1. Cellular Respiration

2. Learning Objectives
Explain where organisms get the energy they need for life processes.
Define cellular respiration.
Compare photosynthesis and cellular respiration.

3. Find the Cell Organelles

4. Cellular Respiration
A process of energy conversion that releases energy from food in the presence of oxygen
Involves a series of controlled reactions that slowly release energy
Explain to students that cellular respiration involves a series of controlled reactions that slowly release energy.
Ask students: In this image, what form is the energy being released from the marshmallow?
Answer: Energy is being released in the form of light and heat.

5. Cellular Respiration The chemical summary of cellular respiration is:
What does the equation look like expressed in symbols?
Click to reveal the chemical summary of cellular respiration in words and discuss what this means.
Then click to reveal the lead-in sentence to how cellular respiration could be expressed in symbols. Ask for volunteers to write any portions of the equation they already know.
Click to reveal the complete equation.
Understand the overall chemical summary for cellular respiration. Explain that the reactions shown are simplifications, or summations, of many sub-reactions.
Verify that the reaction shown in symbols is balanced by counting the molecules of each element on the right and left sides of the reaction.

6. Photosynthesis and Cellular Respiration
Photosynthesis removes CO2 from the atmosphere, and cellular respiration puts it back.
Photosynthesis releases oxygen into the atmosphere, and cellular respiration uses that oxygen to release energy from food.

7. Photosynthesis and Cellular Respiration
Photosynthesis and cellular respiration can be thought of as opposite processes.
Ask: Why doesn’t Earth run out of oxygen?
Possible answer: Cellular respiration is balanced by another process—photosynthesis.
Tell students that photosynthesis removes carbon dioxide from the atmosphere.
Click to highlight this in the image.
Tell students that photosynthesis releases oxygen into the atmosphere—which is then used in cellular respiration to release energy from food.

8. The Process of Cellular Respiration

9. Learning Objectives
Describe what happens during the three stages of Cellular Respiration:
Glycolysis
Krebs cycle
electron transport chain
Identify how much ATP cellular respiration generates.
Amoeba Sisters and Cellular Respiration
ATP and Respiration
Click to reveal each of the learning objectives.
Cellular respiration is a series of steps rather than a single event.

10. Mitochondria Structures
Membrane

11. Three Stages of Cellular Respiration
Glycolysis
Krebs cycle
Electron transport
Where are glucose and oxygen used during cellular respiration?
Answer: Glucose is the molecule that undergoes glycolysis. Oxygen is involved in electron transport.
Where do you see water, carbon dioxide, and energy in this diagram?
Answer: Carbon dioxide is released during the Krebs cycle. Water is released during electron transport. Energy is released at each stage.
Cellular respiration can be divided into three basic stages.

12. Stage 1: Glycolysis
Glucose first enters a chemical pathway called glycolysis. A small amount of energy is captured to produce ATP.
One molecule of glucose is converted to two molecules of pyruvic acid.
At the end of glycolysis, about 90% of the chemical energy available in glucose is still unused, locked in chemical bonds of pyruvic acid.
Glycolysis is the first part of cellular respiration.
What happens to glucose during glycolysis?
Answer: It is broken into two smaller molecules.
At the end of glycolysis, about 90 percent of the chemical energy that was available in glucose is still unused, locked in chemical bonds of a molecule called pyruvic acid.

13. Glycolysis: ATP and NADH Production
ATP and NADH are produced during glycolysis.
NAD+ - electron carrier that becomes NADH
Two Advantages of Glycolysis:
Occurs very fast in a few milliseconds
Occurs without oxygen
What do the six dark balls at the top of the figure represent?
Answer: The six carbon atoms in a molecule of glucose.
Explain to students that some energy, in the form of ATP, is necessary to get the glycolysis process started.
Click to highlight the two ATP molecules entering the system.
Ask: What does it mean to “invest” a molecule of ATP?
Answer: The energy stored in ATP is released and used to help start the process of glycolysis.
Ask: What are the products of glycolysis?
Answer: Two NADH molecules, four ATP molecules, and two pyruvic acid molecules.
Explain that four high-energy electrons are passed to the carrier NAD+ to produce NADH.
Click to highlight the two NADH molecules produced.
Tell them that, overall, four ATP molecules are produced, for a net gain of two ATP per molecule of glucose.
Click to highlight the four ATP produced.
Point out the two pyruvic acid that are a product of glycolysis.
Click to highlight the two pyruvic acid.
Ask: Where do these products go?
Answer: The NADH goes to the electron transport chain, the pyruvic acid goes to the Krebs cycle, and the ATP gets used by cells
Click to highlight this movement of electrons to the electron transport chain.
Misconception: Some students may think that energy is created during glycolysis and the other stages of cellular respiration. Remind students that energy cannot be created or destroyed. Reinforce the fact that the energy used in glycolysis to make ATP is stored in the chemical bonds of glucose. Suggest students investigate how energy is stored as potential energy in chemical bonds and make a presentation to the class of what they learn.

14. Stage 2: The Krebs Cycle
A little more energy is converted. Pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.
Before students study the Krebs cycle, point out that the cycle is a series of chemical reactions mainly involving carbon compounds. Explain that the element carbon has a remarkable ability to easily combine with both itself and other atoms, and the result is a tremendous number of carbon compounds in living things. Point out that following the changing carbon compounds is key to understanding the Krebs cycle.
Tell students that the pyruvic acid, from the glycolysis stage, is broken down into carbon dioxide.

15. The Krebs Cycle
Pyruvic acid from glycolysis passes through the two membranes of the mitochondrion and into the matrix, and is used to make NADH, ATP, and FADH2, with carbon dioxide as a by-product.
Point out to students that, because glycolysis produces two molecules of pyruvic acid from each glucose molecule, the Krebs cycle “turns” twice for each glucose molecule that enters glycolysis.
Pyruvic acid from glycolysis passes through the two membranes of the mitochondrion and into the matrix.
Click to highlight the pyruvic acid entering the mitochondrion.
What happens next to the 3-carbon pyruvic acid?
Answer: One carbon atom from pyruvic acid becomes part of a molecule of carbon dioxide, which is eventually released into the air.
Explain that the other two carbon atoms from pyruvic acid rearrange and form acetic acid, which is joined to a compound called coenzyme A. The resulting molecule is called acetyl-CoA.
Ask: What else do you see happening in this part of the process?
Answer: In the process, two high-energy electrons are passed to NAD+ to produce NADH.

16. The Krebs Cycle: Energy Extraction
For each turn of the cycle, a molecule of ADP is converted to a molecule of ATP.
Focus students’ attention on the ATP in the cycle.
Ask: Do you recall how many molecules of pyruvic acid are produced during glycolysis from one molecule of glucose?
Answer: Glycolysis produces two molecules of pyruvic acid from one glucose.
Ask: Knowing this, how many turns of the Krebs cycle would result from one molecule of glucose?
Answer: Two turns of the Krebs cycle.
Ask: So how many ATP molecules would be produced from one molecule of glucose?
Answer: Two ATP molecules
Click to emphasize.
Tell students that each starting molecule of glucose results in two complete turns of the Krebs cycle and, therefore, two ATP molecules.

17. The Krebs Cycle: Energy Extraction
At five places in the cycle, electron carriers accept a pair of high-energy electrons, and NAD+ and FAD are converted to NADH and FADH2.
Focus students’ attention on the electron carriers, NAD+ and FAD.
Click to highlight the five places where NADH and FADH2 are formed.
Tell students that energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.
Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.

18. Stage 3: Electron Transport
Products from the Krebs cycle and glycolysis feed into the last step of cellular respiration.
Remind students that electron transport is the third stage of cellular respiration.
Point to the arrows from glycolysis and the Krebs Cycle feeding into the electron transport stage.
Ask: What appear to be the overall products of the electron transport stage?
Answer: Energy and H2O.

19. Electron Transport Chain
Electron transport uses the high-energy electrons from glycolysis and the Krebs cycle to synthesize ATP from ADP.
Remind students that NADH and FADH2 are by-products of glycolysis and the Krebs cycle.
Ask for a volunteer to circle where these high-energy electrons are coming into the electron transport chain.
Explain that one way to organize information in a long reading passage is to create a graphic representation of the information. In this case, the reading describes the electron transport process and ATP synthesis, which can be well represented by a flowchart.
Distribute worksheets to students and encourage them to use the worksheets to create a flowchart summarizing this stage of cellular respiration.
Composed of a series of electron carriers located in the inner membrane of the mitochondrion.

20. Electron Transport: ATP Production
Explain to students that the inner mitochondrial membrane contains enzymes known as ATP synthases.
Click to highlight the ATP synthase.
Ask: What causes the H+ ions to rush through the ATP synthase?
Answer: The concentration gradient of H+ across the inner mitochondrial membrane, which it cannot directly cross.
Explain that as H+ ions rush through ATP synthase, the base of the synthase rotates, generating ATP from ADP.
With each rotation, the enzyme grabs an ADP molecule and attaches a phosphate group, producing ATP.
Tell students that, on average, each pair of high-energy electrons that moves down the full length of the electron transport chain provides enough energy to produce three molecules of ATP.
As H+ ions rush through ATP synthase due to concentration gradient, the base of synthase rotates, generating ATP from ADP.

21. Total ATP from Cellular Respiration
Glycolysis, the Krebs cycle, and the electron transport chain release about 36 molecules of ATP per molecule of glucose. 2
Total ATP? 2
Write in the products of each stage, including the number of molecules of ATP.
Write in the total ATP produced through cellular respiration.
This is all the energy that can be generated in an anaerobic condition.
Although 36 is what the numbers add up to, the actual number varies and typically falls in within the range of 30 to 42 ATPs per glucose.
A total of 36 ATPs is reasonable because it assumes two ATPs per FADH2 and three ATPs per NADH (with approximately two ATPs lost due to the cost of transporting NADH produced in the cytoplasm into the mitochondrion for oxidation).
CO2
30 to 42 32

22. Cellular Respiration Review
Glycolysis
leaves 90% of the energy available in glucose unused and locked in bonds of PYRUVIC ACID
Occurs in the cytoplasm of the cell
Anaerobic process – doesn’t require oxygen
Krebs Cycle
Occurs in Mitochondria matrix
Aerobic process – requires oxygen
Electron Transport Chain
Occurs in the Mitochondria cristae
Final stage
Aerobic process

24. Fermentation Cellular Respiration and Fermentation

25. Learning Objectives
Explain how organisms get energy in the absence of oxygen.
Identify the pathways the body uses to release energy during exercise.
Bring to class two loaves of bread—one that is leavened and one that is unleavened. Pass the loaves around and have each student take a small piece of the bread. Have students compare the two pieces of bread and consider the differences and similarities. Point out that yeast is added to dough to make it rise.
Create a Venn diagram to help them remember the common reactants and products in the fermentation process. Fill in the parts of the Venn diagram to indicate what products are different.
At the end of the presentation you should be able to explain how organisms generate energy when oxygen is not available, as well as how the body produces ATP during exercise.

26. Fermentation
In the absence of oxygen (anaerobic), fermentation releases energy from food molecules by producing ATP.
Explain that during fermentation, cells convert NADH to NAD+ by passing high-energy electrons back to pyruvic acid. This action converts NADH back into the electron carrier NAD+, allowing glycolysis to produce a steady supply of ATP.

27. Fermentation
What’s missing in fermentation that available in the mitochondria?
Tell students that fermentation is an anaerobic process that occurs in the cytoplasm of cells.
Point out that sometimes glycolysis and fermentation are together referred to as anaerobic respiration.
What is missing from the illustration of fermentation that was involved in the Krebs cycle and electron transport chain?
Answer: Oxygen.
Explain that fermentation is referred to as anaerobic respiration because it takes place in the absence of oxygen.
Point out the alcoholic fermentation pathway.
Point out the lactic acid fermentation pathway.
While the figure shows both alcoholic and lactic acid fermentation, these processes do not normally occur at the same time in an organism. Most organisms carry out either one or the other.
The figure shows pyruvic acid from glycolysis entering either alcoholic or lactic acid fermentation, not both at once.

28. Fermentation There are two slightly different forms of the process:
Alcoholic fermentation
Lactic acid fermentation
Tell students that fermentation is an anaerobic process that occurs in the cytoplasm of cells.
Point out that sometimes glycolysis and fermentation are together referred to as anaerobic respiration.
What is missing from the illustration of fermentation that was involved in the Krebs cycle and electron transport chain?
Answer: Oxygen.
Explain that fermentation is referred to as anaerobic respiration because it takes place in the absence of oxygen.
Point out the alcoholic fermentation pathway.
Point out the lactic acid fermentation pathway.
While the figure shows both alcoholic and lactic acid fermentation, these processes do not normally occur at the same time in an organism. Most organisms carry out either one or the other.
The figure shows pyruvic acid from glycolysis entering either alcoholic or lactic acid fermentation, not both at once.

29. Alcoholic Fermentation
Yeasts and a few other microorganisms use alcoholic fermentation, which produces ethyl alcohol and carbon dioxide.
Pyruvic acid + NADH → Alcohol +
CO2 + NAD+
Look at the alcoholic fermentation portion of glycolysis.
Alcoholic fermentation is used to produce alcoholic beverages and is also the process that causes bread dough to rise.
When yeast cells in the dough run out of oxygen, the dough begins to ferment, giving off tiny bubbles of carbon dioxide. These bubbles form the air spaces visible in a slice of leavened bread. The small amount of alcohol produced in the dough evaporates when the bread is baked.

30. Lactic Acid Fermentation
Most organisms carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid.
Pyruvic acid + NADH →
Lactic acid + NAD+
Look at the lactic acid fermentation portion of glycolysis.
Which form of fermentation is carried out by your body?
Answer: Lactic acid fermentation
Unlike alcoholic fermentation, lactic acid fermentation does not give off carbon dioxide. Like alcoholic fermentation, lactic acid fermentation also regenerates NAD+ so that glycolysis can continue.

31. Quick Energy
During brief periods without oxygen, cells in our bodies can produce ATP by lactic acid fermentation.
Muscle cells are best adapted for this and often need large supplies of ATP for rapid bursts of activity.
At the beginning of a race, what is the principal source of energy for the runners’ muscles?
ATP that is already in the cell, then ATP produced by lactic acid fermentation.
Humans are lactic acid fermenters. During brief periods without oxygen, many of the cells in our bodies are capable of producing ATP by lactic acid fermentation. The cells best adapted to doing that are muscle cells, which often need very large supplies of ATP for rapid bursts of activity.
What do you think the effects of lactic acid buildup in an athlete’s muscles might be?
Answer: Muscle cramping, soreness, and fatigue.
Until recently, many people thought that lactic acid buildup was responsible for muscle fatigue and soreness. Researchers have since found that lactic acid can actually be used as a fuel by mitochondria to make energy.
At the beginning of a race, what is the principal source of energy for the runners’ muscles?
Answer: ATP that is already in the cell, then ATP produced by lactic acid fermentation.

32. Long-Term Energy
For exercise longer than about 90 seconds, cellular respiration is the only way to continue generating a supply of ATP.
The body stores energy in muscle and other tissues as glycogen - enough to last for 15 or 20 minutes of activity. After that your body breaks down other stored molecules, including fats, for energy.
What exercise would be most beneficial for weight control?
Answer: Aerobic forms of exercise such as running, dancing, and swimming
Cellular respiration releases energy more slowly than fermentation does.
The body stores energy in muscle and other tissues in the form of the carbohydrate glycogen. These stores of glycogen are usually enough to last for 15 or 20 minutes of activity. After that, your body begins to break down other stored molecules, including fats, for energy.
What form of exercise would be most beneficial for weight control?
Answer: Aerobic forms of exercise such as running, dancing, and swimming are beneficial for weight control.
How would a bear look different after hibernation?
Answer: The bear will probably be thinner, because it will have used its stored fat for energy during hibernation.

33. Before and after hibernation
How would a bear look different after hibernation?
Bears use stored fat for energy during hibernation.
How would a bear look different after hibernation?
Answer: The bear will probably be thinner, because it will have used its stored fat for energy during hibernation.