Photosynthesis

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Photosynthesis Cellular Respiration

• Chapter 5 Section 1

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Objectives

• Analyze the flow of energy through living
  systems.
• Compare the metabolism of autotrophs with that of
  heterotrophs.
• Describe the role of ATP in metabolim.
• Describe how energy is released from ATP.

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Key Terms

• Photosynthesis
• Autotroph
• Heterotroph
• Cellular Respiration

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Capturing the Energy of Life

• All organisms require energy
• Some organisms obtain energy directly from the
  sun
• This energy is used to make organic compounds
  that will serve as food for the organisms

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Autotrophs

• Organisms that use energy from the sunlight or
  form chemical bonds in inorganic substances to
  make organic compounds.
• Only 10 of the Earths 40 million species are
  autotrophs.
• Includes plants and some other types of
  organisms.
• Also known as producers.

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Heterotrophs

• Organisms that must get energy from food instead
  of directly from sunlight or inorganic
  substances.
• Includes animals, humans even mushrooms.
• Also known as consumers

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Flow of Energy
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Photosynthesis

• Process in which plants use the energy of
  sunlight to convert water carbon dioxide into
  high-energy carbohydrates (sugars starches) and
  oxygen (waste product)

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Cellular Respiration

• Process by which cells produce energy from
  carbohydrates to do chemical work in the cell.

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ATP

• Principal chemical compounds that cells use to
  store and release energy. The only source of
  energy to do chemical work in the cell.

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Storing Energy

• ADP (adenosine diphosphate) is a compound that
  looks almost like ATP.
• When a cell has energy available, it can store
  small amounts of it by adding a phosphate group
  to ADP molecules.

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Releasing Energy for Chemical Work

• Energy is released by breaking the bond between
  the 2nd and 3rd phosphate.

Mitochondria
ATP Enzymes ADP P Energy
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PHOTOSYNTHESIS
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Objectives

• Summarize how energy is captured from sunlight in
  the first stage of photosynthesis.
• Analyze the function of electron transport chains
  in the second stage of photosynthesis.
• Relate the Calvin cycle to carbon dioxide
  fixation in the third stage of photosynthesis.
• Identify three environmental factors that affect
  the rate of photosynthesis.

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Key Terms

• Pigment
• Chlorophyll
• Carotenoid
• Thylakoid
• Electron Transport Chain

• NADPH
• Carbon Dioxide Fixation
• Calvin Cycle

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Photosynthesis

• Carbon dioxide (CO2) requiring process that uses
  light energy (photons) and water (H2O) to produce
  organic macromolecules (glucose).
• 6CO2 6H2O ? C6H12O6 6O2

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Where does Photosynthesis occur?

• Plants/Autotrophs produce their own food
  (glucose)
• Process called photosynthesis
• Mainly occurs in the leaves
• a. stoma - pores
• b. mesophyll cells

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The Stages of Photosynthesis

• Stage 1
• Energy is captured from sunlight by chlorophyll
  and other pigments present.
• Stage 2
• Light energy is converted to chemical energy,
  which is temporarily stored in ATP the energy
  carrier molecule NADPH
• Stage 3
• The chemical energy stored in ATP NADPH powers
  the formation of organic compounds, using the CO2
  to make Glucose.

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Stages of Photosynthesis
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The Photosynthesis Equation
Light
6CO2 6H20 C6H12O6 6O2
Carbon Dioxide
Water
Sugars
Oxygen
(High Energy)
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Stage 1 Absorption of Light Energy

• How does a human eye or leaf absorb light?

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Visible Spectrum

• Sunlight contains a mixture of all the
  wavelengths (colors) of visible light.
• When sunlight passes through a prism, the prism
  separates the light into different colors.

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Visible Spectrum

• When light strikes an object, it is, absorbed,
  transmitted or reflected.
• When all colors are absorbed the object appears
  black.
• When all colors are reflected the object appears
  white.
• If only one color is reflected the object appears
  that color.

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Pigments

• Light-absorbing substances
• Absorb only certain wavelengths and reflect all
  others.

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Chlorophyll

• The primary pigment in plants.
• Absorbs mostly blue red light
• Reflects green yellow light
• 2 Types of chlorophyll
• Chlorophyll a - blue green
• Chlorophyll b -yellow green

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Carotenoids

• Accessory pigments
• -Carotenoids - orange
• -Xanthrpphyll yellow
• -Anthocyanin red
• -Lutein grey/brown
• Absorb wavelengths of light different from those
  absorbed by chlorophyll a b.

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Light Absorption During Photosynthesis
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Thylakoids

• Saclike photosynthetic membranes located inside
  the chloroplasts.
• Arranged in stacks known as grana (singular
  granum).

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Thylakoids

• When light strikes a thylakoid in a chloroplast,
  energy is transferred to electrons in
  chlorophyll, exciting the chlorophyll.
• This energy transfer causes electrons to jump to
  a higher energy level.
• Electrons with extra energy are said to be
  excited

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Excited Electrons

• Excited electrons jump from chlorophyll molecules
  to other nearby molecules in the thylakoid
  membrane.
• These electrons must be replaced by other
  electrons.
• Plants get these replacement electrons from water
  molecules.

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Replacement Electrons

• Water molecules are split by an enzyme inside the
  thylakoid.
• Chlorophyll molecules take the electrons from the
  hydrogen atoms.
• Oxygen from the disassembled water molecules
  combine to form oxygen gas and this is given off
  at the end of stage 1 as a waste product of
  photosynthesis.

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Stage 2 Conversion of Light Energy

• Light Dependent

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Conversion of Light Energy

• Excited electrons that leave chlorophyll
  molecules are used to produce new molecules,
  including ATP, that temporarily store chemical
  energy.

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Electron Transport Chains

• Excited electrons are passed through a series of
  molecules along the thylakoid membrane.
• This is called the electron transport chain.
• This provides the energy needed to make ATP.

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NADPH

• A second electron transport chain provides energy
  used to make NADPH
• NADPH is an electron carrier that provides the
  high-energy electrons needed to make
  carbon-hydrogen bonds in the 3rd stage of
  photosynthesis

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Light-Dependent Reactions Summarized

1. Pigment molecules in the thylakoids of
   chloroplasts absorb light energy.
2. Electrons in the pigments are excited by light
   move through electron transport chains in
   thylakoid membranes.
3. These electrons are replaced by electrons from
   water molecules that are split.

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Light-Dependent Reactions Summarized (cont)

1. Oxygen atoms from water molecules combine to form
   oxygen gas.
2. Hydrogen ions accumulate inside thylakoids,
   setting up a concentration gradient that provides
   the energy to make ATP and molecules of NADPH to
   be used in the Dark Reaction, the third stage.

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Stage 3 Storage of Energy

• Dark Reaction

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Dark Reaction (third stage) of Photosynthesis

• Carbon atoms from carbon dioxide in the
  atmosphere and the H molecules from the NADPH of
  the light reactions are used to make organic
  compounds in which chemical energy is stored in
  glucose molecules.
• The transfer of carbon dioxide to organic
  compounds (glucose) is called carbon dioxide
  fixation or the Calvin Cycle.

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Calvin Cycle

• Most common method of carbon dioxide fixation.
• Series of enzyme-assisted chemical reactions that
  produce a three-carbon sugar.

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Dark Reaction Summarized

1. Each molecule of carbon dioxide is added to a
   five-carbon compound by an enzyme using the
   energy from the ATP and the splitting of the
   NADPH from the Light Reaction.
2. The resulting six-carbon compound splits into two
   three-carbon compounds. Phosphate groups from
   ATP electrons from NADPH are added to the
   three-carbon compounds, forming three-carbon
   sugars.

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Calvin Cycle Summarized (cont)

1. The resulting three-carbon sugars are used to
   make organic compounds glucose in which energy
   is stored for later use by the organism.

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Factors that Affect Photosynthesis

• Light
• Rate increases as light intensity increases until
  all the pigments are being used.
• Concentration of carbon dioxide
• Once a certain concentration of carbon dioxide is
  present, photosynthesis cannot proceed faster
• Temperature
• Most efficient within a certain range of
  temperatures.

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Question

• During the fall, what causes the leaves to change
  colors?

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Fall Colors

• In addition to the chlorophyll pigments, there
  are other pigments present
• During the fall, the green chlorophyll pigments
  are greatly reduced revealing the other pigments
• Carotenoids are pigments that are either red,
  orange, or yellow

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