Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Transformation of Energy
 Energy is the ability to do work.
 Thermodynamics is the study of the flow and
transformation of energy in the universe.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Laws of Thermodynamics
 First law—energy can be converted from one
form to another, but it cannot be created nor
destroyed.
 Second law—energy cannot be converted
without the loss of usable energy.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Autotrophs and Heterotrophs
 Autotrophs are organisms that make their
own food.
 Heterotrophs are organisms that need to
ingest food to obtain energy.
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
Metabolism
 All of the chemical reactions in a cell
 Photosynthesis—light energy from the Sun is
converted to chemical energy for use by the
cell
 Cellular respiration—organic molecules are
broken down to release energy for use by
the cell
Chapter 8
Cellular Energy
8.1 How Organisms Obtain Energy
ATP: The Unit of Cellular Energy (adenosine
triphosphate)
 ATP releases energy
when the bond between
the second and third
phosphate groups is
broken, forming a
molecule called
adenosine diphosphate
(ADP) and a free
phosphate group.
ATP
Chapter 8
Cellular Energy
8.2 Photosynthesis
Overview of Photosynthesis
 Photosynthesis occurs in two phases.
 Light-dependent reactions
 Light-independent reactions
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase One: Light Reactions
 The absorption of light is the first step in
photosynthesis.
 Chloroplasts capture light energy.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Electron Transport
 Light energy (excites electrons in
photosystem II and also)
 causes a water molecule to split,
releasing an electron into the electron
transport system (source of energy for the
reactions to occur
 H+ (a proton), which helps in the
production of ATP
O2 as a waste product (which we kinda
like)
Chapter 8
Cellular Energy
8.2 Photosynthesis
 The excited electrons move from
photosystem II to an electron-acceptor
molecule in the thylakoid membrane.
 The electron-acceptor molecule transfers the
electrons along a series of electron-carriers
to photosystem I.
Chapter 8
Cellular Energy
8.2 Photosynthesis
 Photosystem I transfers the electrons to a
protein called ferrodoxin.
 Ferrodoxin transfers the electrons to the
electron carrier NADP+, forming the energystoring molecule NADPH.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Phase Two: The Calvin Cycle
 In the second
phase of
photosynthesis,
called the Calvin
cycle, energy is
stored in organic
molecules such
as glucose.
Chapter 8
Cellular Energy
Chapter 8
Cellular Energy
8.2 Photosynthesis
 Six CO2 molecules combine with six 5-carbon
compounds to form twelve 3-carbon molecules
called 3-PGA.
 The chemical energy stored in ATP and
NADPH is transferred to the 3-PGA molecules
to form high-energy molecules called G3P.
Chapter 8
Cellular Energy
8.2 Photosynthesis
 Two G3P molecules leave the cycle to be used
for the production of glucose and other organic
compounds.
 An enzyme called rubisco converts the
remaining ten G3P molecules into 5-carbon
molecules called RuBP.
 These molecules combine with new carbon
dioxide molecules to continue the cycle.
Chapter 8
Cellular Energy
8.2 Photosynthesis
Alternative Pathways
 C4 plants
 CAM plants
The Importance of Pigments
Light absorbing pigments in plants are found in the
thylakoid membranes of chloroplasts
There are several kinds of chlorophyll that each
absorb a different wavelength of light (why could
this be important?)
In addition there are other accessory pigments such
as carotenoids that absorb light
The importance of the Thylakoid
structure
The thylakoid has a stacked structure to allow
more surface area and thus a more efficient
energy transfer during the electron transport.
The folded structure provides the space
needed to hold large numbers of electrontransporting molecules AND the protein
complexes called PHOTOSYSTEMS
(remember them, 1 & 2)
Chemiosmosis
This is the process in which ATP is made in
conjunction with electron transport
Chemiosmosis is the mechanism by which
ATP is produced as a result of the flow of
electrons down a concentration gradient
SO….
The water molecule going into electron
transport gives its electrons to photosystem
II (to make NADP into NADPH) and the H+
(proton) to make ATP (from ADP)
Chapter 8
Cellular Energy
8.3 Cellular Respiration
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
8.3 Cellular Respiration
 Cellular respiration occurs in two main parts.
 Glycolysis
 Aerobic respiration
Anaerobic versus Aerobic
Anaerobic processes do not require oxygen
The first stage of cellular respiration is
glycolysis, it is an anaerobic process
Aerobic processes require oxygen
respiration includes the Krebs cycle and
electron transport
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Glycolysis
 Glucose is broken down in the cytoplasm
through the process of glycolysis.
 Two molecules of ATP and two molecules
of NADH are formed for each molecule of
glucose that is broken down.
Glycolysis (breakdown)
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Krebs Cycle
 Glycolysis has a net result of two ATP 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.
The Krebs Cycle
Is also called:
Tricarboxylic acid cycle (TCA)
or
The Citric Acid Cycle
Chapter 8
Cellular Energy
8.3 Cellular Respiration
 The net yield from the
Krebs cycle is six CO2
molecules, two ATP,
eight NADH, and two
FADH2.
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Electron Transport
 Final step in the breakdown of glucose
 Point at which ATP is produced
 Produces 24 ATP
Chapter 8
Cellular Energy
8.3 Cellular Respiration
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis
 Two main types
 Lactic acid fermentation
 Alcohol fermentation
Cellular
Respiration
Fermentation
• There are two kinds of fermentation
• Fermentation is breaking down sugar without
oxygen
• In one type sugar breaks down into lactic
acid
C6H12O6  2 H+ + 2 C3H5O3-
Lactic Acid Fermentation
• This is done by your muscles when the
demand for ATP is high, but you are low in
oxygen. (while working out) This can cause
soreness in the muscles.
Alcoholic Fermentation
• sugar breaks down into
carbon dioxide and
ethanol
• C6H12O6  2 CO2 + 2 C2H5OH
• Ethanol is the active
ingredient in wine, beer
and spirits.
• The Carbon Dioxide
produced in this manner
can be used to allow
bread to rise