Test: Digestion of Nutrients (Old NCERT) - JAMB MCQ

In stomach, rennin acts on casein (milk protein) and converts it into paracasein. In the presence of calcium ions, paracasein is converted into calcium paracaseinate, ultimately leading to milk coagulation.

• Rennin is a protein-digesting enzyme that curdles milk by transforming caseinogen into insoluble casein.
• The enzyme enterokinase helps in the conversion of 'trypsinogen into trypsin'. It secretes from the intestinal glands.
• Pepsin breaks down proteins into smaller peptides.
• Proteins from the digested food are broken down into smaller peptide chains and amino acids by various enzymes such as carboxypeptidase, aminopeptidase, and dipeptidase.

So the correct option is B.

During prolonged fasting, the body undergoes several biochemical and hormonal changes to make up for the lack of food and hence energy so as to be able to continue the vital processes needed for existence. The glycogen and glucose stored in the body last for a short time. After these, the body moves onto the adipose tissues or the fat accumulated in the body so that the store of vital proteins in the body gets spared or is utilized at last.
So, the correct answer is 'First carbohydrates, next fats and lastly proteins'.

In the small intestine, pancreatic juice containing an enzyme, α-amylase acts on starch and converts it into dissacharide, maltose, isomaltose and 'limit' dextrins

Starch Maltose + Isomaltose + 'Limit' dextrins

Oral cavity (saliva) lacks any fat digesting enzyme. Fat is largely digested in the small intestine. Cellulose is not digested at all in the human beings. Therefore, both fat and cellulose reach the stomach totally undigested.

Secretin is a hormone secreted by the epithelium of duodenum. It stimulates gall bladder to secrete bile, inhibits acid secretion in stomach and stimulates the pancreas to secrete bicarbonate ions.

Sugarcane contains sucrose (disaccharide). In the duodenum, sucrose is acted upon by enzyme invertase which breaks donw it into glucose and fructose.

Pancreatic juice contains lipases and nucleases, Lipase acts on fat and converts it into monoglycerides and fatty acids. Nucleaes convert nucleic acids into nucleotides.

The pH of the stomach (1.5 – 2.5) is maintained by HCl which is essential for the protein-digesting enzymes to act on proteins. So, if pH of stomach is made 7, then digestion of proteins will be affected.

• Proteins are converted into dipeptides in the stomach which is followed by the conversion of dipeptides to amino acids in the small intestine. These amino acids are absorbed through the wall of the intestine as simple absorbable substances.
• Hence In order to absorb and use Proteins by the body, these must be broken down by hydrolysis into proteins.
• So, the correct answer is 'amino acids, proteins'.

Digestion of proteins begins in the stomach as stomach contains protein digesting enzymes like pepsin, rennin etc. Mouth (saliva) does not contain protein digesting enzymes. Digestion of polysaccharides begins in the mouth as the saliva contains enzymes for them

Lactose  Glucose + Galactose

Bile salts of bile bring about emulsification of fat by which fat droplets are broken down into may small droplets this increaes lipase action on fat, by increasing the available surface area.

Bolus is the food particles formed with chewing and mixing with saliva. Chyme is the food which is mixed thoroughly with acidic gastric juice.

Amylase hydrolyzes starch to maltose, isomaltose, and α-dextrins. Hydrochloric acid activates pepsinogen to pepsin, Rennin coagulates the milk protein casein.

Villi, Brunner's glands and crypts of Lieberkuhn are associated with small intestine while gastric glands are associated with stomach. Pepsin, trypsin and rennin are protein digesting enzymes while lipase is a fat digesting enzyme. Bile salts and bile pigments are present in bile which is stored in gall bladder, while gastric juice is secreted by gastric glands

The stomach has lowest pH of 1.5-2.5 which is maintained by secretion of HCl in it. Liver secretes bile that contain bile salts that act as lipid emulsifiers. Large intestine is mainly involved in absorption of water and elimination of waters. Proteases also function in the stomach.

Deglutition (swallowing) starts as a voluntary action in the mouth and then continues as an involuntary action. Striated muscle surrounds the upper one third of the oesophagus and smooth muscle surrounds the lower two thirds.

Oesophagus does not secrete any enzyme. It simply passes the food from mouth to stomach by peristalsis.

Pepsin is an enzyme produced in the mucosal lining of the stomach that acts to degrade protein. Pepsin is one of three principal protein-degrading or proteolytic, enzymes in the digestive system, the other two being chymotrypsin and trypsin (secreted in the small intestine). Optimum pH for pepsin is 1.5-1.6. 

So, the correct option is 'Pepsin'.

In the mouth, saliva moistens and lubricates the food and chewing (by teeth) breaks the food into smaller pieces. This semi-solid food is moulded into a ball known as bolus by tongue and is pushed into the oesophagus via pharynx.

Amylase is a digestive enzyme that acts on starch in food, breaking it down into smaller carbohydrate molecules. It is produced at two sites. First, salivary glands in the mouth make salivary amylase, which begin the digestive process by breaking down starch when the food is chewed. The starch is converted to maltose, a smaller carbohydrate. When starchy foods like rice or potatoes begin to break down in the mouth, a slightly sweet taste is detected, as maltose is released. So, if we chew a piece of bread (made of polysaccharides) long enough, it will begin to taste sweet because amylase is breaking down starches to dissaccharides such as maltose. Thus, option C is correct.

Lipids are a group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E, and K), monoglycerides, diglycerides, triglycerides, phospholipids, and others. The main biological functions of lipids include storing energy, signaling, and acting as structural components of cell membranes.

Triglycerides, stored in adipose tissue, are a major form of energy storage both in animals and plants. The adipocyte, or fat cell, is designed for continuous synthesis and breakdown of triglycerides in animals, with breakdown controlled mainly by the activation of hormone-sensitive enzyme lipase. The complete oxidation of fatty acids provides high caloric content, about 9 kcal/g, compared with 4 kcal/g for the breakdown of carbohydrates and proteins. Migratory birds that must fly long distances without eating use stored energy of triglycerides to fuel their flights.

Carbohydrates form the major fuel in the cells to provide energy for life processes. Carbohydrates form a better fuel than fats and proteins because their molecules have relatively more oxygen and therefore as compared to proteins and fats, they need less oxygen for their oxidation. Therefore, athletes, labourers doing heavy work and mountaineers should live on high carbohydrate diets. 

The yellow colour of the stools is due to the presence of bile pigments. Bile pigments are the excretory products. Bile is a bitter-tasting greenish-yellow alkaline fluid produced by the liver and stored in the gall bladder and secreted into the duodenum. It assists the digestion and absorption of fats by the action of bile salts, which chemically reduce fatty substances and decrease the surface tension of fat droplets so that they are broken down and emulsified. So, the correct answer is (a).

Enterogastrone hormone is released from duodenum and it slows gastric contraction to delay emptying of stomach and stops secretion of gastric juice. Enterogastrone is released when the stomach contents pass into the small intestine.

Trypsinogen is present in pancreatic juice. It is a proenzyme that is converted into active form trypsin by the enzyme enterokinase. Trypsin further acts on proteins to convert them into peptides.

Cholecystokinin (CCK) is produced by the GI cell in the small intestine and acts on pancreas to stimulate the secretion and release of digestive enzymes in pancreatic juice. It also acts on the gall bladder to stimulate contraction and expulsion of bile which is produced in liver and stored in gall bladder.