PHOTOSYNTHESIS by BMY35127

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									PHOTOSYNTHESIS
 Developed by Adam F. Sprague
          Chapter 10
              OBJECTIVES:
• 1. Explain why almost all organisms depend on
  photosynthesis.
  2. Describe the role of chlorophylls and other
  pigments in photosynthesis.
  3. Summarize the main events of light
  reactions.
  4. Explain how ATP is synthesized during the
  light reactions.
              OBTAINING ENERGY
•   1. ENERGY is the ability to do WORK or cause change.
•   2. Work is the ability to CHANGE or MOVE Matter against other Forces. w = F X d
•   3. Work for a Cell includes Growth and Repair, Active Transport, and Reproduction. All which
    require ENERGY.
•   4. The source of Energy for ALL Organisms is FOOD, But, different kinds of Organisms get
    their food in different ways.
•   5. Most AUTOTROPHS or PRODUCERS use PHOTOSYNTHESIS, to Convert the
    Energy in SUNLIGHT, CARBON DIOXIDE, AND WATER into Chemical Energy OR
    FOOD. (GLUCOSE)
•   6. THE FOODS MADE BY AUTOTROPHS ARE stored in various Organic Compounds,
    primarily CARBOHYDRATES, including a SIX-CARBON SUGAR called GLUCOSE.
•   7. Plants, algae, and some prokaryotes (Bacteria) are all types of Autotrophs.
•   8. Only 10 percent of the Earth's 40 million species are Autotrophs.
•   9. Without Autotrophs, all other living things would DIE. Without PRODUCERS you cannot
    have CONSUMERS.
•   10. Autotrophs not only make Food for their own use, but STORE a great deal of Food for use
    by other organisms (CONSUMERS)
             OBTAINING ENERGY
•   11. Most Autotrophs use ENERGY from the SUN to make their food, but there are
    other organisms (CHEMOTROPHS) deep in the ocean that obtain Energy from
    INORGANIC COMPOUNDS. (CHEMOSYNTHESIS)
•   12. Organisms that CANNOT Make their own food are called HETEROTROPHS
    OR CONSUMERS.
•   13. Heterotrophs include animals, fungi, and many unicellular organisms, they stay
    alive by EATING AUTOTROPHS or other HETEROTROPHS.
•   14. Because Heterotrophs must consume other organisms to get Energy, they are
    called CONSUMERS.
•   15. Only part of the energy from the Sun is Used by Autotrophs to make Food, and
    only part of that Energy can be passed on to other Consumers. A Great Deal of the
    Energy is LOST as HEAT.
•   16. Enough Energy is passed from Autotroph to Heterotroph to give the Heterotroph
    the Energy it needs. (Figure 6-1)
•   17. Photosynthesis involves a COMPLEX SERIES of Chemical Reactions, in which
    the PRODUCT of One Reaction is Consumed in the Next Reaction.
•   18. A Series of Reactions linked in this way is referred to as a BIOCHEMICAL
    PATHWAY.
           OBTAINING ENERGY
• 19. Autotrophs use biochemical pathways of photosynthesis to manufacture
  organic compounds from Carbon Dioxide, CO2, and Water. During this
  conversion, molecular OXYGEN, O2, is Released.
• 20. Some of the energy stored in organic Compounds is Released by Cells in
  another set of Biochemical Pathways, Known as CELLULAR
  RESPIRATION. (Chapter 7) (Figure 6-2)
• 21. Both Autotrophs and Heterotrophs Perform Cellular Respiration. (Figure
  6-2)
• 22. During Cellular Respiration in Most Organisms, Organic Compounds are
  Combined with O2 to Produce ADENOSINE TRIPHOSPHATE or
  ATP, Yielding CO2 and Water as Waste Products.
• 23. The PRODUCTS of Photosynthesis, ORGANIC COMPOUNDS and
  O2, are the REACTANTS used in CELLULAR RESPIRATION.
• 24. The WASTE PRODUCTS of CELLULAR RESPIRATION, CO2 and
  WATER, are the REACTANTS used in PHOTOSYNTHESIS.
                 OVERVIEW OF
                PHOTOSYNTHESIS
• "THE BIG PICTURE"
• 1. Photosynthesis is the process that provides energy for almost
  all Life.
• 2. During Photosynthesis, Autotrophs use the Sun's Energy to
  make Carbohydrate Molecules from Water and Carbon Dioxide,
  Releasing Oxygen as a Byproduct.
• 3. The Process of PHOTOSYNTHESIS CAN BE
  SUMMARIZED BY THE FOLLOWING EQUATION:
•           6CO2 +   6H2O   + LIGHT C6H12O2  +     6O2
      CARBON    WATER    ENERGY     6-CARBON    OXYGEN
      DIOXIDE                         SUGAR      GAS



• 4. In this equation the Six-Carbon Sugar GLUCOSE and
  Oxygen are the Products.
                  OVERVIEW OF
                 PHOTOSYNTHESIS
• 5. The Energy Stored in Glucose and other Carbohydrates can be used later
  to produce ATP during Cellular Respiration.
• 6. The Process of Photosynthesis does NOT Happen all at Once; rather it
  occurs in TWO STAGES:
•    STAGE 1 - CALLED THE LIGHT REACTIONS OR LIGHT
  DEPENDENT REACTIONS. Energy is Capture from Sunlight. Water is
  Split into Hydrogen Ions, Electrons, and Oxygen (O2). The O2 Diffuses out
  of the Chloroplasts (Byproduct). The Light Energy is Converted to Chemical
  Energy, which is Temporarily Stored in ATP and NADPH.
•    STAGE 2 - CALLED THE CALVIN CYCLE. The Chemical Energy
  Stored in ATP and NADPH powers the formation of Organic Compounds
  (Sugars), Using Carbon Dioxide, CO2.
• 7. Photosynthesis occurs in the Chloroplasts of Plant Cells and Algae and in
  the Cell Membranes of certain Bacteria.
  CAPTURING LIGHT ENERGY
• 1. In Plants, the INITIAL REACTIONS in Photosynthesis are known as the
  LIGHT REACTIONS.
• 2. They begin with the ABSORPTION of Light in the organelle found in
  Plant Cells and algae called CHLOROPLASTS.
• 3. A Photosynthetic Cell contains anywhere from ONE to Several Thousands
  Chloroplasts.
• 4. A Chloroplasts is surrounded by TWO MEMBRANES. The INNER
  Membrane is Folded into many Layers. (Figure 6-2)
• 5. A Chloroplasts Inner Membrane layers fuse along the edges to Form
  THYLAKOIDS.
• 6. THYLAKOIDS ARE DISK-SHAPED STRUCTURES THAT
  CONTAIN PHOTOSYNTHETIC PIGMENTS.
• 7. Each Thylakoid is a closed Compartment surrounded by a Central
  Space. THE THYLAKOIDS ARE SURROUNDED BY A GEL-LIKE
  MATRIX (SOLUTION) CALLED THE STROMA. (Figure 6-2)
 CAPTURING LIGHT ENERGY
• 8.THE NEATLY FOLDED THYLAKOIDS THAT
  RESEMBLE STACKS OF PANCAKES ARE
  CALLED GRANA. The Thylakoids are
  Interconnected and are Layered on top of one another
  to form the STACKS of Grana.
• 9. Each Chloroplasts may contain hundreds or more
  Grana.
• 10. Hundreds of Chlorophyll Molecules and other
  Pigments in the Grana are organized into
  PHOTOSYSTEMS.
• 11. PHOTOSYSTEMS ARE LIGHT
  COLLECTING UNITS OF CHLOROPLASTS.
          LIGHT AND PIGMENTS
• 1. LIGHT is made of Particles called PHOTONS that move in WAVES.
• 2. The Distance between peaks of the waves is called WAVELENGTH.
• 3. Different Wavelengths of Light Carry different amounts of Energy.
• 4. Sunlight is visible as White, it is actually a variety of Different Colors.
• 5. You can separate White Light into its component colors by passing the
  light through a PRISM.
• 6. The resulting array of colors, ranging from red at one end to violet at the
  other is called the VISIBLE SPECTRUM.
• 7. Each Color of Light has different Wavelengths, and a Different Energy.
        LIGHT AND PIGMENTS
• 8. When light strikes an object, its component colors can be
  Reflected, Transmitted, or Absorbed by an object.
• 9. An Object that ABSORBS ALL COLORS appears BLACK.
• 10. A PIGMENT IS A MOLECULE THAT ABSORBS
  CERTAIN WAVELENGTHS OF LIGHT AND REFLECTS
  OR TRANSMITS OTHERS.
• 11. Objects or Organisms vary in Color because of their specific
  combination of Pigments.
• 12. WAVELENGTHS that are REFLECTED by Pigments are
  SEEN as the object's COLOR.
    CHLOROPLASTS PIGMENTS
• 1. Located in the Membrane of the Thylakoids are a variety of Pigments.
• 2. CHLOROPHYLLS ARE THE MOST COMMON AND IMPORTANT
  PIGMENTS IN PLANTS AND ALGAE.
• 3. The TWO most common Types of Chlorophylls are designated
  Chlorophyll a and Chlorophyll b.
• 4. A Slight difference in molecular structure between Chlorophyll a and
  Chlorophyll b causes the Two molecules to Absorb different colors of light.
• 5. Chlorophyll's ABSORB VIOLET, BLUE AND RED LIGHT. These are
  the Wavelengths of Light that Photosynthesis Occurs. (Figure 6-4)
• 6 Chlorophyll a ABSORBS LESS BLUE Light but MORE RED Light than
  Chlorophyll b Absorbs.
    CHLOROPLASTS PIGMENTS
• 7. ONLY Chlorophyll a is DIRECTLY INVOLVED in the LIGHT
  REACTIONS of Photosynthesis. Chlorophyll b ASSISTS Chlorophyll a in
  Capturing Light Energy and is called an ACCESSORY PIGMENT.
• 8. By Absorbing colors Chlorophyll a CANNOT Absorb, the Accessory
  Pigments enable Plants to Capture MORE of the Energy in Light
• 9. Chlorophylls REFLECT and TRANSMIT GREEN LIGHT, causing
  Plants to appear GREEN.
• 10. Another group of Accessory Pigments found in the Thylakoid
  Membranes, called the CAROTENOIDS, INCLUDES YELLOW, RED,
  AND ORANGE PIGMENTS THAT COLOR CARROTS, BANANAS,
  SQUASH, FLOWERS AND AUTUMN LEAVES.
• 11. The Carotenoids in Green Leaves are usually masked by Chlorophylls
  until Autumn when Chlorophylls break down.
 COVERTING LIGHT ENERGY TO
     CHEMICAL ENERGY
• 1. The Chlorophylls and Carotenoids are
  grouped in Cluster of a Few Hundred Pigment
  Molecules in the Thylakoid Membranes.
• 2. Each Cluster of Pigment Molecules is referred
  to as a PHOTOSYSTEM. There are Two
  Types of Photosystems known as
  PHOTOSYSTEM I AND PHOTOSYSTEM
  II.
           PHOTOSYSTEM I AND
             PHOTOSYSTEM II
• 3. Photosystem I and Photosystem II are similar in terms of
  pigments, but they have Different Roles in the Light reactions.
• 4. The Light Reactions BEGIN when Accessory Pigment
  molecules of BOTH Photosystems Absorb Light.
• 5. By Absorbing Light, those Molecules Acquire some of the
  Energy that was carried by the Light Waves.
• 6. In each Photosystem, the Acquired Energy is Passed to other
  Pigment Molecules until it reaches a Specific Pair of
  CHLOROPHYLL a Molecules.
• 7. The Events occur from this point on can be Divided into 5
  STEPS. (Refer to Figure 6-6)
                              5 STEPS
• STEP 1 - Light Energy Forces Electrons to enter a Higher Energy Level in
  the TWO Chlorophyll a Molecules of Photosystem II. These Energized
  Electrons are said to be "EXCITED".
• STEP 2 - The Excited Electrons have enough Energy to Leave Chlorophyll a
  Molecules. Because they have lost Electrons, the Chlorophyll a Molecules
  have undergone an OXIDATION REACTION (lost of Electrons). Each
  Oxidation Reaction must be accompanied by a REDUCTION REACTION
  (some substance must Accept the Electrons). The Substance is a Molecule in
  the Thylakoid Membrane Known as a PRIMARY ELECTRON
  ACCEPTOR.
• STEP 3 - The Primary Electron Acceptor then Donates (gives) the Electrons
  to the First of a Series of Molecules located in the Thylakoid. This Series of
  Molecules is called an ELECTRON TRANSPORT CHAIN, because it
  Transfers Electrons from One Molecule to the Next in Series. As the
  Electrons are pass from molecule to molecule, they LOSE most of the
  Energy they acquired when they were Excited. The Energy they LOSE is
  Harnessed to Move Protons into the Thylakoid.
                         5 Steps
• STEP 4 - At the same time Light is Absorbed by Photosystem
  II, Light is also Absorbed by Photosystem I. Electrons move
  from a Pair of Chlorophyll a Molecules in Photosystem I to
  another Primary electron Acceptor. The electrons that are
  LOST by these Chlorophyll a Molecules are REPLACED by the
  Electrons that have passed through the electron Transport Chain
  from Photosystem II.
• STEP 5 - The Primary Electron Acceptor of Photosystem I
  donates Electrons to different Electron Transport Chain. This
  Chain brings Electrons to the side of the Thylakoid Membrane
  that FACES THE STROMA. There Electrons COMBINE with
  a PROTON and NADP+. NADP+ is an Organic Molecule that
  ACCEPTS Electrons during REDOX Reactions. This reaction
  causes NADP+ to be Reduced to NADPH.
  REPLACING ELECTRONS IN LIGHT RERACTIONS OR
        RESTORING PHOTOSYSTEM II - PHOTOLYSIS

• . The Electrons from Chlorophyll Molecules on Photosystem II REPLACE
  the Electrons that Leave Chlorophyll Molecules in Photosystem I. (figure 6-7)
• 2. If the electrons were NOT Replaced, both Electron Transport Chains
  would STOP, and Photosynthesis would NOT Occur.
• 3. The Replacement Electrons are provided by WATER MOLECULES.
  Enzymes (RuBP carboxylase or Rubisco) inside the Thylakoid SPLITS
  Water Molecules into PROTONS, ELECTRONS, AND OXYGEN.
•       2H2O 4H+ + 4e- + O2
• 4. For Every TWO Molecules of Water that are Split, FOUR Electrons
  become available to Replace those lost by Chlorophyll Molecules in
  Photosystem II.
• 5. The PROTONS that are produced are left inside the Thylakoid, while
  Oxygen Diffuses out of the Chloroplasts and can Leave The Plant.
  REPLACING ELECTRONS IN LIGHT RERACTIONS OR
     RESTORING PHOTOSYSTEM II - PHOTOLYSIS

• 6. OXYGEN can be regarded as a Byproduct of the
  Light Reaction - it is NOT Needed for Photosynthesis.
• 7. The Oxygen that results from Photosynthesis is
  ESSENTIAL for Cellular Respiration in most
  organisms, including Plants.
• 8. The photochemical splitting of water in the light-
  dependent reactions of photosynthesis, catalyzed by a
  specific enzyme is called Photolysis.
• 9. The enzyme that speeds up this reaction, called
  RuBP carboxylase (Rubisco), about 20-50% of the
  protein content in chloroplast, and it may be one of the
  most abundant proteins in the biosphere.
MAKING ATP IN THE LIGHT REACTIONS -
 CHEMIOSMOSIS (KEM-ee-ahz-MOH-suhs)
• 1. An important part of the Light Reaction is the SYNTHESIS
  of ATP through a process called CHEMIOSMOSIS.
• 2. Chemiosmosis Relies on a CONCENTRATED GRADIENT
  of Protons Across the Thylakoid Membrane. (Figure 6-8)
• 3. Protons are Produced from the Breakdown of Water
  Molecules, Other Protons are Pumped into the Thylakoid from
  the Stroma during Photosystem II.
• 4. Both these mechanisms act to build up a Concentration
  Gradient of Protons. The Concentration of Protons is
  HIGHER in the Thylakoid than in the Stroma.
• 5. The Concentration Gradient Represents Potential
  Energy. The energy is Harnessed by a Protein called ATP
  SYNTHASE, which is located in the Thylakoid Membrane.
MAKING ATP IN THE LIGHT REACTIONS -
 CHEMIOSMOSIS (KEM-ee-ahz-MOH-suhs)
• 6. ATP Synthase makes ATP by ADDING a
  PHOSPHATE GROUP to ADENOSINE
  DIPHOSPHATE, OR ADP. By Catalyzing the
  Synthesis of ATP from ADP, ATP Synthase functions
  as an Enzyme.
• 7. ATP Synthase Converts Potential Energy of the
  Protons Concentrated Gradient into Chemical Energy
  of ATP.
• 8. Together, NADPH and ATP Provide Energy for the
  Second Set of Reactions in Photosynthesis.
        THE CALVIN CYCLE
• The Second Set of reactions in photosynthesis
  involves a biochemical pathway known as the
  CALVIN CYCLE. This pathway produces
  Organic Compounds, using the energy stored in
  ATP and NADPH during the Light
  Reactions. The Calvin Cycle is named after
  Melvin Calvin (1911-1997), the American
  scientist who worked out the details of the
  pathway.
                 OBJECTIVES:

• 1. Summarized the main events of the Calvin Cycle.
  2. Describe what happens to the compounds made in
  the Calvin Cycle.
  3. Distinguish between C3, C4, and CAM Plants.
  4. Summarize how the light reactions and the Calvin
  cycle work together to create the continuous cycle of
  photosynthesis.
  5. Explain how environmental factors influence
  photosynthesis.
        CARBON FIXATION
• 1. In the Calvin Cycle, Carbon Atoms From
  CO2 are Bonded, or "FIXED", into Organic
  Compounds.
• 2. The incorporation of CO2 into Organic
  Compounds is referred to as CARBON
  FIXATION.
• 3. The Calvin Cycle has THREE Major Steps,
  Which OCCUR within the STROMA of the
  Chloroplasts. (Figure 6-8)
                                   Steps
•   STEP 1 - CO2 Diffuses into the Stroma from the surrounding Cytosol. An Enzyme
    combines a CO2 Molecule with a FIVE CARBON CARBOHYDRATE CALLED
    RuBP (ribulose bisphosphate). The PRODUCT is a Six-Carbon Molecule that Splits
    into a Pair of Three-Carbon Molecules known as 3-PGA (3-phosphoglycerate).
•   STEP 2 - PGA is Converted into another Three-Carbon Molecule, G3P or PGAL,
    (glyceraldehyde 3-phosphate G3P) in a Two Part Process:
•      A. Each PGA Molecule Receives a Phosphate Group from a molecule of ATP -
    forming ADP
•      B. The resulting compound then Receives a Proton from NADPH (forming
    NADP+) and Releases a Phosphate Group, Producing PGAL.
•   In addition to PGAL, these Reactions produce ADP, NADP+, and Phosphate. These
    Three Products can be used again in the Light Reactions to Synthesis additional
    Molecules of ATP and NADPH.
•   STEP 3 - ONE G3P Molecules LEAVES the Calvin Cycle and can be used by the
    Plant Cell to Make other Organic Compounds (Carbohydrates).
•    STEP 4- Most of the G3P is Converted back into RuBP in a series of reaction to
    Return to Step 1 and allow the Calvin Cycle to Continue.
     ALTERNATIVE PATHWAYS
• 1. The Calvin Cycle is the MOST Common Pathway for Carbon
  Fixation. Plant Species that fix Carbon EXCLUSIVELY through the Calvin
  Cycle are known as C3 PLANTS.
• 2. Other Plant Species Fix Carbon through alternative Pathways and then
  Release it to enter the Calvin Cycle.
• 3. These alternative pathways are generally found in plants that evolved in
  HOT, DRY Climates.
• 4. Under such conditions, plants can rapidly lose water to the air. Most of the
  water loss from plants occurs through Small Pores on the Undersurface of the
  Leaves called STOMATA. Plants obtain carbon dioxide for photosynthesis
  from the air. Plants must balance their neeed to open their Stomata to receive
  carbon dioxide and release oxygen with their need to close their Stomata to
  prevent water loss. A stoma is bordered by TWO Kidney Shaped GUARD
  CELLS, Guard Cells are modified cells that Regulate Gas and Water
  Exchange.
      ALTERNATIVE PATHWAYS
•   5. Stomata are the major passageway through which CO2 Enters and O2 Leaves a
    Plant.
•   6. When a plant's Stomata are partly CLOSED, the level of CO2 FALLS (Used in
    Calvin Cycle), and the Level of O2 RISES (as Light reactions Split Water Molecules).
•   7. A LOW CO2 and HIGH O2 Level inhibits Carbon Fixing by the Calvin
    Cycle. Plants with alternative pathways of Carbon fixing have Evolved ways to deal
    with this problem.
•   8. C4 PLANTS - Allows certain plants to fix CO2 into FOUR-Carbon
    Compounds. During the Hottest part of the day, C4 plants have their Stomata
    Partially Closed. C4 plants include corn, sugar cane and crabgrass. Such plants Lose
    only about Half as much Water as C3 plants when producing the same amount of
    Carbohydrate.
•   9. THE CAM PATHWAY - Cactus, pineapples have different adaptations to Hot,
    Dry Climates. They Fix Carbon through a pathway called CAM. Plants that use the
    CAM Pathway Open their Stomata at NIGHT and Close during the DAY, the
    opposite of what other plants do. At NIGHT, CAM Plants take in CO2 and fix into
    Organic Compounds. During the DAY, CO2 is released from these Compounds and
    enters the Calvin Cycle. Because CAM Plants have their Stomata open at night, they
    grow very Slowly, But they lose LESS Water than C3 or C4 Plants.
               A SUMMARY OF
              PHOTOSYNTHESIS
• 1. Each Turn of the Calvin Cycle Fixes One CO2
  Molecule. Since PGAL is a Three-Carbon Compound, it takes
  Three Turns of the Cycle to Produce each Molecule of PGAL.
• 2. For Each Turn of the Cycle TWO ATP, and TWO NADPH
  Molecules are used in Step 2, and ONE ATP Molecule used in
  Step 3.
• 3. THREE Turns of the Calvin Cycle uses NINE Molecules of
  ATP and SIX Molecules of NADPH.
• 4. The Simplest OVERALL Equation for Photosynthesis,
  including both Light Reactions and the Calvin Cycle, can be
  written as:
•      6CO2 + 6H20 + LIGHT
  ENERGY C6H12O6 + 6O2
           FACTORS THAT AFFECT
             PHOTOSYNTHESIS
• 1. The Rate at which a plant can carry out photosynthesis is affected by the
  PLANT'S ENVIRONMENT.
• 2. THREE THINGS IN THE PLANT'S ENVIRONMENT AFFECT THE
  RATE OF PHOTOSYNTHESIS: LIGHT INTENSITY, CO2 LEVELS,
  AND TEMPERATURE. (Figure 6-10)
• 3. LIGHT INTENSITY - One of the most Important, As Light Intensity
  INCREASES, the Rate of Photosynthesis Initially INCREASES and then
  Levels Off to a Plateau.
• 4. CO2 LEVELS AROUND THE PLANT - Increasing the level of CO2
  Stimulates Photosynthesis until the rate reaches a Plateau.
• 5. TEMPERATURE - RAISING the Temperature ACCELERATES the
  Chemical Reactions involved in Photosynthesis. The rate of Photosynthesis
  Increase as Temperature Increases. The rate of Photosynthesis generally
  PEAKS at a certain Temperature, and Photosynthesis begins to Decrease
  when the Temperature is further Increased.

								
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