Photosynthesis

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Photosynthesis

• Biology
• Mrs. Volin

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How is light energy turned into food?
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PHOTOSYNTHESIS

• Plants use energy of sunlight to produce
  carbohydrates in a process called photosynthesis

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• Jan Van Helmont, 1600s
• Dutch physician
• Where does all the mass in a large plant come
  from??

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Van Helmonts Experiment

• He concluded that most mass must have come from
  the water
• This accounts for the hydrate portion of
  carbohydrates
• Where does the carbo portion come from?

We now know that the carbon comes from CO2
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• Theologian, scientist
• No interest in science till he met Benjamin
  Franklin and began experimenting with electricity
• Discovered properties of graphite
• Invented soda pop, and was awarded medal from the
  Royal Society
• Discovered laughing gas
• Discovered a gas he called dephlostigated air
  (now called oxygen)
• Invented the eraser and came up with the name
  rubber
• Documented the process of PHOTOSYNTHESIS!

Joseph Priestley, 1733-1804, England

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Priestleys Experiment
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Priestleys Experiment
Priestly The air becomes injured
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Priestleys Experiment

• He then tried a similar experiment with a mouse..

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Priestleys Experiment
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Priestleys Experiment

• He took the experiment another step further

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Priestleys Experiment
Plants restore to the air whatever breathing
animals and burning candles remove.
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• Jan Ingenhousz, Austrian physician
• Proved photosynthesis produces a gas

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• Van Helmont, Priestley, and Ingenhousz gave us
  the basis of what we know about photosynthesis

light
Carbon dioxide water
carbohydrate oxygen
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• Van Helmont, Priestley, and Ingenhousz gave us
  the basis of what we know about photosynthesis

light
Carbon dioxide water
carbohydrate oxygen
light
6 CO2 6 H2O C6H12O6 6
O2 The Basic Equation for
Photosynthesis
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Energy

• Living things require energy
• Autotrophs
• use a source of energy to make their
• own food
• Heterotrophs
• obtain energy from foods

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• The energy of sunlight must be absorbed by a
  photosynthetic organism
• Pigments---substances that absorb light
• Chlorophyll is a pigment that absorbs red
• and blue light very well
• Chlorophyll reflects green light
• Two types of chlorophyll
• Chlorophyll A
• Chlorophyll B

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Absorption of light by pigments
wavelength (nm)
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                                   ltgt
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ATP

• Adenosine triphosphate
• Molecule that temporarily stores energy
• Sometimes called the currency of energy

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ATP

• Released during chemical reactions in the cell
• Then becomes a source of energy for other
  cellular activities

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ATP

• Source of energy for ---
• Muscle contraction
• Protein synthesis
• Active transport across cell membrane
• EXAMPLE sodium potassium pump requires
• 1 molecule of ATP
• Organelle movement

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Energy stored in the bonds between the phosphate
groups
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ATP

• Enzymes control steps in ATP breakdown
• ATP ADP P energy
• ADP AMP P energy

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When a phosphate group is removed from ATP,
energy is released. ADP contains less energy.
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ATP vs Glucose

• ATP temporarily stores energy
• ATP is good for transferring energy
• but not a good way to store energy
• 1 glucose stores over 90x the energy of 1 ATP

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Potato cells at 400X magnification with starch
granules
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The Reactions of Photosynthesis
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Overview
Section 8-3
Chloroplast
Chloroplast
NADP
ADP P
Light- Dependent Reactions
Calvin Cycle
ATP
NADPH
Go to Section
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Photosynthesis takes place within the chloroplast
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Thylakoids

• Composed of sac-like membranes
• Stacks of thylakoids are called grana
• Thylakoids contain
• Clusters of chlorophyll
• Additional pigments
• Photosystem proteins that are able to capture
  energy of sunlight

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Photosynthesis takes place in the chloroplast

• Two stages
• Light-dependent reaction
• Light-independent reaction
• (also called Calvin Cycle or dark reaction)

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Light-dependent Reaction

• Requires light
• Takes place within the thylakoid membrane

Light-independent reaction (Calvin Cycle)

• Does not require light
• Takes place in the stroma (the space
• outside the thylakoid)

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Light reaction in thylakoid
Dark reaction in stroma
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Light energy is trapped

• Sunlight strikes the chlorophyll in the
  thylakoids
• Energy causes electrons in chlorophyll to become
  excited
• The excited electrons require a special carrier
• NADP is carrier molecule carries one pair of
  excited electrons

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Light energy is converted to chemical energy

• NADP 2e- H
• (Light energy converted to chemical energy)

Combine to produce NADPH
from chlorophyll
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Light energy is converted to chemical energy

• Energy from sunlight transforms ADP to ATP
• (Light energy converted to chemical energy)

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Figure 8-10 Light-Dependent Reactions
Section 8-3
Light Reaction of Photosynthesis
Hydrogen Ion Movement
Chloroplast
Photosystem II
ATP synthase
Inner Thylakoid Space
Thylakoid Membrane
Stroma
Electron Transport Chain
Photosystem I
ATP Formation
Go to Section
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Photosystem II
(See diagram pg. 211)

• Light energy transferred to electrons
• Electrons pass on to electron transport chain
• H20 H O2 e-
• (water molecules broken apart)
• These electrons replace the electrons that
  have move on to the
• electron transport chain.

enzymes
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Photosystem II
enzymes

• H20 H O2 e-
• (water molecules broken apart)
• These electrons replace the electrons that have
  move on to the
• electron transport chain.
• The O2 is released into air
• The H ions are released into thylakoid membrane

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Photosystem I

• Electrons are transported from Photosystem II to
  Photosystem I
• Pigments add more energy to electrons
• NADP picks up electrons and H and becomes NADPH

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• Inside of thylakoid becomes positively charged
  due to the buildup of H
• Outside of thylakoid becomes negatively charged
• ATP synthase (a membrane protein in the thylakoid
  membrane) allows H to pass through. ATP
  synthase acts like a turbine, binding ADP to a
  phosphate group. ATP is produced.

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Light reaction summary

• 1 ATP produced (energy!)
• 2 NADPH produced (energy!)
• 2 molecules of water used
• 1 molecule of O2 given off

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Calvin Cycle

• Nobel Prize in Chemistry to
  Melvin Calvin in 1961
• Also called the dark
  reaction of photosynthesis
• In stroma of chloroplast
• Does not depend on sunlight
• Utilizes energy in ATP and NADPH from the light
  reaction
• Produces sugars

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Figure 8-11 Calvin Cycle
Calvin Cycle ( Light-Independent Reaction, see
pg. 212)
Section 8-3
CO2 Enters the Cycle
Energy Input
ChloropIast
5-Carbon Molecules Regenerated
6-Carbon Sugar Produced
Sugars and other compounds!!
Go to Section
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(See diagram on text page 212)
Start with these 2 compounds
6 CO2s from atmosphere go in Energy is input
from 12 ATPs and 12 NADPHs 2 3-C molecules
combine to make a 6-C sugar Remaining 10 3-C
molecules converted back to 6 5-C
molecules Cycle repeats IMPORTANT See that
6 molecules of CO2 are used to produce one
glucose
main product high energy sugars!!
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Factors affecting photosynthesis

• Shortage of water
• Temperature
• (Enzymes function between 0-35C)
• Light intensity