NCERT Solutions for Class 11 Science Biology Chapter 16 - Digestion And Absorption

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The hepato-pancreatic duct opens into the duodenum and is guarded by a sphincter called the sphincter of Oddi. It carries both bile juice and pancreatic juice.
​Hence, the correct answer is option c.

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Tetanus is a severe disease in which the nervous system is affected by a toxin-producing bacterium Clostridium tetani. Rest other options i.e. diarrhoea, jaundice and dysentery are the disorders related to human digestive system.

Hence, the correct answer is option a. 
 

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The adrenal gland is a part of the endocrine system that is located just above the kidney. This gland is responsible for producing fight and flight hormones called adrenaline and nor-adrenaline. Rest other options are a part of alimentary canal.

Hence, the correct answer is option b. 

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Correct match:

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Correct answer:
 

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 An adult human has 32 permanent teeth that are of four different types and they are called Heterodont dentition. They are named as- incisors (I), canine (C), premolars (PM), and molars (M). The 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 in humans is $\frac{2123}{2123}$. 

Hence, the correct answer is option b. 

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Gastrin hormone is a peptide hormone that is secreted by G-cells of the stomach. This hormone stimulates the parietal cells of the stomach to secrete hydrochloric acid. It is not secreted by the liver.
​Hence, the correct answer is option d.

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Inactive enzymes like- trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases, and nucleases are secreted by the pancreatic juice. Trypsinogen enzyme is activated into active trypsin by the enterokinase enzyme that is secreted by the intestinal mucosa, which in turn activates the other enzymes in the pancreatic juice.
​Hence, the correct answer is option a.

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The food mixes thoroughly with the gastric juice produced by the stomach. It is acidic in nature. The mixing of food is facilitated by the churning movement of the muscular wall of the stomach and is called chyme. 

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The absorption of water, simple sugars, alcohol, etc. occurs in the stomach. 

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Nucleotidases and nucleosidases enzymes are involved in the breakdown of nucleotides into sugar and bases. 

$\mathrm{Nucleotide}\stackrel{\mathrm{Nucleotidases}}{\to }\mathrm{Nucleoside}\stackrel{\mathrm{Nucleosidases}}{\to }\mathrm{Sugars}+\mathrm{Bases}$
 

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Digestion is the process of conversion of complex food substances into simple absorbable forms. This process is carried out by the digestive system with the help of mechanical and biochemical methods. 

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Thecodont is a type of attachment in which each tooth is embedded in a socket of jaw bone. While diphyodont is a type of dentition, in which a set of temporary milk or deciduous teeth replaced by a set of permanent or adult teeth. 

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The stomach is located in the upper left portion of the abdominal cavity. It has four major parts – a cardiac portion into which the oesophagus opens, a fundic region, body (main central region), and a pyloric portion which opens into the first part of the small intestine (duodenum).

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a. Goblet cells are located in the intestinal mucosal epithelium and secrete mucus.
b. Fats are broken down into diglycerides and monoglycerides with the help of lipase enzyme.
c. Gastric glands of stomach mucosa have an oxyntic cell that secretes HCl and intrinsic factors.
d. Saliva contains a salivary amylase enzyme that digests the starch and converts it into maltose (disaccharide).

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The major absorption of the digested food occurs in the small intestine. This process takes place in the jejunum and ileum of the small intestine that is lined by the small finger-like projections called villi. 

The absorbed forms of different food materials are- 
1. Carbohydrates are absorbed in the form of glucose.
2. Proteins are absorbed in the form of amino acids.
3. Fats are absorbed in the form of fatty acids and glycerol. 

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The major organs of the human alimentary canal are - the mouth, oesophagus, stomach, small intestine, large intestine, rectum and anus. 

The major digestive glands are- 

(a) Salivary gland present in the mouth. 
(b) Gastric glands are present in the Stomach.
(c) Liver is situated in the abdominal cavity just below the diaphragm. 
(d) Pancreas is situated between the limbs of the ‘C’ shaped duodenum. 

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The gastric glands contain three main types of cells-

(i) Mucus neck cells- These cells secrete mucus.
(ii) Peptic cells or chief cells- These cells secrete the proenzyme pepsinogen.
(iii) Parietal or oxyntic cells- These cells secrete HCl and intrinsic factors. Intrinsic factors are essential for the absorption of vitamin B₁₂. 

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The mucus along with the bicarbonates released from the pancreas provides lubrication and protection to the intestinal mucosa from acid. It also provides an alkaline medium (pH 7.8) for enzymatic activities. 

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The neural system and hormonal system regulate the activities of the gastrointestinal tract for proper coordination of different parts. They are connected by many intrinsic and extrinsic nerves. 

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The breakdown of fats into fatty acids and glycerol occurs in the duodenum region of the small intestine by the enzyme lipases. 

$\mathrm{Fats}\stackrel{\mathrm{Lipases}}{\to } \mathrm{Diglycerides}\to \mathrm{Monoglycerides}$
$\mathrm{Di} \mathrm{and} \mathrm{Monoglycerides}\stackrel{\mathrm{Lipases}}{\to } \mathrm{Fatty} \mathrm{acids}+ \mathrm{Glycerol}$

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Secretions from Gastric Glands: 
The gastric glands secrete gastric juice that contains hydrochloric acid and the enzyme pepsin. 
A proteolytic enzyme rennin is also secreted by the stomach in infants that helps in the digestion of milk.

Secretions from Liver: 
The liver makes the bile juice that plays an important role in the digestion of fats.  
The bile facilitates the emulsification of fats
It also provides an alkaline medium for enzymes in the small intestine. 

Secretions from Pancreas: 
Pancreas secretes pancreatic juice that contains inactive enzymes- – trypsinogen, chymotrypsinogen, procarboxypeptidases, amylases, lipases and nucleases.
Trypsinogen is activated by an enzyme enterokinase that is secreted by the intestinal mucosa into active trypsin, which in turn activates the other enzymes in the pancreatic juice.
Trypsin, chymotrypsin and carboxypeptidases enzymes are involved in the digestion of proteins.
While pancreatic amylase is involved in the digestion of starch into disaccharides.
Lipases enzyme is involved in the digestion of fats.
Nucleases enzyme is involved in the digestion of nucleic acid. 

Secretions from Small Intestine: 
The Goblet cells of the intestinal mucosal epithelium secretes mucus.
The secretion from the Goblet cells and secretions of the brush border cells of the mucosa constitute the intestinal juice called succus entericus that contains  a variety of enzymes like disaccharidases (e.g., maltase), dipeptidases, lipases, nucleosidases, etc.

End Products of Digestion:
The end products of digestion are simple substances such as glucose, amino acids, fatty acids and glycerol.
These substances can be easily absorbed by the villi present in small intestine. 

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Absorption is the biological process in which the end products of digestion can pass through the intestinal mucosa into the blood or lymph. 

This process is carried out by simple diffusion and facilitated diffusion. 

Simple diffusion- 
Small amounts of monosaccharides such as glucose, amino acids, and some electrolytes like chloride ions are absorbed by simple diffusion. 

Facilitated diffusion- 
Some substances such as glucose and amino acids are absorbed with the help of carrier proteins and this mechanism is called facilitated diffusion. 

Transportation of fatty acid and glycerol- 

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The buccal cavity performs two important functions in the process of digestion- mastication of food and facilitation of swallowing. The teeth and the tongue with the help of saliva masticate and mix up the food thoroughly. Mucus present in the saliva helps in lubrication and adhering the masticated food particles into a bolus. The bolus is then conveyed into the pharynx and then into the oesophagus by swallowing or deglutition. The bolus further passes down through the oesophagus by successive waves of muscular contractions called peristalsis. The saliva secreted into the oral cavity contains electrolytes and enzymes, salivary amylase, and lysozyme. The chemical process of digestion is initiated in the oral cavity by the hydrolytic action of the carbohydrate-splitting enzyme, the salivary amylase. About 30 percent of starch is hydrolyzed here by this enzyme that has an optimum pH of 6.8 into a disaccharide – maltose. Lysozyme present in saliva acts as an antibacterial agent that prevents infections.

Arrangement of teeth:- 

The oral cavity has a number of teeth and a muscular tongue. Each tooth is embedded in a socket of jaw bone and this type of attachment is called thecodont. The  human being 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. An adult human has 32 permanent teeth and are of four different types- incisors (I), canine (C), premolars (PM) and molars (M).
The 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 in human is-
$\frac{2123}{2123}$