Chapter 9, Problem 5STP

Summary Introduction

Introduction:

Organisms obtain energy through a process called cellular respiration. During this process complex organic molecules are broken down into simple substances. The main aim of cellular respiration is to harvest electrons from carbon compounds and use that energy to make ATP. ATP is used to provide energy for cells to perform work. This process occurs in two stages; glycolysis and aerobic respiration.

Answer to Problem 5STP

Correct answer :

The correct answer is option D. pyruvate

Explanation of Solution

Explanation/justification for the correct answer:

Option D. pyruvate- The first stage of cellular respiration is glycolysis. It is an anaerobic process. Anaerobic metabolic processes do not require oxygen. In this process glucose is broken down in the cytoplasm of cells to produce two ATP and two NADPH molecules. The 6 carbon compound glucose is broken down to two 3 carbon compounds calledpyruvate. Hence the product of glycolysis is pyruvate. This option is correct.

Explanation for incorrect answer:

Option A. acetyl CoA- Prior to Krebs cycle, pyruvate which is formed as a result of glycolysis reacts with a coenzyme A (CoA) to form a 2 carbon intermediate called acetyl CoA. Hence this option is incorrect.

Option B. glucose- During glycolysis glucose is broken down to form pyruvate which is a 3 carbon compound. Glucose is a 6 carbon compound. Hence this option is incorrect.

Option C. lactic acid- During lactic acid fermentation, the enzymes convert pyruvate made during glycolysis to lactic acid.This occurs when there is insufficient supply of oxygen. Lactic acid is not end product of glycolysis. Hence this option is not correct.