Photosynthesis

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Photosynthesis
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Basic Information

• Light is in the form of radiant energy.
• Electromagnetic spectrum-range of radiant energy
• The forms of radiant energy differ in both
  wavelength and the amount of energy they
  transmit.
• Photons-tiny packages of energy that make-up
  radiant energy.
• When light hits an object it can be reflected,
  absorbed or transmitted.
• The color you see is reflected.
• Leaves mostly absorb blue and red light and
  reflect green.

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Pigments and where you can find them

• Pigment-molecule that can absorb light.
• Ex. Chlorophyll-green pigment primary
  light-absorbing agent for photosynthesis
• 2 Types of Chlorophyll
• chlorophyll a
• chlorophyll b
• Fall colors are produced by yellow and orange
  pigments called carotenoids.
• Photosystem- cluster of pigments used in
  photosynthesis.
• These photosystems are found in the thylakoid
  membranes.
• Most photosynthetic organisms have 2
  photosystems.
• Photosystem I (chlorophyll b)
• Move e- to higher energy levels by absorbing
  light energy (700 nm)
• Photosystem II (chlorophyll a)
• Boost e- by absorbing light energy (680 nm)

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Photosynthesis 6CO2 6 H2O light ?C6H12O6
6O2

• 1)Light reaction-
• Energy in sunlight trapped
• Oxygen released
• 2) Dark Reaction-
• ATP and NADPH react with CO2
• Form glucose
• Electron Transport Chain
• Electron Transport Systems are organized
  sequences of enzymes and coenzymes.
• They are built into cell membranes, such as those
  of chloroplasts and mitochondria.
• Electrons stripped from substrates are
  transferred through these systems.
• During certain transfers, energy is released that
  can be used to do work-for example, to make ATP.

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Light Reactions Photosynthesis
Photosystem II Light enters chlorophyll a
boosts electrons to a higher energy level. Some
of these electrons pass through a series of
reaction called the ETC (electron transport
chain) to produce ATP. Other electrons go to
photosystem I. The ETC acts as a proton pump.
Uses the energy from the excited electrons to
pump protons across the thylakoid membrane into
the thylakoid interior. This process produces
ATP.
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PS I
PS II
Photolysis
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Key Points for light reactions

• Photons are absorbed by photosynthetic pigments
  in photosystems. Photon energy drives the
  transfer of electrons from a specific chlorophyll
  to an acceptor molecule, which donates them to a
  transport system in the membrane.
• In the cyclic pathway of ATP formation, excited
  electrons leave the P700 chlorophyll of
  photosystem I, give up energy in the transport
  system, and return to that photosystem.
• In the noncyclic pathway of ATP formation,
  electrons from the P680 chlorophyll of
  photosystem II pass through a transport system,
  then end up in NADPH. Also, water molecules split
  into hydrogen ions, oxygen, and electrons. These
  electrons replace the ones that P680 give up.
• Operation of electron transport systems moves
  many hydrogen ions into the inner compartment of
  the thylakoid membrane. Hydrogen ions split from
  water molecules that accumulate here also. This
  sets up a gradient for ATP formation

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Dark Reactions The Calvin Cycle

• Does not need light
• Used ATP and NADPH (light reaction)
• Carbon Fixation -taking C and making organic
  molecules
• Most common carbon-fixing pathway-Calvin Cycle
• Basic Steps to the Calvin Cycle
• CO2 enters the plant and combines with a 5C
  compound
• Forms a 6 C compounds which will split
• Forms 2 (3C) compounds
• Used 6 ATP and 6 NADPH
• Forms 2 Reduced 3C compounds

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Dark Reactions Continued

• For every 3 (CO2) that enters the plant, the
  cycle at this point can use the reduced 3C
  compounds to make organic compounds such as
  glucose.
• Not all 2C reduced compounds leave the cycle,
  some have 3 ATP's added to them to form the 5C
  compound used in the first step.
• What effects the rate of photosynthesis?
• Directly affected by the environment
• Light rate of photosynthesis increase with
  intensity until it reaches a point of saturation
• Amount of CO2 increase with the amount until it
  reaches point of saturation.
• Temperature range-- WHY??? Enzymes are effected.

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The Calvin Cycle
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Key Points for Calvin Cycle

• ATP delivers energy and NADPH delivers hydrogen
  and electrons to the stroma of chloroplasts,
  where sugar phosphates form and are combined into
  starch, cellulose, and other end products.
• Sugar phosphates form during the Calvin cycle.
  This cyclic pathway begins when carbon dioxide
  from the air is affixed to RuBP, making an
  unstable intermediate that splits into two PGA.
  ATP donates a phosphate group to each PGA. The
  resulting molecule receives Hydrogen ions and
  electrons from NADPH to form PGAL.
• For every six Carbon dioxide molecules that enter
  the cycle, twelve PGAL are produced. Two of those
  are used to produce a six carbon sugar phosphate.
  The remainder are used to regenerate RuBP for the
  cycle.

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Summary

• Photosynthesis is the main biosynthetic pathway
  by which carbon and energy enter the web of life.
  It consists of two sets of reactions that start
  with the trapping of sunlight energy and proceed
  through the assembly reactions
• IN CHLOROPLASTS-the light dependent reactions
  take place in the thylakoid membrane producing
  ATP and NADPH
• IN CHLOROPLASTS-the light independent reactions
  take place in the stroma around the membrane
  system producing sugar phosphates