CELLULAR RESPIRATION Harvesting Chemical Energy

Harvesting Chemical Energy
Producers and Consumers
• A tiny fraction of a
tiny fraction
• Light powers life
• Light energy from sun
powers the chemical
process that makes
organic molecules
• Called photosynthesis
Producers and Consumers cont.
• Autotrophs – plants and
other self-feeders who can
make all their organic
• Plant nutrients are all
• Heterotrophs – organisms
that cannot make organic
molecules from inorganic
Producers and Consumers
• Producers – plants and
other autotrophs
• Consumers –
heterotrophs who
obtain food by eating
plants or eating
animals that have
eaten plants
Chemical Cycling
• Substrates for
photosynthesis are carbon
dioxide and water
• Products of cellular
respiration are carbon
dioxide and water
• Substrates of cellular
respiration are the
products of photosynthesis
Cellular Respiration
Aerobic Harvest of Food Energy
• A cell requires oxygen to
break down its fuel
• So cellular respiration is
an aerobic process
• Respiration requires a cell
to exchange 2 gases – O2
and CO2- with the
• Breathing requires body to
exchange 2 gases with
Equation – cellular respiration
• Glucose – main fuel for respiration
• Oxygen required
• Products are carbon dioxide, water and energy –
Role of Oxygen in cellular
• Cellular respiration transfers electrons from sugar to
oxygen forming water
• Also transfers hydrogen ions from glucose to oxygen
forming water
Redox Reactions
• Oxidation – reduction reactions transfer electrons from 1
substance to another
• Redox reactions
• Oxidation – loss of electrons
• Reduction – acceptance of electrons
Redox Reactions cont.
• Glucose is oxidized
during cellular
respiration losing
electrons to oxygen
• Oxygen is reduced
during cellular
respiration accepting
electrons and
hydrogen from
Redox Reactions cont.
• When hydrogen and
its bonding electrons
change partners from
sugar to oxygen
energy is released
• Cellular respiration
unlocks chemical
energy in small steps
Cellular Respiration
• 3 stages of respiration
occur in cells
• Glycolysis, Krebs
cycle, electron
transport chain
• Occurs in cytoplasm
• 6 carbon glucose split
into 2 molecules of 3
carbon pyruvic acid
• Must use 2 molecules
of ATP per glucose
but form 4 molecules
of ATP so have net
gain of 2 ATP
• The energy in the high
energy electrons from
the broken carbon
bonds is used to
reduce NAD+ to
Glycolysis cont.
• Most of energy in
glucose still in pyruvic
acid and this energy is
harvested in the Krebs
Krebs cycle
• Pyruvic acid must be
modified before entering
the Krebs cycle
• Krebs cycle uses a 2
carbon compound called
acetic acid
• Enters the cycle as acetylCoA
• Occurs in mitochondria
Krebs cycle cont.
• Pyruvic acid changed
to acetic acid by
removing 1 carbon
• More NAD+ reduced
to NADH as acetic
acid is attached to
Coenzyme A to make
Krebs Cycle cont.
• 2 carbon from pyruvic
acid now present in
acetic acid attached to
acetyl-CoA enters
Krebs cycle
• Both carbons are
removed 1 at a time
and carbon dioxide is
Krebs Cycle cont.
• Small amount of ATP
is formed in Krebs
• Much more NAD+ is
reduced to NADH
• A 2nd electron carrier
is formed FADH2
• Starting molecules are
Krebs Cycle cont.
• At end of Krebs cycle
all carbons in glucose
are now in carbon
• Energy from breaking
of bonds in glucose
molecule now in high
energy electrons
attached to NADH and
Electron Transport
• In glycolysis and the
Krebs cycle NAD+
was reduced to NADH
• Now the NADH is
oxidized back to
NAD+ and the
electrons are passed to
a chain of proteins
called the electron
transport chain
Electron Transport cont.
• Energy in high energy
electrons is not used
directly to synthesize
• Energy used to pump
hydrogen ions across
the inner
Electron Transport cont.
• Sets up a gradient of
hydrogen ions across
the inner
• This gradient has
potential energy due to
location behind the
Electron Transport cont.
• Hydrogen ions cannot
pass through the inner
membrane directly as
it is a lipid bilayer
• A protein complex in
the membrane called
ATP synthase acts as a
channel through the
Electron Transport cont.
• Electrons move down the
concentration gradient
through the ATP synthase
channel and the energy is
used to make lots of ATP
• Oxygen is the final
electron acceptor at the
end of the electron
transport chain
• Water is formed when
oxygen accepts electrons
and hydrogen ions
Cellular Respiration - Summary
• 3 stages
• Glycolysis in
cytoplasm starting
with glucose and
ending with pyruvic
acid little ATP but
some NADH
Cellular Respiration - Summary
• Krebs Cycle – in
• Pyruvic acid carbons
used to form carbon
dioxide and the high
energy electrons in the
bonds are used to
reduce NAD+ to
Cellular Respiration - Summary
• NADH and FADH2 are
oxidized in the
mitochondria back to
NAD+ and FAD and the
electrons are transferred to
a series of proteins which
are reduced and oxidized
• The energy in the high
energy electron bonds is
removed in small steps
Cellular Respiration - Summary
• The energy is used to
form a hydrogen ion
• The hydrogen ions can
only go down their
concentration gradient
through ATP synthase
• Many ATP are formed
as hydrogen ions pass
Cellular Respiration - Versatility
• Cellular respiration
can use a variety of
food molecules
• Each type of food
molecule enters the 3
stages of cellular
respiration at a
particular point.
Human muscle and
• When muscle cells
have insufficient
oxygen they still make
some ATP by
• Pyruvic acid is
converted to lactic
acid so NADH can be
oxidized back to
Fermentation - Microorganisms
• Microorganisms
produce ATP in the
absence of oxygen –
process produces
carbon dioxide and
ethyl alcohol
• NADH is reduced then