ch 10 photosynthesis

Biology 2 with Ewing at California State University - Sacramento

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By: josephine severino
Created: 2011-04-09
Size: 68 flashcards
Views: 10

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photosynthesis

-process that converts solar energy to chemical energy

autotrophs

-sustain themselves without eating anything derived by other organisms

-producers of the biosphere

photoautotrophs

-almost all plants are these

-use energy from the sun to make organic molecules from H2O and CO2

what organisms do photosynthesis?

-plants

-algae

-other protists

-some prokaryotes (bacteria)

heterotrophs

-obtain their organic material from other organisms

-consumers of the biosphere

-almost all heterotrophs depend on photoautotrophs for food and O2

evolution of chloroplasts

-likely evolved from photosynthetic bacteria

-cyanobacteria: likely ancestor

-structurally similar

where does photosynthesis occur?

-leaves

chlorophyll

-green pigment with chloroplasts

what drives the synthesis of organic molecules in the chloroplasts?

-absorption of light energy by the chlorophylls

stomata

-pores on the leaf in which CO2 enters and O2 leaves

mesophyll

-interior tissue of the leaf where chloroplasts are mainly found

-typical mesophyll contains 30-40 chloroplasts

thylakoids

-connected sacs in the chloroplasts

-may be stacked in columns called grana

stroma

-dense fluid contained in the chloroplasts

equation of photosynthesis

6 CO2 + 12 H2O + light energy --> C6H12O6 + 6 O2 + 6 H2O

photosynthesis is a redox reaction

-H2O = oxidized

-CO2 = reduced

components of photosynthesis

-light reactions

-calvin cycle

process of light reactions

-occurs in thylakoids

-split H2O

-release O2

-reduce NADP+ to NADPH

-generate ATP from ADP through photophosphorylation

calvin cycle

-occurs in the stroma

-forms sugar from CO2 using ATP and NADPH

-begins with carbon fixation
-regenerates its starting material after molecules enter and leave the cycle

carbon fixation

-incorporating CO2 into organic molecules

function of light reactions

-convert solar energy to chemical energy of ATP and NADPH

-thylakoids perform this

characteristics of sunlight

-in the form of electromagnetic energy / electromagnetic radiation

-travels in rhythmic waves

-wavelength: distance between the crests of the waves

-wavelength determines the type of electromagnetic energy

electromagnetic spectrum

-entire range of electromagnetic energy, or radiation

visible light

-consists of wavelengths that produce the colors we see

photons

-discrete particles in light

pigments

-substances that absorb visible light

-diff pigments absorb diff wavelengths

-wavelengths not absorbed are reflected/transmitted

why are leaves green?

-because chlorophyll reflects and transmits green light

spectrophotometer

-measures a pigment's ability to absorb various wavelengths

-sends light through pigments and measures the fraction of light transmitted at each wavelength

absorption spectrum

-graph plotting a pigment's light absorption versus wavelength

-for chlorophyll a: its spectrum indicates that blue-violet and and red light works best for photosynthesis

action spectrum

-profiles relative effectiveness of diff wavelengths of radiation driving a process

who first demonstrated the action spectrum of photosynthesis?

-1883

-theodore w. engelmann

chlorophyll a

-main photosynthetic pigment

chlorophyll b

-accessory pigments

-broaden spectrum used for photosynthesis

carotenoids

-accessory pigment that absorbs excessive light that would damage chlorophyll

Mg ++

located in the center of the head portion of chlorophyll molecule

CH3

-chlorophyll a

CHO

-chlorophyll b

phorphyrin ring

light absorbing head of molecule

hydrocarbon tail

-interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts

fluorescence

-afterglow of photons given off when when excited electron falls back to ground state

photosystem

-consists of reaction-center complex (a type of protein complex) surrounded by light-harvesting complex

light harvesting complex

-pigment molecules bound to proteins

-funnel energy of photons to the reaction center

primary electron acceptor

-located in the reaction center

-receives excited electron from chlorophyll a

first step of light reactions

-solar powered transfer of an electron from a chlorophyll a molecule to primary electron acceptor

photosystem II (PS II)

-functions first

-best absorbs wavelengths of 680 nm

P680

-reaction-center chlorophyll a of PS II

photsystem I (PS I)

-best at absorbing wavelengths of 700 nm

P700

-reaction-center chlorophyll a of PS I

linear electron flow

-primary pathway / one of the routes for light reactions

-involves both photosystems

-produces ATP and NADPH using light energy

P680+

-very strong oxidizing agent

-electrons from splitting water are transferred from H+ to P680+

-P680+ gets reduces to P680

-O2 released as byproduct

process leading up to ATP synthesis in

-electron falls down ETC from primary electron acceptor of PS II to PS I
-energy released by fall drives creation of proton gradient across thylakoid membrane
-diffusion of H+ across membrane drives ATP synthesis

how electrons get to calvin cycle

-electron falls down an ETC from primary electron acceptor of PS I to protein ferredoxin (Fd)
-electrons are then transferred to NADP+ and reduce it to NADPH
-electrons of NADPH are available for reactions of the calvin cycle

cyclic electron flow

-uses only PS I and produces ATP but not NADPH
-generates surplus of ATP, satisfying higher demand in calvin cycle
-thought to have evolved before linear electron flow
-pay protect cells from light-induced damage

example of organism that have PS I but not PS II

-purple sulfur bacteria

where does mitochondria obtain chemical energy?

-transfer chemical energy from food to ATP
-protons pumpted to intermembrane space and drive ATP synthesis as they diffuse back into mitochondrial matrix

where do chloroplasts obtain chemical energy?

-transform light energy into chemical energy of ATP
-protons pumped into thylakoid space and drive ATP synthesis as they diffuse back into the stroma

basic function of light reactions

-generate ATP
-increase potential energy of electrons by moving them from H2O to NADPH

input and output of calvin cycle

-carbon enters as CO2 and leaves as a sugar glyceraldehyde-3-phosphate (G3P)
-for net synthesis of 1 G3P, cycle must occur 3x, fixing 3 molecules of CO2

phases of calvin cycle

-carbon fixation (catalyzed by rubisco)
-reduction
-regeneration of the CO2 acceptor (RuBP)

problems with dehydration

-plants close stomata, which conserves H2O but also limits photosynthesis
-closing of stomata = reduces access to Co2 and causes O2 to build up
-favor photorespiration: induced by dehydration, wasteful process

photorespiration

-rubisco adds O2 instead of CO2 in calvin cycle
-in normal conditions: initial fixation of CO2 via rubisco forms 3-carbon compound (in C3 plants)
-basically: consumes O2 and organic fuel and releases CO2 without producing ATP or sugar

what suggests that photorespiration may be an evolutionary relic

-rubisco first evolved when atmosphere had far less O2 and more CO2

affects of photorespiration

-limits damaging products of light reactions that build up in the absence of calvin cycle
-problem in many plants bc on hot day, it can drain as much as 50% of the carbon fixed by the calvin cycle

C4 plants

-minimize cost of photorespiration by incorporating CO2 into 4-carbon compounds in MESOPHYLL CELLS
-this requires enzyme POP carboxylase

PEP carboxylase

-has higher affinity for CO2 than rubisco
-can fix CO2 even when CO2 concc are low

bundle-sheath cells

-where 4-carbon compounds are exported to
-site where CO2 is released that is then used in the calvin cycle

crassulacean acid metabolism

-CAM
-used to fix carbon
-used by plants such as succulents

CAM plants

-open their stomata at night, incorporating CO2 into organic acids
-stomata close during the day and CO2 is released from organic acids and used in the calvin cycle

importance of photosynthesis

-energy that enters chloroplasts as sunlight is stored as chemical energy in organic compounds
-sugar supplies chemical energy
-plants store excess sugar (ie starch) in roots, tubers, seeds, fruits
-produces O2 in our atmosphere

About this deck

By: josephine severino
Created: 2011-04-09
Size: 68 flashcards
Views: 10

About StudyBlue

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy