Ch 10 NOTES part 1: Photosynthesis in Nature

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Ch 10 NOTES (part 1) Photosynthesis in Nature
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PHOTOSYNTHESIS

• ? PHOTOSYNTHESIS the capture of light energy
  the conversion of this energy to stored chemical
  energy (in the form of sugar)
• -AUTOTROPHS producers capable of producing
  their own food ?PHOTOAUTOTROPHS use light energy
  to synthesize food (e.g. plants)

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• ? Photosynthesis occurs in plants, algae, certain
  other protists, and some prokaryotes
• ? These organisms feed not only themselves but
  also the entire living world

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Plants
Unicellular protist
10 µm
Purple sulfur bacteria
1.5 µm
Multicellular algae
Cyanobacteria
40 µm
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• ? HETEROTROPHS consumers live on compounds
  produced by other organisms
• -animals that eat plants or other animals
• ? Almost all heterotrophs, including humans,
  depend on photoautotrophs for food and oxygen

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• some heterotrophs are
• -decomposers live on dead matter

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Chloroplasts The Sites of Photosynthesis in
Plants

• ? Leaves are the major locations of
  photosynthesis
• ? Their green color is from CHLOROPHYLL, the
  green pigment within chloroplasts
• ? Light energy absorbed by chlorophyll drives the
  synthesis of organic molecules in the chloroplast
• ? Through microscopic pores called STOMATA, CO2
  enters the leaf and O2 exits

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CHLOROPLASTS

• ? organelles in which photosynthesis occurs
• ? found primarily in leaves (about 500,000
• per mm2)
• ? contain green pigment CHLOROPHYLL
• (absorbs light energy)
• ? found mainly in mesophyll (tissue inside leaf)
• ? a typical mesophyll cell has 30-40 chloroplasts

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Leaf cross section
Vein
Mesophyll
Stomata
O2
CO2
Mesophyll cell
Chloroplast
5 µm
Outer membrane
Thylakoid
Intermembrane space
Thylakoid space
Granum
Stroma
Innermembrane
1 µm
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• ? CO2 enters and O2 leaves through STOMATA
• ? water is delivered to leaves from the roots via
  veins

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CHLOROPLAST

• ? enclosed by 2 membranes
• ? STROMA fluid within the chloroplast
• ? THYLAKOID MEMBRANES are interconnected
  contain the thylakoid space, or lumen (are
  usually in stacked columns called GRANA)
• ? chlorophyll is stored in the thylakoid
  membranes

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PATHWAYS OF PHOTOSYNTHESIS

• ? TOTAL equation for photosynthesis
• 6CO2 12H2O light ? C6H12O6 6O2 6H2O
  
• energy
• ? NET EQUATION
• 6CO2 6H2O light ? C6H12O6 6O2
• energy

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The Splitting of Water

• ? Chloroplasts split water into hydrogen and
  oxygen, incorporating the electrons of hydrogen
  into sugar molecules

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Tracking Atoms Through Photosynthesis
12 H2O
6 CO2
Reactants
C6H12O6
6 H2O
6 O2
Products
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Photosynthesis as a Redox Process

• ? Photosynthesis is a redox process in which
  water is oxidized and carbon dioxide is reduced

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• ? like respiration, photosynthesis is a series of
  redox reactionsBUT, the electron flow is
  reversed!the electrons increase in potential
  energy as they move from water ? sugar an uphill
  process!
• (the required energy boost comes from light
  energy)

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Two Stages of Photosynthesis

• 1) the LIGHT REACTIONS
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• 2) the CALVIN CYCLE
• (a.k.a. the dark reactions
• or light-independent
• reactions)

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The Two Stages of Photosynthesis A Preview

• ? Photosynthesis consists of the light reactions
  (the photo part) and the Calvin cycle (the
  synthesis part)

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LIGHT REACTIONS

• ? convert solar energy ? chemical energy
• ? light is absorbed by chlorophyll and drives a
  transfer of electrons and H from water to an
  acceptor called NADP
• ? water is split and O2 is produced as a waste
  product
• ? NADP is reduced to NADPHALSO, ATP is
  generated via phosphorylation of ADP
• (photophosphorylation!)

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CALVIN CYCLE

• ? CO2 from air is incorporated into organic
  molecules by carbon fixation
• ? NADPH and ATP from the light reactions power
  the production of sugar
• ? also called the dark reactions or
  light-independent reaction

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• Locations of the Photosynthesis Reactions
• ? Light reactions occur in the THYLAKOIDS
• ? Calvin cycle occurs in the STROMA

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H2O
Light
LIGHT REACTIONS
Chloroplast
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H2O
Light
LIGHT REACTIONS
ATP
NADPH
Chloroplast
O2
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H2O
CO2
Light
NADP
ADP
P

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CALVIN CYCLE
LIGHT REACTIONS
ATP
NADPH
Chloroplast
CH2O (sugar)
O2