Biology: The Unity and Diversity o...

15th Edition
Cecie Starr + 3 others
ISBN: 9781337408332



Biology: The Unity and Diversity o...

15th Edition
Cecie Starr + 3 others
ISBN: 9781337408332
Textbook Problem

The low pH of the _______ aids in protein digestion.

  1. a. stomach
  2. b. small intestine
  3. c. large intestine
  4. d. esophagus

Summary Introduction

Introduction: The stomach is the most important organ where digestive processes take place. The stomach has very low acidic pH for activating the digestive enzyme pepsin and also for killing the pathogenic bacteria that enter the body through food. The gastric gland present in the stomach secretes hydrochloric acid that activates pepsinogen into pepsin (enzyme). The acidic environment in the stomach denatures the proteins and exposes the bonds between them. These bonds are cleaved by pepsin into smaller fragments known as peptides.


Reason for the correct answer: The pH of gastric acid secreted by stomach ranges from 1.5-3.5. Gastric juice contains hydrochloric acid, whose pH is maintained by the proton pump H+/K+ in the stomach. Pepsins are enzymes that are highly active in the acidic condition of the stomach (because of digestive HCl). They can digest complex protein molecules by cleaving the peptide bonds present within the protein.

Option a. is given as “stomach”. Protein digestion is aided by the lower acidic condition of the stomach. Hence, the correct answer is option a.

Reasons for the incorrect answers:

Option b. is given as “small intestine”. The small intestine is a major organ in human body that is involved in the absorption of major nutrients. The digested food from the stomach passes through the small intestine, where the cells absorb the nutrients and transport them to blood vessels...

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