Cellular Energy
Photosynthesis & Respiration
Part 2: Cellular Respiration
How are photosynthesis and respiration linked?
Energy

Why do living things need energy?
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Reproduction
Repair
Growth and development
Movement
ATP – Adenosine Triphosphate

The most usable form of chemical energy in the
body.
ATP is made during cellular respiration. A
molecule of ADP (adenosine diphosphate) is
joined with a phosphate group to make ATP
(an anabolic reaction).
 ATP has a great deal of energy in it because of
the 3 phosphate groups. These groups are all
negative. It takes a lot of energy to hold the 3
negative groups next to each other. When 1
phosphate is separated from the group of 3,
ATP is converted back into ADP and energy
that was in the bond is released (a catabolic
reaction).
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Cellular Respiration

It is the process that converts the chemical energy stored in the bonds
of glucose into chemical energy cells can use (ATP); produces 36-38
ATP
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Equation:
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Reactants: The 6 O2 molecules come from the air. They were put
there by photosynthetic organisms. The C6H12O6 comes from being
generated during photosynthesis. Autotrophs will use the food that
they made. Heterotrophs will consume the glucose.

Products: The CO2 and the H2O are released into the atmosphere.
Most of the energy in glucose is going to be lost as heat (~60%) while
some (~40%) is transformed into ATP for the organism to use.

Occurs in the CYTOPLASM and the MITOCHONDRIA
C6H12O6 + 6O2 ---> 6CO2 + 6H2O + energy (ATP + heat)
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First step occurs in the cytoplasm (Glycolysis); 2nd (Krebs Cycle)
and 3rd (Electron Transport Chain) steps occur in the mitochondria
(In eukaryotic)

Utilized by ALL aerobic eukaryotic organisms (plants, algea, animals)

If an organism is anaerobic, it will perform glycolysis and then
fermentation
Glycolysis – 4 ATP (Net gain 2 ATP)

This is the first step in cellular respiration. It does
not require oxygen to occur (anaerobic). This step
occurs in the cytoplasm of cells.

Here, glucose will undergo a series of reactions
that converts the molecule into two 3-carbon
molecules called pyruvic acid (pyruvate).
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The process will require the use of 2 ATP
molecules.
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The process will make 4 ATP molecules.
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Therefore, the net gain from glycolysis is 2 ATP
molecules.

The process also make 2 molecules of NADH
from 2 molecules of NAD+.
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Reactants: Glucose + 2 ATP + 2 NAD +
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Products: 2 Pyruvic Acids + 4 ATP + 2 NADH

If an organism is going to use oxygen, an aerobic
organism, they will take the 2 molecules of
pyruvic acid to the mitochondria for the Krebs
cycle. If an organism does not use oxygen, an
anaerobic organism, they will continue in the
cytoplasm using fermentation.
Anaerobic Respiration: Fermentation – 0 ATP
No ATP is made during the process of fermentation. The entire purpose of
fermentation is regenerate NAD+ to perform glycolysis again.
Alcoholic Fermentation
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Used by single-celled
organisms, such as yeast cells
Glucose is broken down by
glycolysis, making 2 pyruvic
acid molecules and 2 NADH
molecules.
Through the use of the energy
in NADH, pyruvate is broken
down into CO2 and ethyl
alcohol. The NADH is
converted back into NAD+ to
be used again in glycolysis.
Lactic Acid Fermentation
Occurs
in your muscle cells
when oxygen is not available
Glucose is broken down by
glycolysis, making 2 pyruvic
acid molecules and 2 NADH
molecules.
Through the use of the energy
in NADH, pyruvate is further
broken down and produces the
waste product of lactic acid,
which causes muscle soreness.
The NADH is converted back
into NAD+ to be used again in
glycolysis.
Cellular Respiration – Major Steps
 After
glycolysis, aerobic organisms that have access to
oxygen, will use the Krebs cycle and the electron
transport chain.
 Prokaryotes:
Happens in the cytoplasm and the cell
membrane
 Eukaryotes:
Happens in the mitochondria
 Krebs
Cycle: The oxidation of glucose that began in
glycolysis is completed.
 Electron
Transport Chain (ETC): NADH and FADH2
(energy carriers) are used to make ATP. Oxygen is
used at this step.
Mitochondrion
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Organelle where aerobic
respiration occurs (oxygen
is needed).
The Krebs cycle happens in
the matrix (fluid) of the
mitochondria.
The ETC happens in the
inner membrane of the
mitochondria.
The inner membrane is
highly folded. It is called the
cristae. The cristae allow
for more electron transport
chains to be in the
mitochondria in a smaller
space.
Kreb’s Cycle (Citric Acid Cycle) – 2 ATP
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Happens in the matrix of the
mitochondria. Pyruvic acid diffuses
through the double membrane into
the matrix.
Here, the 2 pyruvic acid molecules
will undergo a series of reactions.
The end result is that the pyruvic
acid is broken down into 6 CO2.
Reactants: 2 Pyruvic Acid + 8 NAD+
+ 2 FAD + 2 ADP
Products: 6 CO2 + 8 NADH + 2
FADH2 + 2 ATP
Only produced 2 ATP in this step.
Most of the energy of glucose is now
trapped in the energy carriers
FADH2 and NADH.
The Electron Transport
Chain – 34 ATP

Embedded in the inner membrane of
the mitochondria.

Electrons in the NADH and FADH2 have
a lot of energy. The electrons transfer
into the chain.

As they pass through the chain, they
use their energy to pull H+ out of the
matrix creating a concentration
gradient.

This drives chemiosmosis to create
ATP by using ATP synthase located in
the membrane.

At the end, the electrons that were
moving through the chain are accepted
by a molecule of O. They also combine
with two molecules of H+ and makes
water.

The energy in NADH and FADH2 make
34 ATP molecules in this step.
The Importance of Oxygen


It is the final acceptor of the
electrons as they move through the
chain.
If the electrons had no where to go,
then they would build up in the
chain, and the chain could not work
again.
The End
At the end, 36-38 molecules of
ATP have been made.
 About 40% of the energy in
glucose is converted into ATP by
the end of all 3 processes. (20x
more efficient than glycolysis
alone).
 The remaining energy is being
lost as heat.
 Cellular Respiration:

C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O + energy

Photosynthesis
6 CO2 + 6 H2O + light energy ---> C6H12O6 + 6 O2