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Section 1
Cellular Energy
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.
Section 1
Cellular Energy
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.
Section 1
Cellular Energy
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.
Section 1
Cellular Energy
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
Section 1
Cellular Energy
How Organisms Obtain Energy
ATP: The Unit of Cellular Energy
 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
Section 2
Cellular Energy
Photosynthesis
Overview of Photosynthesis
 Photosynthesis occurs in two phases.
 Light-dependent reactions
 Light-independent reactions
Section 2
Cellular Energy
Photosynthesis
Phase One: Light Reactions
 The absorption of light is the first step in
photosynthesis.
 Chloroplasts capture light energy.
Section 2
Cellular Energy
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, H+ into the
thylakoid space, and O2 as a waste product.
Section 2
Cellular Energy
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.
Section 2
Cellular Energy
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.
Section 2
Cellular Energy
Section 2
Cellular Energy
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.
Section 2
Cellular Energy
Section 2
Cellular Energy
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.
Section 2
Cellular Energy
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.
Section 2
Cellular Energy
Photosynthesis
Alternative Pathways
 C4 plants
 CAM plants
Section 3
Cellular Energy
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.
Section 3
Cellular Energy
Cellular Respiration
 Cellular respiration occurs in two main parts.
 Glycolysis
 Aerobic respiration
Section 3
Cellular Energy
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.
Section 3
Cellular Energy
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.
Section 3
Cellular Energy
Cellular Respiration
 The net yield from the
Krebs cycle is six CO2
molecules, two ATP,
eight NADH, and two
FADH2.
Section 3
Cellular Energy
Section 3
Cellular Energy
Cellular Respiration
Electron Transport
 Final step in the breakdown of glucose
 Point at which ATP is produced
 Produces 24 ATP
Section 3
Cellular Energy
Cellular Respiration
Anaerobic Respiration
 The anaerobic pathway that follows glycolysis
 Two main types
 Lactic acid fermentation
 Alcohol fermentation
Cellular Respiration