1. Photosynthesis: Life from Light and Air
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2. Honors Biology

3. Energy needs of life All life needs a constant input of energy
Heterotrophs
get their energy from “eating others”
eat food = other organisms = organic molecules
make energy through cellular respiration
Autotrophs
get their energy from “self”
get their energy from sunlight
build organic molecules (food) from CO2
make energy & synthesize sugars through photosynthesis
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4. Energy needs of life Heterotrophs Autotrophs consumers animals fungi
most bacteria
Autotrophs
producers
plants
photosynthetic bacteria (blue-green algae)
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5. Energy Flow through the Environment
Light Energy
3. Foxes (heterotrophs) get energy by eating rabbits. Cellular Respiration.
2. Rabbits (heterotrophs) get energy by eating plants. Cellular Respiration.
1. Plants (autotrophs) convert light energy (sunlight) to chemical energy. Photosynthesis.
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6. How are they connected? Respiration by Heterotrophs 
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6
6O2
6CO2
6H2O
ATP  +
exergonic
Photosynthesis by Autotrophs
So, in effect, photosynthesis is respiration run backwards powered by light.
Cellular Respiration
oxidize C6H12O6  CO2 & produce H2O
fall of electrons downhill to O2
exergonic
Photosynthesis
reduce CO2  C6H12O6 & produce O2
boost electrons uphill by splitting H2O
endergonic
+ water + energy  glucose + oxygen
carbon
dioxide
6CO2
6H2O
C6H12O6
6O2
light
energy  +
endergonic
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7. ATP-Reminder!
ATP (adenosine triphosphate) is the molecule of energy for organisms.
When organic molecules are broken down by organisms, ATP is released.
The ATP that is released, provides energy for metabolism in the organism.
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8. ATP Releases Energy
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9. Energy cycle ATP Photosynthesis Cellular Respiration sun CO2 O2 H2O
plants
H2O
CO2
glucose O2
animals, plants
Cellular Respiration
ATP
It’s the Circle
of Life!
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10. What does it mean to be a plant
Need to…
collect light energy
transform it into chemical energy
store light energy
in a stable form to be moved around the plant & also saved for a rainy day
need to get building block atoms from the environment
C,H,O,N,P,K,S,Mg
produce all organic molecules needed for growth
carbohydrates, proteins, lipids, nucleic acids
ATP
Glucose/starch
H2O
CO2 N P K …
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11. Basic Plant Structure Obtaining raw materials sunlight CO2 H2O
leaves = solar collectors
CO2
stomata = gas exchange
H2O
uptake from roots
nutrients
N, P, K, S, Mg, Fe…
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12. stomate transpiration
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13. Plant structure Chloroplasts Thylakoid membrane contains
double membrane
stroma
fluid-filled interior
thylakoid sacs
grana stacks
Thylakoid membrane contains
pigment molecules
electron transport chain
H+ gradient built up within thylakoid sac
A typical mesophyll cell has chloroplasts, each about 2-4 microns by 4-7 microns long.
Each chloroplast has two membranes around a central aqueous space, the stroma.
In the stroma are membranous sacs, the thylakoids.
These have an internal aqueous space, the thylakoid lumen or thylakoid space.
Thylakoids may be stacked into columns called grana. H+
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14. Pigments Molecules called Pigments absorb light.
The major light-absorbing pigments in plants are called Chlorophyll a & b.
Found in thylackoids
Carotenoids (carotene & xanthrophyll) - pigments that produce yellow and orange fall leaf color, as well as colors of fruits, flowers, & veggies
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15. Light: absorption spectra
Photosynthesis gets energy by absorbing wavelengths of light (photons)
chlorophyll a
absorbs best in red & blue wavelengths & least in green
other pigments with different structures absorb light of different wavelengths
Why are plants green?
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16. Stages of Photosynthesis
Light reactions (LR)
light-dependent reactions
energy production reactions
convert solar energy to chemical energy
ATP & NADPH
Calvin Cycle (CC)
light-independent reactions
sugar production reactions
uses chemical energy (ATP & NADPH) to make (carbohydrates) C6H12O6 from CO2
It’s the Dark Reactions!
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17. Light Reactions (LR)  produces ATP produces NADPH
H2O
ATP O2
light
energy  +
NADPH
H2O
sunlight
produces ATP
produces NADPH
releases O2 as a waste product
Energy Building
Reactions
NADPH
ATP O2
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18. Light Reaction: Part One
Chlorophyll absorbs photons
2. This energy excites chlorophyll’s electrons.
These excited electrons leave the thylackoid (bound for the ETC’s)
The electron “holes” are replaced by splitting a water molecule.
Water molecules are split by an enzyme
Electrons are taken from hydrogen, leaving H+ ions
What does this leave?
Oxygen is released into atmosphere
OXYGEN!!
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19. Light Reaction: Part One
Excited Electrons
Chlorophyll
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20. Light Reaction: Part 2
The excited electrons made in stage 1 are passed along the thylackoid membrane through numerous proteins called electron transport chains.
Like a hot potato being passed down a line of people
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21. Electron Transport Chain 1
The “chain” is made up of protein pumps
Excited electrons lose some of their energy when they pass through each protein
The energy lost is used to pump H+ ions (from split water) in through proton pumps
As H+ ions diffuse back out, a chemical reaction adds a phosphate group to a molecule of ADP making ATP.
This powers the 3rd Stage of photosynthesis
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22. Electron Transport Chains
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23. Electron Transport Chain 2
Made in a second electron transport chain.
Light-excited electrons, hydrogen ions, and NADP+ combine
This forms NADPH
NADPH is another energy rich molecule in cells
The ATP and NADPH will be used to power the last stage of photosynthesis (Calvin Cycle).
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25. Summary of Light Reactions
Pigments absorb light energy
Excited electrons leave to go on to electron transport chains.
Lost electrons are replaced by splitting water molecules…making….
H+ ions diffuse back out making ATP
NADP+ and electrons and H+ combine to form NADPH
OXYGEN AND H+
STAGE 2
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26. Whoops! Wrong Calvin…
The Calvin Cycle
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27. Calvin Cycle (CC)  builds sugars uses ATP & NADPH
CO2
C6H12O6  +
NADP
ATP
NADPH
ADP
CO2
builds sugars
uses ATP & NADPH
recycles ADP & NADP back to make more ATP & NADPH
ADP
NADP
Sugar Building
Reactions
NADPH
ATP
sugars
C6H12O6
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28. Stage 2: Calvin Cycle
The series of light-independent reactions that assembles complex carbohydrates is called the Calvin Cycle.
Uses carbon atoms from CO2 , this is called carbon fixation
The energy needed to power the cycle comes from ATP and NADPH made in the light reactions of photosynthesis.
glucose
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29. More Calvin Cycle
Using energy from ATP, carbon atoms from CO2 in the air and hydrogen atoms from NADPH produce a series of carbon-containing molecules.
Some of these molecules are used to make organic compounds.
Others return to the beginning of the cycle to enable the capture of CO2 to continue.
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31. Putting it all together
CO2
H2O
C6H12O6 O2
light
energy  +
H2O
CO2
Plants make both:
energy
ATP & NADPH
sugars
sunlight
ADP
NADP
Energy Building
Reactions
Sugar Building
Reactions
NADPH
ATP
sugars
C6H12O6 O2
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32. Photosynthesis summary
Light reactions
Consumed photons
consumed H2O
produced H+ ions
produced ATP
produced NADPH
produced O2 as byproduct
Calvin cycle
consumed CO2
Produced C6H12O6
regenerated ADP
regenerated NADP+
ADP
NADP
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33. Summary of Photosynthesis
6 CO2 + 6 H2O  C6H12O6 + 6 O2
Carbon dioxide and water, in the presence of sunlight, will react to form sugars and oxygen gas.
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34. Factors Affecting Photosynthesis
Light intensity
Rate of photosynthesis increases as light intensity increases, until a point
CO2 Concentration
Rate of photosynthesis increases as levels of CO2 increase, until a point
Most efficient within a certain range of temperatures
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35. Supporting a biosphere
On global scale, photosynthesis is the most important process for the continuation of life on Earth
each year photosynthesis synthesizes 160 billion tons of carbohydrate
heterotrophs are dependent on plants as food source for fuel & raw materials

36. The poetic perspective…
All the solid material of every plant was built by sunlight out of thin air
All the solid material of every animal was built from plant material
sun
air
Then all the cats, dogs, rats, people & elephants… are really strands of air woven together by sunlight!
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