The action of the above enzymes on proteins is as follows;

(i) Trypsin and Chymotrypsin act on native proteins splitting or reducing them into shorter protein chains namely proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 22

(ii) Carboxypeptidases and amino peptidases act on the protein molecules got from the digestion of native proteins converting them into tripeptides, dipeptides and amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 23

(iii) The tri and dipeptides resulted from the above reactions are acted upon by tri and dipeptidases and split into amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 24
Finally, resulting in a pool of amino acids which can be easily absorbed.

Question 4.
Describe the digestive process in the stomach and small intestine of man. (April 84)
Answer:
Digestion in the stomach: The chief organic molecules in food that are digested in the stomach are the proteins (native) and short chain simple lipids. The cells of the mucosal wall produce the gastric juice and it consists of the following enzymes apart from HCI and mucin.

  • Pepsin- proteolytic enzyme(endopeptidase)
  • Renin – milk curdling enzyme (Calf and infants of humans)
  • Gastric lipase – acts on simple lipids. Pepsin acts on native protein molecules of food in the lumen of the stomach converting them into proteoses, peptones, and polypeptides.

1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 25

In Infants & calf, where the chief source of food is milk, renin is an additional enzyme which helps in the curdling of milk protein casein, and later this curdled casein is digested by the action of pepsin and converted to proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 26

proteoses, peptones, and polypeptides. Digestion in Small Intestine: Two types of juices are secreted into the intestinal lumen namely the pancreatic juice and intestinal juice. Both their juices possess enzymes digesting all types of complex organic molecules namely carbohydrates, proteins, lipids & nucleic acids.
The digestion by this enzyme in the small intestine proceeds as follows:

Carbohydrates: Polysaccharides starch (plant source) and glycogen (animal source) are acted upon by pancreatic amylase (amylopsin) in the small intestinal lumen and converted to a pool of maltose, a disaccharide.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 27

The disaccharides, in the intestinal lumen namely maltose (obtained from the digestion of polysaccharides or direct source); sucrose, and Lactose (from diet) are acted upon disaccharide digesting (disaccharidases) enzyme into a pool of monosaccharides, glucose, fructose, and galactose.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 28
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 29
Proteins: The proteins reaching the small intestinal lumen are in the form of native proteins, proteoses, peptones, and polypeptides. They are acted upon by the following enzymes.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 30
Thus resulting in a final pool of absorbable amino acids.

Lipids: The Lipids are first emulsified by bile salts in the intestinal lumen. The emulsified lipids are then worked upon by the pancreatic lipase to a pool of glycerol, fatty acids and monoglycerides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 31
Fattyacids, monoglycerides

Nucleic acids: Nucleases from the pancreas” acts upon the RNA & DNA nucleic acids breaking them into nucleotides and these nucleotides are later acted upon by nucleotidases & nucleosidases of the intestinal juice.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 32
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 33
deoxyribose sugar; ribose sugar; nucleic acid bases.

KSEEB Solutions

Question 5.
Are mention two enzymes present in pancreatic juice? Explain their role In intestinal digestion. (April 86)
Answer:
The acid chyme released from the stomach into the intestinal lumen may contain digested protein (by pepsin) or native protein (untouched by pepsin if any) apart from carbohydrates and fats. The acid chyme is first neutralized by bicarbonates of pancreatic juice and then acted upon by various enzymes. The proteins in the chyme are acted upon by the proteolytic enzymes of the

  • Pancreatic juice – namely trypsin, chymotrypsin and carboxypeptidase.
  • ‘Intestinal juice – aminopeptidase, tripeptidase and dipeptidases.

Among these trypsin and chymotrypsin are endopeptidases (attacking internal peptide bonds) acting on native protein and the carboxypeptidases, aminopeptidases, tri and dipeptidases are exopeptidases (attacking superficial peptide bonds at the carbxyl end or amino end respectively) acting on protein fragments produced from whole or native proteins.

The action of the above enzymes on proteins is as follows;

(i) Trypsin and Chymotrypsin act on native proteins splitting or reducing them into shorter protein chains namely proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 34

(ii) Carboxypeptidases and aminopeptidases act on the protein molecules got from the digestion of native proteins converting them into tripeptides, dipeptides and amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 35

(iii) The tri and dipeptides resulted from the above reactions are acted upon by tri and dipeptidases and split into amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 36
Finally, resulting in a pool of amino acids which can be easily absorbed.

Question 6.
Explain the digestion of food in the small intestine by the enzymes of intestinal glands. (Oct. 87)
Answer:
The secretion produced by the intestinal glands is known as the intestinal juice or succus entries. It is a clear yellow fluid with a pH of around 7.6 and contains water, mucous and some digestive enzymes produced by intestinal cells. The enzymes found in the intestinal juice and their action is as follows on food in the small intestine.

(1) Carbohydrases: Maltase, Lactase, Sucrase these are disaccharides digesting disaccharides Maltose, Lactose, and sucrose in the intestinal lumen as follows at pH 7.1 – 8.2.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 37

(2) Proteases: Aminopeptidase, tripeptidase, and dipeptidase-(Exopeptdases) are proteolytic enzymes digesting the intermediate polypeptides produced by the action of endopeptidases of the stomach & pancreas. Their action is as follows in the small intestinal at pH 7.1 – 8.2
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 38
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 39
(Enterokinase, an activator enzyme, activates gastric glands to produce gastric juice)

(3) Lipase: A fat-digesting enzyme. It is not as strong as pancreatic lipase but it completes the digestion of fat in the small intestinal lumen.

(4) Nucleases: Act on nucleoside molecules of nucleoproteins, splitting them into corresponding nitrogenous bases and sugar molecules.

Question 7.
Explain the role of the pancreas in the process of digestion. (Oct. 87, 88)
Answer:
The pancreas is a dual gland composed of two portions, an exocrine portion having cells producing enzymes required for digestion of food and an Endocrine portion having groups of cells producing hormones required for metabolism and homeostasis.

As a digestive gland, it plays a very important role in the process of digestion by possessing the most potent or powerful enzymes required for digestion of all types of food molecules namely carbohydrates, proteins, fats, and nucleic acids.

The pancreatic juice secreted by the pancreatic exocrine glands reaches the intestine through the pancreatic duct (duct of wiring) which usually joins the bile duct before opening into the first part of the duodenum. It is a clear, colourless liquid, containing some salts and sodium bicarbonate apart from enzymes.

As soon as food enters the duodenum, a series of neurogenic and hormonal mechanism’s come into play and maintain a steady secretion of these fluids into the duodenum. These secretions mix with the acid chyme released from the stomach’ in the duodenum. The salts and bicarbonates neutralize and alkalize the acid chyme whereas the enzymes work upon the complex food molecules converting them into smaller molecules which are later on acted upon by intestinal juice enzymes converting them into absorbable forms.

The pancreatic digestive action can be summarized as follows :

(1) Carbohydrases (carbohydrate splitting): Pancreatic amylase acts on polysaccharides starch (plant origin) and glycogen (animal origin) converting these into disaccharide molecules, namely maltose.

(2) Proteases (Protein-splitting):

  • Trypsin, Chymotrypsin (Endopeptidases) act on native proteins splitting them into proteases, peptones, and polypeptide molecules.
  • Carboxypeptidase (exopeptidase) acts on proteins, peptones, and polypeptides splitting them into tripeptides, dipeptides, and amino acids.

(3) Pancreatic lipase: act on fats emulsified by brie salts splitting them into glycerol, fatty acids, and monoglycerides.

(4) Nucleases: Ribonuclease and deoxyribonuclease – splitting nucleic acids (RNA & DNA) into simple nucleotides of respective types. These are later acted upon by nucleotides, splitting them into nucleosides of RNA & DNA and PO

Question 8.
Explain how carbohydrates and protein are digested by intestinal juice. (Oct. 90)
Answer:
The undigested food in terms of polysaccharides, starch and glycogen and disaccharides, sucrose & lactose (got from diet), maltose (produced from digestive action of salivary amylase on polysaccharides or those got directly as a food source) are acted upon by the carbohydrates of the pancreas and intestinal juice in the lumen of the intestine.

(i) The polysaccharides starch (plant source) and glycogen (animal source) are acted upon by the pancreatic amylase (or amylopsin) splitting them into a pool of maltose, a disaccharide.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 40

(ii) The final pool of disaccharides produced by the action of polysaccharides (Pancreatic and salivary amylases) or those obtained directly through diet are acted upon by the di- saccharases Sucrase, Lactase and Maltase

(disaccharide splitting enzymes) of the intestinal juice in the intestinal lumen as follows, (a) Sucrose (s) are acted upon by sucrase enzyme and split into a molecule of glucose and a molecule of Fructose each.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 41

(b) Maltose (s) are acted upon by Maltase -enzyme and split into two glucose molecules each.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 42

(c) Lactose (s) are acted upon by Lactase enzyme and split into a molecule of glucose and galactose
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 43

Finally resulting in an absorbable pool of monosaccharides in the intestinal lumen.

The acid chyme released from the stomach into the intestinal lumen may contain digested protein (by pepsin) or native protein (untouched by pepsin if any) apart from carbohydrates and fats. The acid chyme is first neutralised by bicarbonates of pancreatic juice and then acted upon by various enzymes. The proteins in the chyme are acted upon by the proteolytic enzymes of the

  • Pancreatic juice – namely trypsin, chymotryrin, and carboxypeptidase.
  • ‘Intestinal juice – aminopeptidase, tripeptidase and dipeptidases.

Among these trypsin and chymotrypsin are endopeptidases (attacking internal peptide bonds) acting on native protein and the carboxypeptidases, aminopeptidases, tri and dipeptidases are exopeptidases (attacking superficial peptide bonds at the carboxyl end or amino end respectively) acting on protein fragments produced from whole or native proteins.

The action of the above enzymes on proteins is as follows;

(i) Trypsin and Chymotrypsin act on native proteins splitting or reducing them into shorter protein chains namely proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 44

(ii) Carboxypeptidases and amino peptidases act on the protein molecules got from the digestion of native proteins converting them into tripeptides, dipeptides and amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 45

(iii) The tri and dipeptides resulted from the above reactions are acted upon by tri and dipeptidases and split into amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 46
Finally, resulting in a pool of amino acids which can be easily absorbed.

Question 9.
Explain the Digestion of protein In the human digestive system. (Oct. 92)
Answer:
Digestion in the stomach: The chief organic molecules in food that are digested in the stomach are the proteins (native) and short-chain simple lipids. The cells of the mucosal wall produce the gastric juice and it consists of the following enzymes apart from HCI and mucin.

  • Pepsin- proteolytic enzyme(endopeptidase)
  • Renin – milk curdling enzyme (Calf and infants of humans)
  • Gastric lipase – acts on simple lipids. Pepsin acts on native protein molecules of food in the lumen of the stomach converting it into proteoses, peptones and polypeptides.

1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 47

In Infants & calf, where the chief source of food is milk, renin is an additional enzyme which helps in the curdling of milk protein casein and later this curdled casein is digested by the action of pepsin and converted to proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 48

proteoses, peptones and polypeptides. Digestion in Small Intestine: Two types of juices are secreted into the intestinal lumen namely the pancreatic juice and intestinal juice. Both their juices possess enzymes digesting all types of complex organic molecules namely carbohydrates, proteins, lipids & nucleic acids.
The digestion by this enzyme in the small intestine proceeds as follows:

Carbohydrates: Polysaccharides starch (plant source) and glycogen (animal source) are acted upon by pancreatic amylase (amylopsin) in the small intestinal lumen and converted to a pool of maltose, a disaccharide.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 49

The disaccharides, in the intestinal lumen namely maltose (obtained from the digestion of polysaccharides or direct source); sucrose and Lactose (from diet) are acted upon disaccharide digesting (disaccharidases) enzyme into a pool of monosaccharides, glucose, fructose and galactose.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 50
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 51
Proteins: The proteins reaching the small intestinal lumen are in the form of native proteins, proteoses, peptones and polypeptides. They are acted upon by the following enzymes.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 52
Thus resulting in a final pool of absorbable amino acids.

Lipids: The Lipids are first emulsified by bile salts in the intestinal lumen. The emulsified lipids are then worked upon by the pancreatic lipase to a pool of glycerol, fatty acids, and monoglycerides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 53
Fatty acids, monoglycerides

Nucleic acids: Nucleases from the pancreas” acts upon the RNA & DNA nucleic acids breaking them into nucleotides and these nucleotides are later acted upon by nucleotidases & nucleosidases of the intestinal juice.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 54
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 55
deoxyribose sugar; ribose sugar; nucleic acid bases.

(ii) The acid chyme released from the stomach into the intestinal lumen may contain digested protein (by pepsin) or native protein (untouched by pepsin if any) apart from carbohydrates and fats. The acid chyme is first neutralised by bicarbonates of pancreatic juice and then acted upon by various enzymes. The proteins in the chyme are acted upon by the proteolytic enzymes of the

  • Pancreatic juice – namely trypsin, chymotryr.in and carboxypeptidase.
  • ‘Intestinal juice – aminopeptidase, tripeptidase and dipeptidases.

Among these trypsin and chymotrypsin are endopeptidases (attacking internal peptide bonds) acting on native protein and the carboxypeptidases, aminopeptidases, tri and dipeptidases are exopeptidases (attacking superficial peptide bonds at the carbxyl end or amino end respectively) acting on protein fragments produced from whole or native proteins.

The action of the above enzymes on proteins is as follows;

(i) Trypsin and Chymotrypsin act on native proteins splitting or reducing them into shorter protein chains namely proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 56

(ii) Carboxypeptidases and aminopeptidases act on the protein molecules got from the digestion of native proteins converting them into tripeptides, dipeptides and amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 57

(iii) The tri and dipeptides resulted from the above reactions are acted upon by tri and dipeptidases and split into amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 58
Finally, resulting in a pool of amino acids which can be easily absorbed.

Question 10.
What is digestion? Explain the physiology of digestion of carbohydrates and protein In the small intestine. (Oct. 94, March 2011)
Answer:
Digestion is a process by which complex organic food molecules are broken down or hydrolysed into simple (or small) absorbable forms by the action of digestive enzymes.

The undigested food in terms of polysaccharides, starch and glycogen and disaccharides, sucrose & lactose (got from diet), maltose (produced from digestive action of salivary amylase on polysaccharides or those got directly as a food source) are acted upon by the carbohydrates of the pancreas and intestinal juice in the lumen of the intestine.

(i) The polysaccharides starch (plant source) and glycogen (animal source) are acted upon by the pancreatic amylase (or amylopsin) splitting them into a pool of maltose, a disaccharide.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 59

(ii) The final pool of disaccharides produced by the action of polysaccharides (Pancreatic and salivary amylases) or those obtained directly through diet are acted upon by the di- saccharases Sucrase, Lactase and Maltase

(disaccharide splitting enzymes) of the intestinal juice in the intestinal lumen as follows, (a) Sucrose (s) are acted upon by sucrase enzyme and split into a molecule of glucose and a molecule of Fructose each.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 60

(b) Maltose (s) are acted upon by Maltase -enzyme and split into two glucose molecules each.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 61

(c) Lactose (s) are acted upon by the Lactase enzyme and split into a molecule of glucose and galactose
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 62

Finally resulting in an absorbable pool of monosaccharides in the intestinal lumen.

The acid chyme released from the stomach into the intestinal lumen may contain digested protein (by pepsin) or native protein (untouched by pepsin if any) apart from carbohydrates and fats. The acid chyme is first neutralised by bicarbonates of pancreatic juice and then acted upon by various enzymes. The proteins in the chyme are acted upon by the proteolytic enzymes of the

  • Pancreatic juice – namely trypsin, chymotryr.in and carboxypeptidase.
  • ‘Intestinal juice – aminopeptidase, tripeptidase and dipeptidases.

Among these trypsin and chymotrypsin are endopeptidases (attacking internal peptide bonds) acting on native protein and the carboxypeptidases, aminopeptidases, tri and dipeptidases are exopeptidases (attacking superficial peptide bonds at the carbxyl end or amino end respectively) acting on protein fragments produced from whole or native proteins.

The action of the above enzymes on proteins is as follows;

(i) Trypsin and Chymotrypsin act on native proteins splitting or reducing them into shorter protein chains namely proteoses, peptones and polypeptides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 63

(ii) Carboxypeptidases and amino peptidases act on the protein molecules got from the digestion of native proteins converting them into tripeptides, dipeptides and amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 64

(iii) The tri and dipeptides resulted from the above reactions are acted upon by tri and dipeptidases and split into amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 65
Finally, resulting in a pool of amino acids which can be easily absorbed.

KSEEB Solutions

Question 11.
Give an account of the digestion of proteins in man. (Oct. 2001)
Answer:
Protein digestion in man:
(a) Protein digestion in the mouth: Proteins do not undergo any change as there is no protease in the mouth.
(b) Protein digestion in the stomach: Gastric juice has two proteases pepsin and rennin.

(i) Pepsin is first secreted as pepsinogen: It is converted to pepsin by HCI. One HCI has converted some pepsinogen, further conversion is autocatalytic. Pepsin is an endopeptidase. It acts on internally situated peptide bonds of proteins. In the end, the proteins are converted to proteoses, peptones and polypeptides.

1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 66

(ii) Rennin (also called chymosin): It is a milk curdling enzyme that is mostly present in infants. It is secreted as prorennin. Renin acts on the soluble milk protein, casein, converting it into paracasein. In the presence of Ca2+ of milk, it is further converted into calcium para caseinate, which coagulates preventing the rapid passage of milk into the duodenum. It is then hydrolyzed by pepsin to proteoses, peptones & polypeptides
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 67
As digestion proceeds in the stomach, the food becomes more or less liquified and is referred to as chyme.

(c) Protein digestion in the Intestine: Here it comes under the action of
(i) Pancreatic proteases &
(ii) Intestinal proteases.

(i) Pancreatic proteases: These are Trypsin, chymotrypsin, and carboxypeptidase. The first two are endopeptidases and the third is an exopeptidase. Trypsin is secreted as trypsinogen & it is activated by enterokinase (enteropeptidase) of the intestinal juice.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 68

chymotrypsinogen which is activated by trypsin. It, too, converts proteins into protein fragments.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 69

Carboxypeptidase an endopeptidase, hydrolyzes terminally situated bonds. The products are tripeptides, Depeptides, and amino acids.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 70

(ii) Intestinal proteases: They may be termed peptidases because they act on the protein fragments. Proteoses, peptones, and polypeptides aminopeptidase tripeptides, dipeptides and
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 71
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 72

The proteins have been completed digested and the products are free amino acids. They are now ready to be absorbed.

Question 12.
Draw a neat labelled diagram of the human alimentary canal. (M.Q.P.)
OR
Draw a neat labelled diagram of digestive
Answer:
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 73

Question 13.
Write the functions of intestinal juice.
Answer:

  • Intestinal mucus protects the intestinal epithelia.
  • Disaccharidases like maltase, lactase, and sucrase bring complete hydrolysis of disaccharides into monosaccharides (see carbohydrate digestion).
  • Aminopeptidases hydrolyse peptides of different lengths into amino acids.
  • Dipeptidase hydrolyse dipeptides into amino acids, (see protein digestion).
  • Nucleotidase and Nucleosidase hydrolyse Nucleotides and convert them into purines, pyrimidine, and inorganic phosphate.

KSEEB Solutions

Question 14.
Describe the process of Lipid digestion in small intestine of man. (Oct. 2004)
Answer:
Fats or lipids mainly contain triglycerides i.e. consists of 3 fatty acid molecules attached to a molecule of glycerol. The major fat-digesting enzyme is pancreatic lipase.

The fats are first emulsified i.e. the bile salts combine with fats and break them down into small droplets which form a soapy mixture. The small droplets are acted by lipase which breaks them into fatty acids, glycerol, mono and diglycerides.
1st PUC Biology Question Bank Chapter 16 Digestion and Absorption 74
The bile salts then combine with the products and form water-soluble complexes which are absorbed.

Question 15.
Briefly explain the disorders of the digestive system.
Answer:
The disorder of the digestive system are:-

  • The inflammation of the intestinal tract is the most common ailment due to bacterial or viral infections. The infections are also caused by the parasites of the intestine like tapeworm, roundworm, threadworm, hookworm, pinworm etc.
  • Jaundice:- The liver is affected, skin and eyes turn yellow due to the deposit of bile pigments.
  • Vomiting: It is the ejection of stomach contents through the mouth. This reflex action is controlled by the vomiting centre in the medulla. A feeling of nausea precedes vomiting.
  • Diarrhoea: The abnormal frequency of bowel movement and increased liquidity of the faecet discharge is known as diarrhoea. It reduces the absorption of food.
  • Constipation: In constipation, the faeces are retained with the rectum as the bowel movements occur irregularly.
  • Indigestion: In this condition, the food is not properly digested leading to a feeling of fullness. The causes of indigestion are inadequate enzyme secretion, anxiety food poisoning, overeating, and spicy food.

Question 16.
Fill in the blanks.

(a) The type of dentition in humans is called ……………..
(b) ……………..has …………….. cells which secrete mucus that help In lubrication.
(c) Each lobule of liver is covered by a thin connective tissue sheath called ……………..
(d) Hepate pancreatic duct is guarded by ……………..
(e) Alcohol is absorbed in ……………..
Answer:
(a) Diphyodont
(b) Mucosal epithelium, goblet cells
(c) Glisson’s capsule
(d) Sphincter of Oddi
(e) Stomach.

Question 17.
Match the following:
(a) Trypslnogen – (i) Goblet cells
(b) Saliva – (ii) Oxyntic cells
(c) HCL- (iii) Pancreas
(d) Pepsinogen – (iv) Parotids
(e) Mucus – (v) Chief cells
Answer:
(a) → (iii)
(b) → (iv)
(c) → (ii)
(d)→ (v)
(e) → (i)

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