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Section Objectives

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This reaction is called photolysis. ... The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe. ... – PowerPoint PPT presentation

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Title: Section Objectives


1
  • Section Objectives
  • Relate the structure of chloroplasts to the
    events in photosynthesis
  • Describe light-dependent reactions.
  • Explain the reactions and products of the
    light-independent Calvin cycle.

2
Trapping Energy from Sunlight
  • The process that uses the suns energy to make
    simple sugars is called photosynthesis.

3
Trapping Energy from Sunlight
  • Photosynthesis happens in two phases.
  • The light-dependent reactions convert light
    energy into chemical energy.
  • 2. The molecules of ATP produced in the
    light-dependent reactions are then used to fuel
    the light-independent reactions that produce
    simple sugars.
  • The general equation for photosynthesis is
    written as 6CO2 6H2O?C6H12O6 6O2

4
The chloroplast and pigments
  • To trap the energy in the suns light, the
    thylakoid membranes contain pigments, molecules
    that absorb specific wavelengths of sunlight.
  • Although a photosystem contains several kinds of
    pigments, the most common is chlorophyll.(chlorog
    reenish yellow, phyllon leaf)
  • Chlorophyll absorbs most wavelengths of light
    except green.

Reflectedlight
Light
Chloroplast
Absorbedlight
5
An overview of photosynthesis
Chloroplast
Light
CO2
H2O
NADP
ADPP
LIGHTREACTIONS(in grana
CALVINCYCLE(in stroma
ATP
NADPH
Sugar
O2
O2
6
Light-Dependent Reactionsabsorption of light
energy by chlorophyll
  • As sunlight strikes the chlorophyll molecules in
    a photosystem of the thylakoid membrane, the
    energy in the light is transferred to electrons.
  • These highly energized, or excited, electrons are
    passed from chlorophyll to an electron transport
    chain, a series of proteins embedded in the
    thylakoid membrane.
  • At each step along the transport chain, the
    electrons lose energy.

7
Light-Dependent Reactions
  • This lost energy can be used to form ATP from
    ADP, or to pump hydrogen ions into the center of
    the thylakoid disc.
  • Electrons are re-energized in a second
    photosystem and passed down a second electron
    transport chain.

8
Light-Dependent Reactions
  • The electrons are transferred to the stroma of
    the chloroplast. To do this, an electron carrier
    molecule called NADP is used.
  • NADP can combine with two excited electrons and a
    hydrogen ion (H) to become NADPH.
  • NADPH will play an important role in the
    light-independent reactions.

9
Restoring electrons
  • To replace the lost electrons, molecules of water
    are split in the first photosystem. This
    reaction is called photolysis.
  • The O2 liberated by photosynthesis is made from
    the oxygen in water

Chlorophyll
O2 2H
2
2e-
H2O
H2O 2H
O2 2e-
10
Restoring electrons
  • The oxygen produced by photolysis is released
    into the air and supplies the oxygen we breathe.
  • The electrons are returned to chlorophyll.
  • The hydrogen ions are pumped into the thylakoid,
    where they accumulate in high concentration.

11
Light Dependent Reactions Summary
  • Absorptions of light energy by chlorophyll-takes
    place in thylakoid
  • 1. Split water molecule (PHOTOLYSIS) Oxygen
    combines with other oxygen to produce O2 which is
    given off as a by-product
  • 2. Hydrogen produced by splitting of water is
    attached to hydrogen carrier NADP -gt NADPH
    (energy in this molecule)
  • 3. Then energy from excited electronsis used
    to take ADP P -gtATP

12
Light Independent Reactions or The Calvin Cycle
  • CO2 put into organic molecules called Carbon
    fixation
  • Does not require light but must have ATP and
    NADPH which are produced by light dependent
    reactions
  • Also called Calvin Cycle (Melvin Calvin won Nobel
    prize in chemistry)
  • Takes place in stroma of chloroplast

13
Light Independent Reactions or The Calvin Cycle
  • The Calvin cycle constructs G3P using
  • carbon from atmospheric CO2
  • electrons and H from NADPH
  • energy from ATP
  • Energy-rich sugar is then converted into glucose

INPUT
CALVINCYCLE
OUTPUT
14
Factors Affecting Rate of Photosynthesis
  • Temperature increases rate up to a certain point
  • Light Intensity increases rate up to a certain
    point
  • CO2 level Increases rate up to a certain point
  • Water decrease water, decrease photosynthesis
  • Minerals Ex. Magnesium, Nitrogen
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