Book cover for Campbell Biology Concepts & Connections

Campbell Biology Concepts & Connections

Martha R. Taylor, Jean L. Dickey, Eric J. Simon, Kelly Hogan, Jane B. Reece

ISBN #9780134296012

9th Edition

631 Questions

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82,520 Students Helped

Homework Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This chapter delves into the intricate processes by which cells harvest chemical energy from organic molecules. Through a series of well-coordinated stages—glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation—cells convert glucose into ATP, the energy currency necessary for life. The chapter also highlights the role of oxygen in aerobic respiration, the alternative pathways under anaerobic conditions, and the broader implications of these processes for bodily functions, biosynthesis, and energy regulation.

Learning Objectives

1

Explain the overall process of cellular respiration and its three main stages: glycolysis, the citric acid cycle, and oxidative phosphorylation.

2

Describe how ATP is produced from the energy stored in organic molecules through substrate-level phosphorylation, chemiosmosis, and redox reactions.

3

Understand the role of oxygen in aerobic respiration and how anaerobic fermentation serves as an alternative pathway for energy production.

4

Illustrate the connection between cellular respiration and broader biological functions such as breathing and biosynthesis from food-derived organic molecules.

5

Recognize the evolutionary significance and diversity of fuel sources used in cellular respiration.

Key Concepts

CONCEPT

DEFINITION

Cellular Respiration

A set of metabolic pathways that convert the energy stored in organic molecules into ATP, the usable form of energy for cells.

Glycolysis

The first stage of cellular respiration, occurring in the cytosol, where glucose is oxidized to produce pyruvate, ATP, and NADH.

Citric Acid Cycle

A series of reactions in the mitochondria that complete the oxidation of organic molecules, generating electron carriers (NADH and FADH2) and ATP.

Oxidative Phosphorylation

The final stage of cellular respiration that occurs in the mitochondria, where ATP is produced via the electron transport chain and chemiosmosis.

ATP (Adenosine Triphosphate)

The primary energy currency of the cell, which stores energy released during cellular respiration.

Substrate-Level Phosphorylation

A process in which ATP is produced by the direct transfer of a phosphate group to ADP in a metabolic reaction.

Chemiosmosis

The movement of ions across a selectively permeable membrane, down their electrochemical gradient, used to drive ATP synthesis.

Redox Reactions

Chemical reactions involving the transfer of electrons, crucial for the process of electron transport in cellular respiration.

Fermentation

An anaerobic process that allows cells to produce ATP from glucose without oxygen by regenerating NAD+.

Brown Fat

A type of fat tissue that is rich in mitochondria and specialized in generating heat through ATP hydrolysis and uncoupling proteins.

Example Problems

Example 1

Fill in the blanks in this summary map to help you review the key concepts of cellular respiration.

Example 2

A biochemist wanted to study how various substances were used in cellular respiration. In one experiment, she allowed a mouse to breathe air containing $\mathrm{O}_{2}$ "labeled" by a particular isotope. In the mouse, the labeled oxygen first showed up in a. ATP. b. NADH. c. $\mathrm{CO}_{2}$ d. $\mathrm{H}_{2} \mathrm{O}$

Example 3

In glycolysis, ___________ is oxidized and ___________ is reduced. a. $\mathrm{NAD}^{+}$... glucose b. glucose... Oxygen c. ATP... ADP d. glucose... $\mathrm{NAD}^{+}$

Example 4

Most of the $\mathrm{CO}_{2}$ from cellular respiration is released during a. glycolysis. b. pyruvate oxidation. c. the citric acid cycle. d. oxidative phosphorylation.

Example 5

Which of the following is the most immediate source of energy for making most of the ATP in your cells? a. the transfer of $(P)$ from intermediate substrates to ADP b. the movement of $\mathrm{H}^{+}$ across a membrane down its concentration gradient c. the splitting of glucose into two molecules of pyruvate d. electrons moving through the electron transport chain
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Step-by-Step Explanations

QUESTION

How does glycolysis convert glucose into pyruvate while producing ATP and NADH?

STEP-BY-STEP ANSWER:

Step 1: Glucose is phosphorylated using ATP to form glucose-6-phosphate, which helps trap the molecule inside the cell.
Step 2: The glucose-6-phosphate is rearranged and further phosphorylated, eventually being split into two three-carbon molecules.
Step 3: These three-carbon molecules are oxidized, leading to the formation of pyruvate along with the production of NADH (by reducing NAD+).
Step 4: Substrate-level phosphorylation in several steps yields a net gain of ATP molecules from the initial investment.
Final Answer: Glycolysis transforms one glucose molecule into two pyruvate molecules, concurrently producing ATP and NADH.

Glycolysis

QUESTION

How does the citric acid cycle contribute to energy harvesting from organic molecules?

STEP-BY-STEP ANSWER:

Step 1: Pyruvate is first converted into acetyl-CoA during pyruvate oxidation, releasing CO2.
Step 2: Acetyl-CoA enters the citric acid cycle, condensing with oxaloacetate to form citrate.
Step 3: A series of enzymatic reactions transforms citrate back into oxaloacetate, releasing CO2 and capturing high-energy electrons in NADH and FADH2.
Step 4: A small amount of ATP (or GTP) is produced directly through substrate-level phosphorylation.
Final Answer: The citric acid cycle oxidizes acetyl-CoA, releases carbon dioxide, and generates NADH, FADH2, and a small amount of ATP, all of which fuel further ATP production in oxidative phosphorylation.

Citric Acid Cycle

QUESTION

How is ATP produced through oxidative phosphorylation via the electron transport chain and chemiosmosis?

STEP-BY-STEP ANSWER:

Step 1: Electrons from NADH and FADH2 are transferred through a series of protein complexes in the mitochondrial inner membrane.
Step 2: As electrons move through the chain, energy is used to pump protons from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient.
Step 3: Protons flow back into the matrix through ATP synthase, a process known as chemiosmosis, which drives the synthesis of ATP.
Step 4: Oxygen serves as the final electron acceptor, combining with electrons and protons to form water.
Final Answer: Oxidative phosphorylation harnesses the energy from electrons transferred along the electron transport chain to generate ATP through chemiosmosis.

Oxidative Phosphorylation

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Common Mistakes

  • Confusing cellular respiration with photosynthesis; the two are distinct processes with different functions and pathways.
  • Thinking that oxygen is directly used to make ATP, rather than acting as the final electron acceptor in the electron transport chain.
  • Underestimating the importance of heat loss as an inevitable byproduct of energy conversion in cellular respiration.
  • Believing that all ATP is generated during glycolysis, ignoring the substantial contribution from oxidative phosphorylation.
  • Overlooking the adaptability of cells to anaerobic conditions, and not appreciating fermentation as a viable alternative when oxygen is scarce.