Chapter 10 Study Guide
Vocabulary:
Word Roots:
auto- = self
-troph = food
chloro- = green
-phyll = leaf
electro- = electricity
hetero- = other
meso- = middle
photo- = light
Key Terms:
autotroph: An organism that obtains organic food molecules without eating other
organisms or substances derived from other organisms. Autotrophs use energy
from the sun or from the oxidation of inorganic substances to make organic
molecules from inorganic ones.
Calvin cycle: The second of two major stages in photosynthesis (following the light
reactions), involving atmospheric CO2 fixation and reduction of the fixed carbon into
carbohydrate.
Carbon fixation: The incorporation of carbon from CO2 into an organic compound
by an autotrophic organism
Carotenoid: An accessory pigment, either yellow or orange, in the chloroplasts of
plants.
Chlorophyll: A green pigment located within the chloroplasts of plants.
Chlorophyll a: A type of blue-green photosynthetic pigment that participates
directly in the light reactions.
Chlorophyll b: A type of yellow-green accessory photosynthetic pigment that
transfers energy to chlorophyll a.
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Cyclic electron flow: A route of electron flow during the light reactions of
photosynthesis that involves only photosystem I and that produces ATP but not
NADPH or oxygen.
Glyceraldehyde-3-phosphate: The carbohydrate produced directly from the Calvin
cycle.
Heterotroph: An organism that obtains organic food molecules by eating other
organisms or their by-products.
Light reactions: The steps in photosynthesis that occur in the thylakoid membranes
of the chloroplast and that convert solar energy to the chemical energy of ATP and
NADPH, evolving oxygen in the process.
Mesophyll: The ground tissue of a leaf, sandwiched between the upper and lower
epidermis and specialized for photosynthesis.
NADP+: Nicotinamide adenine dinucleotide phosphate, an acceptor that
temporarily stores energized electrons produced during the light reactions.
Non-cyclic electron flow: A route of electron flow during the light reactions of
photosynthesis that involves both photosystems and produces ATP, NADPH, and
oxygen.
Photon: A quantum, or discrete amount, of light energy.
Photophosphorylation: The process of generating ATP from ADP and phosphate by
means of a proton-motive force generated by the thylakoid membrane of the
chloroplast during the light reactions of photosynthesis.
Photosynthesis: The conversion of light energy to chemical energy that is stored in
glucose or other organic compounds
Photosystem: Light-capturing unit located in the thylakoid membrane of the
chloroplast, consisting of a reaction center surrounded by numerous lightharvesting complexes.
Photosystem I: One of two light-capturing units in a chloroplast’s thylakoid
membrane; it has two molecules of P700 chlorophyll a at its reaction center.
Photosystem: II: One of two light-capturing units in a chloroplast’s thylakoid
membrane; it has two molecules of P680 chlorophyll a at its reaction center.
Primary electron acceptor: A specialized molecule sharing the reaction center with
the pair of reaction-center chlorophyll a molecules; it accepts an electron from one
of these two chlorophylls.
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Reaction center: Complex of proteins associated with two special chlorophyll a
molecules and a primary electron acceptor.
Rubisco: Ribulose carboxylase, the enzyme that catalyzes the first step of the Calvin
cycle
Stoma: A microscopic pore surrounded by guard cells in the epidermis of leaves and
stems that allows gas exchange between the environment and the interior of the
plant.
Stroma: The fluid of the chloroplast surrounding the thylakoid membrane
Thylakoid: A flattened membrane sac inside the chloroplast, used to convert light
energy to chemical energy.
Visible light: That portion of the electromagnetic spectrum detected as various
colors by the human eye, ranging in wavelength from about 380 nm to about 750
nm.
Wavelength: The distance between crests of waves, such as those of the
electromagnetic spectrum.
Chapter 10 Important Points:
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Photosynthesis is the process of converting light energy to chemical energy
Only producers or autotrophs can turn inorganic carbon molecules into
organic molecules
Consumers or heterotrophs are dependent on the producers for their organic
molecules
Photosynthesis is an anabolic pathway with a series of redox reactions
Summary equation for photosynthesis (does not happen in one reaction however)
6CO2 + 12H2O + Light energy
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C6 H12 O6 + 6O2 + 6 H2O
Light energy is a form of kinetic energy and a subtype of electromagnetic
energy
Only the visible light range (380nm-750nm wavelengths) is used by
photosynthesis
o Within the visible light, only purple/blue and orange/red light waves
are used by photosynthesis
o The green light waves are NOT used by photosynthesis
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2 major stages of photosynthesis:
1.) Light reactions
 Take place in the green thylakoid membranes inside the chloroplast
 When light energy hits chlorophyll pigment molecules, that energy is
captured by raising the electrons in the chlorophyll to an excited state
 Chlorophyll is organized into photosystems, I (700) and II (680)
 In non-cyclic electron flow, the excited electrons from chlorophyll molecules
are captured by primary electron acceptors in photosystem II.
o These electrons are passed down a short ETC and through
chemiosmosis, ATP is generated (photophosphorylation)
 Electrons removed from chlorophyll in PSII are replaced by splitting water
o Oxygen is made as a byproduct
 Meanwhile, light energy also excites electrons in photosystem I which are
captured by a primary electron acceptor in PSI
o These electrons are replaced by the ones moving down the ETC from
PS II
o PS I’s primary acceptor passes its electrons to NADP+ reducing it to
NADPH
 The ATP and NADPH made by the light reactions are then used by the next
stage, Calvin Cycle, to make sugar
 In cyclic electron flow, only Photosystem I is used so no NADPH or oxygen is
produced
o Electrons stay in a “loop” of moving through the ETC to make ATP
only
2.) Calvin Cycle
 Takes place in stroma (fluid area around thylakoids)
 With energy provided by ATP and reducing power of NADPH from light
reactions, carbon dioxide is fixed into sugar (specifically G3P)
3 stages of Calvin Cycle
1.) Carbon Fixation
 Inorganic carbon dioxide is “fixed” into organic form with help of enzyme
rubisco which joins CO2 to ribulouse biphosphate (RuBP)
2.) Reduction
 Gradual reduction of using ATP and NADPH from light reactions to make
Glyceraldehyde 3-phosphate (G3P)
 One molecule of G3P leaves the cycle and can be converted to other organic
molecules such as glucose
3.) Regeneration
 Remaining 5 G3P molecules are converted with more ATP from light
reactions back into RuBP to start cycle over again as long as more CO2 enters
and ATP and NAHPH keeps coming from the light reactions
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