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Chapter 8
Cellular Energy
Section 1
How Organisms Obtain Energy
Section 1: How Organisms Obtain Energy
All living organisms use energy to carry out all biological processes.
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Transformation of Energy
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Cellular processes require energy – the ability to do work.
•
Thermodynamics is the study of the flow and transformation of energy in the
universe.
How Organisms Obtain Energy
Transformation of Energy
Laws of thermodynamics
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First law—the law of conservation of energy: energy can be converted from
one form to another, but it cannot be created nor destroyed.
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Second law: energy cannot be converted without the loss of usable energy,
that is, entropy—disorder or unusable energy--increases.
How Organisms Obtain Energy
Transformation of Energy
Autotrophs and Heterotrophs
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Directly or indirectly, nearly all the energy for life comes from the Sun.
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Autotrophs make their own food, either with energy from the sun or from
inorganic substances.
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Heterotrophs ingest other organisms to obtain energy.
How Organisms Obtain Energy
Metabolism
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All of the chemical reactions in a cell are referred to as the cell’s metabolism.
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A series of chemical reactions in which the product of one is the substrate for
the next is called a metabolic pathway.
• Catabolic pathways release energy by breaking down larger molecules.
• Anabolic pathways use energy to build larger molecules.
How Organisms Obtain Energy
Metabolism
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Photosynthesis – anabolic pathway in which light energy from the Sun is
converted to chemical energy for use by the cell
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Cellular respiration – catabolic pathway in which organic molecules are
broken down to release energy for use by the cell
How Organisms Obtain Energy
ATP: The Unit of Cellular Energy
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In living things, chemical energy is stored in biological molecules.
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Adenosine triphosphate (ATP) is the most important biological molecule that
provides chemical energy.
How Organisms Obtain Energy
ATP Crash Course
https://www.youtube.com/watch?v=
00jbG_cfGuQ
ATP: The Unit of Cellular Energy
ATP structure
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Most abundant energy-carrier in cells
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Nucleotide made of an adenine base, a ribose sugar, and three phosphate
groups
How Organisms Obtain Energy
ATP: The Unit of Cellular Energy
ATP function
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Releases energy when the bond between the second and third phosphate
groups is broken.
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Transforms into a molecule called adenosine diphosphate (ADP) and a free
phosphate group.
How Organisms Obtain Energy
ATP
• When chlorophyll absorbs light, it is absorbing
energy
bonds
• It stores it in the __________
of Adenosine
Triphosphate (ATP)
ATP, continued.
• Carbs are most commonly broken down to make ATP.
• Breakdown of glucose yields 36 ATP.
• ATP = Energy currency of the cell.
• Cells use ATP for functions such as building molecules &
moving materials by Active Transport.
• ATP releases energy when phosphate group released.
• Becomes Adenosine DiPhosphate (ADP).
– Can be converted back to ATP by adding phosphate.
ATP vs. ADP
ATP ADP Cycle
Video
• ATP
Essential Questions
•
What are the two laws of thermodynamics?
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What is the difference between an anabolic pathway and a catabolic
pathway?
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How does ATP work in a cell?
How Organisms Obtain Energy
Section 2
Photosynthesis
Section 2: Photosynthesis
Light energy is trapped and converted into chemical energy
during photosynthesis.
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Crash Course: Photosynthesis
https://www.youtube.com/watch?v=
sQK3Yr4Sc_k
Overview of Photosynthesis
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Most autotrophs make organic compounds using photosynthesis.
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Photosynthesis is the process of converting light energy into chemical
energy.
Photosynthesis
THE FORMULA, continued.
Overview of Photosynthesis
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Photosynthesis occurs in two phases.
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In the light-dependent phase, light energy is converted into chemical energy.
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In the light-independent phase, chemical energy used to synthesize glucose.
Photosynthesis
Bill Nye: Photosynthesis
https://www.youtube.com/watch?v=
pdgkuT12e14
Phase One: Light Reactions
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The absorption of light is the first step in photosynthesis.
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Once light energy is captured, it can be stored as ATP or NAPDH.
Photosynthesis
Phase One: Light Reactions
Chloroplasts
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Are organelles that capture light energy
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Contain two main compartments:
• Thylakoids: flattened saclike membranes
• Stacks of thylakoids are called grana.
• The fluid filled space outside the grana called the stroma
Photosynthesis
Chloroplast structure
Phase One: Light Reactions
Pigments
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Light-absorbing colored molecules called pigments are found in the thylakoid
membranes.
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Different pigments absorb specific wavelengths of light.
• Most common pigment in plants is chlorophyll.
• Plants also have accessory pigments.
Photosynthesis
Video
• Chlorophyll Borophyll
Phase One: Light Reactions
Electron transport
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The thylakoid membrane has a large surface area, providing space for a
large number of electron transporting molecules and two types of protein
complexes called photosystems.
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Photosystems house the light-capturing pigments.
Photosynthesis
Phase One: Light Reactions
Electron transport
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Light energy excites electrons in photosystem II.
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This light energy causes a water molecule to split – releasing an electron into
the electron transport system, a hydrogen ion (H+ or proton) into the
thylakoid space, and oxygen as a waste product.
Photosynthesis
Phase One: Light Reactions
Electron transport
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The activated electrons move from photosystem II to an acceptor molecule in
the thylakoid membrane.
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The electron acceptor molecule transfers the electrons along a series of
electron carriers to photosystem I.
Photosynthesis
Phase One: Light Reactions
Electron transport
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In the presence of light, photosystem I transfers the electrons to a protein.
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The protein transfers the electrons to the carrier molecule NADP+, forming
the energy storage molecule NADPH.
Photosynthesis
Phase One: Light Reactions
Electron transport
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ATP is produced in conjunction with the electron transport system through
chemiosmosis
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ATP is produced through the flow of electrons down a concentration gradient
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The breakdown of water provides the necessary protons for ATP synthesis
Photosynthesis
Phase Two: The Calvin Cycle (light independent reactions)
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In the second phase of photosynthesis, called the Calvin cycle, energy is stored
in organic molecules such as glucose.
Photosynthesis
Phase Two: The Calvin Cycle
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The first step of the Calvin cycle is called carbon fixation.
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CO2 molecules combine with 5-carbon molecules to form 3phosphoglycerate (3-PGA)
Photosynthesis
Phase Two: The Calvin Cycle
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In the second step, chemical energy stored in ATP and NADPH is transferred
to the 3-PGA to form glyceraldehyde 3-phospate (G3P).
Photosynthesis
Phase Two: The Calvin Cycle
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In the third step, some G3P molecules leave the cycle to be used for the
production of glucose and other organic compounds.
Photosynthesis
Phase Two: The Calvin Cycle
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In the fourth and final step, an enzyme called rubisco converts the remaining
G3P molecules into 5-carbon molecules called ribulose 1,5-bisphospates
(RuBP).
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These molecules combine with new CO2 and continue the cycle.
Photosynthesis
2 Main steps of PS - Summary
1. Light reactions—occurs only in the presence
light
of ___________
– Occurs in the grana (thylakoids) of the
chloroplasts
– Also known as Photolysis because light is used to
split _________
water
__________
molecules into hydrogen
and oxygen
2 Main steps of PS - Summary
or
2. Dark Reactions—can occur in light ____
darkness. Follows light reactions
– Occurs in the stroma of the chloroplasts
– Also known as Carbon fixation because CO will get
“fixed up” with the hydrogens and energy from
the light reaction
2
Light Reactions
Take place within the membrane of the
thylakoid.
1. Chlorophyll absorbs energy from sunlight.
broken _________
down
– Water is __________
released
– Oxygen is ______________
2. Oxygen leaves the plant and goes into the air
The Dark Reactions
Occur in stroma of chloroplasts.
CO2
1. _________ is added to a cycle of
reactions to build larger molecules
2. A molecule of simple sugar is
formed
glucose
– _____________
Video
• Summary of Photosynthesis
Alternative Pathways
C4 plants
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The C4 pathway allows plants to maintain photosynthesis while reducing
water loss.
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Significant structural modification in the arrangement of cells within the
leaves – separate CO2 uptake from location of Calvin cycle
Photosynthesis
Alternative Pathways
CAM plants
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Crassulacean acid metabolism (CAM) is found in desert plants.
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Collect CO2 at night and store it in organic compounds
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During the day, release CO2 from organic compounds for the light-dependent
cycle of photosynthesis
Photosynthesis
Bozeman Science:
Photosynthesis
https://www.youtube.com/watch?v=
g78utcLQrJ4
Essential Questions
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What are the two phases of photosynthesis?
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What is the function of a chloroplast during the light reactions?
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How can electron transport be described and diagramed?
Photosynthesis
Section 3
Cellular Respiration
Section 3: Cellular Respiration
Living organisms obtain energy by breaking down organic
molecules during cellular respiration.
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Crash Course: Cellular
Respiration
https://www.youtube.com/watch?v=
00jbG_cfGuQ
Overview of Cellular Respiration
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Organisms obtain energy in a process called cellular respiration.
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Respiration harvests electrons from organic molecules and uses the energy
to make ATP.
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The equation for cellular respiration is the opposite of the equation for
photosynthesis:
Cellular Respiration
Overview of Cellular Respiration
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Cellular respiration occurs in two main parts: glycolysis and aerobic
respiration.
• Glycolysis is an anaerobic process, meaning it does not require oxygen.
• Aerobic respiration involves the Krebs cycle and electron transport.
• Aerobic processes require oxygen.
Cellular Respiration
Glycolysis
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Glucose is broken down in the
cytoplasm through the process of
glycolysis.
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Two molecules of ATP and two
molecules of NADH are formed for
each molecule of glucose that is
broken down.
Cellular Respiration
Khan Academy: Glycolysis
https://www.youtube.com/watch?v=
FE2jfTXAJHg
Krebs Cycle
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Glycolysis has a net result of two ATP and two pyruvate.
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Most of the energy from the glucose is still contained in the pyruvate.
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In the presence of oxygen, pyruvate is transported into the mitochondrial
matrix, where it is converted into carbon dioxide.
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The series of reactions in which pyruvate is broken down into carbon dioxide
is the Krebs cycle, also know as the tricarboxylic acid (TCA) cycle
Cellular Respiration
Krebs Cycle
Steps of the Krebs cycle
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Prior to the Krebs cycle,
pyruvate reacts with coenzyme
A (CoA) to form acetyl CoA.
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Acetyl CoA moves into the
mitochondrial matrix.
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Acetyl CoA combines with a 4carbon compound to form citric
acid.
Cellular Respiration
Krebs Cycle
Steps of the Krebs cycle
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Citric acid is broken down
releasing two molecules of
carbon dioxide and generating
one ATP, three NADH, and one
FADH2.
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Finally, acetyl CoA and citric
acid are generated and the
cycle continues.
Cellular Respiration
Steps of Kreb’s
1.
2.
3.
4.
5.
6.
Pyruvate broken down
Coenzyme A
Citric acid formed
Citric acid broken down
5-carbon molecule broken down
4-carbon molecule rearranged
Up to 38 ATP molecules are made from the
breakdown of 1 glucose molecule.
Khan Academy: Kreb Cycle
https://www.youtube.com/watch?v=
juM2ROSLWfw
Video
• Kreb's cycle
Electron Transport
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In aerobic respiration, electron transport is the final step in the breakdown of
glucose.
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NADH and FADH2 from the Krebs cycle are used to convert ADP to ATP.
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Electron transport and chemiosmosis in aerobic respiration are similar to the
processes of photosynthesis.
Cellular Respiration
Electron Transport
Prokaryotic cellular respiration
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Some prokaryotes undergo aerobic respiration.
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They do not have mitochondria, so they use the cellular membrane as the
location of electron transport.
Cellular Respiration
Steps of ETC - Summary
1. Electrons removed – High energy electrons from
NADH & FADH2.
2. Hydrogen ions transported – High energy electrons
travel through the proteins in the ETC.
3. ATP Produced – ATP synthase adds phosphate
groups to ADP to make ATP. For each pair of
electrons that passes through the ETC, 3 ATPs are
made.
4. Water formed – Oxygen enters cellular respiration
process & picks up electrons & hydrogen ions to
form water.
Khan Academy: ETC
https://www.youtube.com/watch?v=
mfgCcFXUZRk
Anaerobic Respiration
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When oxygen is unavailable, cells cannot follow glycolysis with the aerobic
respiration (Krebs cycle and electron transport).
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The anaerobic process that follows glycolysis is anaerobic respiration, or
fermentation.
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Fermentation occurs in the cytoplasm of the cell, and produces NAD+ and
ATP.
Cellular Respiration
• Two types
Fermentation
Alcoholic
– _______________
fermentation
Lactic
acid
– __________
________ fermentation
Anaerobic Respiration
Lactic acid fermentation
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Enzymes convert the pyruvate made during glycolysis into lactic acid.
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Skeletal muscles produce lactic acid when the body cannot supply enough
oxygen, such as during periods of strenuous exercise.
Cellular Respiration
Anaerobic Respiration
Alcohol fermentation
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Occurs in yeast and some bacteria
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Converts pyruvate into ethyl alcohol and carbon dioxide
Cellular Respiration
Photosynthesis & Cellular Respiration
PHOTOSYNTHESIS
CELLULAR RESPIRATION
Organelle for process
Chloroplast
Mitochondrion
Reactants
CO2 & H2O
Sugars (C6H12O6) & O2
Electron Transport Chain
Proteins within thylakoid
membrane
Proteins within inner
mitochondrial membrane
Cycle of chemical
reactions
Calvin cycle in stroma of
chloroplasts builds sugar
molecules
Krebs cycle in matrix of
mitochondria breaks down
carbon-based molecules
Equation
Products
6CO2 + 6H2O
C6H12O6 + 6O2
Sugars (C6H12O6) & O2
C6H12O6 + 6O2
CO2 & H2O
6CO2 + 6H2O
Photosynthesis and Cellular Respiration
Cellular Respiration
Bozeman Science: Cellular
Respiration
https://www.youtube.com/watch?v=
Gh2P5CmCC0M
Essential Questions
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What are the stages of cellular respiration?
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What is the role of electron carriers in each stage of cellular respiration?
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What are the similarities between alcoholic fermentation and lactic acid
fermentation?
Cellular Respiration

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