Chapter 10, Problem 4STP

Summary Introduction

Introduction:

Organisms obtain energy through a process called cellular respiration. This process occurs in two stages; glycolysis and aerobic respiration. Glycolysis is an anaerobic process while aerobic respiration includes Krebs cycle and electron transport.

Answer to Problem 4STP

Correct answer :

The correct answer is option B. creation of NADPH and FADH₂ during the Krebs cycle

Explanation of Solution

Explanation/justification for the correct answer:

OptionB. creation of NADPH and FADH₂ during the Krebs cycle- The final step in breakdown of glucose is electron transport during which high energy electrons and hydrogen ions from NADH and FADH₂ are used to convert ADP to ATP. As NADH and FADH₂ release electrons, the energy carriers are converted to NAD+ and FAD. Oxygen is the final electron acceptor in electron transport system. Protons and electrons are transferred to oxygen to form water. Hence this is the right option.

Explanation for incorrect answer:

Option A. formation of acetyl CoA- Just before Krebs cycle begins, pyruvate formed during glycolysis reacts with coenzyme A to form acetyl CoA. Krebs cycle starts with acetyl CoA combining with a 4- carbon compound to form a 6- carbon compound known as citric acid. This process is not the source of electrons in electron transport chain. Hence this is not the correct option.

Option C. fermentation of lactic acid-The anaerobic pathway that follows glycolysis when there is insufficient supply of oxygen is called fermentation. Fermentation occurs in cytoplasm and regenerates cell’s supply of NAD+ while producing a small amount of ATP.This process is not the source of electrons in electron transport chain. Hence this is not the correct option.

Option D. breaking of bonds in glycolysis- The first stage of cellular respiration is glycolysis. In this process each glucose molecule is broken down in the cytoplasm of cells to produce two ATP and two NADPH molecules.This process is not the source of electrons in electron transport chain. Hence this is not the correct option.