Photosynthesis

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Photosynthesis!!!

• One incredible cell process!!!
• All of life depends upon it.

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Energy in light is captured and stored in organic
compounds (food).
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Plants, algae, and some bacteria can do
photosynthesis so we call them

• AUTOTROPHS
• We are heterotrophswe dont make food.

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Biochemical Pathway

• A complex series of chemical reactions. The
  products of one step are used in the next.

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photosynthesis
autotrophs heterotrophs
light
autotrophs
cellular respiration
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CO2 H2O ? Glucose O2
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Where Does Photosynthesis occur?
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draw the chloroplast
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Some cells may have 50 chloroplasts!!
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Cloroplasts are made of

• Outer membrane
• Inner membrane
• Thylakoids flattened sacs
• Grana stacks of thylakoids
• Stroma a fluid surrounding the thylakoids

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2 parts of photosynthesis

• Light reactions require light energy
• Dark reactions do not require light energy

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Visible Spectrumorder of decreasing wavelength
and increasing energy

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

The light we see.
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Prisms
white light
visible spectrum
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When white light hits an object, it can be

• Absorbed
• Transmitted
• reflected

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Pigments are
Compounds that absorb colors. What is not
absorbed gets reflected. ( That is the color of
the object.)
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Cloroplast Pigments

• (Embedded in the thylakoid membrane)
• Chlorophylls
• Chlorophyll a(absorbs less blue and more red)
• Chlorophyll b (absorbs more blue and less red)

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Accessory Pigments

• B helps A capture light energy
• Yellow, brown and
• orange carotenoids help
• absorb light

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Carotenoids
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Photosystems groups of pigments in thylakoid
memb.

• Photosystem I
• Photosystem II
• Both absorb light energy and pass energy on

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Steps of the light reactions

• 1. Light energy causes e- in chlorophyll a in p.
  s. II to become excited they have more energy.
• Electron e-

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e-
excited
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Next

• 2. Excited e- leave chlorophyll a and are
  accepted by the primary electron acceptor
  molecule also in the thylakoid memb.

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accepted
e-
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Next

• 3. P.E.A. donates the e- to the electron
  transport chain. As the excited e- get passed
  they gradually lose energy. No more excited.
• lost energy is used to move protons into the
  thylakoid.
• The e- is given to p. s. I.

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Next

• 4. P. s. I has also begun to work. Light has
  been absorbed. e- are excited.They are passed on
  to a P.E.A. then to the electron transport chain.
• Lost energy goes to make ADP ? ATP

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Next

• 5. The e- combine with a proton and are accepted
  by NADP.
• NADP ? NADPH
• Proton e- ? H

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HNADP NADPH
Light
ATP ADP
Light
H
ETC
ETC
PSI
PSII
e-
e-
e-
Less energy
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Restoring P.S. II

• It gives e- to p.s. I.
• If e- were not replacedp.s. would stop!
• Replacement e- come from split water molecules
• 2H2O ---gt 4H 4e- O2
• (Protons)

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That is why plants need water and why they
produce oxygen.
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Take a big breath

• We are half- way done.

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The Dark Reactions

• Also known as the Calvin Cycle.

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Melvin Calvin

• 1911-1997
• Nobel Prize
• Fixation of Carbon

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Carbon Fixation

• CO2 molecules are bonded into organic compounds
• 3 major steps
• Takes place in stroma
• No light is needed.

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Step 1

• CO2 diffuses into the stroma from cytosol
• C carbon
• CO2 RuBP (5 C)? 6-C molecule ? 2 PGA (each with
  3 C)

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Step 2

• PGA takes a P from ATP
• PGA takes a p from NADPH
• PGA then loses a P group
• Now it is PGAL(3 Cs also)
• ADP, NADP, and P ? light rxns

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Step 3

• Most of PGAL converted back to RuBP
• ATP is needed
• Some PGAL are not converted but used for misc.
  organic compounds

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P.S. Equation
CO2 H2O? (CH2O) O2
carbohydrate
like glucose
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What effects the rate of P.S.?

• Light intensity
• Temperature
• Amount of CO2

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rate of p.s.
Light intensity/ CO2 level
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rate of p.s.
Temperature
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