chapter 9: cellular respiration (test 4)

Question 1

Photosynthesis generates ___ and ___, which are used in cellular respiration

Cells use chemical energy stored in organic molecules to generate ATP, which powers work

Answer 1

O2

organic molecules

Question 2

The breakdown of organic molecules is ___

___ is a partial degradation of sugars that occurs without O2

___ consumes organic molecules and O2 and yields ATP

___ is similar to aerobic respiration but consumes compounds other
than O2

Answer 2

exergonic

Fermentation

Aerobic respiration

Anaerobic respiration

Question 3

___ includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration

Carbohydrates, fats, and proteins are all consumed as fuel if necessary.

Cellular respiration with glucose

C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat)

Answer 3

Cellular respiration

Question 4

The transfer of electrons during chemical reactions releases energy stored in organic molecules. These reactions are called ___.

This released energy is ultimately used to synthesize ___

In ___, a substance loses electrons,
or is oxidized

In ___, a substance gains electrons, or is reduced (the amount of positive charge is reduced)

Answer 4

redox reactions

ATP

oxidation

reduction

Question 5

In cellular respiration, glucose and other organic molecules are broken down in a series of steps

Electrons from organic compounds are usually first transferred to ___, a coenzyme or FAD

Each NADH (the reduced form of NAD+) and FADH2 (the reduced form of FAD) represents stored energy that is tapped to synthesize ATP

Answer 5

NAD+

Question 6

NADH and FADH2 pass the electrons to the ___

Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction

O2 pulls electrons down the chain in an energy-yielding tumble

The energy yielded is used to regenerate ATP

Answer 6

electron transport chain

Question 7

(The Stages of Cellular Respiration: A Preview)

Harvesting of energy from glucose has three stages

___ (breaks down glucose into two molecules of pyruvate)

___ (completes the breakdown of glucose)

___ (accounts for most of the ATP synthesis). The process is powered by redox reactions.

Answer 7

Glycolysis

The citric acid cycle

Oxidative phosphorylation

Question 8

___ accounts for almost 90% of the ATP generated by cellular respiration

A smaller amount of ATP is formed in glycolysis and the citric acid cycle by ___

For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to ___ molecules of ATP

Answer 8

Oxidative phosphorylation

substrate-level phosphorylation

32

Question 9

(Glycolysis harvests chemical energy by oxidizing glucose to pyruvate)

Glycolysis (“sugar splitting”) breaks down glucose into ___

Glycolysis occurs in the ___ and has two major phases

___

___

Glycolysis occurs whether or not O2 is present

Answer 9

two molecules of pyruvate

cytoplasm

Energy investment phase

Energy payoff phase

Question 10

(After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules)

In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed

Before the citric acid cycle can begin, pyruvate must be converted to ___, which links glycolysis to the citric acid cycle

This process yields ___ for every pyruvate that enters the mitochondrion.

Answer 10

acetyl Coenzyme A (acetyl CoA)

1 NADH

Question 11

(The Citric Acid Cycle)

The citric acid cycle, also called the Krebs cycle, completes the ___

The cycle oxidizes organic fuel derived from pyruvate, generating ___ per turn

Answer 11

breakdown of pyruvate to CO2

1 ATP, 3 NADH, and 1 FADH2

Question 12

The citric acid cycle has ___ steps, each catalyzed by a specific enzyme

The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate

The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle

The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain

Answer 12

eight

Question 13

(During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis)

Following glycolysis and the citric acid cycle, ___ account for most of the energy extracted from food

These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via ___

Answer 13

NADH and FADH2

oxidative phosphorylation

Question 14

(The Pathway of Electron Transport)

The electron transport chain is in the ___ of the mitochondrion

Most of the chain’s components are ___,
which exist in multiprotein complexes

The carriers alternate reduced and oxidized states as they___

Electrons drop in free energy as they go down the chain and are finally passed to ___

Answer 14

inner membrane (cristae)

proteins

accept and donate electrons

O2, forming H2O

Question 15

Electrons are transferred from ___ to the ___

Electrons are passed through a number of proteins including ___ (each with an iron atom) to O2

The electron transport chain generates no ATP directly

It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts

Answer 15

NADH or FADH2

electron transport chain

cytochromes

Question 16

(Chemiosmosis: The Energy-Coupling Mechanism)

Electron transfer in the electron transport chain causes proteins to pump ___ from the mitochondrial matrix to the ___

H+ then moves back across the membrane, passing through the protein complex, ___

ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP

This is an example of ___, the use of energy in a H+ gradient to drive cellular work

Answer 16

H+

intermembrane space

ATP synthase

chemiosmosis

Question 17

The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis

The H+ gradient is referred to as a ___, emphasizing its capacity to do work

Answer 17

proton-motive force

Question 18

(An Accounting of ATP Production by Cellular Respiration)

During cellular respiration, most energy flows in this sequence:

glucose → NADH → electron transport chain → proton-motive force → ATP

About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about ___ ATP

Answer 18

32

Question 19

(Fermentation and anaerobic
respiration enable cells to produce ATP without the use of oxygen)

Most cellular respiration requires ___ to produce ATP

Without O2, the electron transport chain will cease to operate

In that case, glycolysis couples with anaerobic respiration or___ to produce ATP

Answer 19

O2

fermentation

Question 20

___ uses an electron transport chain with a final electron acceptor other than O2, for example sulfate

*Fermentation uses ___ instead of an electron transport chain to generate ATP

Answer 20

Anaerobic respiration

substrate-level phosphorylation

Question 21

(Types of Fermentation)

Fermentation consists of glycolysis plus reactions that regenerate ___, which can be___

Two common types are___ and ___

Answer 21

NAD+

reused by glycolysis

alcohol fermentation and lactic acid fermentation

Question 22

In alcohol fermentation, ___ is converted to ethanol in two steps

The first step releases ___

The second step produces ___

Alcohol fermentation by yeast is used in brewing, winemaking, and baking

Answer 22

pyruvate

CO2

ethanol

Question 23

In ___, pyruvate is reduced by NADH, forming lactate (lactic acid) as an end product, with no release of CO2

Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt

Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

Answer 23

lactic acid fermentation