Physiology of digestion Questions in English

(D) In humans, the milk protein-digesting enzyme in the stomach is $Pepsin$.
In calves, the enzyme responsible for this is $Rennin$.
$Rennin$ is present in small amounts in human infants but is absent in adults.
In adults, $Pepsin$ acts on the water-soluble milk protein $Caseinogen$ to convert it into $Casein$.
This $Casein$ then combines with calcium salts to form insoluble $Calcium \text{ } paracaseinate$, which is subsequently digested by proteolytic enzymes.

(A) The reaction in option $A$ is incorrect. Nucleic acids are first broken down by nucleases into nucleotides. Nucleotides are then acted upon by nucleotidases to form nucleosides and inorganic phosphate $(H_3PO_4)$. Finally, nucleosidases break down nucleosides into nitrogenous bases and pentose sugars. Therefore, nucleotidases do not directly convert nucleic acids into nitrogen bases and pentose sugars.

(A) The $Caecum$ is a large,pouch-like structure located at the junction of the small intestine and the large intestine. In herbivores like horses,rabbits,and hares,the $Caecum$ contains symbiotic microorganisms that produce enzymes necessary for the digestion of cellulose. This process allows these animals to derive energy from plant cell walls.

(A) Intestinal juice,also known as $succus$ $entericus$,is the combined secretion of goblet cells and brush border cells of the intestinal mucosa. It contains a variety of enzymes such as maltase,lipase,dipeptidase,and nucleosidases. Partially hydrolysed proteins,carbohydrates,and fats from the stomach enter the small intestine. Pancreatic enzymes convert these into dipeptides,disaccharides,and monoglycerides,respectively. Finally,the enzymes present in the $succus$ $entericus$ act on these end products to convert them into simple absorbable forms (e.g.,dipeptidases convert dipeptides into amino acids).

(D) In ruminants (e.g.,cow,goat,and camel),the stomach is four-chambered as follows:
$(a)$ Rumen: Cellulose is fermented by microorganisms.
$(b)$ Reticulum: Acts as a filter and helps in regurgitation.
$(c)$ Omasum: Primarily absorbs water and nutrients.
$(d)$ Abomasum: Known as the 'true stomach'.
Gastric glands are found only in the abomasum,which secrete gastric juices containing enzymes like pepsin for protein digestion. Therefore,the abomasum is the site where enzymatic digestion primarily occurs before the food passes to the small intestine.

(B) The gastric glands secrete an inactive proenzyme called $Pepsinogen$.
When $Pepsinogen$ comes in contact with $HCl$ (hydrochloric acid) secreted by the parietal cells of the stomach,it is converted into the active proteolytic enzyme $Pepsin$.
$Pepsinogen \xrightarrow{HCl} Pepsin$.
$Trypsinogen$ is activated by $Enterokinase$ in the small intestine,while $Renin$ is a hormone involved in the regulation of blood pressure and electrolyte balance.

(C) The breakdown of biomolecules like dipeptides,lactose,maltose,and sucrose occurs mainly in the small intestine,specifically in the duodenum and jejunum. This is because the enzymes required for the digestion of these disaccharides and dipeptides (such as dipeptidases,lactase,maltase,and sucrase) are present in the succus entericus (intestinal juice) secreted by the intestinal mucosa.

(B) Bile contains bile salts (such as bilirubin and biliverdin) which help in the emulsification of fats.
Emulsification is the process of breaking down large fat globules into smaller micelles,which increases the surface area for the action of lipase enzymes.
Bile does not contain any digestive enzymes; therefore,it does not participate in the chemical digestion of proteins or other macromolecules.

(C) The wave-like muscular contractions of the digestive tract are known as $Peristalsis$.
$Mastication$ refers to the process of chewing food.
$Assimilation$ is the process where absorbed food materials reach the tissues via blood and lymph and are utilized for activities such as growth,energy,and repair.
$Stimulation$ refers to the act of exciting or activating a process or organ.

(C) The food in the stomach is mixed with gastric juice,which contains $HCl$.
Due to the presence of $HCl$,the stomach environment is highly acidic with a $pH$ ranging from $1.8$ to $3.2$.
This acidic,semi-digested food mass that passes from the stomach into the small intestine is called chyme.
Therefore,the food entering the intestine from the stomach is acidic chyme.

(C) The pyloric sphincter is a muscular valve located at the junction of the stomach and the small intestine. It specifically regulates the passage of partially digested food (chyme) from the pyloric region of the stomach into the duodenum,which is the first part of the small intestine.

(B) Lysozyme is an antibacterial enzyme that protects against infection.
Pepsin is a protease enzyme secreted in the stomach for protein digestion.
Rennin is a proteolytic enzyme found in the gastric juice of infants.
Salivary amylase (also known as ptyalin) is the enzyme present in saliva that initiates the chemical digestion of carbohydrates (starch) into maltose in the oral cavity.

(B) $Renin$: It is a hormone/enzyme involved in the regulation of blood pressure and osmoregulation.
$Rennin$ (also known as chymosin): It is a proteolytic enzyme found in the gastric juice of infants that specifically helps in the digestion of milk proteins like casein.
$Salivary \text{ } amylase$: It is an enzyme present in saliva that helps in the digestion of carbohydrates.
$Lysozyme$: It is an antibacterial enzyme present in saliva and tears that prevents bacterial infection.

(D) Emulsification of fat is the process of breaking down large fat globules into smaller droplets to increase the surface area for enzyme action.
This process is carried out by bile salts present in the bile juice.
Although bile is produced in the liver and stored in the gall bladder,it is released into the $Duodenum$ (the first part of the small intestine) to perform the emulsification of fats during digestion.

(B) Bread contains carbohydrates in the form of starch. When it is chewed in the mouth,the enzyme salivary amylase (ptyalin) present in the saliva acts on the starch and breaks it down into maltose. Maltose is a disaccharide sugar,which gives a sweet taste.

(B) The process of digestion is completed in the small intestine. Specifically,the final stages of chemical digestion occur in the ileum,where enzymes break down remaining nutrients into their simplest absorbable forms,such as amino acids,monosaccharides,and fatty acids.

(A) Gastrectomy is the surgical removal of the stomach or a portion of it.
The stomach secretes $HCl$ (hydrochloric acid) from the oxyntic (parietal) cells.
$HCl$ is essential for the conversion of ferric ions $(Fe^{3+})$ into ferrous ions $(Fe^{2+})$,which are the absorbable form of iron in the small intestine.
Without the stomach,the production of $HCl$ is significantly reduced or absent,leading to impaired iron absorption and subsequent iron deficiency anaemia.
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

(A) The liver produces bile,which is stored and concentrated in the gallbladder.
Bile contains bile salts (such as sodium glycocholate and sodium taurocholate) that play a crucial role in the emulsification of fats.
Emulsification breaks down large fat globules into smaller droplets,thereby increasing the surface area for the action of the enzyme lipase.
Therefore,both the Assertion and the Reason are correct,and the Reason is the correct explanation of the Assertion.

(B) The term $Succus \ entericus$ is the scientific name for intestinal juice.
It is secreted by the glands of the small intestine,specifically the crypts of $Lieberkühn$ and Brunner's glands.
It contains a variety of enzymes such as disaccharidases (e.g.,maltase,lactase,sucrase),dipeptidases,lipases,and nucleosidases,which complete the final stages of digestion of food in the small intestine.

(B) The stomach stores food for $4-5$ hours. The churning movements of the muscular wall of the stomach mix the food thoroughly with the acidic gastric juice. This acidic,semi-digested food is called $Chyme$.

(A) The absorption of water,simple sugars,and alcohol occurs primarily in the stomach.
Additionally,some fat-soluble drugs are also absorbed through the stomach wall.

(N/A) The process of conversion of complex food substances into simple absorbable forms by mechanical and biochemical methods is called digestion.

(C) Salivary glands secrete saliva,which contains salivary amylase (ptyalin),mucus,and lysozyme.
$1$. Salivary amylase helps in the digestion of complex carbohydrates (starch) into maltose.
$2$. Mucus helps in the lubrication of the oral cavity and the formation of the food bolus.
$3$. Lysozyme acts as an antibacterial agent to control the bacterial population in the mouth.
$4$. Salivary glands do not secrete enzymes for the digestion of disaccharides (like maltase,sucrase,or lactase). Disaccharide digestion occurs in the small intestine.

(C) Bile juice,secreted by the liver and stored in the gallbladder,contains bile salts (sodium glycocholate and sodium taurocholate). These salts reduce the surface tension of fat droplets and break them into smaller globules,a process known as emulsification. This increases the surface area for the action of the enzyme lipase.

(C) The digestive system performs two main types of processes to break down complex food substances into simpler absorbable forms:
$1$. Mechanical processes: These include mastication (chewing) in the mouth,churning in the stomach,and peristalsis in the alimentary canal,which physically break down food into smaller particles.
$2$. Biochemical processes: These involve the action of various digestive enzymes (e.g.,amylase,pepsin,lipase) that chemically break down complex macromolecules like carbohydrates,proteins,and fats into their simpler monomeric forms (glucose,amino acids,fatty acids).
Therefore,both mechanical and biochemical processes are essential for digestion.

(D) Digestion is the process of converting complex food substances into simple absorbable forms.
Macromolecules like $I-$ Lipids,$II-$ Carbohydrates,$IV-$ Nucleic acids,and $VII-$ Proteins are complex and require enzymatic hydrolysis (digestion) to be broken down into simpler forms (like fatty acids,monosaccharides,nucleotides,and amino acids) that can be absorbed by the intestinal mucosa.
$III-$ Water,$V-$ Vitamins,and $VI-$ Minerals are already in simple forms and do not require digestion; they are absorbed directly by the body.
Therefore,the components that require digestion are $I, II, IV,$ and $VII$.

(B) Emulsification is the process of breaking down large fat globules into smaller droplets to increase the surface area for the action of enzymes like lipase.
Bile juice,secreted by the liver,contains bile salts such as sodium glycocholate and sodium taurocholate.
These bile salts are amphipathic molecules that reduce the surface tension of fat droplets and break them into smaller micelles,thus facilitating the digestion of fats.
Bile pigments (bilirubin and biliverdin) do not participate in the digestion or emulsification of fats; they are excretory products.
Therefore,bile salts are the primary components responsible for the emulsification of fats.

(A) $Amylase$ is a hydrolytic enzyme that breaks down starch (a polysaccharide) into disaccharides like maltose,not directly into monosaccharides. Therefore,statement $III$ is incorrect.
$Amylase$ (specifically salivary $amylase$ and pancreatic $amylase$) acts in the oral cavity at $pH$ $6.8$ and in the small intestine at $pH$ $7.8$ respectively. Thus,statements $I$ and $II$ are correct.
$Amylase$ is indeed a hydrolytic enzyme,making statement $IV$ correct.
$Lysozyme$ acts as an antibacterial agent in the oral cavity,not $amylase$. Thus,statement $V$ is incorrect.
Therefore,the correct statements are $I, II,$ and $IV$.

(B) Statement $I$ is correct: The stomach acts as a storage organ for food for $4$ to $5$ hours.
Statement $II$ is incorrect: Food mixes with acidic gastric juice (not alkaline) to form chyme.
Statement $III$ is correct: The gastric juice contains $HCl$,which provides an acidic $pH$ of $1.8$.
Statement $IV$ is correct: Gastric glands secrete small amounts of lipases,which are involved in the digestion of fats.
Therefore,statements $I, III,$ and $IV$ are correct.

(A) In the process of protein digestion,the enzyme pepsin acts on proteins in the stomach.
Proteins are broken down into smaller units called proteoses and peptones.
This reaction is represented as: $\text{Proteins} \xrightarrow{\text{Pepsin}} \text{Proteoses} + \text{Peptones}$.

(D) The digestion of macromolecules in the small intestine results in the following products:
$1$. Proteins,Peptones,and Proteoses are acted upon by pancreatic enzymes (like trypsin,chymotrypsin,and carboxypeptidase) to form $P =$ Dipeptides.
$2$. Starch is acted upon by pancreatic amylase to form $Q =$ Maltose.
$3$. Lipids are acted upon by lipases (with the help of bile salts) to form $R =$ Diglycerides and Monoglycerides.
$4$. Nucleic acids are acted upon by nucleases to form $S =$ Nucleotides.
Therefore,the correct sequence is $P =$ Dipeptides,$Q =$ Maltose,$R =$ Diglycerides,$S =$ Nucleotides.

(D) The alimentary canal wall consists of four layers: Serosa,Muscularis,Submucosa,and Mucosa.
$1$. The Mucosa is the innermost lining of the lumen of the alimentary canal.
$2$. This layer is responsible for the secretion of enzymes,mucus,and hormones,and it is the site where the final stages of digestion and absorption occur.
$3$. Therefore,the process of digestion occurs in close proximity to the Mucosa layer.

(D) Lipids (fats) are primarily digested in the small intestine with the help of bile salts and the enzyme lipase.
Bile salts emulsify large fat globules into smaller droplets,increasing the surface area for enzyme action.
Pancreatic lipase then breaks down these emulsified fats into their final absorbable forms,which are fatty acids and glycerol.
Therefore,the end products of lipid digestion are fatty acids and glycerol.

(D) Saliva contains salivary amylase (ptyalin),which initiates the partial digestion of complex carbohydrates (starches) into maltose. It also contains lysozyme,which acts as an antibacterial agent,and mucus,which helps in the lubrication and binding of food particles into a bolus. However,the digestion of disaccharides (like maltose,sucrose,or lactose) into monosaccharides occurs in the small intestine by disaccharidases,not by salivary gland secretions.

(A) Maltose is a disaccharide composed of two glucose molecules linked by an $\alpha-1,4$-glycosidic bond.
During the process of digestion,the enzyme maltase acts on maltose to hydrolyze this bond.
This reaction results in the formation of two molecules of glucose.
Therefore,the digestion of maltose yields glucose only.

(B) The correct matching is as follows:
$1$. Amylase acts on starch to produce disaccharides $(c)$.
$2$. Trypsin acts on proteins to produce polypeptides $(d)$.
$3$. Chymotrypsin acts on proteins to produce dipeptides $(b)$.
$4$. Rennin acts on casein (milk protein) to produce coagulated milk protein $(a)$.
Therefore,the correct sequence is $1-c, 2-d, 3-b, 4-a$.

(D) In the human digestive system,food undergoes different stages of processing in various organs.
$1$. In the buccal cavity,food is chewed and mixed with saliva to form a small,rounded mass called a 'Bolus' $(x)$.
$2$. This bolus passes through the esophagus into the stomach,where it is mixed with gastric juices to form an acidic,semi-digested,pasty mass called 'Chyme' $(y)$.
$3$. Therefore,the correct analogy is: Buccal cavity: Bolus :: Stomach: Chyme.

(B) Salivary amylase is an enzyme that functions optimally at a neutral $pH$ (approximately $6.8$) in the mouth.
When food enters the stomach,it mixes with gastric juice,which contains hydrochloric acid $(HCl)$.
This makes the environment highly acidic (a $pH$ of approximately $1.8$ to $2.0$).
Salivary amylase is sensitive to $pH$ changes and becomes denatured or inactive in this highly acidic environment,thereby stopping the digestion of starch.

(A) The digestion of fats occurs in the small intestine.
Emulsified fats are broken down by the enzyme lipases into fatty acids and monoglycerides.
Therefore,$(Y)$ represents monoglycerides.
Thus,the correct option is $(A)$.

(C) Indole and skatole are putrefactive products formed by the bacterial decomposition of the amino acid tryptophan.
This process occurs primarily in the large intestine,where the gut microbiota acts upon undigested proteins that reach the colon.
Therefore,the bacterial breakdown of proteins in the large intestine results in the production of indole and skatole,which contribute to the characteristic odor of feces.

(B) In the stomach,the gastric glands secrete inactive pepsinogen.
$HCl$ (hydrochloric acid) provides an acidic medium with a $pH$ of approximately $1.8$.
This acidic environment is essential for the conversion of inactive pepsinogen into the active enzyme pepsin.
Pepsin is a proteolytic enzyme that breaks down proteins into peptides.

(A) The parietal cells (also known as oxyntic cells) of the stomach secrete a glycoprotein called the intrinsic factor (Castle's intrinsic factor).
This factor is essential for the absorption of vitamin $B_{12}$ (cyanocobalamin) in the ileum of the small intestine.
Without the intrinsic factor,vitamin $B_{12}$ cannot be absorbed,which can lead to pernicious anemia.

(A) $Statement-I$ is correct: Chymotrypsin is a proteolytic enzyme that acts on proteins, proteoses, and peptones to break them down into smaller peptides (polypeptides).
$Statement-II$ is correct: Trypsin is a proteolytic enzyme that acts on polypeptides to break them down into dipeptides.
Both statements accurately describe the roles of these pancreatic enzymes in protein digestion.

(C) After mastication of starchy food,the enzyme salivary amylase present in saliva acts on starch.
This enzyme initiates the breakdown of starch into smaller carbohydrate units.
The primary product of this initial digestion in the oral cavity is maltose,which is a disaccharide composed of two glucose molecules linked together.

(C) Trypsin is a proteolytic enzyme secreted by the pancreas in an inactive form called trypsinogen,which is activated by enterokinase in the small intestine.
Trypsin acts on proteins,proteoses,and peptones to break them down into smaller peptides (polypeptides).
Therefore,in the reaction $A \xrightarrow{\text{Trypsin}} B$,$A$ represents Proteins (or proteoses/peptones) and $B$ represents Polypeptides.
Option $C$ correctly identifies this relationship.

(C) Pepsin is a proteolytic enzyme that is highly active in an acidic environment.
It shows its highest activity at an optimum pH of $2.0$.
This acidic pH is maintained in the stomach due to the secretion of $HCl$ (hydrochloric acid) by the gastric glands.

(B) Pepsin is a protein-digesting enzyme secreted by the gastric glands located in the stomach.
It functions optimally in an acidic medium provided by $HCl$ in the stomach.
In contrast,enzymes in the small intestine function in an alkaline medium.

(B) Trypsin is a proteolytic enzyme that is secreted by the pancreas into the duodenum in an inactive form called trypsinogen.
It is activated by the enzyme enterokinase,which is present in the intestinal juice.
Trypsin functions optimally in an alkaline environment,which is provided by the bile and pancreatic juice in the duodenum.
The optimum pH for the activity of trypsin is approximately $8.0$ to $9.0$,and among the given options,$9.5$ is the closest value representing the alkaline range required for its activity.

(A) $Succus$ $entericus$ is the intestinal juice secreted by the intestinal glands. It contains a variety of enzymes such as disaccharidases (e.g.,maltase,lactase,sucrase),dipeptidases,lipases,and nucleosidases. However,nucleases (which break down nucleic acids into nucleotides) are primarily secreted by the pancreas into the small intestine,not by the intestinal mucosa itself. Therefore,nucleases are not considered a component of $Succus$ $entericus$.

(D) In the process of protein digestion in the human digestive system:
$1$. $A$ represents the action of pepsin in the stomach, which breaks down proteins into peptones and proteoses.
$2$. $B$ represents the action of trypsin (a pancreatic enzyme) in the small intestine, which further breaks down these products into polypeptides.