Chapter 8 Cellular Energy
Section 1: How Organisms Obtain Energy
Section 2: Photosynthesis
Section 3: Cellular Respiration
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Chapter 8
Cellular Energy
Overview of Cellular Respiration
 Organisms obtain energy in a process called
cellular respiration.
 The equation for cellular respiration is the
opposite of the equation for photosynthesis.
Chapter 8
Cellular Energy
Cellular respiration occurs in two main parts.
 Anaerobic respiration
- doesn’t require oxygen such as glycolysis.
 Aerobic respiration
- requires oxygen.
Chapter 8
Cellular Energy
Glycolysis
Glycolysis : is anaerobic process that breaks down
glucose in the cytoplasm
Chapter 8
Cellular Energy
Glycolysis ( In the Cytoplasm)
By referring to the adjacent figure
1) What happens during the first step
of glycolysis?
2) How many ATP is used when
glucose is transformed into 2 G3P
molecules?
3) How many ATP and NADH are
produced when G3P molecules
change into Pyruvate?
4) Calculate the total ATP and NADH
produced for one molecule of
glucose
Glycolysis ( In the Cytoplasm)
When ATP is converted to ADP 
6- carbon molecule is broken down into
3 carbon molecules (G3P).
Phosphates, electrons and hydrogen
ions are added to form ATP and NADH
molecules ( see fig)
Last the two 3 Carbon compounds are
converted into 2 molecules of pyruvate.
Net energy value : 2 ATP
( Produced : 4 ATPs – 2 ATPs used)
Chapter 8
Cellular Energy
Krebs Cycle
pyruvate breaks down into carbon dioxide in the
mitochondria
Chapter 8
Cellular Energy
Krebs Cycle
 Glycolysis has a net result of two ATP, 2
NADH and two pyruvate.
 Most of the energy from the glucose is
still contained in the pyruvate.
 The series of reactions in which pyruvate is
broken down into carbon dioxide is called the
Krebs cycle.
Prior to KREBS, pyruvate reacts with coenzyme A forming a 2
carbon molecule called : Acetyl CoA
Think : Knowing that pyruvate is a 3 carbon molecule and acetyl CoA is 2
carbon molecule. How can you explain the disappearance of 1 carbon from
pyruvate ?
Krebs begins when : Acetyl CoA combines
with 4 carbon compound to form 6- carbon
compound: citric acid
Citric acid is then broken down
into 5 carbon molecule and then
into 4 carbon molecule
- generating 1 ATP, 3 NADH and 1
FADH2
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 1 pyruvate generates 1 ATP, 4 NADH,
1 FADH2 and 3CO2
 Recall that 2 molecules of pyruvate
are formed during glycolysis
resulting in two turns of KREBS
cycle
SO
 The net yield from the Krebs cycle of 1
glucose molecule is six CO2
molecules, two ATP, eight NADH,
and two FADH2.
https://youtu.be/pNzFYBA2Ofg
Chapter 8
Cellular Energy
Electron Transport- Final step
 In aerobic respiration, electron transport
is the final step in the break down of
glucose .
 It is also the point at which most of ATP
is produced.
Chapter 8
Cellular Energy
Electron Transport- Final step
NADH and FADH are converted to NAD+ and FAD+ . As a result,
electrons and H+ ions are released.
 The electrons activate the proteins in the mitochondrial membrane.
 H + ions are released in the mitochondrial matrix.
Note : As electrons move in proteins embedded in the membrane, H+
ions are released to the intermembrane space
Electron Transport- Final step
• Oxygen is the final electron acceptor in the electron transport
system in cellular respiration , protons and electrons are
transferred to oxygen to form water.
• H+ ions move with the concentration gradient to the mitochondrial
matrix through an ion channel protein : ATP synthase
• As H+ ions cross the ATP synthase, ADP is converted to ATP. A
process known as chemiosmosis
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Electron Transport
 Final step in the breakdown of glucose
 Point at which ATP is produced
 Produces 32 ATP.
Net Value
 In eukaryotes, one molecule of glucose yields 36 ATP
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis
is called fermentation. It happens in cytoplasm
and generate the cell’s supply of NAD+ . It is
divided into two main types.
 1-Lactic acid fermentation
 2-Alcohol fermentation
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 Lactic acid fermentation:
skeletal muscles produce lactase when
the body cannot supply oxygen , such
as during periods of strenuous exercise
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 Alcohol fermentation, occurs in yeast and some bacteria .
Pyruvate is converted into ethanol and carbon dioxide.