Ch 10: Photosynthesis: Energy from Sunlight
photosynthesis – anabolic process carried out by green plants / some microorganisms in which
visible light (sunlight) is captured and used to convert carbon dioxide CO2 into compounds such
as ATP / glucose
light reaction – initial phase of photosynthesis, in which light energy is converted into chemical
energy; takes place in thylakoid
carbon-fixation reaction – phase of photosynthesis in which chemical energy captured in the
light reactions is used to drive reduction of CO2 to form carbohydrates; chemical energy = ATP,
NADPH; takes place in stroma (bed) of chloroplast
Calvin Benson cycle – stage of photosynthesis in which CO2 reactions with rubisco to form 3PG,
3PG is reduced to a sugar, and rubisco is regenerated, while other products are released to the
rest of the plant
autotrophs – organisms capable of living exclusively on inorganic materials, water, and some
energy source such as sunlight or chemically reduced matter; make their own carbohydrate
“food” which can be used directly or converted into other molecules for anabolic and catabolic
processes
- include plants, algae, cyanobacteria
- heterotrophs – organisms that require pre-formed organic molecules as food
chloroplast – a plastid (organelle) in green plant cells that contains chlorophyll; location in
which photosynthesis takes place
photons – a quantum of visible radiation; a “packet” of light energy
,chlorophylls – any of several green pigments associated with chloroplasts or with certain
bacterial membranes; responsible for trapping light energy for photosynthesis
- absorbs both blue and red light
reaction center – a group of electron transfer proteins that receive energy from light-absorbing
pigments and convert it to chemical energy by redox reactions
photosystem – biochemical mechanism in plants by which chlorophyll absorbs light energy for
photosynthesis; chlorophylls and carotenoids are embedded in membrane proteins combined
with other molecules such as electron carriers
- 2 mechanisms (photosystems I & II) involve different chlorophyll-protein complexes
non-cyclic electron transport – in photosynthesis, the flow of electrons that forms ATP, NADPH,
and O2
cyclic electron transport – in photosynthetic light reactions, flow of electrons that produces
ATP but not NADPH or O2; uses photosystem I and electron transport system
- called cyclic because electron is passed from excited chlorophyll and recycles back to
the same chlorophyll
chemiosmosis
photophosphorylation – mechanism for ATP formation in chloroplasts in which electron
transport is coupled to the transport of hydrogen ions (protons) across the thylakoid
membrane; requires ATP synthase
ribulose biphosphate carboxylase / oxygenase (rubisco) – enzyme that combines CO2 or O2
with ribulose biphosphate to catalyze the first step of photosynthetic carbon fixation or
, photorespiration; most abundant protein in the world – constitutes up to 50% of all proteins in
every plant leaf
glyceraldehyde 3-phosphate (G3P) – a phosphorylated 3-carbon sugar; an intermediate in
glycolysis and photosynthetic carbon fixation; also called triose phosphate
stomata – small pores in plant epidermis that permit gas exchange and prevent water from
evaporating from the leaf by closing
photorespiration – fixation of O2 instead of CO2 in chloroplasts on hot, sunny days resulting in
the release of some CO2 fixed in photosynthesis; consumes O2, releases CO2, occurs only in the
light
thylakoid
10.1
Photosynthesis Uses Light to Make Carbohydrates
- energy stored in chemical bonds in almost all organisms ultimately comes from the sun
- plants, algae, cyanobacteria live in aerobic environments and carry out oxygenic
photosynthesis
o 6CO2 + 6H2O C6H12O6 + 6O2
o sugars, the organic products of photosynthesis, are transported throughout the
plant body
o CO2 enters and O2 and H2O exit the leaves through pores on the leaf surface
(stomata)
o endergonic reaction
Experiments with isotopes show that O2 comes from H2O in oxygenic photosynthesis
- all oxygen gas produced during photosynthesis comes from water
o 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
photosynthesis – anabolic process carried out by green plants / some microorganisms in which
visible light (sunlight) is captured and used to convert carbon dioxide CO2 into compounds such
as ATP / glucose
light reaction – initial phase of photosynthesis, in which light energy is converted into chemical
energy; takes place in thylakoid
carbon-fixation reaction – phase of photosynthesis in which chemical energy captured in the
light reactions is used to drive reduction of CO2 to form carbohydrates; chemical energy = ATP,
NADPH; takes place in stroma (bed) of chloroplast
Calvin Benson cycle – stage of photosynthesis in which CO2 reactions with rubisco to form 3PG,
3PG is reduced to a sugar, and rubisco is regenerated, while other products are released to the
rest of the plant
autotrophs – organisms capable of living exclusively on inorganic materials, water, and some
energy source such as sunlight or chemically reduced matter; make their own carbohydrate
“food” which can be used directly or converted into other molecules for anabolic and catabolic
processes
- include plants, algae, cyanobacteria
- heterotrophs – organisms that require pre-formed organic molecules as food
chloroplast – a plastid (organelle) in green plant cells that contains chlorophyll; location in
which photosynthesis takes place
photons – a quantum of visible radiation; a “packet” of light energy
,chlorophylls – any of several green pigments associated with chloroplasts or with certain
bacterial membranes; responsible for trapping light energy for photosynthesis
- absorbs both blue and red light
reaction center – a group of electron transfer proteins that receive energy from light-absorbing
pigments and convert it to chemical energy by redox reactions
photosystem – biochemical mechanism in plants by which chlorophyll absorbs light energy for
photosynthesis; chlorophylls and carotenoids are embedded in membrane proteins combined
with other molecules such as electron carriers
- 2 mechanisms (photosystems I & II) involve different chlorophyll-protein complexes
non-cyclic electron transport – in photosynthesis, the flow of electrons that forms ATP, NADPH,
and O2
cyclic electron transport – in photosynthetic light reactions, flow of electrons that produces
ATP but not NADPH or O2; uses photosystem I and electron transport system
- called cyclic because electron is passed from excited chlorophyll and recycles back to
the same chlorophyll
chemiosmosis
photophosphorylation – mechanism for ATP formation in chloroplasts in which electron
transport is coupled to the transport of hydrogen ions (protons) across the thylakoid
membrane; requires ATP synthase
ribulose biphosphate carboxylase / oxygenase (rubisco) – enzyme that combines CO2 or O2
with ribulose biphosphate to catalyze the first step of photosynthetic carbon fixation or
, photorespiration; most abundant protein in the world – constitutes up to 50% of all proteins in
every plant leaf
glyceraldehyde 3-phosphate (G3P) – a phosphorylated 3-carbon sugar; an intermediate in
glycolysis and photosynthetic carbon fixation; also called triose phosphate
stomata – small pores in plant epidermis that permit gas exchange and prevent water from
evaporating from the leaf by closing
photorespiration – fixation of O2 instead of CO2 in chloroplasts on hot, sunny days resulting in
the release of some CO2 fixed in photosynthesis; consumes O2, releases CO2, occurs only in the
light
thylakoid
10.1
Photosynthesis Uses Light to Make Carbohydrates
- energy stored in chemical bonds in almost all organisms ultimately comes from the sun
- plants, algae, cyanobacteria live in aerobic environments and carry out oxygenic
photosynthesis
o 6CO2 + 6H2O C6H12O6 + 6O2
o sugars, the organic products of photosynthesis, are transported throughout the
plant body
o CO2 enters and O2 and H2O exit the leaves through pores on the leaf surface
(stomata)
o endergonic reaction
Experiments with isotopes show that O2 comes from H2O in oxygenic photosynthesis
- all oxygen gas produced during photosynthesis comes from water
o 6CO2 + 12H2O C6H12O6 + 6O2 + 6H2O
