NCERT Exemplar Class 11 Biology Solutions Digestion and Absorption

Multiple Choice Questions
1.Select what is not true of intestinal villi among following.
(a) They possess microvilli.
(b) They increase the surface area.
(c) They are supplied with capillaries and the lacteal vessels.
(d) They only participate in digestion of fats.
Solution.(d) : Intestinal villi are finger like projections, present in small intestine which increases surface area for absorption of fats, amino acids, monosaccharides, vitamins, water etc. Villi do not participate in digestion of fat.

2. Hepato-pancreatic duct opens into the duodenum and carries
(a) bile
(b) pancreatic juice
(c) both bile and pancreatic juice
(d) saliva.
Solution.(c) : The bile duct (carrying bile juice from liver) and the pancreatic duct (carrying pancreatic juice from pancreas) open together into the duodenum as the common hepato-pancreatic duct, the opening of which is guarded by the sphincter of Oddi.

3.One of the following is not a common disorder associated with digestive system.
(a) Tetanus (b) Diarrhoea
(c) Jaundice (d) Dysentery
Solution.(a) : Tetanus is caused by bacterium Clostridium tetani. Its symptoms are spasm of muscies (of jaw and face) and severe pain. Diarrhoea is the frequent defecation of liquid faeces. It reduces absorption of food. Jaundice is the disease of liver characterised by yellowing of eyes and skin due to large quantities of bilirubin pigment in extracellular fluid. Dysentry is an inflammatory disorder of the intestine, especially the colon, that results in severe diarrhoea containing blood and mucus in faeces with fever, abdominal pain and painful passing of stool.

4.A gland not associated with the alimentary canal is
(a) pancreas
(b) adrenal
(c) liver
(d) salivary glands.
Solution.(b) : Adrenal glands are hormone secreting endocrine glands which are located on the top of kidneys and do not take part in digestion.

5.Match the two columns and select the correct among options given.
Column-I                                                  Column-ll
A. Biomacromolecule of food              (i)Alimentary canal and associated gland
B.Human digestive system                  (ii)Embedded in jawbones
C.Stomach                                               (iii)Outer wall of visceral organs
D.Thecodont                                           (iv) Converted into simple substances
E.Serosa                                                   (v) J-shaped bag like structure
A-(ii), B-(i), C-(v), D-(iii), E-(iv)
A-(iv), B-(i), C-(v), D-(ii), E-(iii)
A-(i), B-(ii), C-(iii), D-(iv), E-(v)
A-(i), B-(iii), C-(ii), D-(iv), E-(v)

6.Match the two columns and select the right one among options given.
Column-I                                           Column-ll
A.Duodenum                                   (i) A cartilaginous flap
B.Epiglottis                                      (ii)Small blind sac
C.Glottis                                           (iii)’U’shaped structure emerging from the stomach
D. Caecum                                        (iv)Opening of wind pipe
(a) A-(i), B-(ii), C-(iii), D-(iv)
(b) A-(iv), B-(iii), C-(ii), D-(i)
(c) A-(iii), B-(i), C-(iv), D-(ii)
(d) A-(ii), B-(iv), C-(i), D-(iii)

7.Match the enzymes with their respective substrates and choose the right one among options given.
Column-I                                                     Column-II
A.Lipase                                                      (i)Dipeptides
B.Nuclease                                                 (ii)Fats
C.Carboxypeptidase                                (iii)Nucleic acids
D.Dipeptidases                                         (iv)Proteins,peptones and proteoses
(a) A-(ii), B-(iii), C-(i), D-(iv)
(b) A-(iii), B-(iv), C-(ii), D-(i)
(c) A-(iii), B-(i), C-{iv), D-(ii)
(d) A-(ii), B-(iii), C-(iv), D-(i)

8.Dental formula in human beings is
(a) 3223/  3223   (b) 2123/2123
(c) 1232/1232     (d) 2233/2233
Solution.(b) : Dental formula represents the number of teeth in each half of the jaw. Dental
Number of permanent teeth in human beings are 32 i.e., 8 incisors, 4 canines, 8 premolars and 12 molars.

9.Liver is the largest gland and is associated with various functions, choose one which is not correct.
(a) Metabolism of carbohydrate
(b) Digestion of fat
(c) Formation of bile
(d) Secretion of hormone called gastrin
Solution.(d) : Gastrin hormone is secreted by gastrin cells (G-cells) in the pyloric region of the stomach. It stimulates gastric glands to secrete and release the gastric juice. It also stimulates gastric mobility.

10. Mark the right statement among the following.
(a) Trypsinogen is an inactive enzyme.
(b) Trypsinogen is secreted by intestinal mucosa.
(c) Enterokinase is secreted by pancreas.
(d) Bile contains trypsin.
Solution.(a): Trypsinogen is secreted by the pancreas. It is concerned with protein digestion. Enterokinase is secreted by the intestine. Bile does not contain any enzyme.

Very Short Answer Type Questions
1.The food mixes thoroughly with the acidic gastric juice of the stomach by the churning movements of its muscular wall. What do we call thfe food then?
Solution.The food at this stage is called chyme.

2. Try psinogen is an inactive enzyme of pancreatic juice. An enzyme, enterokinase, activates it. Which tissue/ cells secrete this enzyme?/ How is it activated?
Solution. An enzyme enterokinase, secreted by the intestinal mucosa activates proenzyme trypsinogen into active trypsin, which in turn activates the other enzymes in the pancreatic juice.

3.In which part of alimentary canal does absorption of water, simple sugars and alcohol takes place?
Solution. The absorption of water, simple sugars, alcohol and some drugs takes place in the stomach.

4.Name the enzymes involved in the breakdown of nucleotides into sugars and bases.
Solution. Nucleotidases and nucleosidases.

5.Define digestion in one sentence.
Solution.The process of conversion of complex food substances into simple absorbable forms with the help of enzymes is called digestion.

6.What do we call the type of teeth attachment to jaw bones in which each tooth is embedded in a socket of jaw bones?
Solution.The type of attachment in which each tooth is embedded in a socket of jaw bone called thecodont.

7.Stomach is located in upper left portion of the abdominal cavity and has three major parts. Name these three parts.
Solution. The three major parts of stomach are cardiac, fundus and pylorus.

8.Does gall bladder make bile?
Solution. NO, bile is secreted by hepatic cells (liver cells) and is stored and concentrated in the gall bladder.

9.Correct the following statements by deleting  one of entries (given in italics).
(a) Goblet cells are located in the intestinal mucosal epithelium and secrete chymotrypsin / mucus.
(b) Fats are broken down into di-and monoglycerides with the help of amylase/ lipases.
(c) Gastric glands of stomach mucosa have oxynticcell/chief cells which secrete HCl.
(d) Saliva contains enzymes that digest starch /protein.
Solution. (a) Goblet cells are located in the intestinal mucosal epithelium and secrete mucus.
(b) Fats are broken down into di-and monoglycerides with the help of lipases.
(c) Gastric glands of stomach mucosa have oxyntic cells which secrete HCI.
(d) Saliva contains enzymes that digest starch.

Short Answer Type Questions
1.What is pancreas? Mention the major secretions of pancreas that are helpful in digestion.
Solution. Pancreas is a heterocrine (both exocrine and endocrine) gland situated between the limbs of the ‘U’ shaped duodenum. The exocrine part of pancreas secrete pancreatic juice which contains three proenzymes; trypsinogen, chymotrypsinogen and procarboxypeptidase and some enzymes; DNase, RNase, pancreatic amylase and lipase. Pancreatic juice helps in digestion of starch, proteins, fats and nucleic acids. Endocrine part of pancreas consists of islets of Langerhans which contains a-and P-cells which secrete hormone glucagon and insulin respectively, which regulate blood glucose level.
Proteins, proteoses and peptones present in the chyme, on reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice as given below:
Carbohydrates, fats and nucleic acids present in the food are also hydrolysed by pancreatic juice.

2.Name the part of the alimentary canal where major absorption of digested food takes place. What are the absorbed forms of different kinds of food materials?
Solution. Absorption is a process by which nutrients pass from the alimentary canal into the blood and lymph through its mucous membrane. Small intestine is the principal organ for absorption of nutrients. The absorbed forms of different kinds of food materials are glucose, fructose, fatty acids, glycerol, amino acids and vitamins etc.

3. List the organs of human alimentary canal and name the major digestive glands with their location.
Solution. Human digestive system consists of two main parts : alimentary canal and digestive glands. The organs of human alimentary canal are mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus.
Major digestive glands with their location are as follows:

4.What is the role of gall bladder? What may happen if it stops functioning or is removed?
Solution. Gall bladder is a pear shaped sac like structure that is attached to posterior surface of liver by connective tissue. Bile is secreted by liver and is stored and concentrated in the gall bladder. If gall bladder stops functioning or is removed, then bile would directly move from liver into intestine and would be less concentrated. After gall bladder removal, low fat diet is recommended because fat digestion reduces significantly.

5.Correct the statement given below by the right option shown in the bracket against them.  Absorption of amino acids and glycerol takes place in the (small intestine/ large intestine).  The faeces in the rectum initiate a reflex causing an urge for its removal (neural / hormonal).  Skin and eyes turn yellow in infection, (liver/stomach).  Rennin is a proteolytic enzyme found in gastric juice of (infants / adults).  Pancreatic juice and bHe are released through (intestine-pancreatic/hepato ¬pancreatic duct).  Oipeptides, disaccharides and glycerides are broken down into simple substances in region of small intestine (jejunum/duodenum).
(a) Small intestine (b) neural (c) liver (d) infants (e) hepato-pancreatic duct (f) duodenum

6.What are three major types of cells found in the gastric glands? Name their secretions.
Solution. The -mucosa of stomach has gastric glands. Three major types of cells found in the gastric glands and their secretions are as follows :
(i) Mucus neck or goblet cells which secrete mucus.
(ii) Peptic or chief cells which secrete gastric digestive enzymes as proenzyme e.g., small amount of gastric amylase and gastric lipase.
(iii) Parietal or oxyntic cells which secrete HC1 and castle intrinsic factor.

7.How is the intestinal mucosa protected from the acidic food entering from stomach?
Solution.The intestinal mucosal epithelium has goblet cells which secrete mucus. The mucus along with bicarbonates present in the gastric juice help in lubrication and protection of mucosal epithelium from the acidic food entering from the stomach.

8.How are the activities of gastro-intestinal tract regulated?
Solution. The activities of the gastro-intestinal tract are under both neural and hormonal control. The gastro-intestinal tract is innervated by intrinsic nerves as well as by extrinsic nerves. The sight, smell and/or the presence of food in the oral cavity can stimulate the secretion of saliva. Neural signals stimulate the gastric and intestinal secretions. 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 such as gastrin, cholecystokinin and secretin etc.

9.Distinguish between constipation and indigestion. Mention their major causes.
Solution. Differences between constipation and indigestion are as follows:

10.Describe the enzymatic action on fats in the duodenum.
Solution. Fat is largely digested in the small intestine (duodenum). Bile secreted by liver is released into duodenum which break down fat droplets into small micelles by the process, known as emulsification. This increases lipase action, on fats. Pancreatic juice and intestinal juice contain lipase. The pancreatic lipase converts triglycerides, first into diglycerides and then into monoglycerides, releasing a fatty acid at each step. The intestinal lipase converts remaining fats into monoglycerides and fatty acids. Finally all fats are converted into fatty acids, glycerol and monoglycerides.

Long Answer Type Questions
1.A person had roti and dal for his lunch.Trace the changes in those during its passage through the alimentary canal.
Solution. Roti contains starch while dal contains proteins. When the food is taken into the buccal cavity the teeth and tongue with the help of saliva masticate and mix up the food thoroughly. Mucus in saliva helps in lubricating and adhering the masticated particles into a bolus. By swallowing, the bolus is then passed into the pharynx and then into the oesophagus. In the oral cavity, about 30% of the starch present in roti is hydrolysed by salivary amylase present in saliva into maltose.
The food then moves into the stomach. In the stomach, the food mixes thoroughly with the acidic gastric juice by the churning movements of its muscular wall and is called chyme. A proteolytic enzyme pepsin present in the gastric juice converts proteins into proteoses and peptones. Gastric juice does not contain any starch digesting enzyme. Proteins, proteoses and peptones in the chyme reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice as follows:
Carbohydrates in the chyme are hydrolysed by pancreatic amylase into disaccharides.
The enzymes in the intestinal juice act on dipeptides and maltose to form the respective simple absorbable forms.
Finally, the amino acids and glucose are absorbed through the mucosa of the small intestine into the blood stream. The absorbed substances finally reach the tissues which utilise them for their activities. This process is called assimilation.
The undigested and unabsorbed substances of roti and dal are passed on to the large intestine for defecation (egestion of faeces).

2.What are the various enzymatic types of glandular secretions in our gut helping digestion of food? What is the nature of end products obtained after complete digestion of food?
Solution. ln the buccal cavity, saliva secreted by the salivary glands contains salivary amylase that acts as follows:
Gastric juice of the stomach contains proenzyme pepsinogen, which on exposure to hydrochloric acid gets converted into active enzyme, pepsin. Pepsin is a proteolytic enzyme that converts proteins into proteoses and peptones. Rennin is a proteolytic enzyme found in the gastric juice of infants which helps in the digestion of milk proteins. Small amounts of lipases are also secreted by gastric glands.
Bile, pancreatic juice and intestinal juice (succus erttericus) are the secretions released into the small intestine. Pancreatic juice and bile are released through hepato-pancreatic duct into duodenum. Pancreas secretes pancreatic juice that contains inactive enzymes like trypsinogen, chymotrypsinogen, procarboxypeptidases and enzymes like amylases, lipases and nuclease. An enzyme, enterokinase, secreted by the intestinal mucosa converts trypsinogen into active trypsin, which in turn activates the other enzymes in the pancreatic juice. The food reaching the small intestine is acted upon by the enzymes of pancreatic juice as follows:
Bile secreted by liver does not contain any enzyme. It only helps in emulsification of fats and activation of lipases.
In the duodenum of the small intestine, the enzymes of the succus entericus act on the end products of the above reactions to form the respective simple absorbable form.
The end products of the carbohydrate digestion are glucose, protein digestion are amino acids, fat digestion are fatty acids and glycerol and nucleic acid digestion are sugars and bases.

3.Discuss mechanisms of absorption.
Solution. Absorption is the process by which the end products of digestion pass through the intestinal mucosa into the blood or lymph. It is carried out by passive, active or facilitated transport mechanisms. Small amounts of monosaccharides like glucose, amino acids and some of electrolytes like chloride ions are absorbed by simple diffusion. Some of the substances like fructose and some amino acids are absorbed with the help of the carrier ions like Na+ by the mechanism known as facilitated transport. Water is transported along osmotic gradient. Various nutrients like amino acids, monosaccharides like glucose, electrolytes like Na+ are absorbed by active transport.
Fatty acids and glycerol are insoluble, thus they cannot be absorbed into the blood. They are first incorporated into small droplets called micelles which move info the. intestinal mucosa. They are reformed into very small protein coated fat globules called the chylomicrons which are transported into the lacteals in the villi. The lacteals ultimately release the absorbed substances into the blood stream. The maximum absorption of food takes place in small intestine.

4.Discuss the role of hepato – pancreatic complex in digestion of carbohydrate, protein and fat components of food.
Solution.The hepato-pancreatic complex is common duct for pancreatic duct and bile duct, which opens into duodenum. It is guarded by a sphincter called the sphincter of Oddi. Pancreatic juice contains enzymes for digestion of starch, proteins and fats. Bile helps in emulsification of fats only.
Starch digesting enzyme of pancreatic juice, called pancreatic amylase converts starch into maltose, isomaltose and a-dextrins. Three proenzymes present in pancreatic juice; trypsinogen, chymotrypsinogen and procarboxypeptidase are concerned with protein digestion.
Bile provide alkaline medium required for various reactions Bile salts break down fats into small fat droplets, by process called emulsification. Bile increases lipase action on fats. Pancreatic lipase is the principal enzyme for digestion of fats. It converts emulsified fats (triglycerides) into diglycerides and then into monoglycerides and release a fatty acid at each step.

5. Explain the process of digestion in the buccal cavity with a note on the arrangement of teeth.
Solution. The buccal cavity has a number of teeth. Each tooth is embedded in a socket of jaw bone. This type of attachment is called thecodont. Human beings have diphyodont type of teeth which means that they have two sets of teeth during their life, a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. An adult human has 32 permanent teeth which are of four types : incisors (i), canines (c), premolars (pm) and molars (m). This type of dentition is called heterodont dentition. Arrangement of teeth in each half of the upper and lower jaw in the order i, c, pm, m is represented by  a dental formula, which in human is 2123 /2123?  Surface of the teeth is made up of a hard substance called enamel, which helps in the mastication of food.
Fig.: Arrangement of different types of teeth in the jaws on one side and the sockets on the other side.
The buccal cavity performs two major functions: mastication of food and facilitation of swallowing. The salivary glands secrete saliva in the buccal cavity. The teeth and tongue with the help of saliva masticate and mix up the food thoroughly and convert it into a bolus. The saliva contains, electrolytes like Na+, K+, Cl-, HC03- and enzymes, salivary amylase and lysozyme. Salivary amylase is a starch digesting enzyme that acts upon the starch present in the food. About 30% of the starch is hydrolysed in the buccal cavity by this enzyme (pH 6.8) into a dissacharide-maltose.
Lysozyme is an antibacterial agent that acts on bacteria that have come along with the food.