Photosynthesis

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ENERGY System (CONT)
Photosynthesis Cellular Respiration
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Sun, Earth and Energy

• Lifeforms use the energy of the sun

• To organize the materials of the Earth

• Into themselves!

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Sun, Earth and Energy

• The foundation of this extraordinary process is
  photosynthesis.
• Carried out by plants, algae and others.

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• Name two types of organisms that carry out
  photosynthesis.

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Sun, Earth and Energy

• Without photosynthesis, the lifeforms we know,

and we ourselves,
would not grow from the materials of the Earth.
The great diversity of life on Earth would not
exist!
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The big picture
How does photosynthesis organize Earth materials
into life?

• Energy is needed to organize matter.
• In photosynthesis, energy from the sun

• is used to organize CO2 and H2O (basic Earth
  materials) into simple carbohydrates (sugars).

Molecules of life Proteins, nucleic acids,
carbohydrates, lipids
sugars
Suns energy CO2 H2O ? Glucose O2

• This is the beginning

• Enzyme pathways then reorganize the sugars into
  all the carbon-based molecules of life.

• These molecules make up the living cell.

• So the carbon-chain molecules (sugars) built in
  photosynthesis are the foundation of life.

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• What is needed to organize matter?
• In photosynthesis-
• What is the source of energy?
• What basic Earth materials are utilized?
• What is produced?
• Enzyme pathways reorganize the sugars produced by
  photosynthesis. What do the pathways produce?

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How does photosynthesis organize Earth materials
into life?
The molecules created by photosynthesis and by
enzyme pathways are life.

• Some are the actual structure and function of
  life.

• Examples Proteins, DNA, phospholipids

• Others are used to store energy.

Molecules of life Proteins, nucleic acids,
carbohydrates, lipids
sugars

• Examples Sugars, starches, oils

• Energy storage molecules are broken down later to
  release energy as needed

Structure/Function molecules
Energy molecules
This process is Cellular Respiration
Breakdown to release energy
Next slide
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What are the two basic purposes for the
carbon-based molecules produced by photosynthesis
and enzyme pathways?
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What does cellular respiration accomplish?
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Non-photosynthesizers depend on photosynthesizers

• While photosynthesizers can organize non-living
  materials into life
• Non-Photosynthesizers (e.g.- animals like us)
  must obtain both energy and material from other
  organisms (food) and reorganize that material
  into themselves.
• Food organisms (wheat, turkey, fish, broccoli,
  etc., etc.) are
• Photosynthesizers or
• Organisms that have eaten photosynthesizers.

• So non-photosynthesizers are completely dependent
  on photosynthesizers.

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• From where do non-photosynthesizers obtain both
  energy and materials?
• Even though non-photosynthesizers can consume
  other non-photosynthesizers, explain how,
  ultimately, non-photosynthesizers depend on
  photosynthesizers.

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Energy carriers

• Photosynthesis and cellular respiration involve
  energy Capturing it, using it, storing it,
  releasing it.
• To understand the processes involved, we need to
  look at molecules that carry energy.

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• List the two long-term energy carriers.
• What are the medium-term energy carriers and what
  are their 2 functions?
• List the 3 short-term energy carriers. What is
  their function?

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Short-term energy carriers are re-used
Releases energy and returns to low energy form
Low energy form
Receives energy
High energy form
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• List the low and high energy forms of the 3
  short-term energy carriers.

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Photosynthesis The Chloroplast

• The chloroplast performs photosynthesis.
• Triple membrane system Outer, inner, thylakoid
  (stacks of disks).
• Stroma Fluid-filled space where thylakoid disks

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• Describe the membranes of the chloroplast.
• What is the location of the stroma?

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Photosynthesis Overview
Light Reactions
Energy to Chlorophyll
Energy to ATP and NADPH
Light energy
Carbon Fixation
Build sugars from CO2 and H2O
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Photosynthesis Overview The light reactions and
carbon fixation

• Light reactions
• Energy in light goes to chlorophyll and then to
  short term carriers (ATP, NADPH).
• Water broken, O2 released

Carbon fixation Energy in short term carriers
used to build sugars from CO2
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• What occurs in the the light reactions?
• What occurs in carbon fixation?

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The Light Reactions Pairs of photosystems carry
out the light reactions

• The two photosystems work together
• Photosystem II (comes first). Makes ATP

• Photosystem I. Makes NADPH

There are many pairs of photosystems in each
thylakoid membrane

• Each photosystem is composed two parts

• Antenna Complex Hundreds of chlorophyll
  molecules in thylakoid membrane.

• Electron Transport Chain Series of membrane
  proteins in thylakoid membrane.

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• Which photosystem comes first?
• Which short-term energy carrier is produced by-
• Photosystem II?
• Photosystem I?
• What are the two parts of a photosystem. Briefly
  describe each.

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The Light Reactions How light is absorbed by
chlorophyll in antenna complexes

• Electrons in orbitals of chlorophyll absorb light
  energy.
• Electrons move to higher orbital. This higher
  energy.
• Electrons now excited. They have energy that
  was in light.

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Briefly describe the process by which light is
absorbed by chlorophyll molecules.
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The Light Reactions Photosystem Details
Antenna complexes
Process

• Light energy excites a chlorophyll electron.

• Energy ( but not electron) transfers from one
  chlorophyll to next, etc.

• The last chlorophyll molecule in antenna complex
  to receive energy is called the Reaction Center
  Chlorophyll and is located at the start of the
  electron transport chain.

• Unlike other chlorophylls, it does physically
  pass its excited electron on. It goes to the
  first protein in the electron-transport chain,
  the Electron-accepting Protein.

• The Reaction Center chlorophyll now has one less
  electron and is charged

Note The antenna complexes for both Photosystem
II and Photosystem I work this way.
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• Do electrons travel from chlorophyll to
  chlorophyll or just the energy?
• What is the location of the chlorophyll that
  releases an excited electron. To where is it
  passed?

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The Light Reactions Photosystem Details
Photosystem II Electron transport

• The energy that was in the electron is now in the
  pent up protons. (Like water behind a dam).

• The excited electron is passed through a series
  of membrane proteins called the
  electron-transport chain.

• The protons pass back through a thylakoid
  membrane protein called ATP Synthase.

• The proteins in the chain take the energy from
  the electron and use it to pump hydrogen ions
  (protons) across the thylakoid membrane into the
  thylakoid space.

• ATP Synthase uses the energy of the protons to
  synthesize ATP.

• Hydrogen ions (protons) accumulate in the
  thylakoid space.

• Energy has now passed from light to electrons to
  protons to ATP

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• For what does the electron transport chain use
  the energy in the excited electron?
• Where are the pumped hydrogen ions (protons)
  pent up?
• Describe the process by which ATP synthase makes
  ATP.

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The Light Reactions Photosystem Details
Photosystem II Replenishing electron
The missing electron in the Reaction Center
chlorophyll must be replaced.

• To replace the electron, a molecule of water is
  split.

• The electron replaces the lost electron in the
  chlorophyll
• The oxygen is released to the air. This is the
  oxygen we breathe!

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• How is the electron replaced in the Reaction
  Center chlorophyll of Photosystem II?
• What is produced and released to the air in this
  process?

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Summary of Photosystem II
Light
Chlorophyll
Excited electrons in chlorophyll
Electron transport chain
Hydrogen ions (protons) pumped across membrane
to thylakoid spaee
Hydrogen ions return across membrane through the
enzyme ATP synthase
ATP synthase synthesizes ATP
Hydrogen ions accumulate on in the thylakoid
space
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The Light Reactions Photosystem Details
Photosystem I Electron transport
Differences from Photosystem II

• Similarities to Photosystem II
• Has antenna complex

• Reaction Center Chlorophyll receives electrons
  from Photosystem II rather than from breakdown of
  water.

• Has electron transport chain

• Energy in transported electrons used to
  synthesize NADPH rather than to pump hydrogen
  ions and synthesize ATP

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• What are two similarities between Photosystem II
  and Photosystem I.
• From where does the Photosystem I Reaction Center
  Chlorophyll receive its replace electrons?

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Summary of Photosystem I
Light
Chlorophyll
Excited electrons in chlorophyll
Electron transport chain
Energy used to synthesize NADPH
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The light reactions of photosynthesis are the
gateways through which energy enters the realm of
life.
This energy is used, first and foremost, to
organize Earth materials into the molecules of
life from which living cells are constructed.
This depends on the process of carbon fixation
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Carbon Fixation builds the molecules of life

• Carbon-based molecules are the foundation of
  life!
• Carbon fixation organizes CO2 into carbon-based
  molecules.
• Sugars first then, via pathways, all the
  carbon-based molecules of life.

• Energy is supplied by ATP and NADPH from the
  light reactions.

Molecules of life Proteins, nucleic acids,
carbohydrates, lipids
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• What is the raw material used to produce
  carbon-based molecules?
• What are the first carbon-based molecules made?
• What process produces all the other carbon-based
  molecules?

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The molecules of life have two purposes
Structure/Function molecules
Energy molecules
Breakdown to release energy
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Cellular Respiration

• Obtaining energy from carbon-based molecules.
• Energy molecules sugars, starch, oils, fat
• Occurs in both
• Photosynthesizers (plants, algae)
• Breakdown of energy storage molecules (sugars,
  oils)
• Non-photosynthesizers (animals)
• Breakdown of food molecules.

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Overall, what does cellular respiration
accomplish?
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Cellular Respiration Overview
Energy to ATP and NADH
Breakdown
Energy molecules
Molecules enter cells
NADH
ATP
Bloodstream
Power cell activities
Digest
Food
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Stages of Cellular Respiration

• Oxidative
• phosphorylation
• Energy in NADH from previous steps used to make
  more ATP
• O2 we breathe is actually used here to make H2O.

• Glycolysis
• Initial glucose breakdown.
• Occurs in cytoplasm
• Some energy from glucose transferred to ATP and
  NADH.
• Pyruvate product of glycolysis.
• Product of partial breakdown of glucose

• Citric Acid Cycle
• Completes glucose breakdown.
• Remaining energy transferred to ATP and NADH
• Carbon in glucose released as CO2

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Glycolysis

• Key points
• Partial breakdown of glucose
• Series of chemical reactions in cytoplasm
• Some ATP, NADH (energy carriers) produced
• Pyruvate end product of glycolysis.

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Glycolysis

• Glycolysis is a series of chemical reactions
• Each reaction catalyzed by an enzyme (a protein).
  DNA contains blueprint for each enzyme.
• End product pyruvate
• 6-carbon glucose molecule broken down into two
  3-carbon pyruvate molecules.
• Energy
• Pyruvate contains some of the energy of glucose.
• Some of energy of glucose captured in ATP, NADH.
• Energy in ATP will be used for cell activities.
• Energy in NADH will be used later (during
  oxidative phosphorylation) to make more ATP.

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• Overall, what is accomplished during glycolysis?
• Where does glycolysis occur?
• What short-term energy carriers are powered up
  during glycolysis?
• What partial breakdown product of glucose is
  produced during glycolysis?

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Stages of Cellular Respiration Presence or
absence of Oxygen

• Glycolysis- Initial breakdown of glucose.
• Occurs in cytoplasm in presence or absence of
  oxygen.

• Citric Acid Cycle --gt
• Oxidative Phosphorylation
• Occurs in mitochondria only in presence of
  oxygen.
• Efficient

• Fermentation
• Occurs in cytoplasm only in absence of oxygen.
• Produces no energy

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Stages of Cellular Respiration Presence or
absence of Oxygen
Glycolysis (O2 present or absent)
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Fermentation

• Follow-up to glycolysis when low or no oxygen.
• Muscle during strenuous exercise (heart/lungs
  cant keep up O2).
• Yeast when growing in low oxygen.
• No additional energy capture occurs.

Yeast end-product Alcohol in beer, wine, etc.
Muscle end-product Responsible for pain during
strenuous exercise.
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• Under what circumstances does fermentation occur?
• Is energy captured?
• What are the end products of fermentation in
  yeast?
• What are the end products of fermentation in
  muscle?

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Citric Acid Cycle

• Completes breakdown of remnant of glucose
  (pyruvate) and extraction of energy
• At end All carbons of original glucose have
  been released as CO2
• Produces ATP, NADH (energy carriers)

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Citric Acid Cycle

• Series of chemical reactions catalyzed by enzymes
• Occurs in mitochondrial matrix

• Stages
• 3-carbon pyruvate --gt
• 2-carbon acetyl CoA
• The cycle
• 2-carbon acetyl CoA 4-carbon oxaloacetate
• --gt 6-carbon citric acid
• --gt 5-carbon molecule
• --gt4-carbon molecules
• --gt oxaloaceteate (again)

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• What happens to the remnant of glucose (pyruvate)
  during the citric acid cycle?
• What short term energy carriers are powered up
  during the citric acid cycle?
• Why is the citric acid cycle referred to as a
  cycle?

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Oxidative Phosphorylation Overview

• Energy temporarily stored in NADH (by Glycolysis
  Citric Acid Cycle) used to produce ATP.

• Involves electron transport --gt H pumping --gt
  ATP synthase system like Photosystem II

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Oxidative Phosphorylation (continued)

• Electron transport chain on inner mitochondrial
  membrane.

• High energy electrons from NADH breakdown at
  start of chain.

• Hydrogen ions pumped as electron passes along
  chain.

• Pent up on one side.

• Pass back through ATP synthase. ATP produced.

• Differences from photosystem II
• Energy from NADH not light.
• Hydrogen ions pumped outward, not inward.

• Fate of the electron
• Used to make water.
• This is where O2 we breath is actually used!
• This is why mitochondrion doesnt operate without
  O2

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• What short-term energy carrier directly supplies
  the energy used in oxidative phosphorylation?
• What short-term energy carrier is powered up by
  oxidative phosphorylation?
• What is the fate of the electron at the end of
  the electron transport chain?
• Why is O2 needed?
• Describe how ATP is made
• What are two differences between the electron
  transport/ATP synthase system of Cellular
  Respiration compared to Photosystem II?

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Food!