CHAPTER 9 - CELLULAR
RESPIRATION
CELLULAR RESPIRATION
Process that releases energy by
breaking down food molecules in the
presence of oxygen
6 O2 + C6H12O6 --> 6 CO2 + 6 H20+ATP
oxygen + glucose --> carbon dioxide
+ water + energy
3 Stages of Cellular Respiration
1. Glycolysis
2. Krebs Cycle
3. Electron Transport Chain
Each stage captures some of the
chemical energy available in food
molecules and uses it to produce
ATP
Energy Molecules of Cellular
Respiration
In cellular respiration, several
molecules are used as energy
carriers. These molecules carry
energy from one step of cellular
ADP + P = ATP
NAD + H = NADH
FAD+ + H2 = FADH2
GLYCOLYSIS
Glycolysis – First step in
releasing the energy of glucose.
A molecule of glucose is broken
into two molecules of pyruvic
acid (a 3-carbon compound).
–takes place in the cytoplasm
–does not require oxygen anaerobic
GLYCOLYSIS
Requires: 1 Glucose molecule
(C6H12O6), 2 ATP
Produces: 2 ATP, 2 NADH and 2
pyruvic acid
Second Stage: Fermentation or
Krebs Cycle
Glycolysis can be followed by
fermentation or the Krebs cycle
depending if oxygen is present.
– Fermentation will occur if no oxygen is
present.
– Krebs Cycle will occur if oxygen is
present.
Glycolysis
Anaerobic
(no oxygen)
Fermentation
Aerobic
(oxygen)
Krebs
Cycle
Without Oxygen - Fermentation
Anaerobic - without the presence of
oxygen
Fermentation - releases energy from
food molecules in the absence of
oxygen
two types: Alcoholic and Lactic Acid
Fermentation
Occurs in the cytoplasm
Types of Fermentation
Alcoholic - causes bread to rise, used
to make beer and wine
Lactic Acid - produced in muscles
during rapid exercise when body
can’t supply enough O2
– causes painful, burning sensation and
muscle soreness
With Oxygen - Kreb’s Cycle
Aerobic - in the presence of oxygen
Kreb’s Cycle also called Citric Acid
Cycle
Kreb’s Cycle - 2nd stage of cellular
respiration, in which pyruvic acid is
broken down into CO2 in a series of
energy-extracting reactions,
creating energy molecules.
– Occurs in the mitochondria
Kreb’s Cycle
Requires: 1 Pyruvic Acid
Produces: CO2, NADH, FADH2, ATP
Kreb’s Cycle
As a pyruvic acid molecule enters the
mitochondria, a carbon is removed,
forming CO2.
Carbons continue to be rearranged,
releasing more CO2, while allowing
the energy carriers to be charged.
This cycle will happen twice for every
molecule of glucose broken down in
glycolysis.
Third Stage: Electron Transport
Chain
The electron transport chain uses the
high-energy electrons from the Krebs
cycle to convert ADP into ATP.
– Occurs in the mitochondrial matrix.
Electron Transport Chain
(ETC)
Requires: NADH, FADH2, ADP
Produces: H2O, NAD, FAD, ATP
Electron Transport Chain
1. The Krebs Cycle generates highenergy electrons that are passed to
NADH and FADH2.
2. The high-energy electrons (H+)
from NADH and FADH2 are used up
and passed along the proteins in the
ETC.
Electron Transport Chain
3. Oxygen serves as the final electron
acceptor forming a water molecule.
4. As H+ ions move through the ETC,
ATP synthase spins adding ADP to P
forming ATP.
Cellular Respiration Totals
1 molecule of glucose produces:
– 2 ATP in glycolysis
– 34 ATP in Kreb’s Cycle and Electron
Transport Chain
– water
– CO2
Types of Energy
Quick Energy - Muscles only contain enough
ATP for a few seconds of intense activity.
Then, muscle cells produce their ATP by
lactic acid fermentation.
Long Term Energy - Cellular Respiration is
the only way to generate a continuing
supply of ATP
– energy is released more slowly than
fermentation, which is why athletes have to pace
themselves
– 15 to 20 min. of activity from carbohydrate
stored in the body
– after 20 min., energy comes from break down of
fats
Photosynthesis vs. Respiration
Photosynthesis and cellular respiration
take place in opposite directions!
Photosynthesis: Use light energy to build a sugar.
carbon dioxide + water + light energy → sugars
+ oxygen
Respiration: Break down sugar to release energy.
oxygen + sugars → carbon dioxide + water +
energy
Photosynthesis vs. Respiration
Photosynthesis:
– Use light energy to
build a sugar.
– Process that “deposits”
or captures energy.
– Removes carbon
dioxide from the
atmosphere.
– Releases oxygen into
the atmosphere.
Photosynthesis vs.
Respiration
Respiration:
– Break down sugar to
release energy.
– Process that
“withdraws” or
releases energy.
– Removes oxygen from
the atmosphere.
– Releases carbon
dioxide into the
atmosphere.