Click this link for a Cellular Respiration Student Learning Guide

Click here for an overview video.

1. Introduction: Cellular respiration is how cells take the energy in food and make it into ATP, the cell’s moment to moment energy source

ATP with letters on phosphate bondsThink about how important eating is. As I pointed out in the previous tutorial (about ATP), there are two reasons why we eat. The first is to replenish our store of the molecules that make us up, which we need in order grow and repair ourselves. The second is to take the chemical bond energy in the molecules in the food we eat, and to use it to attach a phosphate group onto ADP (adenosine diphosphate), creating ATP (adenosine triphosphate). Creating ATP from ADP and phosphate is endergonic: it requires energy to drive the process forward, and that energy comes from food. Once the cell has ATP, it can use the bond energy in the bond between the second and third phosphate groups in ATP (bond “A” in the diagram to the left) to power all of life’s endergonic reactions.

The overall chemical equation for cellular respiration is:

C6H12O6 + 6O2 –> 6CO2 + 6H2O + energy (in the form of ATP)

In plain English, glucose (C6H12O6) is combined with oxygen (O2) in order to create ATP. Carbon dioxide (CO2) and water (H2O) are released as waste products.

Cells carry out this transfer of energy from food to ATP very efficiently. During cellular respiration, cells can transform the energy in one molecule of glucose into somewhere between 30 and 32 molecules of ATP (I’ll explain why there’s a range in another tutorial). This transfer of energy is about 39% efficient (according to Reference.com). That’s a lot more efficient than a car, which converts between 14 and 30% of the fuel energy you put into a car into movement(source: US Dept. of Energy). Cells, of course, have been working on this for billions of years, so human engineers (who’ve been at it for a much shorter period of time) shouldn’t feel bad.

Creating ATP is a cellular process, so let’s look at the cell parts that are involved.

2. Where cellular respiration happens: the cellular context

05_cellular_respiration_in_cells-v3

In the diagram at left, “1” represents the cell exterior. In the cells of any non-photosynthetic eukaryote (such as a person, bread mold, or a paramecium), glucose and oxygen are going to come from outside the cell. Because cellular respiration consumes glucose and oxygen, there’s always a concentration gradient allowing glucose and oxygen to diffuse through the cell’s membrane (shown at “2”) into the cytoplasm (at “3”). As we’ve learned in our studies of membrane transport, the cell has special protein channels for glucose, a polar molecule, while oxygen can diffuse directly through the membrane’s phospholipid bilayer.

In eukaryotic cells, the organelle that does the lion’s share of the work of cellular respiration is the mitochondrion (shown at “4”). I’ve included only one mitochondrion in this drawing, but the cells in your body can have thousands (note, by the way, that mitochondrion is the singular form of mitochondria, which is plural). Mitochondria evolved from a once-independent bacterial ancestor that, about two billion years ago, took up residence inside another prokaryotic cell, creating the eukaryotic lineage that we animals (along with the fungi, protists, and plants) are a part of. If you’re interested in the origins of mitochondria, you can read more about it in this article in Nature, or in this articlefrom the National Center for Biotechnology Information. Both of them will be challenging. Go for it!

Mitochondria have a double membrane. The inner one is shown at “6,” and the outer one at “8.” In between the two is the intermembrane space, shown at “7.”

Oxygen will diffuse from the cell’s exterior, into the cytoplasm, and then into the mitochondria. Glucose, by contrast, will be partially broken down for energy in the cytoplasm, and then continue into the central fluid of the mitochondria, known as the matrix (shown at “5”).

3. Substrate level phosphorylation creates a small amount of ATP

As we’ll see in this tutorial and ones that follow, there are only two ways that cells make ATP:

substrate-level-phosphorylationThe first is called substrate-level phosphorylation. This term tells you exactly what it’s about. In the diagram at left, you can see an enzyme (1) transfer a phosphate from some organic substrate (2) to ADP (3), creating ATP (5). “Substrate-level” means that the process is catalyzed by an enzyme, working on a substrate that’s losing its phosphate group, and passing that phosphate to a second substrate, ADP. “Phosphorylation” means that ADP is gaining a phosphate, becoming ATP. And, just in case you were worried about  what “4” is, it’s one of the two products of this reaction (the other one being ATP).

During cellular respiration, substrate-level phosphorylations occur in the cell’s cytoplasm, and in the mitochondrial matrix, generating a small amount of ATP. But we’ll see that the majority of the ATP is made through a less direct process called oxidative phosphorylation. Oxidative phosphorylation belongs to a class of chemical reactions called oxidation/reduction reactions, so let’s see how these reactions work.

But first, let’s make sure you’re getting the key points of this section, and the one above.

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Cellular Respiration Overview (M10)”]

[h]Cellular Respiration Overview Quiz 1

[i]

 

[!]++++Question1+++[/!!!]

[q]Which number is the cell membrane?

[textentry single_char=”true”]

[c*] 2

[f] Yes, “2” is the cell membrane

[c]*

[f]No. The membrane is the cell’s outer boundary. If the glucose and oxygen (C6H12O6  6O2) are outside the cell, and the cytoplasm is at “3,” then what number would be representing the membrane?

[!]++++Question2+++[/!!!]

[q]Which number is the cytoplasm?

[textentry single_char=”true”]

[c*] 3

[f] Yes, “3” is the cytoplasm.

[c]*

[f]No. The cytoplasm is the fluid region between the cell’s membrane and the nucleus (which isn’t shown in this diagram). Which number is just inside the membrane (but not part of any other structure)?

[!]++++Question 3+++[/!!!]

[q]Which number is the mitochondrion?

[textentry single_char=”true”]

[c*] 4

[f] Yes, “4” is the mitochondrion.

[c]*

[f]No. Look for the cell-like organelle inside the cytoplasm.

[!]++++Question4+++[/!!!]

[q]Which number is the mitochondrial matrix?

[textentry single_char=”true”]

[c*] 5

[f] Yes, “5” is the matrix.

[c]*

[f]No. The matrix is analogous to the cytoplasm of a mitochondrion. If that’s not enough of a hint, it’s the region inside of a mitochondrion’s inner membrane.

[!]++++Question 5+++[/!!!]

[q]Which number is the mitochondrial inner membrane?

[textentry single_char=”true”]

[c*] 6

[f] Yes, “6” is the mitochondrial inner membrane.

[c]*

[f]No. Start by finding a mitochondrion (the only structure shown, in this diagram, inside the cell). Not that it has two membranes. The inner one is highly folded.

[!]++++Question 6+++[/!!!]

[q]Which number is the intermembrane space?

[textentry single_char=”true”]

[c*] 7

[f] Yes, “7” is the intermembrane space.

[c]*

[f]No. The intermembrane space is the region of a mitochondrion in-between the inner and outer membrane. If the mitochondrion itself is at “4,” then what number would be the intermembrane space?

[!]++++Question 7+++[/!!!]

[q]Which number is the mitochondrial outer membrane?

[textentry single_char=”true”]

[c*] 8

[f] Yes, “8” is the mitochondrial outer membrane.

[c]*

[f]No. The outer mitochondrial membrane is the selectively permeable barrier that separates the mitochondrion (“4”) from the cytoplasm (“3”). Keeping in mind the fact that mitochondria have a double membrane, which number has to be the outer one?

[!]++++Question 8+++[/!!!]

[q]Which number is the outside of the cell?

[textentry single_char=”true”]

[c*] 1

[f] Yes, “1” is the outside of the cell.

[c]*

[f]No. The outside of the cell, or cell exterior, is the region outside of the cell’s membrane. What’s exterior to the membrane?

[!]++++Question1+++[/!!!]

[q]Which numbered part of the image is the enzyme?

[textentry single_char=”true”]

[c*] 1

[f] Yes, “1” is the enzyme.

[c]*

[f]No. Here’s a hint. Enzymes are large proteins, usually much larger than their substrates. What’s the biggest thing in this diagram?

[!]++++Question 2+++[/!!!]

[q]Which numbered part of the image is the source of the phosphate that will convert ADP to ATP?

[textentry single_char=”true”]

[c*] 2

[f] Yes, “2” is the molecule that provides the phosphate used to phosphorylate ADP to ATP.

[c]*

[f]No. Here’s a hint. Look for a phosphate containing molecule that’s not ADP or ADP.

[!]++++Question 3+++[/!!!]

[q]Which numbered part of the image is ADP?

[textentry single_char=”true”]

[c*] 3

[f] Yes, “3” is ADP.

[c]*

[f]No. Here’s a hint. ADP stands for adenosine diphosphate. “Di” means “two.” Find a molecule with two phosphate groups (represented by “p” within a circle).

[!]++++Question 4+++[/!!!]

[q]Which numbered part of the image is ATP?

[textentry single_char=”true”]

[c*] 5

[f] Yes, “5” is ATP.

[c]*

[f]No. Here’s a hint. ATP stands for adenosine triphosphate. “Tri” means “three.” Find a molecule with three phosphate groups (represented by “p” within a circle).

[!]++++Question 5+++[/!!!]

[q]This substrate level phosphorylation has two products. ATP is one. Which number indicates the other one?

[textentry single_char=”true”]

[c*] 4

[f] Yes, “4” is the dephosphorylated product of the reactions.

[c]*

[f]No. Here’s a hint. ATP is one of this reactions products. The other product donated the phosphate that is now part of ATP. Which number points to a molecule that lost its phosphate during this substrate level phosphorylation?

[!]++++Question 6+++[/!!!]

[q]In this substrate level phosphorylation, there are two substrates. Which number represents the substrate that is not ADP?

[textentry single_char=”true”]

[c*] 2

[f] Yes, “2” is the substrate that is not ADP: the molecule that provides the phosphate used to phosphorylate ADP to ATP.

[c]*

[f]No. Here’s a hint. Look for a phosphate containing molecule nestled into part of this enzyme’s active site, but which is not ADP.

[x][restart]

[/qwiz]

 

4. Oxidation and reduction reactions are how most ATP is made during cellular respiration

04_burning-gas_1-1246450967k9xkAs you read above, substrate level phosphorylations account for only a small amount of the ATP generated during cellular respiration (about an eighth of the ATP produced). Much more ATP is produced by oxidizing glucose, and using the energy harvested from that oxidation to set up the conditions to generate ATP from ADP and phosphate. So what is oxidation?

Oxidation means loss of electrons. Oxidation is paired with a complementary process called reduction, which means gain of electrons. Oxidation-reduction reactions happen all the time. Every time you drive your car, light a match, or operate a gas stove, you’re involved with an oxidation-reduction reaction.

In all of the processes listed above, an energy-rich fuel (gasoline, wood, or natural gas, respectively) gets oxidized, losing its energy-rich electrons and hydrogen atoms. At the same time, oxygen gets reduced, gaining electrons and hydrogen atoms.

Here’s the equation for what happens when methane, CH(commonly called “natural gas”) is burned:

CH4 + 2O2 –> CO2 + 2H2O + energy (in the form of heat and light)

Methane, an energy rich fuel, is oxidized. The result is energy (heat and light), along with carbon dioxide and water (two exhaust products)

From a biology student’s perspective, it’s useful to roughly equate oxidation with release of energy, and reduction with gain of energy. In other words, when a fuel like methane is oxidized, it releases energy. Oxidized substances (like carbon dioxide) don’t have free energy for accomplishing cellular work. That’s why carbon dioxide is an exhaust product. Think of this oxidized compound as being exhausted: unable to do work. By contrast, substances that are reduced (like methane) have available free energy can be harvested in order to do work.

What are some other examples of reduced substances?

  • gasoline
  • peanut butter
  • alcohol
  • spaghetti
  • meat
  • sugar

Note that foods are all reduced substances. They’re full of high energy electrons that we can use to power the work that we organisms need to stay alive, to grow, and to reproduce. When cells need energy, they take a reduced fuel (which means foods like glucose) and oxidize it. The result, just like in the combustion of methane shown above, is release of energy, and production of the waste products carbon dioxide and water. Here, once again, is the overall chemical equation for the oxidation of glucose that happens in your cells.

C6H12O6 + 6O2 –> 6CO2 + 6H2O + energy (in the form of ATP)

But while the chemical equations for the oxidation of methane during combustion and the oxidation of glucose during cellular respiration are similar, the details couldn’t be more different. But before going into these details, let’s make sure you’ve mastered the overall equation for cellular respiration.

[qdeck random = “true” qrecord_id=”sciencemusicvideosMeister1961-Cellular Respiration Equation Flashcards (M10)”]

[h]Flashcards: The equation for cellular respiration

[i]C6H12O6 + 6O2 –>
6CO2 + 6H2O + energy (in the form of ATP)

[!!!!!] Card 1 [/!!!!!]
[q]Complete this word equation for cellular respiration
________ + oxygen –> ATP + carbon dioxide + water

[textentry]

[a]glucose + oxygen –> ATP + carbon dioxide + water

[!!!!!] Card 2 [/!!!!!]
[q]Complete this word equation for cellular respiration
glucose+ _________ –>ATP + carbon dioxide + water

[textentry]

[a]glucose+ oxygen –>ATP + carbon dioxide + water

[!!!!!] Card 3 [/!!!!!]
[q]Complete this word equation for cellular respiration

glucose+ oxygen –> ______ + carbon dioxide + water

[textentry]

[a]glucose+ oxygen –> ATP + carbon dioxide + water

[!!!!!] Card 4 [/!!!!!]
[q]Complete this word equation for cellular respiration

glucose+ oxygen –> ATP + ______ ________ + water

[textentry]

[a]glucose+ oxygen –> ATP+ carbon dioxide + water

[!!!!!] Card 5 [/!!!!!]
[q]Complete this word equation for cellular respiration

glucose+ oxygen –> ATP+ carbon dioxide+ __________

[textentry]

[a]glucose+ oxygen –> ATP+ carbon dioxide+ water

[!!!!!] Card 6 [/!!!!!]
[q]Complete this word equation for cellular respiration

________+ ________–> ATP + carbon dioxide+ water

[textentry]

[a] glucose+ oxygen –> ATP+ carbon dioxide+ water (glucose and oxygen in either order)

[!!!!!] Card 7 [/!!!!!]
[q]Complete this word equation for cellular respiration

glucose+ oxygen –> ____ + ______+ _______

[textentry]

[a] glucose+ oxygen –>? ATP+ carbon dioxide+ water (these three in any order)

[!!!!!] Card 8 [/!!!!]
[q]Complete this chemical equation for cellular respiration

_______ + 6O2 –> energy(ATP) + 6CO2 + 6H2O (don’t worry about typing subscripts)
[textentry]
[a] C6H12O6 + 6O2 –> energy(ATP) + 6CO2 + 6H2O

[!!!!!] Card 9 [/!!!!]
[q]Complete this chemical equation for cellular respiration

C6H12O6 + ______ –> energy(ATP) + 6CO2 + 6H2O (don’t worry about typing subscripts)

[textentry]

[a] C6H12O6 + 6O2 –> energy(ATP) + 6CO2 + 6H2O

[!!!!!] Card 10 [/!!!!]

[q]Complete this chemical equation for cellular respiration

C6H12O6 + 6O2 –> _______ + 6CO2 + 6H2O
[textentry]

[a] C6H12O6 + 6O2 –> energy (ATP) + 6CO2 + 6H2O

[!!!!!] Card 11 [/!!!!]
[q]Complete this chemical equation for cellular respiration

C6H12O6 + 6O2 –> energy(ATP) + _____ + 6H2O (don’t worry about typing subscripts)
[textentry]

[a] C6H12O6 + 6O2 –> energy(ATP) + 6CO2 + 6H2O

[!!!!!] Card 12 [/!!!!]
[q]Complete this chemical equation for cellular respiration

C6H12O6 + 6O2 –> energy(ATP) + 6CO2 + _____ (don’t worry about typing subscripts)
[textentry]

[a]C6H12O6 + 6O2 –> energy(ATP) + 6CO2 + 6H2O

[!!!!!] Card 13 [/!!!!!]
[q]The goal of cellular respiration is production of ______.

[textentry]

[a]The goal of cellular respiration is production of ATP.

[!!!!!] Card 14 [/!!!!!]
[q]An important molecule used as a fuel in cellular respiration is ______.

[textentry]

[a]An important molecule used as a fuel in cellular respiration is glucose.

[!!!!!] Card 15 [/!!!!!]
[q]One of the waste products of cellular respiration is a gas that contains a carbon atom. This gas is  ______ _______.

[textentry]

[a]One of the waste products of cellular respiration is a gas that contains a carbon atom. This gas is carbon dioxide.

[!!!!!] Card 16 [/!!!!!]
[q]One of the waste products of cellular respiration contains the element hydrogen. This substance is ______.

[textentry]

[a]One of the waste products of cellular respiration contains a hydrogen atom. This substance is water.

 

 

[x]

[restart]

[/qdeck]

5. The oxidations and reductions in cellular respiration involve electron carriers

When glucose (or other foods) get oxidized to create ATP, the oxidation happens in many small steps. During these steps, glucose and the intermediate products that it gets broken down into it as it slowly gets transformed into carbon dioxide and water get oxidized. As this oxidation occurs, electrons and hydrogen atoms get transferred to two mobile electron carriers: NAD+, and FAD. When NAD+ and FAD accept these electrons, they become reduced. NAD+ becomes NADH. FAD becomes FADH2.

NADH and FADH2: Mobile Electron carriers
08a_nadh-nad-copy
08b_fadh2-fad

It’s useful to think of NADH and FADH2 as charged up, rechargeable batteries. When you place a charged battery into a device like a radio, the battery can create an electrical current. An electrical current is a flow of electrons that can be used to do some work (like taking a radio signal, amplifying it, and converting it into sound). NADH and FADH2 do a similar thing. They carry electron energy from either the cytoplasm or the mitochondrial matrix, and bring it to the inner mitochondrial membrane. Once there, they release their electrons to a series of membrane-embedded electron carriers called the electron transport chain. The electron transport chain uses this electron energy to create ATP.

Just think of it this way: If cellular respiration were a game of football and energetic electrons were the ball, then the end zone would be the inner membrane of the mitochondria, where the electron transport chain is found. NADH and FADH2 are like fullbacks: they carry the ball (the electrons) to the end zone.

We’ll learn the astounding details of how this ATP is generated in a later tutorial, but for now, study this diagram.

01_high-concept-energy-flow-with-nadh-and-fadh2-etc-with-numbers

“1” represents the source of all the energy: food. A series of oxidations take the energy in glucose and transfer it to NADH and FADH2 (shown at “2”). NADH and FADH2 are mobile electron carriers: they carry bring these energetic electrons from the cell’s cytoplasm or the mitochondrial matrix to the electron transport chain, which located in the inner membrane of the mitochondria. There, the proteins that make up the electron transport chain use the energy in these electrons to synthesize ATP. At the end of the process, these electrons flow to oxygen, the final acceptor in the chain.

6. Cellular respiration occurs in four phases

Let’s take stock of what we’ve covered so far

  1. The purpose of cellular respiration is to convert the potential chemical energy in food into the potential chemical energy in ATP, life’s moment to moment energy currency.
  2. During cellular respiration, a small amount of ATP is generated through substrate level phosphorylations that occur in the cell’s cytoplasm and in the mitochondrial matrix.
  3. Much more ATP is generated through a several step process involving:
    1. The step by step oxidation of glucose
    2. The reduction of the mobile electron carriers NAD+ and FAD to NADH and FADH2, respectively.
    3. The transport of energetic electrons by NADH and FADH2 to the electron transport chain in the inner membrane of the mitochondria, where most of the ATP generated during cellular respiration is synthesized.

This brings us almost to the end of this overview of cellular respiration. The last things to learn are the names of the four phases of cellular respiration. Don’t let the diagram below panic you. Soon, it will be as familiar as an old friend. Let’s look at each phase.

06_for-every-glucose-w-etc_for-every-glucose-w-etc

  1. Phase 1 is glycolysis. It produces ATP and NADH. Glucose is split apart and oxidized, resulting in a three carbon molecule that still has lots of potential energy. This molecule is called pyruvic acid, or pyruvate. Note that there are two molecules of pyruvate produced for every glucose that enters glycolysis.
  2. Pyruvate then diffuses into the mitochondrial matrix. There, in the link reaction, pyruvate is oxidized, producing more NADH. In this process, a carboxyl group (COO) is removed, leaving a two carbon molecule called acetyl Co-A.
  3. This two carbon acetyl Co-A still has plenty of potential energy. In the Krebs cycle, this energy is harvested to generate ATP, NADH, and FADH2.
  4. In the electron transport chain, the cell harvests the electron energy it has stored away in the reduced mobile electron carriers NADH and FADH2. The majority of the ATP generated during cellular respiration is synthesized in this final step.

7. Cellular Respiration Overview: Checking Understanding

Before exploring each phase of cellular respiration in more detail, let’s consolidate our understanding with the following quiz.

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Cellular Respiration Quiz 2 (M10)”]

[h]Cellular Respiration Overview Quiz 2

[i]

[!]++++Question1+++[/!!!]

[q]Which phase is glycolysis?

[textentry single_char=”true”]

[c*] 1

[f] Yes, “1” is glycolysis

[c]*

[f]No. Here’s a hint. Glycolysis means “splitting sugar.” Look for a sugar, and look for a process that splits it apart.

[!]++++Question 2+++[/!!!]

[q]Which phase is the link reaction?

[textentry single_char=”true”]

[c*] 2

[f] Yes, “2” is the link reaction.

[c]*

[f]No. Here’s a hint. The link reaction links glycolysis (which means “splitting sugar”) with the krebs cycle. Which number indicates a process that links something that splits sugar with something that looks cyclical?

[!]++++Question 4+++[/!!!]

[q]Which phase of cellular respiration is the electron transport chain?

[textentry single_char=”true”]

[c*] 4

[f] Yes. The descending stairway on the far right with production of 26 or 28 ATPs is the electron transport chain.

[c]*

[f]No. Here’s a hint. The electron transport chain involves a series of enzymes that accept and hand off energetic electrons from NADH and FADH2, creating conditions for generating more ATP than any other part of cellular respiration. Which phase of cellular respiration generates the most ATP?

[!]++++Question 5+++[/!!!]

[q]Which phase of cellular respiration occurs in the cytoplasm?

[textentry single_char=”true”]

[c*] 1

[f] Yes. Glycolysis occurs in the cytoplasm.

[c]*

[f]No. Here’s a hint. It involves splitting glucose into two molecules of pyruvate.

[!]++++Question 6+++[/!!!]

[q]Which phase of cellular respiration occurs primarily along the inner mitochondrial membrane?

[textentry single_char=”true”]

[c*] 4

[f] Yes. The electron transport chain, shown at “4,” happens along the inner mitochondrial membrane.

[c]*

[f]No. Here’s a hint. This phase, which occurs along the inner mitochondrial membrane, involves a series of enzymes that accept and hand off energetic electrons from NADH and FADH2, creating conditions for generating more ATP than any other part of cellular respiration. Which phase of cellular respiration generates the most ATP?

[!]++++Question 7 +++[/!!!]

[q]Glycolysis occurs in which area of the cell?

[textentry single_char=”true”]

[c*] 3

[f] Yes. Glycolysis occurs in the cytoplasm, at number 3.

[c]*

[f]No. Here’s a hint. This is the one phase that occurs outside of the mitochondrion.

[!]++++Question 8+++[/!!!]

[q]Where does the Krebs cycle occur?

[textentry single_char=”true”]

[c*] 5

[f] Yes. The Krebs cycle occurs in the mitochondrial matrix, number 5.

[c]*

[f]No. Here’s a hint. Krebs occurs in the central fluid (homologous to the cytoplasm) of the mitochondrion.

[!]++++Question 9+++[/!!!]

[q]Where is the electron transport chain found?

[textentry single_char=”true”]

[c*] 6

[f] Yes. The electron transport chain is located along the inner membrane of the mitochondrion

[c]*

[f]No. Here’s a hint. The electron transport chain involves membrane-embedded enzymes. There are membranes shown in this diagram at 2, 6, and 8. Which one would have the electron transport chain?

[!]++++Question 10+++[/!!!]

[q]Which of the molecules below can be made by substrate level phosphorylation?

[c]NADH

[c]FADH2

[c*]ATP

[f]No. NADH is made by oxidizing glucose (or other foods), which reduces NAD+ to NADH

[f]No. FADH2 is made by oxidizing glucose (or other foods), which reduces FAD to FADH2

[f]Yes! ATP can be made by through a substrate level phosphorylation, which involves enzymes transferring a phosphate from some organic substrate to ADP, creating ATP.

[!]++++Question 11+++[/!!!]

[q]NADH is

[c]oxidized

[c*]reduced

[f]No. NADH is the reduced form of this electron carrier. NAD+ is the oxidized form.

[f]Yes. NADH is the reduced form of this electron carrier. NAD+ is the oxidized form.

[!]++++Question 12+++[/!!!]

[q]NAD+ is

[c*]oxidized

[c]reduced

[f]Nice. NAD+ is the oxidized form of this electron carrier. NADH is the reduced form.

[f]No. NAD+ is the oxidized form of this electron carrier. NADH is the reduced form.

[!]++++Question 13+++[/!!!]

[q]FADH2 is

[c]oxidized

[c*]reduced

[f]No.FADH2 is the reduced form of this electron carrier. FAD is the oxidized form.

[f]Yes.FADH2 is the reduced form of this electron carrier. FAD is the oxidized form.

[!]++++Question 14+++[/!!!]

[q]FAD is

[c*]oxidized

[c]reduced

[f]Yes. FAD is the oxidized form of this electron carrier. FADH2 is the reduced form.

[f]No. FAD is the oxidized form of this electron carrier. FADH2 is the reduced form.

[!]++++Question 15+++[/!!!]

[q]Foods like sugar (including glucose) are

[c]oxidized

[c*]reduced

[f]No. Foods are highly reduced substances, with lots of energetic electrons that can be harvested for energy during cellular respiration.

[f]Yes. Foods are highly reduced substances, with lots of energetic electrons that can be harvested for energy during cellular respiration.

[!]++++Question 16+++[/!!!]

[q]The exhaust products of cellular respiration, particularly carbon dioxide (CO2) are

[c*]oxidized

[c]reduced

[f]Yes. Carbon dioxide (CO2) is the oxidized waste product (exhaust) of cellular respiration.

[f]No. Carbon dioxide (CO2) is the oxidized waste product (exhaust) of cellular respiration.

[!]++++Question 17+++[/!!!]

[q]Which process below occurs in the inner mitochondrial membrane?

[textentry single_char=”true”]

[c*] 3

[f] Yes. the Electron transport chain occurs along the inner mitochondrial membrane.

[c]*

[f]No. Here’s a hint. The process, which occurs along the inner mitochondrial membrane, involves many small steps, arranged in a series. Of the processes above, which is the only one that could fit that description?

[!]++++Question 18+++[/!!!]

[q]When a cell needs to release a small amount of energy to do some work, it removes a phosphate from ATP by breaking the bond at ____ and attaching the phosphate to something else.

[textentry single_char=”true”]

[c*] A

[f] Yes. When a cell needs to release a small amount of energy, it will break off the last phosphate on ATP and attach that phosphate to another molecule.

[c]*

[f]No. It’s the bond that hold the third phosphate to the the second that needs to be broken (so that the phosphate can be attached to something else, releasing energy).

[!]++++Question 19+++[/!!!]

[q]Which best describes the process shown below?

[c]oxidation

[c]reduction

[c*]substrate level phosphorylation

[f]No. Here’s a hint. Notice the transfer of a phosphate group by an enzyme to ATP.

[f]No. Here’s a hint. Notice the transfer of a phosphate group by an enzyme to ATP.

[f]Excellent. This diagram depicts a substrate level phosphorylation.

[!]++++Question 20+++[/!!!]

[q]Which phase of cellular respiration is the Krebs cycle?

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[c*] 3

[f] Yes. The Krebs cycle is shown at “3.”

[c]*

[f]No. Here’s a hint. The Krebs cycle produces more NADH and FADH2 than any other part of cellular respiration. Which phase is producing the most NADH and FADH2?

[x][restart]

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