Transcript Ch 6-1 Notes

Chapter 6
Photosynthesis
Section 6.1
Energy Processes for Life
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Autotrophs manufacture their own food from
inorganic substances
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Use photosynthesis to convert light energy
from the sun into chemical energy
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Heterotrophs cannot manufacture their own
food
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Must obtain food by eating autotrophs or other
heterotrophs
Photosynthesis
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Involves a complex series of chemical
reactions in which the product of one reaction
is consumed in the next reaction
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Biochemical pathway
6CO2 + 6H2O + solar energy  C6H12O6 + 6O2
Solar energy drives a series of chemical
reactions that require carbon dioxide and water
Light Absorption in Chloroplasts
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Light reactions- the initial reactions in
photosynthesis
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Begin with the absorption of light in
chloroplasts
Chloroplasts
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Each chloroplast is surrounded by a pair of
membranes
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Inside the membranes are stacks of thylakoids
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The stacks are called grana
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The fluid surrounding the grana is called stroma
Light and Pigments
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Visible spectrum- white light can be separated
into an array of colors when passed through a
prism
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ROY G. BIV
Light
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Light travels in waves
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The distance from the crest of one wave to the
crest of another wave is called a wavelength
Chloroplast Pigments
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Pigments- compounds that absorb light
Chlorophyll a – absorbs more red light
Chlorophyll b – absorbs more blue light
Carotenoids – absorbs more green light
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Only chlorophyll a is directly involved in the
light reactions of photosynthesis
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Chlorophyll b assists chlorophyll a in
capturing light energy (accessory pigment)
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In the leaves of a plant, chlorophylls are
abundant
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In Fall, plants lose their chlorophylls and their
leaves take on the color of the carotenoids
Electron Transport
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Each cluster of pigment molecules is a
photosystem
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Two types of photosystems: photosystem I &
photosystem II
Light Reactions
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1. light energy excites electrons in chlorophyll
a molecules of photosystem II
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2. These electrons move to a primary electron
acceptor
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3. The electrons are then transferred along a
series of molecules called an electron
transport chain
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4. light excites electrons in chlorophyll a molecules
of photosystem I. As these electrons move to another
primary electron acceptor, they are replaced by
electrons from photosystem II
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5. The electrons from photosystem I are transferred
along a second electron transport chain. At the end of
this chain, they combine with NADP+ and H+ to make
NADPH
Restoring Photosystem II
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Replacement electrons come from water
molecules
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An enzyme inside the thylakoid splits water
molecules into protons, electrons, and oxygen
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2H2O  4H+ + 4e- + O2
Chemiosmosis
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Synthesis of ATP
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Depends on a concentration gradient of
protons across a thylakoid membrane
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The concentration of protons is higher inside
the thylakoid
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ATP synthase makes ATP by adding a
phosphate group to ADP

ATP synthase functions as a carrier protein