chapter 3 - photosynthesis: the details. photosynthesis using the sun to make useful forms of energy...
TRANSCRIPT
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Chapter 3 - Photosynthesis:The Details
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Photosynthesis• Using the sun to make useful forms of energy• Sunlight plays a much larger role in our
sustenance than we may expect: all the food we eat and all the fossil fuel we use is a product of photosynthesis, which is the process that converts energy in sunlight to chemical forms of energy that can be used by biological systems
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How does this occur
• Various forms of radiation surround us, from the sun and other sources.
• Some are visible and some are invisible.
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Wave model of light
• Electromagnetic radiation travels at 300000000m/s
• Frequencies of visible radiation (light) are perceived as different colours
We can remember the visible spectrum with ROYGBIV!
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• Frequencies of visible radiation (light) are perceived as different colours.
•Highest frequency, smallest wavelength = violet
•Lowest frequency, largest wavelength = red
•All frequencies and wavelengths = white
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Properties of Light
• http://wps.prenhall.com/esm_krogh_biology_3/0,8750,1135943-,00.html
• http://www.sumanasinc.com/webcontent/animations/content/harvestinglight.html
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Photon model of light• Light travels in energy
packets called photons• Photons travel at
300000000m/s• The amount of energy in a
photon depends on the frequency of the light. The higher the frequency of light, the more energy the photon carries
• Light can transmitted reflected or absorbed
• Air, water ….mirror…plants
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How Does a Plant Capture Light?
Light can be • transmitted (light passes through an object.
• Reflected (light bounces off object)
• Absorbed (light goes into object)
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How Does a Plant Capture Light?
• Plants have chlorophyll PIGMENTS (molecules that can absorb specific wavelengths of light)
Plant leaves appear green. Therefore, what colours must the chlorophyll pigments absorb? reflect?
GREENEverything but Green
http://www.johnkyrk.com/photosynthesis.html
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Chlorophyll Pigments• There are 2 types
of cholorophyll
• Yellow - green
• Blue – green
• Found in the highly folded plant organelle
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Chlorophyll Absorption Whatever chlorophyll a does
not absorb, chlorophyll b will absorb – they are good complements to each other.
• As you can see, the region between 500-600 nm is not absorbed very well, thus plants appear green.
• As the amount of chlorophyll in autumn decays, the green colour fades and is replaced with oranges and reds of carotenoids (other plant pigments).
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• Plants are the only photosynthetic organisms to have leaves (and not all plants have leaves). A leaf may be viewed as a solar collector crammed full of photosynthetic cells. http://wps.prenhall.com/esm_krogh_biology_3/0,8750,1135943-,00.html
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Photosynthesis in plants• Light energy is used to transform carbon
dioxide and water to energy rich food molecules composed of glucose monomers
• There are 2 stages in this process
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Photosynthesis
Divided into two steps:
1. The Light Reactions• Noncyclic electron flow
2. The Calvin Cycle• Cyclic electron flow
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The Light Reactions
Divided into three steps:
1. Photoexcitation
2. Electron Transport Chain
3. Chemiosmosis
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The Light Reactions
Photosystems are embedded in the thylakoid membrane.
They contain chlorophyll and accessory pigments that are associated with proteins.
A photosystem consists of an antenna complex and a reaction centre.
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The Light Reactions
The antenna complex absorbs a photon and transfers energy to the reaction centre.
The reaction centre contains chlorophyll a, whose electrons absorb energy and begin photosynthesis.
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The Light Reactions
Photosystem II (P680) Two photons strike photosystem II and
excite 2 electrons from chlorophyll P680. The excited electrons are captured by a
primary electron acceptor and are then transferred to plastoquinone (PQ) and the ETC.
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The Light Reactions
Photosystem II (P680) In the ETC, the 2 electrons pass through a
proton pump (Q cycle). The Q cycle transports 4 protons from the
stroma into the thylakoid lumen to create a proton gradient.
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The Light Reactions
Photosystem II (P680) The electrochemical gradient drives the
photophosphorylation of ADP to ATP. 1 ATP forms for every 4 protons that pass
through ATPase from the thylakoid lumen into the stroma.
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The Light Reactions
Photosystem II (P680) A Z protein splits water into 2 protons, 2
electrons and 1 oxygen atom.The electrons replace those lost from
chlorophyll P680.The protons remain in the thylakoid space to
add to the proton gradient.Oxygen leaves as a byproduct.
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The Light Reactions
Photosystem I (P700) Two photons strike photosystem I and excite 2
electrons from chlorophyll P700 (replaced by electrons from P680).
These electrons pass through another ETC. The enzyme NADP reductase uses the 2
electrons and a proton from the stroma to reduce 1 NADP+ to 1 NADPH.
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The Calvin Cycle Occurs in the stroma of chloroplasts. Cyclical reactions similar to the Krebs
Cycle.
Divided into three phases:
1. Carbon Fixation
2. Reduction Reactions
3. Regeneration of RuBP
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The Calvin Cycle
Phase 1: Carbon Fixation 3 CO2 are added to RuBP to form 3
unstable 6-carbon intermediates. The intermediates split into six 3-carbon
molecules called PGA. These reactions are catalyzed by rubisco.
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The Calvin Cycle
Phase 2: Reduction Reactions 6 PGAs are phosphorylated by 6 ATPs to
form 6 molecules of 1, 3-BPG. 6 NADPH molecules reduce the six 1,3-
BPG to 6 G3P or PGAL. One molecule of G3P exits the cycle as a
final product.
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The Calvin Cycle
Phase 3: Regeneration of RuBP 3 ATP are used to rearrange the
remaining 5 G3P into 3 molecules of RuBP.
The cycle continues with the RuBP fixing more CO2.
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To Produce One G3P…
3 RuBP + 3 CO2 + 9 ATP + 6 NADPH + 5 H2O 9 ADP + 8 Pi + 6 NADP+ + G3P + 3 RuBP