Photosynthesis

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Photosynthesis

• Chapter 7

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Photosynthesis

• In photosynthesis, organisms trap radiant energy
  from sunlight and convert it into the energy of
  chemical bonds in large molecules.
• Chlorophyll is a green pigment that absorbs light
  energy.
• Photosynthesis transforms light energy into
  chemical bond energy in the form of ATP.
• ATP is then used to form complex organic
  molecules such as glucose.

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Chloropasts

• Chloroplasts are the organelles in which
  photosynthesis takes place.
• Two distinct regions in chloroplasts
• Grana stacks of membranous stacks containing
  chlorophyll.
• Stroma the spaces between the membranes.

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Summary of Photosynthetic Events

• Light energy carbon dioxide water ? glucose
  oxygen
• Light energy 6CO2 6H2O ? C6H12O6 6 O2

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3 Distinct Events In The Photosynthetic Pathway

• Light-Capturing events chlorophyll and other
  pigments absorb specific wavelengths of light.
• Light energy is captured by photosynthetic and
  other pigments resulting in excited electrons.
• When specific amounts of light are absorbed by
  the photosynthetic pigments, the electrons become
  excited and can enter into chemical reactions
  responsible for the production of ATP.
• Takes place in the grana of the chloroplast.

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3 Distinct Events In The Photosynthetic Pathway

• Light-dependent reactions (light reactions)
• Energy from the excited electrons is used to
  dissociate water molecules into hydrogen and
  oxygen.
• use the excited electrons to produce ATP.
• Takes place in the grana of the chloroplast.
• Light-independent reactions (dark reactions)
• Organic molecules such as glucose is produced.
• Takes place in the stroma.

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Light-Capturing Events

• Chlorophyll and other pigments such as
  carotenoids use light energy to drive
  photosynthesis.
• Chloroplasts are membranous, saclike organelles
  containing many thin, flattened sacs called
  thylakoids.

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Light-Capturing Events

• The thyylakoids contain chlorophyll and are
  stacked in groups called grana.
• The pigments embedded in the thylakoids capture
  light energy and some of the electrons in the
  pigments become excited.

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Light-Capturing Events

• The chlorophylls are arranged in clusters called
  photosystems.
• Photons of light energy ? excited electrons from
  chlorophyll.

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Light-Dependent Reactions

• The excited electrons from the light-capturing
  stage are passed through a series of
  electron-transport steps.

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Light-Dependent Reactions

• The chloroplast in the electron transport system
  regains electrons from water thereby producing
  hydrogen ions, electrons, and oxygen gas.
• Excited electrons H20 ADP NADP ? ATP
  NADPH O2

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Light-Independent Reactions

• The light-independent reactions are a series of
  oxidation-reduction reactions, which combine
  hydrogen from water with carbon dioxide from the
  atmosphere to form simple organic molecules such
  as sugar.
• ATP NADPH ribulose CO2 ? ADP NADP
  complex organic molecule ribulose

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Plant Metabolism

• Photosynthetic organisms are able to manufacture
  organic molecules (including fats, proteins, and
  complex carbohydrates) from inorganic molecules.
• Vitamins are another important organic molecule
  derived from plants. Vitamins are organic
  molecules that we cannot manufacture, but must
  have in small amounts to maintain health.

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Interrelationships Between Autotrophs and
Heterotrophs

• Autotrophs can capture energy and create organic
  molecules from inorganic molecules.
• Heterotrophs must have organic molecules as
  starting points.
• All organisms must do some form of respiration.

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Interrelationships Between Autotrophs and
Heterotrophs

• Plants, like animals, require oxygen for the ETS
  portion of aerobic cellular respiration.
• Plants give off more oxygen to the atmosphere
  than they take in during respiration.

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Interrelationships Between Autotrophs and
Heterotrophs

• The surplus oxygen given off is the source of
  oxygen for cellular respiration in both plants
  and animals.
• Animals supply the raw materials of CO2, H20, and
  nitrogen needed by plants, and plants supply the
  raw materials of sugar, oxygen, amino acids,
  fats, and vitamins needed by animals.