Click this link for a Cellular Respiration Student Learning Guide

1. Introduction

[qwiz]

[h]Three examples of…

[q]What do beer, yogurt, and a sprinter have in common?

[c]Show the Answer

[f]They all involve fermentation. On the left is alcohol fermentation (for making beer); in the center is lactic acid fermentation (for making yogurt); and on the right is the kind of lactic acid fermentation animals (like humans) do when they run short on oxygen. 

[/qwiz]

2. Aerobic and Anaerobic Respiration

11_very-simplified-glycolysisWe’ve seen in a previous tutorial that glycolysis produces three products

  • ATP
  • NADH, and
  • the  3-carbon molecule pyruvic acid, or pyruvate.

Despite the fact that energy from glucose was used to make the ATP and the NADH, the third product, pyruvic acid, still has lots of chemical energy.

10_aerobic-v-anaerobic-respirationThe ATP produced by glycolysis can immediately be used for cellular work. But what happens to the NADH and pyruvate that comes out of glycolysis depends on the presence or absence of oxygen.

If oxygen is present, then pyruvate and NADH enter the mitochondria. Pyruvate gets completely oxidized in the Link Reaction and the Krebs cycle. The NADH from glycolysis joins with the NADH and FADH2 produced by the Krebs cycle and Link Reaction to power the electron transport chain and oxidative phosphorylation. This complete oxidation of pyruvate, along with production of ATP through oxidative phosphorylation is called aerobic respiration: respiration with oxygen.

This kind of easy, flat riding is definitely aerobic for the kids…and probably for the Dad, too.

2a. Aerobic respiration consumes oxygen at a sustainable pace

If you’re sitting and reading this tutorial on a computer or some other device, you’re doing it while performing aerobic respiration. If you got up and got on a bicycle and cycled at a leisurely pace, you’d still be doing aerobic respiration. Aerobic respiration is done when you can supply your muscles and other organs with enough oxygen to completely oxidize glucose. Aerobic respiration is sustainable. For example (assuming that you’re in reasonable shape), if you’re walking at an aerobic pace you’ll never need to stop to catch your breath.

2b. Anaerobic respiration happens when there’s not enough oxygen. It’s not sustainable.

Harder work requires a switch to anaerobic respiration

Back to our bike ride. You reach a long, steep hill. Your muscles strain to keep the bike moving upward and forward. You start breathing harder to get more oxygen into your lungs. Your heart is beating faster to deliver that oxygen to your muscles.

After a while, your breathing rate and your heart rate reach their maximum. Yet even this maximum isn’t delivering enough oxygen to your system. At that point, you switch over to anaerobic respiration.

Anaerobic respiration is about continuing glycolysis in the absence of oxygen. Why? Simply, it’s because two ATPs are a lot better than no ATP. Anaerobic activities include sprinting (whether running, biking, or swimming) and weightlifting. You can’t sustain these activities, but you can do them in short bursts. During these bursts, your muscles are going to need every ATP they can get.

Look again at glycolysis04_glycolysis-partially-numbered

In order to move past the “cleavage” phase (phase 2), G3P (at “F”) needs to be oxidized. That oxidation can only happen if NAD+ is present (at “G”). But glycolysis converts NAD+ to NADH. So, in order for glycolysis to continue to create its two ATPs/glucose, there needs to be a way for the cell to resupply itself with NAD+. That way is called fermentation. Fermentation oxidizes NADH, converting it to NAD+ so that  glycolysis can continue.

Fermentation happens in people in a process called lactic acid fermentation. Lactic acid fermentation is also used by the bacteria that make yogurt. And yeast carry out fermentations that produce alcohol. Let’s start with that one.

3. Alcohol Fermentation

3a. Fermentation Virtual Demonstration

[qwiz]

[h]Alcohol fermentation demonstration

[q]Here’s an experiment to try at home. Take three flasks.

Put a spoonful of yeast in the first. Put a spoonful of sugar in the second. Put a spoonful of yeast AND a spoonful of sugar in the third. Add water and wait a few hours. Predict what will happen.

[c]Click when you’re ready to confirm your prediction

[f]Nothing happened in the flask with only yeast, because the yeast had nothing to eat. In the second, there was fuel, but no organism to break it down. In the third flask the yeast broke sugar down to alcohol (dissolved in the liquid) and carbon dioxide (the gas that’s causing the balloon to expand). Here are the details.

[/qwiz]

3b. Alcohol Fermentation: the details

“A” is glycolysis. Glucose is converted to two molecules of pyruvate (C3H3O3), with a net yield of two ATP and two NADH.

In step “B,” enzymes break the carboxyl group off of pyruvate, producing the two carbon molecule acetaldehyde. The carboxyl group becomes a CO2 molecule. This CO2 becomes the bubbles in beer or champagne or bread. In other alcohol fermentation processes, such as in wine-making, the CO2 is allowed to escape.

Step “C” is about regenerating NAD+ so that glycolysis can continue. The cell does this by a redox reaction in which acetaldehyde is reduced to ethanol (a two carbon alcohol), while NADH is oxidized. Thise oxidation and reduction is paired together, with the electrons (and hydrogens) flowing from NADH (which is being oxidized) to acetaldehyde (which is being reduced).  You can see this by comparing the formulas for acetaldehyde (C2H3O) and ethanol (C2H6O). Ethanol, with all of those hydrogens, is a more reduced (and more energetic compound). Ethanol, in fact, is a fuel. You can drive a car with it. In California, where I live, up to 10% of the fuel that I put in my car is ethanol (with the other 90% being petroleum-derived gasoline).

4. Lactic Acid Fermentation

Lactic acid fermentation occurs in yogurt making bacteria, and in our very own muscle cells. Whenever we’re low on oxygen (every time we sprint, weightlift, etc). our cells will temporarily shift to lactic acid fermentation. This allows us to keep on producing two ATPs/glucose for a short period of time by continuing glycolysis, without oxidative phosphorylation. Here’s how it works.

19_lactate-fermentation-with-letters

As with alcohol fermentation, the process begins with glycolysis (“A”). In the absence of oxygen, enzymes take pyruvate and reduce it to lactate, or lactic acid. This reduction is accompanied by the simultaneous oxidation of NADH to NAD+. With NAD+ available, glycolysis can continue, at least for a short while.

As you move towards the top of your aerobic zone, your body will try to maximize oxygen delivery to your cells through increasing your heart and breathing rate. As you exceed your aerobic capacity, anaerobic respiration begins. You’ll accumulate lactic acid in your muscle tissue, leading to what athletes experience as a “lactic acid burn.” At a certain point, as lactic acid and other waste products build up, you’ll have to slow down or stop altogether. As you do, you’ll reduce oxygen demand. You’re heart rate and breathing rate will decrease as you shift back to aerobic respiration (with its more efficient production of ATP). The lactic acid, a high energy compound, diffuses out of your muscles into your blood, which carries it to your liver. Liver cells, in turn, convert lactic acid into glucose, which can then diffuse back into the bloodstream to power cellular respiration.

yogurt: a product of lactic acid fermentation

If you’re interested in making yogurt, the process is quite simple. You add yogurt making bacteria such as Lactobacillus and Acidophilus to pasteurized milk (pasteurization lowers the amount of other bacteria in the milk). The Lactobacillus and Acidophilus will take lactose (milk sugar) and use it as a fuel to create ATP. Lactic acid is a metabolic waste product. As it accumulates, the pH of the milk drops to where it causes milk proteins to change from a liquid form to more a a gel, giving yogurt its texture and sourness.

5. Quiz: Anaerobic Respiration and Fermentation

[qwiz random = “true” qrecord_id=”sciencemusicvideosMeister1961-Anaerobic Respiration and Fermentation (M10)”]

[h]Fermentation and Anaerobic Respiration

[i]

[!]++++++question 1 ++++++++[/!]

[q]Which letter or number represents glycolysis?

[textentry single_char=”true”]

[c*]A

[f] Yes. “A” represents glycolysis.

[c]*

[f]No. Here’s a hint. Glycolysis is the part of fermentation which produces useful energy for the cell. Where do you see useful energy being produced?

[!]++++++question 2 ++++++++[/!]

[q]Which letter or number represent a process that removes of a carboxyl group from pyruvic acid?

[textentry single_char=”true”]

[c*]B

[f] Yes. In step “B” a carboxyl group is removed from pyruvic acid, which exits the system as CO2

[c]*

[f]No. Here’s a hint. A carboxyl group is a carbon bonded to two oxygen atoms (with one of the bonds being a double bond). When carboxyl is removed, a molecule of CO2 is formed. Where do you see a CO2 leaving the system?

[!]++++++question 3 ++++++++[/!]

[q]Which letter or number represents a redox (oxidation/reduction) reaction?

[textentry single_char=”true”]

[c*]C

[f] Yes. In step “C” acetaldehyde (molecule 3) is reduced so that NADH can be oxidized to NAD+. This regenerates NAD+ so that glycolysis can continue to function.

[c]*

[f]No. Here’s a hint. To find a redox (oxidation/reduction) reaction, look for a place where molecules are gaining or losing hydrogen atoms (along with electrons, which can be harder to track in a diagram like the one above).

[!]++++++question 4 ++++++++[/!]

[q]The biological purpose of the reactions below is to generate _________ so that glycolysis can continue.

[c]ATP       [c]pyruvate      [c]NADH      [c*]NAD+      [c]alcohol

[f]No, but this could have been a clever answer if you were thinking that ATP is required during the “investment” phase of glycolysis. Think of a molecule that is absolutely required in order for the redox reactions that occur during the “harvest” phase of glycolysis to proceed.

[f]No. Glycolysis produces pyruvate, and doesn’t require it. Think of a molecule that is absolutely required in order for the redox reactions that occur during the “harvest” phase of glycolysis to proceed.

[f]No. Glycolysis produces NADH, and doesn’t require it. Think of a molecule that is absolutely required in order for the redox reactions that occur during the “harvest” phase of glycolysis to proceed.

[f]Yes. NAD+ is required in order for the redox reactions that occur during the “harvest” phase of glycolysis to proceed.

[f]No. Glycolysis produces CO2, and doesn’t require it. Think of a molecule that is absolutely required in order for the redox reactions that occur during the “harvest” phase of glycolysis to proceed.

[!]++++++question 5 ++++++++[/!]

[q]Which letter or number represents glucose?

[textentry single_char=”true”]

[c*]1

[f] Yes. Glucose is number 1.

[c]*

[f]No. Here’s a hint. What’s the starting substrate for glycolysis?

[!]++++++question 6 ++++++++[/!]

[q]Which letter or number represents pyruvic acid?

[textentry single_char=”true”]

[c*]2

[f] Yes. Pyruvic acid is number 2.

[c]*

[f]No. Here’s a hint. What is the 3 carbon molecule that comes out of glycolysis?

[!]++++++question 7 ++++++++[/!]

[q]Which letter or number represents ethanol?

[textentry single_char=”true”]

[c*]4

[f] Yes. Ethanol is number 4.

[c]*

[f]No. Here’s a hint. What molecule results after pyruvic acid (number 2) is modified by enzymes in such a way that it first loses a CO2 and then gets chemically reduced?

[!]++++++question 8 ++++++++[/!]

[q]Of the molecules listed below, the only one that results from alcohol fermentation which can directly power cellular work is

[c*]ATP       [c]pyruvate      [c]NADH      [c]NAD+      [c]alcohol

[f]Yes. ATP is the cell’s energy currency, and it’s the molecule used to get work done for the cell.

[f]No. Pyruvate can serve as an fuel for some of the reactions of cellular respiration, but can’t directly power cellular work. What molecule can?

[f]No. NADH, an electron carrier, can power ATP synthesis in oxidative phosphorylation. But that’s not a part of alcohol fermentation, and it can’t directly power cellular work. What molecule can?

[f]No. NAD+ is required to keep glycolysis (and alcohol fermentation going), but it’s an oxidized molecule that can’t power work. What molecule can.

[f]No. Alcohol has lots of chemical energy, but it’s actually a waste product of fermentation, and can’t directly power cellular work. What molecule can?

[!]++++++question 9 ++++++++[/!]

[q]The reaction responsible for filling the balloon in the flask on the right is…

 

[textentry single_char=”true”]

[c*]B

[f] Yes. The reaction at “B” produces the CO2 that’s filling the balloon. This production of CO2 during alcohol fermentation is responsible for the bubbles in beer, bread, and champagne.

[c]*

[f]No. Here’s a hint. Look for a reaction where the gas CO2 is produced.

[!]++++++question 10 ++++++++[/!]

[q]Which letter or number represents pyruvic acid?

[textentry single_char=”true”]

[c*]2

[f] Yes. Pyruvic acid is number 2.

[c]*

[f]No. Here’s a hint. What is the 3 carbon molecule that comes out of glycolysis?

[!]++++++question 11 ++++++++[/!]

[q]Which letter or number represents lactic acid?

[textentry single_char=”true”]

[c*]3

[f] Yes. Lactic acid is number 3.

[c]*

[f]No. Here’s a hint. Lactic acid results when pyruvic acid (at “2”) gets reduced. Which molecule looks like a reduced version of pyruvic acid?

[!]++++++question 12 ++++++++[/!]

[q]Which letter or number represents glucose?

[textentry single_char=”true”]

[c*]1

[f] Yes. Glucose is number 1.

[c]*

[f]No. Here’s a hint. What’s the starting substrate for glycolysis?

[!]++++++question 13 ++++++++[/!]

[q]What type of fermentation is being shown below?

[c*]alcohol       [c]lactic acid

[f]Yes. The two clues that indicate that this is an alcohol fermentation are the production of CO2 in step “B,” and the production of the highly reduced two-carbon molecule ethanol (C2H6O), which is molecule 4.

[f]No. Lactic acid fermentation doesn’t produce any CO2 (which is occurring in step “B”) and it results in lactate (lactic acid) which is a three carbon molecule.

[!]++++++question 14 ++++++++[/!]

[q]What type of fermentation is being shown below?

[c]alcohol       [c*]lactic acid

[f]No. Alcohol fermentation produces  COand produces ethanol (C2H6O) as a waste product.

[f]Yes. This is Lactic acid fermentation, as you can see by the direct reduction of pyruvic acid (molecule “2”) to lactic acid (molecule “3”) in step “B”

[!]++++++question 15 ++++++++[/!]

[q]What type of fermentation occurs in animal cells when there’s not enough oxygen for oxidative phosphorylation of ADP to ATP?

[c]alcohol       [c*]lactic acid

[f]No. Alcohol fermentation is typically associated with yeast cells.

[f]Yes. Lactic acid fermentation occurs in animal cells when there’s not enough oxygen for oxidative phosphorylation of ADP to ATP.

[!]++++++question 16 ++++++++[/!]

[q]Which letter or number shows a redox (oxidation/reduction) reaction?

[textentry single_char=”true”]

[c*]B

[f] Yes. Step “B” shows pyruvic acid being reduced to lactic acid as NADH is oxidized to NAD+

[c]*

[f]No. Here’s a hint. To find a redox (oxidation/reduction) reaction, look for a place where molecules are gaining or losing hydrogen atoms (along with electrons, which can be harder to track in a diagram like the one above).

[!]++++++question 17 ++++++++[/!]

[q]In cells, fermentation occurs in

[c]mitochondria

[c]lysosomes

[c*]the cytoplasm

[c]the nucleus

[f]No. Mitochondria are where oxidative phosphorylation occurs.

[f]No. Lysosomes are where intracellular digestion and recycling of worn out cell parts occurs.

[f]Yes. Fermentation is carried out by enzymes in the cytoplasm.

[f]No. The nucleus is where genetic information is stored.

[!]++++++question 18 ++++++++[/!]

[q]Activities that can be sustained indefinitely (or, at least for a very long period of time) are

[c]fun

[c*]aerobic

[c]anaerobic

[f]Well, doesn’t it depend on the activity? Get serious, and try another answer!

[f]Yes. Activities that are aerobic are carried out at a sustainable pace.

[f]No. With a measly production of 2 ATPs/glucose and the buildup of lactic acid, anaerobic respiration can occur only for a relatively short period of time (a few minutes).

[!!!!!!] question 19 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]When food is broken down for energy in cells with oxygen, the process is

[c*] aerobic

[c] anaerobic

[f] Yes. Breakdown of food with oxygen is aerobic.
[f] No. ‘Anaerobic’ means ‘without oxygen.’ If there’s oxygen, it can’t be anaerobic.

[!!!!!!] question 20 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Breakdown of food for energy WITHOUT oxygen is called

[c] aerobic

[c*] anaerobic

[f] No. ‘Aerobic’ means ‘with oxygen.’ If there’s no oxygen, it can’t be aerobic.
[f] Yes. ‘Anaerobic’ means ‘without oxygen.’

[!!!!!!] question 21 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]You’re riding your bike on a flat road. The pace is nice and easy. You could do it all day. Your production of ATP is

[c*] aerobic

[c] anaerobic

[f] Yes. Athletic activities that can be sustained for long periods of time, and which can be accomplished with moderate, sustainable heart and breathing rates, are aerobic.
[f] No ‘Anaerobic’ means ‘without oxygen.’ Anaerobic activities require short, intense bursts of energy, at levels that can’t be sustained for long period of time (meaning, you have to stop and rest).

[!!!!!!] question 22 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]You’re lifting weights. After ten repetitions, your muscles start to burn, and you’re having more and more difficulty lifting the weight. Your production of ATP is

[c] aerobic

[c*] anaerobic

[f] No. Athletic activities that can be sustained for long periods of time, and which can be accomplished with moderate, sustainable heart and breathing rates, are aerobic. The weight lifting described above is not aerobic.

[f] Yes ‘Anaerobic’ means ‘without oxygen.’ Anaerobic activities require short, intense bursts of energy, at levels that can’t be sustained for long period of time (meaning, you have to stop and rest). The weightlifting described above is anaerobic.

[!!!!!!] question 23 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]When humans and other animals perform anaerobic respiration, one of the byproducts is

[c] glucose

[c] oxygen

[c] carbon dioxide

[c*] lactic acid

[f] No. Glucose is the starting fuel source for most forms of respiration, not a byproduct.
[f] No. Oxygen is required for aerobic respiration. This question is about ‘anaerobic respiration,’ so oxygen is not involved.
[f] No. Carbon dioxide is a byproduct of aerobic respiration in humans.
[f] Yes. When humans and other animals lack sufficient oxygen, they’ll create ATP through a form of anaerobic respiration that produces lactic acid as a byproduct.

[!!!!!!] question 24 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Lactic acid fermentation is a form of _____________ respiration.

[c] aerobic

[c*] anaerobic

[f] No. Cells produce ATP through lactic acid fermentation only under when they lack sufficient oxygen.
[f] Yes ‘Anaerobic’ means ‘without oxygen. Cells will produce ATP through lactic acid fermentation only under when they lack sufficient oxygen.

[!!!!!!] question 25 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Yogurt is sour because the bacteria used to create yogurt from milk create

[c] alcohol

[c] glucose

[c*] lactic acid

[c] carbon dioxide

[f] No. Alcohol is produced by yeast during alcohol fermentation, which is another form of anaerobic respiration.
[f] No. Glucose is a sugar that is the starting fuel for most forms of respiration. It tastes sweet, not sour.
[f] Yes. The bacteria used to create yogurt ferment the sugars in milk to lactic acid, which gives yogurt its sour taste.
[f] No. While carbon dioxide is a product of some kinds of fermentation, it’s not produced by yogurt-creating bacteria when they ferment milk sugars.

[!!!!!!] question 26 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Beer and wine are made through

[c*] alcohol fermentation

[c] lactic acid fermentation

[c] aerobic respiration

[f] Yes. The alcohol in beer and wine are produced by yeast that ferment plant sugars into alcohol. Carbon dioxide is released as a byproduct.
[f] No. Lactic acid fermentation occurs under anaerobic conditions in animal muscle tissue, and in certain bacteria that ferment milk sugars to lactic acid.
[f] No. Aerobic respiration takes glucose and breaks it down all the way to carbon dioxide and water. Think of the kind of beverage beer and wine are, and you’ll have the answer.

[!!!!!!] question 27 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]The bubbles in beer are made of

[c] alcohol

[c*] carbon dioxide

[c] oxygen

[c] lactic acid

[f] No. Beer contains alcohol, but the bubbles are filled with the gas that gets produced as a byproduct during alcohol fermentation.
[f] Yes. During alcohol fermentation, yeast ferment plant sugars to alcohol, and release carbon dioxide as a byproduct.
[f] No. The only oxygen producing-process we’ve discussed is photosynthesis. Try to remember the name of the gas that gets produced along with alcohol during alcohol fermentation.
[f] No. Lactic acid is what gets produced when animals do aerobic respiration. When beer is produced, it’s alcohol fermentation. Try to remember the name of the gas that gets produced along with alcohol during alcohol fermentation.

[!!!!!!] question 28 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Yeast are placed in a flask containing sugar and water. A balloon is placed over the mouth of the flask. Several hours later, the balloon has inflated. What happened?

[c] Oxygen released during aerobic respiration caused the balloon to inflate.

[c] Carbon dioxide released during aerobic respiration caused the balloon to inflate.

[c*] Carbon dioxide released during alcohol fermentation caused the balloon to inflate.

[f] No. First of all, aerobic respiration consumes oxygen (as opposed to releasing it). The gas you’re looking for is the one produced during alcohol fermentation.
[f] No. The gas is carbon dioxide, but the reaction in the flask is not aerobic respiration.
[f] Yes. In the flask, the yeast are fermenting plant sugars down to alcohol. Carbon dioxide is released as a by-product, and it fills the balloon.

[!!!!!!] question 29 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Alcoholic fermentation is a form of

[c] aerobic respiration.

[c*] anaerobic respiration.

[c] photosynthesis.

[f] No. Alcohol fermentation only occurs when oxygen is lacking (so it can’t be aerobic)
[f] Yes. Alcohol fermentation is a form of anaerobic respiration.
[f] No. Photosynthesis is how plants produce carbohydrates. Alcohol fermentation involves breaking down carbohydrates to alcohol and carbon dioxide.

[!!!!!!] question 30 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]Aerobic respiration requires

[c] carbon dioxide.

[c*] oxygen.

[c] lactic acid.

[c] alcohol.

[f] No. Aerobic respiration creates carbon dioxide (and doesn’t require it).
[f] Yes. Aerobic means ‘with oxygen,’ and it only occurs when sufficient oxygen is present.
[f] No. Lactic acid is produced in one form of anaerobic respiration, and it’s not required for aerobic respiration to occur.
[f] No. Alcohol is produced in one form of anaerobic respiration, and it’s not required for aerobic respiration to occur.

[!!!!!!] question 31 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]The release of energy from food molecules in the absence of oxygen is

[c] photosynthesis

[c] aerobic respiration.

[c] protein synthesis

[c*] anaerobic respiration.

[f] No. Photosynthesis involves the creation of high energy food molecules from carbon dioxide and water.
[f] No. Aerobic means ‘with oxygen.’ If oxygen is absent, then the type of respiration can’t be aerobic.
[f] No. Protein synthesis is about making proteins. It requires energy, but otherwise, there’s no connection with release of energy from food.
[f] Yes. Release of energy from food molecules in the absence of oxygen is anaerobic respiration.

[!!!!!!] question 32 +++++++++[/!!!!!!]
[q topic= “aerobic_and_anaerobic_respiration”]The processes of fermentation and aerobic respiration are similar in that both produce

[c] carbon dioxide and water

[c] carbon dioxide and alcohol

[c*] energy in the form of ATP

[c] glucose

[f] No. Carbon dioxide and water are released only in aerobic respiration. For the answer, think about why, from a cell’s perspective, fermentation or respiration are necessary.
[f] No. Carbon dioxide and alcohol are produced only during alcohol fermentation. For the answer, think about why, from a cell’s perspective, fermentation or respiration are necessary.
[f] Yes. The purpose of cellular respiration, from a cell’s perspective, is to create ATP. Both aerobic respiration and fermentation create ATP, though aerobic respiration creates much more.
[f] No. Glucose is the starting fuel for aerobic respiration and for many types of fermentation, but neither aerobic respiration or fermentation release glucose. For the answer, think about why, from a cell’s perspective, fermentation or respiration are necessary.

[x][restart]

[/qwiz]

Next steps

This tutorial ends this series on cellular respiration. From here, you can go back to the Cellular respiration main menu, or choose a new tutorial from the menu above.