Book cover for Biology

Biology

Sylvia S. Mader, Michael Windelspecht

ISBN #9780078024269

12th Edition

687 Questions

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153,501 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

Cellular respiration is a complex, multi-step process that efficiently converts glucose into ATP through a series of redox reactions. Aerobic pathways, including glycolysis, the preparatory reaction, the citric acid cycle, and the electron transport chain, work in concert to extract energy, with the mitochondria playing a central role by establishing a proton gradient for ATP synthesis through chemiosmosis. When oxygen is limited, fermentation provides an alternative pathway to sustain ATP production, underscoring the adaptability and regulatory efficiency of cellular energy production.

Learning Objectives

1

Understand the sequence and role of the different steps in cellular respiration.

2

Describe the processes of glycolysis and fermentation and distinguish where they occur within the cell.

3

Explain how the structure of the mitochondria aids in ATP production through the electron transport chain and chemiosmosis.

4

Compare aerobic respiration pathways (glycolysis, preparatory reaction, citric acid cycle, and electron transport chain) with anaerobic fermentation.

5

Analyze the importance of redox reactions in the conversion of glucose into chemical energy.

Key Concepts

CONCEPT

DEFINITION

Cellular Respiration

A multi-step metabolic process that converts the chemical energy stored in glucose into ATP through a series of redox reactions.

Glycolysis

An anaerobic process occurring in the cytoplasm that breaks down glucose into pyruvate, producing a net gain of 2 ATP and NADH.

Preparatory Reaction

A series of reactions that convert pyruvate into acetyl-CoA, setting the stage for the citric acid cycle inside the mitochondria.

Citric Acid Cycle

A cyclic series of reactions in the mitochondria that oxidizes acetyl-CoA, releasing CO2 and generating high-energy electron carriers (NADH and FADH2).

Electron Transport Chain (ETC)

A series of protein complexes located in the inner mitochondrial membrane that transfer electrons from NADH and FADH2, pumping protons to create a gradient used for ATP synthesis.

Chemiosmosis

A process where the proton gradient created by the ETC is used to drive ATP synthesis via ATP synthase.

Fermentation

An anaerobic process that regenerates NAD+ from NADH when oxygen is scarce, allowing glycolysis to continue producing ATP on a limited scale.

Redox Reactions

Chemical reactions involving the transfer of electrons, crucial in the oxidation of glucose and generation of energy.

Example Problems

Example 1

The metabolic process that produces the most ATP molecules is a. glycolysis. b. the citric acid cycle. c. the electron transport chain. d. fermentation.

Example 2

Which one of these pathways would not be active in an aerobic condition? a. glycolysis b. electron transport chain c. citric acid cycle d. fermentation e. All of these would be active.

Example 3

The reduction of NAD+ produces a. acetyl CoA. b. pyruvate. c. NADH. d. oxygen gas.

Example 4

During glycolysis, what is the net production of ATP per glucose molecule? a. 0 d. 8 b. 1 e. 32 c. 2

Example 5

The process of glycolysis occurs where in the cell? a. chloroplasts b. mitocondrion c. nucleus d. cytoplasm
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Step-by-Step Explanations

QUESTION

How does glycolysis convert glucose into ATP?

STEP-BY-STEP ANSWER:

Step 1: Glucose is phosphorylated using ATP to form glucose-6-phosphate, which prevents the glucose from leaving the cell.
Step 2: The molecule undergoes several transformations, eventually splitting into two three-carbon molecules.
Step 3: These molecules are further processed to produce NADH and a small amount of ATP through substrate-level phosphorylation.
Step 4: The overall net result is the production of 2 ATP molecules for each glucose molecule processed.
Final Answer: Glycolysis converts one molecule of glucose into 2 molecules of pyruvate, yielding a net gain of 2 ATP and generating NADH in the process.

Glycolysis

QUESTION

How does the electron transport chain (ETC) lead to the production of ATP?

STEP-BY-STEP ANSWER:

Step 1: High-energy electrons from NADH and FADH2 are transferred through a series of protein complexes in the inner mitochondrial membrane.
Step 2: As electrons move through these complexes, energy is released and used to pump protons (H+) from the mitochondrial matrix into the intermembrane space, creating a proton gradient.
Step 3: The accumulated proton gradient represents stored energy, which is then utilized by ATP synthase to synthesize ATP; this process is known as chemiosmosis.
Step 4: Oxygen acts as the final electron acceptor, combining with electrons and protons to form water.
Final Answer: The electron transport chain creates a proton gradient across the mitochondrial membrane that drives ATP synthesis via chemiosmosis.

Electron Transport Chain and Chemiosmosis

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Common Mistakes

  • Assuming that glycolysis occurs inside the mitochondria rather than in the cytoplasm.
  • Mixing up the roles and locations of aerobic respiration and fermentation.
  • Overlooking the importance of redox reactions in the energy conversion process.
  • Failing to appreciate how the proton gradient and chemiosmosis are linked to ATP production.
  • Thinking that fermentation can fully replace aerobic respiration in terms of ATP yield.