Cellular respiration has three main stages: glycolysis, the Krebs cycle, and the electron transport chain. Glycolysis occurs in the cytoplasm and breaks down glucose for energy. In the presence of oxygen, the Krebs cycle and electron transport chain take place in the mitochondria to further extract energy from glucose through oxidative phosphorylation, producing up to 38 ATP molecules. Without oxygen, fermentation pathways like lactic acid fermentation take over after glycolysis to regenerate NAD+ and allow glycolysis to continue at a lower energy yield of 2 ATP.

1. Cellular Respiration
• How do living things release energy???
• Quick Review…
– Most energy used thru conversion of ATP
molecules into ADP molecules
– Thus cells must continually convert ADP molecules
back into ATP molecules
– This process is known as……….
CELLULAR RESPIRATION

2. Lesson Objectives
• Name the three stages of cellular respiration.
• Give an overview of glycolysis.
• Explain why glycolysis probably evolved before the other stages of aerobic
respiration.
• Describe the structure of the mitochondrion and its role in aerobic respiration.
• List the steps of the Krebs cycle, and identify its products.
• Explain how electron transport results in many molecules of ATP.
• Describe how chemiosmotic gradients in mitochondria store energy to
produce ATP.
• State the possible number of ATP molecules that can result from aerobic
respiration.
• Define fermentation.
• Describe lactic acid fermentation and alcoholic fermentation.
• Compare the advantages of aerobic and anaerobic respiration.
• Compare cellular respiration to photosynthesis

3. Breathing versus Cellular
Respiration
• Breathing: physical process that allows
animals and humans to come into contact
with gases in the air
• Cellular respiration: chemical process that
releases energy from organic compounds
(food), gradually converting it into energy
that is stored in ATP molecules

4. Correlation between a campfire
and Cellular Respiration
• Analyzing a campfire can clarify your
understanding of cellular respiration.
– A campfire breaks chemical bonds in wood,
releasing stored energy as light and heat
– Cellular respiration breaks chemical bonds in
glucose, releasing stored energy and transferring
some to 38 ATP; some energy is lost
as heat.

5. Chemical Pathways
☼ Food is the raw material that provides the
energy for your body to function
☼ Cells use food to synthesize new molecules
to carry out their life processes

6. • Cells do not BURN glucose, they slowly release
energy from it and other food compounds
through several pathways (processes)
– 1st pathway  glycolysis: releases only a small
amount of energy (2 net ATP)
• If oxygen present, it will lead to two other pathways that
release a lot of energy: Krebs cycle & Electron Transport
Chain
• If oxygen absent glycolysis is followed by a different
pathway: Alcoholic Fermentation or Lactic Acid
Fermentation

7. Overview of Cellular Respiration
• In presence of oxygen (aerobic) glycolysis is
followed by: ______________
______________
Krebs Cycle
Electron Transport Chain

8. – All three combined make up Cellular Respiration:
Glycolysis + Krebs Cycle + Electron Transport
Chain
• Process that releases energy by breaking down food
molecules in the presence of oxygen
Each of these 3 stages captures some of the chemical
energy available in food molecules and uses it to produce
ATP
Equation for cellular respiration:
6O2 + C6H12O6 ------- 6CO2 + 6H2O + energy (ATP)
oxygen + glucose ----- carbon dioxide + water + energy
1 2 3

9. What is the process of
glycolysis????

10. Glycolysis
• Process takes place in the cytosol of the
cytoplasm outside of mitochondria; coverts
glucose with the help of 2 ATP molecules and
eventually releases 4 ATP molecules; for a net
gain of 2 ATP molecules.

12. ATP & NADH
production in
Glycolysis
Step 1: breaks 1 molecule of glucose in
half, producing 2 molecules of pyruvic
acid (a 3-carbon compound)
Step 2: 2 NAD+ ;electron carrier accepts
4 high-energy electrons and transfers them
to 2 NADH molecules and 2 H+ thus
passing the energy stored in the glucose
Step 3: 4 ADP added producing 4 ATP
Step 4: 2 remaining pyruvic acids enter
Krebs Cycle in presence of oxygen; IF
no oxygen another pathway is followed
NAD+ (nicotinamide adenine dinucleotide)
2 NADH
& 2 H+
produced
2 ATP
used up
become
2 ADP
4 ATP
produced
Net gain =
2 ATP

13. • Glycolysis is a fast process
• Cells produce thousands of ATP molecules in a few
milliseconds
• Glycolysis alone DOES NOT require oxygen
– It can supply chemical energy to cells when oxygen is NOT
available
However if a cell generates large amounts of ATP from
glycolysis it can run into problems
a. the cell’s available NAD+ molecules become filled
up with electrons
b. glycolysis shuts down, cannot proceed without
available NAD+ molecules
c. ATP production stops

14. Anaerobic to Aerobic Respiration
• Glycolysis evolved before the other stages
of cellular respiration; other stages need
oxygen
• No oxygen in Earth’s atmosphere when
life first evolved about 3.5 to 4 b.y.a.
• Without oxygen  anaerobic respiration
• 2 or 3 billion years ago, oxygen was
gradually added to the atmosphere by
early photosynthetic bacteria; period the
“oxygen catastrophe” aerobic organisms

15. Let’s look at the
pathway that follows
gycolysis with the
presence of oxygen…..
aerobic respiration

16. BUT FIRST…Mitochondrion
Structure
• Mitochondrion has two separate membranes:
inner and outer membrane.
• Three compartments: intermembrane space,
cristae space, and matrix

17. AEROBIC RESPIRATION:
The Krebs Cycle and Electron Transport
• End of glycolysis 90% of chemical
energy from glucose still unused, locked in
high-energy electrons of pyruvic acid
• Extracted by world’s most powerful
electron receptor
• Krebs and Electron Transport require
oxygen thus they are aerobic processes
OXYGEN

18. The Krebs Cycle
1. 2nd stage of cellular respiration
2. Named after Hans Krebs, British
biochemist in 1937
3. Here pyruvic acid is broken down
into carbon dioxide in a series of
energy-extracting reactions
4. Citric acid is the 1st compound
formed in this series of reactions,
so Krebs is sometimes called the
Citric or Citric Acid Cycle.

19. Pyruvic acid enters from glycolysis;
One carbon removed = CO2 formed
NAD+ again changed to NADH
CoA joins remaining 2 carbons =
Acetyl-CoA
Acetyl-CoA added to 4 carbon
Compound = Citric acid (6-C)
Citric acid broken down to 5-carbon
then 4 carbon; more CO2 released
Along the way more NADH and
FADH2 formed
One molecule of ATP also made
2 turns & 2 pyruvic acid (from
glycolysis)
yield:
10 NADH (2 from glycolysis)
2 FADH2
4 ATP (2 from glycolysis)
Cycle starts anew

20. Uses for the products of the Krebs
Cycle
• Carbon dioxide is exhaled (waste product)
• ATP can be used for cellular activities
• High-energy electrons (stored in NADH &
FADH2) can be used to make huge
amounts of ATP in the presence of oxygen

21. 1. Electrons from Krebs cycle are passed to electron transport chain by NADH
& FADH2
2. At end of the chain an enzyme combines electrons from the electron chain
with H+ ions and oxygen to form water
3. Each time 2 high-energy electrons transport down the electron
chain, their energy is used to transport H+ ions across the membrane
4. H+ ions build up in intermembrane space it is now positively charged,
other side of membrane negatively charged (DISPLAY)
5. Electrochemical gradient (chemiosmotic gradient) created for ATP
synthase to work (OFF)
6. ATP synthase converts ADP into ATP (DISPLAY)

22. The Total ATP production of Aerobic CR
• How much chemical energy comes from one
molecule of glucose??
– Absence of oxygen:
• Only 2 ATP molecules from glycolysis
– Presence of oxygen:
• 2 net ATP molecules from glycolysis
• 36 more ATP molecules from Krebs Cycle and electron
transport
These 38 ATP molecules represent 38% of the total energy
of glucose, remaining 62% is released as heat, thus your
body feels warmer after vigorous exercise and does not
freeze in winter.

23. Let’s look at the
pathway that follows
gycolysis without the
presence of oxygen…..
anaerobic respiration

24. Anaerobic Respiration:
Fermentation
This occurs after glycolysis when oxygen absent, thus
anaerobic process
• Fermentation releases energy from food
molecules in absence of oxygen
– In this process cells convert NADH to NAD+ by
passing high-energy electrons back to pyruvic acid
– Now glycolysis has NAD+ and can continue
producing ATP
– There are 2 types of fermentation:
• Alcoholic fermentation
• Lactic acid fermentation

25. • Anaerobic and aerobic respiration share the
glycolysis pathway. If oxygen is absent,
fermentation may take place, producing lactic
acid or ethyl alcohol and carbon dioxide.
Products of fermentation still contain chemical
energy, and are used widely to make foods and
fuels.

26. Alcoholic Fermentation
1. Yeast and a few other microorganisms use
alcoholic fermentation, forming ethyl alcohol
and carbon dioxide as wastes
2. Equation for alcoholic fermentation:
pyruvic acid + NADH  ethyl alcohol + CO2 + NAD+

27. Lactic Acid Fermentation
1. Many cells convert accumulated pyruvic acid from gycolysis
to lactic acid; lactic acid fermentation regenerates NAD+ so
glycolysis can continue
2. Equation for lactic acid fermentation:
pyruvic acid + NADH  lactic acid + NAD+
4. When your body cannot supply enough oxygen to muscle
tissues during exercise, this is produced
5. Without oxygen the body is unable to produce all the ATP it
requires, so lactic acid fermentation takes over

28. Running, swimming, or riding a bike as fast as you can =
large muscles in your legs and arms that quickly run
out of oxygen…muscles begin to rapidly produce ATP
by lactic acid fermentation.
The buildup of lactic acid fermentation causes a painful
burning sensation making your
muscles feel sore…
How do you stop it?????
NEED TO INTAKE OXYGEN

29. Energy and Exercise
• Initially body uses ATP which is already available in
muscles
• Then new ATP made by Lactic Acid Fermentation and
Cellular Respiration
• Eventually energy supply runs out
A. Quick Energy
1. ATP in muscles only lasts a few seconds
2. ATP from lactic acid fermentation lasts
about 90 seconds
- this then creates a by-product (lactic acid)
which the body must get rid of, the body
releases it by panting heavily (intake of oxygen)

30. B. Long-Term Energy
- exercise lasting longer than 90 seconds utilizes
cellular respiration to generate a continuous supply
of ATP
- cellular respiration releases energy slower than
fermentation, thus athletes can pace themselves
- body stores energy in muscles and tissues in the
form of glycogen (carbohydrate)
-- stores of glycogen usually lasts for 15-20 minutes
of activity, then the body starts to break down
other molecules like fat for energy
HOW LONG DO YOU NEED TO ACTIVE BEFORE
YOU START TO BURN FAT????? 17-22 minutes

31. Aerobic vs. Anaerobic
Respiration: A Comparison
• Advantages of Aerobic Respiration
• Major advantage  more energy released
• Enough energy to produce up to 38 ATP
• Advantages of Anaerobic Respiration
• Lets organisms live in places where there
is little or no oxygen
• Quickly produces ATP

32. Relationship between Cellular Respiration and
Photosynthesis
Equation for Cellular Respiration:
6O2 + C6H12O6  6CO2 + 6H2O + energy (ATP)
Equation for Photosynthesis:
6CO2 + 6H2O + energy (sunlight)  6O2 + C6H12O6

34. LET’S REVIEW…
• How many stages does cellular respiration
have? ____________
• What are the stages of cellular respiration?
____________________________________
____________________________________
• Where does glycolysis take place?
____________________________________
• Where does the Krebs cycle take place?
___________________________________
3
GLYCOLYSIS, KREBS CYCLE, AND
ELECTRON TRANSPORT CHAIN
CYTOSOL OF THE CYTOPLASM OF MITOCHONDRIA
IN THE MATRIX OF MITOCHONDRIA

35. • Where is the Electron Transport Chain
located?
__________________________________
• What do high-energy electrons help the
cells build?
__________________________________
__________________________________
• What are the stage(s) of aerobic
respiration?
__________________________________
__________________________________
INNER MEMBRANE OF MITOCHONDRIA
MOLECULES LIKE GLUCOSE; ATP
GLYCOLYSIS, KREBS CYCLE, AND ELECTRON
TRANSPORT CHAIN

36. • What are the stage(s) of anaerobic
respiration?
__________________________________
__________________________________
• What are the two types of fermentation?
__________________________________
__________________________________
• Which fermentation process do humans
use?
__________________________________
GLYCOLYSIS, FOLLOWED BY FERMENTATION
ALCOHOLIC FERMENTATION AND
LACTIC ACID FERMENTATION
LACTIC ACID FERMENTATION

37. Lesson Summary
In the two to three billion years since photosynthesis added oxygen to
earth’s atmosphere, life has become mostly aerobic. Some organisms
and types of cells retain the older, anaerobic pathways for making ATP;
these pathways comprise anaerobic respiration or fermentation.
• Muscle cells can continue to produce ATP when O2 runs low using
lactic acid fermentation, but muscle fatigue and pain may result.
• Both alcoholic and lactic acid fermentation pathways change
pyruvate in order to continue producing ATP by glycolysis.
• Aerobic respiration is far more energy-efficient than anaerobic
respiration.
• Aerobic processes produce up to 38 ATP per glucose. Anaerobic
processes yield only 2 ATP per glucose.