Unit 6: Cell Energy Photosynthesis

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Unit 6 Cell Energy - Photosynthesis

• Integrated Inquiry Science Sequence One - 2008

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Definitions

• Photosynthesis plants convert the energy of
  sunlight into the energy of chemical bonds of
  carbohydrates (sugars and starches)
• Chloroplast organelle in which the process of
  photosynthesis takes place
• Autotrophs use the suns energy directly to
  produce food
• Heterotrophs obtain energy from the foods they
  eat
• Pigments colored substances that absorb or
  reflect light
• Chlorophyll primary pigment of green plants

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Requirements for Photosynthesis

• carbon dioxide water ? carbohydrate
  oxygen
• photosynthesis produces a particular carbohydrate
  called GLUCOSE
• carbon dioxide water ? GLUCOSE
  oxygen

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Light and Dark Reactions

• Photosynthesis is divided into 2 parts, the light
  reactions and the dark reactions

You mean like this? Duct tape is like the
force it has a light side and a dark side, and
it binds the Universe together Carl
Zwanzig
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Light Reactions 4 Steps

• In the light reactions, the energy of sunlight is
  captured and used to make energy-storing
  compounds
• There are 4 steps to the light reactions
• Step 1. Light Absorption
• the photosynthetic membranes of the chloroplast
  (grana) contain PHOTOSYSTEMS which are able to
  capture the energy of SUNLIGHT
• each photosystem contains several hundred
  CHLOROPHYLL molecules and accessory pigments
• absorption of light causes electrons to be passed
  down the PIGMENT MOLECULES until they reach the
  special chlorophyll molecules
• the chlorophyll molecules process the light energy

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Light Reactions

• Step 2 Electron Transport
• electrons travel from the chlorophyll molecules
  to an ELECTRON CARRIER
• electrons are transferred down a line of electron
  carriers known as the ELECTRON TRANSPORT CHAIN
• at the end of the electron transport chain an
  ENZYME passes the electrons to an electron
  carrier called NADP and it converts it to NADPH
  (energy in chemical form)

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Light Reactions

• Step 3 Oxygen Production
• the photosynthetic membrane supplies the
  chlorophyll with new ELECTRONS to replace the
  ones that ended up in NADPH
• the electrons are taken from breaking down WATER
• WATER MOLECULES are split
• the OXYGEN is released into the air, the HYDROGEN
  and ELECTRONS are used in ATP formation

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Light Reactions

• Step 4 ATP Formation
• the hydrogen ions left in oxygen production are
  released inside the PHOTOSYNTHETIC MEMBRANE
• as electrons are passed down from chlorophyll to
  NADP more hydrogen ions are pumped across the
  membrane
• after a while, the inside of the membrane fills
  up with POSITIVELY CHARGED HYDROGEN IONS and the
  outside of the membrane is NEGATIVELY CHARGED
  (electrons)
• the charge difference creates ENERGY
• an ENZYME takes the energy and attaches it to ADP
  forming ATP (energy in chemical form)

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AT WHAT?

• ATP adenosine triphosphate
• adenosine monophosphate P E ?
  adenosine diphosphate
• adenosine diphosphate P E ?
  adenosine triphosphate

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Dark Reactions

• The dark reactions convert the energy-storing
  compounds NADPH and ATP to a more convenient form
• NADPH and ATP are REQUIRED for the dark reaction
  and it takes place in the STROMA of the
  chloroplast

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Dark Reactions

• Dark Reaction also called the CALVIN CYCLE
  because it is a circular series of reactions
• a 5-CARBON SUGAR forms with CO2 to make two
  3-CARBON compounds, this reaction is slow so the
  chloroplast uses the enzyme RUBISCO as a catalyst
• using or reusing the energy of ATP and NADPH the
  3 carbon compounds are converted to PGAL
  (phosphoglyceraldehyde)
• most PGAL are recycled for the dark reactions,
  but 1 of every 6 is used to make GLUCOSE

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Questions

• What is the function of water in photosynthesis?
  Explain.
• Why are the light reactions important to the
  Calvin Cycle? Explain.
• Where do the light and dark reactions take place?
  Explain.
• What are the products of the light and dark
  reactions? Explain.
• Where does the oxygen that is produced in oxygen
  production go? Explain.
• When glucose is formed in the dark reactions
  NADP and ADP are given off. Where do they go?
  Why?
• If the plant could not take up water through the
  roots where would the process of photosynthesis
  break down? Why? Short term effects? Long term
  effects?
• What would happen if the plant could not absorb
  light? Why?