Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen

Question 1

there are two general mechanisms by which certain cells can oxidize organic fuel and generate ATP without the use of oxygen:

Answer 1

anaerobic respiration and fermentation.

Question 2

The distinction between these two is that an electron transport chain is used in

Answer 2

anaerobic respiration but not in fermentation.

Question 3

anaerobic respiration organisms have an electron transport chain but do not use oxygen as a final electron acceptor at the end of the

Answer 3

chain.

Question 4

Oxygen performs this function very well because it is extremely electronegative, but other, less electronegative substances can also serve as

Answer 4

final electron acceptors

Question 5

is a way of harvesting chemical energy without using either oxygen or any electron transport chain—in other words, without cellular respiration

Answer 5

Fermentation

Question 6

oxidation simply refers to the loss of electrons to an electron acceptor, so it does not need to involve

Answer 6

oxygen.

Question 7

Glycolysis oxidizes glucose to two molecules of

Answer 7

pyruvate.

Question 8

The oxidizing agent of glycolysis is NAD+, and neither

Answer 8

oxygen nor any electron transfer chain is involved.

Question 9

Overall, glycolysis is exergonic, and some of the energy made available is used to produce 2 ATP (net) by

Answer 9

substrate-level phosphorylation

Question 10

If oxygen is present, then additional ATP is made by oxidative phosphorylation when NADH passes electrons removed from

Answer 10

glucose to the electron transport chain.

Question 11

But glycolysis generates 2 ATP whether oxygen is present or not—that is, whether conditions are

Answer 11

aerobic or anaerobic.

Question 12

As an alternative to respiratory oxidation of organic nutrients, fermentation is an extension of glycolysis that allows continuous generation of ATP by the

Answer 12

substrate-level phosphorylation of glycolysis.

Question 13

For this to occur, there must be a sufficient supply of NAD+ to accept electrons during the oxidation step of

Answer 13

glycolysis

Question 14

Under aerobic conditions, NAD+ is recycled from NADH by the transfer of

Answer 14

electrons to the electron transport chain.

Question 15

An anaerobic alternative is to transfer electrons from _____________________ , the end product of glycolysis.

Answer 15

NADH to pyruvate

Question 16

Fermentation consists of glycolysis plus reactions that regenerate by transferring electrons from NADH to

Answer 16

pyruvate or derivatives of pyruvate.

Question 17

The can then be reused to oxidize sugar by glycolysis, which nets two molecules of ATP by

Answer 17

substrate-level phosphorylation.

Question 18

There are many types of fermentation, differing in the end products formed from pyruvate. Two types are ____________________________________, and both are harnessed by humans for food and industrial production.

Answer 18

alcohol fermentation and lactic acid fermentation

Question 19

pyruvate is converted to ethanol (ethyl alcohol) in two steps.

Answer 19

alcohol fermentation

Question 20

the first step releases carbon dioxide from the pyruvate, which is converted to the

Answer 20

two-carbon compound acetaldehyde.

Question 21

In the second step, acetaldehyde is reduced by

Answer 21

NADH to ethanol.

Question 22

Many bacteria carry out alcohol fermentation under

Answer 22

anaerobic conditions

Question 23

in addition to aerobic respiration, also carries out alcohol fermentation

Answer 23

Yeast (a fungus),

Question 24

pyruvate is reduced directly by NADH to form lactate as an end product, regenerating NAD+ with no release of CO2 .

Answer 24

lactic acid fermentation

Question 25

Human muscle cells make ATP by lactic acid fermentation when

Answer 25

oxygen is scarce.

Question 26

are three alternative cellular pathways for producing ATP by harvesting the chemical energy of food.

Answer 26

Fermentation, anaerobic respiration, and aerobic respiration

Question 27

All three use glycolysis to oxidize glucose and other organic fuels to pyruvate, with a net production of 2 ATP by

Answer 27

substrate-level phosphorylation.

Question 28

And in all three pathways, NAD+ is the oxidizing agent that accepts electrons from food during

Answer 28

glycolysis.

Question 29

key difference is the contrasting mechanisms for oxidizing NADH back to

Answer 29

NAD+ which is required to sustain glycolysis

Question 30

In fermentation, the final electron acceptor is an organic molecule such as

Answer 30

pyruvate (lactic acid fermentation) or acetaldehyde (alcohol fermentation)

Question 31

In cellular respiration, by contrast, electrons carried by NADH are transferred to an electron transport chain, which regenerates the NAD+ required for

Answer 31

glycolysis.

Question 32

Another major difference is the amount of

Answer 32

ATP produced.

Question 33

Fermentation yields two molecules of ATP, produced by

Answer 33

substrate-level phosphorylation

Question 34

In the absence of an electron transport chain, the energy stored in pyruvate is

Answer 34

unavailable

Question 35

in cellular respiration, however, pyruvate is completely oxidized in the

Answer 35

mitochondrion

Question 36

Most of the chemical energy from this process is shuttled by NADH and FADH2 in the form of

Answer 36

electrons to the electron transport chain.

Question 37

There, the electrons move stepwise down a series of redox reactions to a final

Answer 37

electron acceptor.

Question 38

carry out only fermentation or anaerobic respiration.

Answer 38

obligate anaerobes

Question 39

an organism that makes ATP by aerobic respiration is oxygen is present but that switches to anaerobic respiration or fermentation if oxygen is not present

Answer 39

facultative anaerobes

Question 40

On the cellular level, our muscle cells behave as

Answer 40

facultative anaerobes