Test: Physiology of Digestion - 1 (Old NCERT) - JAMB MCQ

The production of biliverdin from heme is the first major step in the catabolic pathway, after which the enzyme biliverdin reductase performs the second step, producing bilirubin from biliverdin. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases.

Ruminants like cows and sheep contain certain symbiotic anaerobic bacteria (such as Cellulomonas and Ruminococcus spp.) in the caecum, and these bacteria produce enzymes called cellulases that help the microorganism to digest cellulose and they also contain Ruminococcus albus, and Ruminococcus flavefaciens are the principle cellulose degrading organisms.

In cow's milk, approximately 82% of milk protein is casein and the remaining 18% is serum, or whey protein. The casein family of protein consists of several types of caseins (α-s1, α-s2 , ß, and 6) and each has its own amino acid composition, genetic variations, and functional properties.

Amylase is a digestive enzyme that acts on starch in food, breaking it down into smaller carbohydrate molecules. The enzyme is made in two places. 
First, salivary glands in your mouth make salivary amylase, which begins the digestive process by breaking down starch when you chew your food, converting it into maltose, a smaller carbohydrate.
Cells in your pancreas make another type of amylase, called pancreatic amylase, which passes through a duct to reach your small intestine. Pancreatic amylase completes digestion of carbohydrate. Hence, the amylase enzyme acts on the starch.
So, the correct answer is 'starch'.

The sugar present in the sugarcane is known as sucrose. It is a disaccharide which is formed by the glycosidic linkage of first carbon of the glucose and second carbon of the fructose. The molecular formula of sucrose is C₁₂​H₂₂​O₁₁​. On hydrolysis, the glycosidic linkage breaks and the sucrose is converted into simple sugars.

Hindgut fermentation is a digestive process seen in monogastric herbivores, animals with a simple, single-chambered stomach. Cellulose is digested with the aid of symbiotic bacteria. The microbial fermentation occurs in the digestive organs that follow the small intestine: the large intestine and caecum.

The liver cells secrete about 800 to 1,000 ml of bile, which contains bile salts needed for the digestion of fats in the diet.

Peristalsis is the series of involuntary movements in the digestive tract. It is characterized by waves of alternate circular contraction and relaxation of the longitudinal smooth muscle of tube by which the contents are propelled onward. Medulla is responsible for the peristaltic movement of food. Muscle contraction also mixes food with the digestive juices. They also act as valves preventing back flow in the tract. The control allows time for digestion and absorption to take place. The rectum is a slightly dilated section of the colon about 13 cm long. It leads from the sigmoid colon and terminates in the anal canal. The large intestine does not exhibit peristaltic movement as it is seen in other parts of the digestive tract.

Rennin is a proteolytic enzyme found in gastric juice of infants which helps in the digestion of milk proteins. Its action on milk is called curdling of milk. Rennin is secreted as pro rennin, which changes into active rennin in the presence of HCl. Rennin curdle milk protein caseinogens, which is hydrolysed into casein. It converts casein into solid calcium paracaseinate in presence of Ca²⁺. 

Invertase is an enzyme, that catalyzes the hydrolysis (breakdown) of sucrose. The resulting mixture of fructose and glucose is called inverted sugar syrup. Sucrase is also called invertase. Invertase hydrolyze sucrose to give the same mixture of glucose and fructose.

Small intestine are the principal organ for 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 the blood stream and lymph. Absorption is the process by which the end products of digestion pass through the intestinal mucosa (blood capillaries of villi) into the blood or lymph. It is carried out by passive, active or facilitated transport mechanisms.

Digestion of starch begins with the action of salivary alpha-amylase/ptyalin, although its activity is slight in comparison with that of pancreatic amylase in the small intestine.The action of the salivary amylase is inhibited by the acidic pH of the stomach.

Explanation:
Trypsin:
- Trypsin is a digestive enzyme that helps in the breakdown of proteins into smaller peptides.
- It is produced in an inactive form called trypsinogen, which is then activated in the small intestine.
- The active form of trypsin plays a vital role in the digestion of proteins.
Source of Trypsin:
- Trypsin is primarily secreted by the pancreas.
- The pancreas is an organ located in the abdominal cavity, behind the stomach.
- It produces and releases various digestive enzymes, including trypsin, into the small intestine.
- The release of trypsin is stimulated by the presence of food in the small intestine.
Functions of Trypsin:
- Trypsin helps in the digestion of proteins by breaking them down into smaller peptides.
- It specifically cleaves peptide bonds next to the amino acids lysine and arginine.
- The smaller peptides formed by trypsin are further broken down by other enzymes to produce individual amino acids.
Conclusion:
Trypsin is primarily secreted by the pancreas and plays a crucial role in protein digestion. It is activated in the small intestine and helps in breaking down proteins into smaller peptides.

Once a protein source reaches your stomach, hydrochloric acid, and enzymes called proteases to break it down into smaller chains of amino acids. Amino acids are joined together by peptides, which are broken by proteases. Hence, Proteins are broken down into amino acids completely in Intestine.

Starvation mode is a state in which the body is responding to prolonged periods of low energy intake levels. The body responds to reduced energy intake by burning fat reserves and consuming muscle and other tissues. Specifically, the body burns fat after first exhausting the contents of the digestive tract along with glycogen reserves stored in muscle and liver cells. After prolonged periods of starvation, the body will utilize the proteins within muscle tissue as a fuel source. 

Explanation:
The correct answer is A: Inactive due to HCl.
Reasoning:
Ptyalin is an enzyme present in saliva, specifically in the salivary glands. It is responsible for the breakdown of starch into maltose, a disaccharide. However, ptyalin cannot work in the stomach due to the following reasons:
- Inactive due to HCl: The stomach secretes hydrochloric acid (HCl), which creates an acidic environment. The low pH of the stomach acid denatures and inactivates ptyalin, rendering it ineffective in breaking down starch.
- Inactive due to Renin: Renin is an enzyme present in the stomach that helps in the digestion of milk proteins. However, renin does not directly affect the activity of ptyalin.
- Inactive due to Pepsin: Pepsin is another enzyme present in the stomach that helps in the digestion of proteins. Pepsin does not directly affect the activity of ptyalin.
- None of these: This option is incorrect because ptyalin does become inactive in the stomach due to the presence of HCl.
Therefore, the correct answer is A: Inactive due to HCl.

Bile is a fluid that is made and released by the liver and stored in the gallbladder. Bile helps with digestion. It breaks down or emulsify fats into fatty acids, which can be taken into the body by the digestive tract. Bile contains mostly cholesterol, bile acids (also called bile salts), and bilirubin (a breakdown product of red blood cells). It also contains water, body salts (such as potassium and sodium), copper and other metals. Bile does not function in digest fat by enzymatic action, eliminate waste product or regulate process of digestion.

Proteolytic enzymes are those which help break down and digest proteins. They are essential for cell division, immune function, and protein recycling. Trypsin, Erepsin, and pepsin are the essential proteolytic enzymes. These enzymes help to break down protein in meat, eggs, and fish into simpler amino acids.
So, the correct answer is Trypsin, Erepsin, pepsin.

Explanation:
When bacteria enter the stomach through contaminated food, they are killed by the following mechanisms:
1. Hydrochloric Acid (HCl):
- The stomach secretes hydrochloric acid, which creates an acidic environment with a pH between 1 and 3.
- HCl helps in the digestion of proteins and also acts as a defense mechanism against pathogens.
- The low pH of stomach acid kills most bacteria that enter the stomach.
2. Pepsin:
- Pepsin is an enzyme produced by the stomach lining cells.
- It helps in the breakdown of proteins into smaller peptides.
- Pepsin works best in an acidic environment, which is provided by the hydrochloric acid in the stomach.
- It can also help in killing bacteria by breaking down their proteins.
Therefore, the correct answer is option D: HCl. The hydrochloric acid present in the stomach kills bacteria that enter the stomach with contaminated food.

The Brunner's glands are branched tubular glands and. They secrete alkaline watery fluid, a little enzyme, and mucus. They open into the crypts of Lieberkuhn. The mixture of secretions is called Intestinal juice, or succus entericus.

Answer:

Contents in the blood:

- Haemoglobin: Haemoglobin is a protein found in red blood cells that is responsible for carrying oxygen from the lungs to the body's tissues and returning carbon dioxide from the tissues back to the lungs.
- Amylase: Amylase is an enzyme that helps in the digestion of carbohydrates. It is produced by the pancreas and salivary glands. While it is present in the digestive system, it is not normally found in the blood.
- Trypsin: Trypsin is an enzyme involved in the digestion of proteins. It is produced by the pancreas and released into the small intestine. Like amylase, it is not normally found in the blood.
- Lipase: Lipase is an enzyme that helps in the digestion of fats. It is produced by the pancreas and released into the small intestine. While it is present in the digestive system, it is not normally found in the blood.
Based on the options given, the correct answer is C: Haemoglobin, as it is the only component mentioned that is naturally present in the blood.

Chymotrypsin is a proteolytic enzyme (serine protease) acting in the digestive systems of many organisms. It facilitates the cleavage of peptide bonds by a hydrolysis reaction, which despite being thermodynamically favorable, occurs extremely slowly in the absence of a catalyst.

Secretion and synthesis of bile is the main function of liver. Bile is yellowish-green, alkaline fluid. In bile juice, bile salts, sodium carbonate, glycolate, taurocholate, bile pigments, cholesterol, lecithin etc. are present. Bile salts help in emulsification of fats in small intestine. It mainly act at the duodenum part of the small intestine.

Urea cycle in liver helps in conversion of excess of amino acids into urea. It takes place in five major steps. The extra proteins in the body are degraded by the process of deamination where the NH2​ group is removed and it is converted into ammonium ions in the liver. The ammonium ions enter urea cycle and get converted into urea. The urea formed in liver is transported to kidney through circulation and finally gets excreted. So, the correct answer is "liver".

Option ( b) intestine and stimulate pancreatic glands  is correct answer. 

Explanation :- 

Secretin is a hormone that regulates water hemostasis,  Throughout the body & by regulating secretion in stomach, pancreas & liver. It is a peptide hormone produced in the S-Cells of duodenum, which are located in intestinal glands. Hence, secretin hormone is produced in the intestine & stimulates Pancreatic glands.

Answer:
Carbohydrates, proteins, and fats are macronutrients that require digestion in order to be broken down into smaller molecules that can be absorbed by the body. Here is a detailed explanation of where the digestion of each macronutrient takes place:
1. Carbohydrates:
Carbohydrates are broken down into simple sugars such as glucose, which can be easily absorbed by the body. The digestion of carbohydrates occurs in the following steps:
- Mouth: Salivary amylase, an enzyme present in saliva, begins the digestion of carbohydrates by breaking down starch into smaller molecules.
- Stomach: The digestion of carbohydrates does not occur in the stomach.
- Small Intestine: The majority of carbohydrate digestion takes place in the small intestine. Pancreatic amylase, as well as enzymes produced by the cells lining the small intestine, break down the remaining complex carbohydrates into simple sugars.
- Large Intestine: The large intestine does not play a significant role in carbohydrate digestion.
2. Proteins:
Proteins are large molecules made up of amino acids. The digestion of proteins occurs in the following steps:
- Mouth: Protein digestion does not occur in the mouth.
- Stomach: In the stomach, the enzyme pepsin begins the breakdown of proteins into smaller peptide chains.
- Small Intestine: The majority of protein digestion occurs in the small intestine. Pancreatic enzymes and enzymes produced by the cells lining the small intestine further break down proteins into individual amino acids.
- Large Intestine: The large intestine does not play a significant role in protein digestion.
3. Fats:
Fats are broken down into fatty acids and glycerol. The digestion of fats occurs in the following steps:
- Mouth: Fat digestion does not occur in the mouth.
- Stomach: In the stomach, fat digestion does not occur to a significant extent.
- Small Intestine: The majority of fat digestion takes place in the small intestine. Bile, produced by the liver and stored in the gallbladder, emulsifies fats, breaking them down into smaller droplets. Pancreatic lipase, along with other enzymes, then breaks down these smaller droplets into fatty acids and glycerol.
- Large Intestine: The large intestine does not play a significant role in fat digestion.
From the above explanation, it is clear that the digestion of carbohydrates, proteins, and fats completes in the small intestine.

Rennin is a milk protein digesting enzyme found in gastric juice of stomach in infants.

Digestion and absorbtion primarily occurs in Small intestine because in inner surface of small intestine Millon's of tiny finger like projection present collectively know as Villi which help in digestion and absorbtion.

Bile juice has bile pigments such as bilirubin and biliverdin. These break down large fat globules into smaller globules so that the pancreatic enzymes can easily act on them. This process is known as emulsification of fats. The pancreatic juice contains enzymes that complete the digestion of starch called pancreatic amylase. It also contains pancreatic enzymes that complete the digestion of protein called trypsin, chymotrypsin and carboxypeptidase. Hence pancreatic juice plays a vital role in the digestion of proteins.

Trypsin is produced in the pancreas as the inactive proenzyme trypsinogen. In the duodenum, trypsin catalyzes the hydrolysis of peptide bonds, breaking down proteins into smaller peptides.