Ch. 9 Outline
I. Energy
A. Energy is the ability to do work
B. Work is the ability to change or move matter.
1. Examples of work: growth, repair, and movement.
C. Autotrophs use the energy from the sun to make food from water and carbon dioxide. The
food is called glucose.
1. Autotrophs account for 10% of the living organisms on the Earth.
2. The food made that cannot be used by the autotroph is stores and other then used
by other organisms.
3. Some autotrophs use chemosynthesis.
D. Heterotrophs are organisms that cannot make their own food. They obtain their food by
eating autotrophs or other heterotrophs.
1. Much of the energy obtained from the food eaten is lost as heat.
II. ATP and energy transfer
A. Energy is stored in chemical bonds. The energy storage molecule is known as ATP (adenosine
triphosphate)
B. Energy that is released from the breakdown of food is stored in ATP molecules. Energy that
is not used is stored then as fat or starch. In order to be used again it must be converted to ATP.
C. ATP is made of three major parts:
1. ribose- a 5 carbon sugar
2. adenine- a nucleotide also found in DNA or RNA
3. phosphate- actually, three phosphates form a triphosphate group
D. Ribose bonds with adenine to form adenosine. The triphosphate bonds to the adenosine.
E. When the bonds in the molecule are broken, the energy that is stored in the bonds is
transferred to other reactions.
1. The enzyme ATPase breaks a phosphate off the end of the ATP. Now there are only
two phosphates and the molecule is called ADP. The breaking of the bond releases
energy
2. There are no phosphates left and no more energy that can be released. ADP is then
used to add another phosphates to recharge the molecule.
F. Some molecules just exchange energy instead of storing it. The reactions in which energy is
exchanged is called reduction reactions. Reduction is the addition of electrons to an atom or
ion. (Adding an electron reduced the charge of the atom since an electron is negative)
1. A hydrogen ion (H+) is also added to the reaction to balance the charge.
2. When an electron is added and a molecule is reduced, the molecule gains energy.
When a proton is added (H+), the molecule loses energy. This is called oxidation.
3. There is a series of gains and losses of energy (and electrons). These reactions are
then called redox reactions.
MG
+
S

Mg2+ +
oxidized
S2reduced
III. Glycolysis and aerobic respiration
A. The process by which food molecules are broken down to release energy for work is called
cellular respiration. The reaction for cell respiration is the opposite of photosynthesis.
B. Glycolysis is the process by which glucose is converted into pyruvate and energy is released.
This process occurs in the cytoplasm.
Glucose (6C) 2 phosphoglyceraldehyde (3C) + 2 ATP ---> 2 pyruvate + NADH
1. Glucose is split into two 3 carbon molecules called PGAL which is then changed into
pyruvate. The cell needs to spend two molecules of ATP to start the reaction.
2. In the end, a net of two ATP are produced and two molecules of NAD+ are reduced
to form NADH. The NADH will go on later to make ATP.
3. So far, we have only broken down 2% of the total energy found in a glucose
molecule. The pyruvate will have to be broken down to obtain the rest. If there is
enough oxygen, it will be broken down by aerobic respiration.
C. Aerobic respiration- the breakdown of pyruvate in the presence of oxygen. Carbon dioxide,
water, and energy will be formed.
1. This process occurs inside the mitochondria.
2. The process can be divided into two parts: The Krebs cycle and the electron
transport chain
3. Krebs cycle
4. From the Krebs cycle and glycolysis, one glucose molecule produces 4 ATP, 10 NADH,
and 2 FADH2. One molecule of glucose also produces 2 acetyl-CoA (therefore the Krebs
cycle happens twice).
D. Electron Transport
1. Energy still remains in a form the cell cannot use. This is in the form of NADH and
FADH2.
2. In order to use this energy, it must first be converted to ATP.
3. Energy is transferred from electron carriers to ATP along the electron transport
chain.
a. This occurs along the inner membrane of the mitochondrion.
b. Electrons move from a high energy level (NADH and FADH2) to a low level
final acceptor. This passage of electrons pumps hydrogen across the inner
membrane. The amount of H+ increases on one side. When it is diffused
through a special protein, ADP is converted to ATP.
c. Electron transport provides 90% of the ATP during aerobic respiration.
d. Oxygen is the final electron acceptor. It is reduced by NADH and forms
water. The NAD+ and FAD are now available to pick up more electrons. If there
is no oxygen available, there will be no final electron acceptor, and ATP is no
longer produced.
4. A total of 36 ATP are produced by aerobic respiration.
IV. Anaerobic respiration- chemical reactions that release energy from food molecules in the absence of
oxygen. Organisms live on the small amount of energy provided by glycolysis. Therefore, only 2 ATP
molecules can be used for energy.
A. Alcohol fermentation- pyruvate is converted to carbon dioxide and ethanol.
1. The NADH is recycled to NAD+ for reuse in glycolysis.
2. Importance: bread baking (CO2 is released and trapped in the bread causing the
bread to rise and the alcohol evaporates), making wine and beer, making ethanol for
auto fuel.
B. Lactic acid fermentation- pyruvate is converted to lactic acid.
1. During strenuous activity, breathing does not give your body enough oxygen to
continue aerobic respiration. The cells then switch to lactic acid fermentation. The
NADH is also converted back to NAD+.
2. Lactic acid fermentation causes muscle fatigue. The lactic acid diffuses into the
bloodstream and is converted back to pyruvate in the liver.