Digestive Enzymes Practice Questions
20 free Digestive Enzymes practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which enzyme initiates the digestion of carbohydrates in the oral cavity?
- A Pancreatic amylase
- B Salivary amylase
- C Maltase
- D Sucrase
Correct answer: Salivary amylase
Salivary amylase, also known as ptyalin, begins the chemical digestion of starch in the mouth. It breaks down about 30 percent of starch into the disaccharide maltose at an optimum pH of 6.8.
The inactive enzyme pepsinogen is converted into active pepsin in the stomach by the action of:
- A Enterokinase
- B Bile salts
- C HCl (gastric acid)
- D Bicarbonate ions
Correct answer: HCl (gastric acid)
Pepsinogen is a proenzyme secreted by the gastric chief cells. Upon exposure to hydrochloric acid (HCl) secreted by parietal cells, it is converted into the active proteolytic enzyme pepsin, which digests proteins into peptones and proteoses.
Which enzyme is specifically responsible for the digestion of milk proteins in infants?
- A Gastric pepsin
- B Pancreatic trypsin
- C Rennin
- D Steapsin
Correct answer: Rennin
Rennin is a proteolytic enzyme found in the gastric juice of infants. It helps in the curdling and digestion of milk proteins (casein), though it is absent or significantly reduced in adults.
Which of the following enzymes is NOT a component of pancreatic juice?
- A Trypsinogen
- B Chymotrypsinogen
- C Procarboxypeptidase
- D Nucleosidase
Correct answer: Nucleosidase
Trypsinogen, chymotrypsinogen, and procarboxypeptidase are the proteolytic proenzymes of pancreatic juice. Nucleosidases are found in the intestinal juice (succus entericus) and act on nucleosides.
The activation of trypsinogen into trypsin is triggered by which enzyme?
- A Pepsin
- B Enterokinase
- C Chymotrypsin
- D Lipase
Correct answer: Enterokinase
Enterokinase (also called enteropeptidase) is secreted by the intestinal mucosa. It specifically activates trypsinogen into active trypsin, which then activates the other enzymes in pancreatic juice.
Bile juice contains no enzymes, yet it is essential for the digestion of:
- A Carbohydrates
- B Proteins
- C Dietary fats
- D Nucleic acids
Correct answer: Dietary fats
Bile helps in the emulsification of fats, breaking them down into very small micelles. This increase in surface area allows pancreatic and intestinal lipases to act efficiently on the lipid molecules.
Which enzyme converts proteins, proteoses, and peptones into dipeptides in the small intestine?
- A Pepsin
- B Trypsin
- C Dipeptidase
- D Enterokinase
Correct answer: Trypsin
Trypsin, chymotrypsin, and carboxypeptidase from the pancreatic juice act on partially digested proteins in the chyme. They break down these large polypeptides into smaller dipeptides.
Intestinal juice (succus entericus) contains which of the following enzymes for the final stage of carbohydrate digestion?
- A Amylase
- B Nuclease
- C Maltase
- D Trypsin
Correct answer: Maltase
The intestinal juice contains disaccharidases like maltase, sucrase, and lactase. These enzymes break down disaccharides into their constituent monosaccharides (e.g., maltose into two glucose molecules).
The breakdown of fats into diglycerides and monoglycerides is primarily catalyzed by:
- A Salivary amylases
- B Gastric proteases
- C Pancreatic lipases
- D Intestinal nucleases
Correct answer: Pancreatic lipases
Lipases, particularly pancreatic lipase (steapsin), are the primary enzymes for fat digestion. They act on emulsified fat droplets to yield fatty acids and glycerides.
What is the final product of the action of nucleotidases and nucleosidases?
- A Nucleotides only
- B Nucleosides only
- C Sugars and bases
- D Amino acids only
Correct answer: Sugars and bases
Nucleotidases in the succus entericus convert nucleotides into nucleosides. Subsequently, nucleosidases break down nucleosides into nitrogenous bases and pentose sugars.
Which enzyme is active only at a highly acidic pH (around 1.8)?
- A Salivary amylase
- B Pancreatic trypsin
- C Gastric pepsin
- D Pancreatic lipase
Correct answer: Gastric pepsin
Pepsin is a gastric enzyme that requires a very low pH (around 1.8) for optimal activity. The HCl secreted by parietal cells provides the acidic environment necessary for pepsin to break down proteins.
Dipeptidases are enzymes that act on dipeptides to produce:
- A Gastric pepsin
- B Enterokinase
- C Chymotrypsin
- D Pancreatic lipase
Correct answer: Enterokinase
Enterokinase (also called enteropeptidase) is secreted by the intestinal mucosa. It specifically activates trypsinogen into active trypsin, which then activates the other enzymes in pancreatic juice.
Pancreatic amylase acts on polysaccharides to convert them into:
- A Simple glucose
- B Amino acids
- C Disaccharides
- D Fatty acids
Correct answer: Disaccharides
Pancreatic amylase continues the work started by salivary amylase, hydrolyzing the remaining starch and polysaccharides into disaccharides like maltose in the duodenum.
Which of the following enzymes is responsible for the digestion of nucleic acids into nucleotides?
- A Nucleosidases
- B Nucleases (DNase/RNase)
- C Nucleotidases
- D Dipeptidases
Correct answer: Nucleases (DNase/RNase)
Nucleases (DNase and RNase) are present in the pancreatic juice. They act on nucleic acids to form nucleotides, which are further processed by intestinal nucleotidases and nucleosidases.
The optimum pH for the action of enzymes in the small intestine is approximately:
- A 1.8
- B 6.8
- C 7.8
- D 5.5
Correct answer: 7.8
The environment in the small intestine is alkaline (pH 7.8) due to the presence of bicarbonates from the pancreas and mucus. This alkalinity is essential for the activation and function of pancreatic enzymes.
Sucrase, an enzyme found in the intestinal juice, acts on sucrose to yield:
- A Glucose + Glucose
- B Glucose + Fructose
- C Glucose + Galactose
- D Fructose + Galactose
Correct answer: Glucose + Fructose
Sucrase (also called invertase) hydrolyzes sucrose (cane sugar) into its two monosaccharide components, glucose and fructose, in the brush border of the small intestine.
Which of the following statements about lactase is correct?
- A It digests dietary fats into fatty acids and glycerol.
- B It breaks down milk sugar (lactose) into glucose and galactose.
- C It is secreted by the liver into the small intestine.
- D It acts in the acidic stomach environment at pH 2.0.
Correct answer: It breaks down milk sugar (lactose) into glucose and galactose.
Lactase is a disaccharidase found in the succus entericus. It specifically breaks down lactose, the sugar found in milk, into glucose and galactose.
Which of the following prevents the auto-digestion of the stomach wall by pepsin?
- A Bile pigments from the liver
- B Mucus and bicarbonates
- C Trypsin inhibitor from pancreas
- D Salivary amylase in gastric juice
Correct answer: Mucus and bicarbonates
The mucus and bicarbonates present in the gastric juice play a vital role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated HCl and pepsin.
The enzyme steapsin is another name for:
- A Gastric protease
- B Salivary amylase
- C Pancreatic lipase
- D Intestinal nuclease
Correct answer: Pancreatic lipase
Steapsin is the historical name for pancreatic lipase. It is the most potent lipase in the digestive system, capable of hydrolyzing the majority of dietary triglycerides.
Which of these is the correct end-product of protein digestion?
- A Peptones and proteoses
- B Di- and tripeptides
- C Amino acids
- D Glycerol and lipids
Correct answer: Amino acids
While proteins are broken down into proteoses, peptones, and dipeptides during the process, the ultimate, simplest absorbable units of protein digestion are amino acids.