Photosynthesis

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Photosynthesis

• A definition
• Photosynthesis is the process a plant uses to
  make food and grow.

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Four things are needed for photosynthesis
SUNLIGHT
Gives the plant energy
CHLOROPHYLL
The green stuff where the chemical reactions
happen
WATER
Travels up from the roots
CARBON DIOXIDE
Enters the leaf through small holes on the
underneath
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The word and chemical equations for
photosynthesis
Sunlight
Carbon dioxide water glucose
oxygen 6CO2 6H20 C6H12O6 6O2
Chlorophyll
Sunlight
Chlorophyll
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THE SUN MAIN SOURCE OF ENERGY FOR LIFE ON EARTH
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THE BASICS OF PHOTOSYNTHESIS
Almost all plants are photosynthetic autotrophs,
as are some bacteria and protists
Autotrophs generate their own organic matter
through photosynthesis Sunlight energy is
transformed to energy stored in the form of
chemical bonds
(c) Euglena
(d) Cyanobacteria
(b) Kelp

• (a) Mosses, ferns, and
• flowering plants

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AN OVERVIEW OF PHOTOSYNTHESIS

• Photosynthesis is the process by which
  autotrophic organisms use light energy to make
  sugar and oxygen gas from carbon dioxide and
  water

Carbondioxide
Water
Glucose
Oxygengas
PHOTOSYNTHESIS
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AN OVERVIEW OF PHOTOSYNTHESIS

• The light reactions convert solar energy to
  chemical energy
• Produce ATP NADPH

Light
Chloroplast
NADP?
ADP P
Calvin cycle
The Calvin cycle makes sugar from carbon
dioxide ATP generated by the light reactions
provides the energy for sugar synthesis The NADPH
produced by the light reactions provides the
electrons for the reduction of carbon dioxide to
glucose
Light reactions
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Light Energy Harvested by Plants Other
Photosynthetic Autotrophs
6 CO2 6 H2O light energy ? C6H12O6 6 O2
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WHY ARE PLANTS GREEN?
It has to do with sunlight! Sunlight is a form
of electromagnetic energy, which travels in waves.
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Electromagnetic Spectrum and Visible Light
Gammarays
Infrared Microwaves
X-rays
UV
Radio waves
Visible light
Wavelength (nm) Distance between two waves
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WHY ARE PLANTS GREEN?
Different wavelengths of visible light are seen
by the human eye as different colors.
Gammarays
Micro-waves
Radio waves
X-rays
UV
Infrared
Visible light
Wavelength (nm)
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The feathers of male cardinals are loaded with
carotenoid pigments. These pigments absorb some
wavelengths of light and reflect others.
Reflected light
Sunlight minus absorbed wavelengths or colors
equals the apparent color of an object.
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THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

• Chloroplasts absorb light energy and convert it
  to chemical energy

Reflected light
Light
Absorbed light
Transmitted light
Chloroplast
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Photosynthesis occurs in chloroplasts

• In most plants, photosynthesis occurs primarily
  in the leaves, in the chloroplasts
• A chloroplast contains
• stroma, a fluid (site of Calvin Cycle)
• grana, stacks of thylakoids (site of Light
  reactions)
• The thylakoids contain chlorophyll
• Chlorophyll is the green pigment that captures
  light for photosynthesis

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• The location and structure of chloroplasts

Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
Intermembrane space
CHLOROPLAST
Outer membrane
Granum
Innermembrane
Stroma
Grana
Thylakoidcompartment
Stroma
Thylakoid
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Chloroplast Pigments

• Chloroplasts contain several pigments

• Chlorophyll a absorbs mainly violet and red
  light the best
• Chlorophyll b absorbs blue and orange light the
  best
• Carotenoids absorbs blue and green best

Figure 7.7
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Different pigments absorb light differently
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Paper Chromatography

• A laboratory test used to separate and analyze
  different pigments in a leaf.
• Example
• https//www.pearsonsuccessnet.com/snpapp/iText/get
  TeacherHomepage.do?newServiceId6000newPageId101
  00

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PhotosystemsClusters of pigments in thylakoid
membrane

• Photosystem I
• Traps light energy and transfers the
  light-excited electrons to an electron transport
  chain.
• Those excited electrons are replaced by splitting
  a molecule of water, which releases oxygen.
• The electron transport chain releases energy,
  which is used to make ATP
• Photosystem II
• Produces NADPH by transferring excited electrons
  and hydrogen ions to NADP.

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Light Reactions Photosystem I and Photosystem II

• SUMMARY In the light reactions, electron
  transport chains generate ATP, NADPH, O2
• Two connected photosystems collect photons of
  light and transfer the energy to chlorophyll
  electrons
• The excited electrons are passed from the primary
  electron acceptor to electron transport chains
• The light reactions convert light energy to the
  chemical energy of ATP and NADPH
• Watch the following animation
• http//www.youtube.com/watch?veY1ReqiYwYs

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• Two types of photosystems cooperate in the light
  reactions
• Inputs
• Water
• Sunlight energy
• Outputs
• Oxygen
• ATP
• NADPH

Photon
ATP mill
Photon
Water-splitting photosystem
NADPH-producing photosystem
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Plants produce O2 gas by splitting H2O

• The O2 liberated by photosynthesis is made from
  the oxygen in water (H and e-)

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How the Light Reactions Generate ATP and NADPH
Primary electron acceptor
NADP?
Energy to make
Primary electron acceptor
3
2
Light
Electron transport chain
Light
Primary electron acceptor
Reaction- center chlorophyll
NADPH-producing photosystem
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Water-splitting photosystem
2 H? 1/2
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• The production of ATP in photosynthesis

Thylakoidcompartment(high H)
Light
Light
Thylakoidmembrane
Antennamolecules
Stroma(low H)
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II
PHOTOSYSTEM I
ATP SYNTHASE
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• A Photosynthesis Road Map

Chloroplast
Light
Stroma
NADP?
Stack of thylakoids
ADP P
Light reactions
Calvin cycle
Sugar used for
? Cellular respiration
? Cellulose
? Starch
? Other organic compounds
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Calvin Cycle

• Called a cycle because the starting material,
  RuBP, is regenerated.
• Uses carbon from carbon dioxide, the energy from
  ATP, and high energy electrons and hydrogen ions
  from NADPH to make a small sugar named G3P.
• The plant uses G3P to make glucose and other
  organic molecules.
• Overall input
• CO2, ATP, NADPH
• Overall output
• Glucose

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Calvin Cycle

• Watch the following animation
• http//www.youtube.com/watch?vmHU27qYJNU0NR1

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Review Photosynthesis uses light energy to make
food molecules

• Light reactions use water and produce oxygen.
• The Calvin Cycle uses ATP and NADPH created in
  the the light reactions to convert carbon dioxide
  to glucose.

Chloroplast
Light
Photosystem IIElectron transport chains
Photosystem I
CALVIN CYCLE
Stroma
Electrons
Cellular respiration
Cellulose
Starch
Other organic compounds
LIGHT REACTIONS
CALVIN CYCLE
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• Animation is of the Calvin Cycle Note what
  happens to the carbon dioxide and what the end
  product is.
• Second animation of the Calvin Cycle is very
  clear and even does the molecular bookkeeping for
  you.