Human Anatomy and Physiology : II. Digestive System

Total Questions: 42

21. In human body, the digestion of protein begins in which of the following organs? [U.P. P.C.S. (Pre) 2020]

(a) Liver
(b) Mouth
(c) Small intestine
(d) Stomach

Correct Answer: (d) Stomach

Solution:In the human body, the digestion of protein begins in the stomach with the action of enzyme pepsin. Pepsin is secreted by the gastric glands of the stomach which digests the protein into smaller peptides and amino acids, which can be readily absorbed by the small intestine.

22. Which one of the following enzymes convert proteins into amino acids? [U.P. RO./A.R.O. (Pre) 2017]

(a) Pepsin
(b) Lactase
(c) Urease
(d) Zymase

Correct Answer: (a) Pepsin

Solution:Pepsin is a protein-digestive enzyme which is secreted by gastric glands of the stomach which digests the protein into smaller peptides and amino acids, which can be readily absorbed by the small intestine. Lactase is a milk-digesting enzyme which converts lactose into glucose and galactose. Urease enzyme catalyzes the hydrolysis of urea forming carbon dioxide and ammonia. Zymase enzyme occurs naturally in yeast that catalyzes the fermentation of sugar into ethanol and carbon dioxide.

23. Assertion (A) : All the proteins in our food are digested in the small intestine only. [I.A.S. (Pre) 2005]

Reason (R) : The protein-digesting enzyme from the pancreas are released into the small intestine.

Code :

(a) Both (A) and (R) are individually true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are individually true, but (R) is not a correct explanation of (A).
(b) Both (A) and (R) are individually true, but (R) is not a correct explanation of (A).
(d) (A) is false, but (R) is true.

Correct Answer: (d) (A) is false, but (R) is true.

Solution:Protein digestion begins in the stomach with the action of an enzyme called pepsin. Pepsin is the active protein-digesting enzyme of the stomach. Protein-digesting enzyme trypsin is produced in an inactive form in the pancreas and is activated in the small intestine, where it digests protein. The duodenum is the first and shortest segment of the small intestine. In the duodenum, trypsin catalyzes the hydrolysis of peptide bonds, breaking down proteins into smaller peptides. Enzymes continue to break down polypeptides and peptides into amino acids. As amino acids are very small, they are able to be absorbed through the small intestine lining and into the bloodstream.

24. An enzyme which helps in the digestion of protein is : [U.P.P.C.S (Pre) 2010]

(a) Urease
(b) Sulfatase
(c) Trypsin
(d) Protease

Correct Answer: (c) Trypsin

25. Which of the following changes is catalyzed by the enzyme trypsin? [R.A.S./R.T.S. (Pre) 1999]

(a) Proteins to peptones
(b) Proteins to peptides
(c) Proteins to amino acids
(d) Starch to glucose

Correct Answer: (c) Proteins to amino acids

Solution:In the duodenum, trypsin catalyzes the hydrolysis of peptide bonds, breaking down proteins into smaller peptides. The peptide products are then further hydrolyzed into amino acids via other proteases, rendering them available for absorption into the bloodstream.

26. In the human body, which structure is the appendix attached to? [I.A.S. (Pre) 2007]

(a) The large intestine
(b) The small intestine
(c) The gall bladder
(d) The stomach

Correct Answer: (a) The large intestine

Solution:The appendix is a blind-ended tube connected to the cecum, which is considered to be the beginning of the large intestine and in which it develops embryologically. The cecum is a small pouch-like structure, located at the junction of the small and the large intestines.

27. Which one of the following is the correct sequence in the order decreasing the length of the three structural part given below, of the small intestine in the human body? [I.A.S. (Pre) 2007]

(a) Jejunum - Duodenum - Ileum
(b) Ileum - Duodenum - Jejunum
(c) Jejunum - Ileum - Duodenum
(d) Ileum - Jejunum - Duodenum

Correct Answer: (d) Ileum - Jejunum - Duodenum

Solution:The small intestine is divided into three structural parts. The duodenum is a short structure (about 20–25 cm long) continuous with the stomach and shaped like 'C'. It surrounds the head of the pancreas. The duodenum contains Brunner's glands, which produce a mucus-rich alkaline secretion containing bicarbonate. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the gastric chyme. The jejunum is the midsection of the small intestine, connecting the duodenum to the ileum. It is about 2.5m long and contains the plicae circulares and villi that increase its surface area. The ileum is the final section of the small intestine. It is about 3.5 m long and contains villi similar to the jejunum.

28. Given below are two statements – [U.P.P.C.S. (Pre) 2017]

Assertion (A) : Human body is incapable of digesting cellulose.
Reason (R) : Starch degrading enzyme, diastase, is found in human body.

Choose the correct answer from the code given below:

Codes :

(a) Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

Correct Answer: (b) Both (A) and (R) are true but (R) is not the correct explanation of (A).

Solution:In human digestive system, enzymes that can digest cellulose are not found, but starch abrasive enzymes, diastase which break starch into maltose are found in human saliva. Thus both the statements are correct, but the cellulose cannot be digested due to diastase. So, the second statement does not explain the first statement.

29. Identify the correct pair of enzyme and its function : [R.A.S./R.T.S. (Re. Exam) (Pre) 2013]

(a) Acid phosphatase – Mitochondrial marker enzyme related to oxidative functions
(b) E. coli restriction endonuclease – cuts DNA at specific places
(c) Acrosin – cortical granules of ovum secrete it to prevent polyspermic fertilization
(d) Succinic dehydrogenase – Lysosomal marker enzyme, hydrolyses metabolites

Correct Answer: (b) E. coli restriction endonuclease – cuts DNA at specific places

Solution:Restriction endonuclease Eco R II (pronounced 'eco R two'), an enzyme of restriction modification system (RM) naturally found in Escherichia coli, are a special class of enzyme that recognize and cleave (cuts) DNA at specific places. They produce small well-defined fragments of DNA that help to characterize genes and genomes and that produce recombinant DNAs.

30. Match List-I with List-II and select the correct answer using the codes given below the lists: [I.A.S. (Pre) 2001]

List-I	List-II
A. Ptyalin	1. Converts angiotensinogen in blood into angiotensin
B. Pepsin	2. Digests starch
C. Renin	3. Digests proteins
D. Oxytocin	4. Hydrolyses fats
	5. Induces contraction of smooth muscles

Code	A	B	C	D
(a)	2	3	1	5
(b)	3	4	2	5
(c)	2	3	5	1
(d)	3	1	2	4

Correct Answer: (a)

Solution:

Ptyalin (Amylase): An enzyme in the saliva that converts starch into dextrin and maltose.
Pepsin: An enzyme that splits proteins into proteoses and peptones.
Renin: A proteolytic enzyme secreted by the kidneys that converts angiotensinogen into angiotensin.
Oxytocin: A polypeptide hormone produced by the posterior lobe of the pituitary gland that stimulates contraction of the smooth muscle of the uterus.

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