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Chapter 9
Section 1: Chemical Pathway
Food
 We all need food
 Provides
organisms with
building blocks
for growth and
reproduction
 Provides energy
Chemical Energy and Food
 How much energy in
food?
 1 gram glucose =
3811 calories of heat
energy
 Calorie- amount of
energy needed to
raise the
temperature of 1
gram of water 1
degree Celsius
 1 kilocalorie = 1
Calorie = 1000
calories
Chemical Energy and Food
 Cells don’t
“burn” glucose
 They release the
energy from
glucose and other
food products
Cellular Respiration
Chemical Energy and Food
 Cellular respiration
begins with glycolysis
 Releases small
amount of energy
 Oxygen must be
present
 Will lead to one of
three pathways
depending on the
presence of oxygen
Overview of Cellular Respiration
 In oxygen environment
 Glycolysis  Krebs
Cycle  electron
transport chain
 Equation:


6O2 + C6H12O6  6CO2 +
6H2O + energy
Controlled reaction

Otherwise we would
burst in flames
Glycolysis
 One molecule of
glucose is broken
in half, producing
two molecules of
pyruvic, a three
carbon compound
Glycolysis
 Occurs in cytoplasm
 Needs 2 ATP to jumpstart the
reaction
 Center bond of glucose is broken
 Energy harvested and used to
make ATP
 Energized electrons harvested
and used to make NADH
 Two 3 carbon molecules are
produced...pyruvate
 Very fast


1000s of ATP in milliseconds
NAD+ supply limits production
Glycolysis
 In oxygen
 To Krebs cycle
 To be discussed
next section
Krebs Cycle
 Without oxygen
Alcoholic
Fermentation
 Alcoholic
fermentation
 Lactic acid
fermentation
Fermentation
 Releases energy from
food by producing
ATP without oxygen
 Therefore
considered
anaerobic
 Changes NADH to
NAD+
 The electrons then
go back to
glycolysis
 Allows glycolysis
to continue
Alcoholic Fermentation
 Yeasts
 Breads- cause it to
rise, making small
bubbles of CO2, any
alcohol evaporates as
bread is baked.
 Few other microbes
 Produces ethyl alcohol
and carbon dioxide
 Equation:
 Pyruvic acid + NADH
 alcohol + CO2 +
energy
Lactic Acid Fermentation
 Occurs in many cells
(prokaryotes and
eukaryotes), even
humans (muscle
cramps)
 Equation:
 Pyruvic acid + NADH
 lactic acid + NAD+
 Used to make many
food products