Photosynthesis (chap 10) (this goes well with Cellular
respiration) Slide 2 Autotrophs sustain themselves without eating
anything derived from other organisms Autotrophs are the producers
of the biosphere, producing organic molecules from CO 2 and other
inorganic molecules Almost all plants are photoautotrophs, using
the energy of sunlight to make organic molecules from H 2 O and CO
2 Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings Slide 3 Photosynthesis occurs in plants, algae,
certain other protists, and some prokaryotes These organisms feed
not only themselves but also most of the living world Copyright
2008 Pearson Education, Inc., publishing as Pearson Benjamin
Cummings Slide 4 Fig. 10-2 (a) Plants (c) Unicellular protist 10 m
1.5 m 40 m (d) Cyanobacteria (e) Purple sulfur bacteria (b)
Multicellular alga Slide 5 Heterotrophs obtain their organic
material from other organisms Heterotrophs are the consumers of the
biosphere Almost all heterotrophs, including humans, depend on
photoautotrophs for food and O 2 Copyright 2008 Pearson Education,
Inc., publishing as Pearson Benjamin Cummings Slide 6 Concept 1:
Photosynthesis converts light energy to the chemical energy of food
Chloroplasts are structurally similar to and likely evolved from
photosynthetic bacteria The structural organization of these cells
allows for the chemical reactions of photosynthesis Copyright 2008
Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Slide 7 Slide 8 Chloroplasts: The Sites of Photosynthesis in Plants
Leaves are the major locations of photosynthesis Their green color
is from chlorophyll, the green pigment within chloroplasts Light
energy absorbed by chlorophyll drives the synthesis of organic
molecules in the chloroplast CO 2 enters and O 2 exits the leaf
through microscopic pores called stomata Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 9
Chloroplasts are found mainly in cells of the mesophyll, the
interior tissue of the leaf A typical mesophyll cell has 3040
chloroplasts The chlorophyll is in the membranes of thylakoids
(connected sacs in the chloroplast); thylakoids may be stacked in
columns called grana Chloroplasts also contain stroma, a dense
fluid Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings Slide 10 Fig. 10-3 Leaf cross section Vein
Mesophyll Stomata CO 2 O2O2 Chloroplast Mesophyll cell Outer
membrane Intermembrane space 5 m Inner membrane Thylakoid space
Thylakoid Granum Stroma 1 m Slide 11 Tracking Atoms Through
Photosynthesis: Scientific Inquiry Photosynthesis can be summarized
as the following equation: 6 CO 2 + 12 H 2 O + Light energy C 6 H
12 O 6 + 6 O 2 + 6 H 2 O Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings Chloroplasts split H 2 O
into hydrogen and oxygen, incorporating the electrons of hydrogen
into sugar molecules Slide 12 Reactants: Fig. 10-4 6 CO 2 Products:
12 H 2 O 6 O 2 6 H 2 O C 6 H 12 O 6 Photosynthesis is a redox
process in which H 2 O is oxidized and C O 2 is reduced Slide 13
Light Fig. 10-5-1 H2OH2O Chloroplast Light Reactions NADP + P ADP i
+ Slide 14 Light Fig. 10-5-2 H2OH2O Chloroplast Light Reactions
NADP + P ADP i + ATP NADPH O2O2 Slide 15 Light Fig. 10-5-3 H2OH2O
Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin
Cycle CO 2 Slide 16 Light Fig. 10-5-4 H2OH2O Chloroplast Light
Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2
O] (sugar) Slide 17 The Nature of Sunlight Light is a form of
electromagnetic energy, also called electromagnetic radiation Like
other electromagnetic energy, light travels in rhythmic waves
Wavelength is the distance between crests of waves Wavelength
determines the type of electromagnetic energy Copyright 2008
Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Slide 18 Slide 19 The electromagnetic spectrum is the entire range
of electromagnetic energy, or radiation Visible light consists of
wavelengths (including those that drive photosynthesis) that
produce colors we can see Light also behaves as though it consists
of discrete particles, called photons Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 20
UV Fig. 10-6 Visible light Infrared Micro- waves Radio waves X-rays
Gamma rays 10 3 m 1 m (10 9 nm) 10 6 nm 10 3 nm 1 nm 10 3 nm 10 5
nm 380 450 500 550 600 650 700 750 nm Longer wavelength Lower
energyHigher energy Shorter wavelength Slide 21 Fig. 10-7 Reflected
light Absorbed light Light Chloroplast Transmitted light Granum
Slide 22 A spectrophotometer measures a pigments ability to absorb
various wavelengths This machine sends light through pigments and
measures the fraction of light transmitted at each wavelength
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings Slide 23 Fig. 10-8 Galvanometer Slit moves to
pass light of selected wavelength White light Green light Blue
light The low transmittance (high absorption) reading indicates
that chlorophyll absorbs most blue light. The high transmittance
(low absorption) reading indicates that chlorophyll absorbs very
little green light. Refracting prism Photoelectric tube Chlorophyll
solution TECHNIQUE 1 23 4 Slide 24 An absorption spectrum is a
graph plotting a pigments light absorption versus wavelength The
absorption spectrum of chlorophyll a suggests that violet-blue and
red light work best for photosynthesis An action spectrum profiles
the relative effectiveness of different wavelengths of radiation in
driving a process Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings Slide 25 Fig. 10-9
Wavelength of light (nm) (b) Action spectrum (a) Absorption spectra
(c) Engelmanns experiment Aerobic bacteria RESULTS Rate of
photosynthesis (measured by O 2 release) Absorption of light by
chloroplast pigments Filament of alga Chloro- phyll a Chlorophyll b
Carotenoids 500 400 600700 600 500 400 Slide 26 Chlorophyll a is
the main photosynthetic pigment Accessory pigments, such as
chlorophyll b, broaden the spectrum used for photosynthesis
Accessory pigments called carotenoids absorb excessive light that
would damage chlorophyll Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings Slide 27 Fig. 10-10
Porphyrin ring: light-absorbing head of molecule; note magnesium
atom at center in chlorophyll a CH 3 Hydrocarbon tail: interacts
with hydrophobic regions of proteins inside thylakoid membranes of
chloroplasts; H atoms not shown CHO in chlorophyll b Slide 28 Fig.
10-11 (a) Excitation of isolated chlorophyll molecule Heat Excited
state (b) Fluorescence Photon Ground state Photon (fluorescence)
Energy of electron ee Chlorophyll molecule Slide 29 Fig. 10-12
THYLAKOID SPACE (INTERIOR OF THYLAKOID) STROMA ee Pigment molecules
Photon Transfer of energy Special pair of chlorophyll a molecules
Thylakoid membrane Photosystem Primary electron acceptor
Reaction-center complex Light-harvesting complexes Slide 30 There
are two types of photosystems in the thylakoid membrane Photosystem
II (PS II) functions first (the numbers reflect order of discovery)
and is best at absorbing a wavelength of 680 nm The reaction-center
chlorophyll a of PS II is called P680 Photosystem I (PS I) is best
at absorbing a wavelength of 700 nm The reaction-center chlorophyll
a of PS I is called P700 Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings The Photosystems.. Slide 31
Linear Electron Flow During the light reactions, there are two
possible routes for electron flow: cyclic and linear Linear
electron flow, the primary pathway, involves both photosystems and
produces ATP and NADPH using light energy Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 32
Pigment molecules Light P680 ee Primary acceptor 2 1 ee ee 2 H +
O2O2 + 3 H2OH2O 1/21/2 4 Pq Pc Cytochrome complex Electron
transport chain 5 ATP Photosystem I (PS I ) Light Primary acceptor
ee P700 6 Fd Electron transport chain NADP + reductase NADP + + H +
NADPH 8 7 ee ee 6 Fig. 10-13-5 Photosystem II (PS II ) Slide 33
Fig. 10-14 Mill makes ATP ee NADPH Photon ee ee ee ee ee ATP
Photosystem II Photosystem I ee Slide 34 Cyclic Electron Flow
Cyclic electron flow uses only photosystem I and produces ATP, but
not NADPH Cyclic electron flow generates surplus ATP, satisfying
the higher demand in the Calvin cycle Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 35
Fig. 10-15 ATP Photosystem II Photosystem I Primary acceptor Pq
Cytochrome complex Fd Pc Primary acceptor Fd NADP + reductase NADPH
NADP + + H + Slide 36 Some organisms such as purple sulfur bacteria
have PS I but not PS II Cyclic electron flow is thought to have
evolved before linear electron flow Cyclic electron flow may
protect cells from light-induced damage Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 37
In mitochondria, protons are pumped to the intermembrane space and
drive ATP synthesis as they diffuse back into the mitochondrial
matrix In chloroplasts, protons are pumped into the thylakoid space
and drive ATP synthesis as they diffuse back into the stroma
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings Slide 38 Fig. 10-17 Light Fd Cytochrome complex
ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H +
concentration) Thylakoid membrane THYLAKOID SPACE (high H +
concentration) STROMA (low H + concentration) Photosystem II
Photosystem I 4 H + Pq Pc Light NADP + reductase NADP + + H + NADPH
+2 H + H2OH2O O2O2 ee ee 1/21/2 1 2 3 Slide 39 Concept 10.3: The
Calvin cycle uses ATP and NADPH to convert CO 2 to sugar The Calvin
cycle, like the citric acid cycle, regenerates its starting
material after molecules enter and leave the cycle The cycle builds
sugar from smaller molecules by using ATP and the reducing power of
electrons carried by NADPH Copyright 2008 Pearson Education, Inc.,
publishing as Pearson Benjamin Cummings Slide 40 Carbon enters the
cycle as CO 2 and leaves as a sugar named glyceraldehyde-3-phospate
(G3P) For net synthesis of 1 G3P, the cycle must take place three
times, fixing 3 molecules of CO 2 The Calvin cycle has three
phases: Carbon fixation (catalyzed by rubisco) Reduction
Regeneration of the CO 2 acceptor (RuBP) Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 41
Fig. 10-18-1 Ribulose bisphosphate (RuBP) 3-Phosphoglycerate
Short-lived intermediate Phase 1: Carbon fixation (Entering one at
a time) Rubisco Input CO 2 P 3 6 3 3 P P P P Slide 42 Fig. 10-18-2
Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived
intermediate Phase 1: Carbon fixation (Entering one at a time)
Rubisco Input CO 2 P 3 6 3 3 P P P P ATP 6 6 ADP P P 6
1,3-Bisphosphoglycerate 6 P P 6 6 6 NADP + NADPH i Phase 2:
Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar)
Glucose and other organic compounds Calvin Cycle Slide 43 Fig.
10-18-3 Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived
intermediate Phase 1: Carbon fixation (Entering one at a time)
Rubisco Input CO 2 P 3 6 3 3 P P P P ATP 6 6 ADP P P 6
1,3-Bisphosphoglycerate 6 P P 6 6 6 NADP + NADPH i Phase 2:
Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar)
Glucose and other organic compounds Calvin Cycle 3 3 ADP ATP 5 P
Phase 3: Regeneration of the CO 2 acceptor (RuBP) G3P Slide 44 :
Alternative mechanisms of carbon fixation have evolved in hot, arid
climates Dehydration is a problem for plants, sometimes requiring
trade-offs with other metabolic processes, especially
photosynthesis On hot, dry days, plants close stomata, which
conserves H 2 O but also limits photosynthesis The closing of
stomata reduces access to CO 2 and causes O 2 to build up These
conditions favor a seemingly wasteful process called
photorespiration Copyright 2008 Pearson Education, Inc., publishing
as Pearson Benjamin Cummings Slide 45 Slide 46 Photorespiration: An
Evolutionary Relic? In most plants (C 3 plants), initial fixation
of CO 2, via rubisco, forms a three-carbon compound In
photorespiration, rubisco adds O 2 instead of CO 2 in the Calvin
cycle Photorespiration consumes O 2 and organic fuel and releases
CO 2 without producing ATP or sugar Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 47
Photorespiration may be an evolutionary relic because rubisco first
evolved at a time when the atmosphere had far less O 2 and more CO
2 Photorespiration limits damaging products of light reactions that
build up in the absence of the Calvin cycle In many plants,
photorespiration is a problem because on a hot, dry day it can
drain as much as 50% of the carbon fixed by the Calvin cycle
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings Slide 48 C 4 Plants C 4 plants minimize the cost
of photorespiration by incorporating CO 2 into four-carbon
compounds in mesophyll cells This step requires the enzyme PEP
carboxylase PEP carboxylase has a higher affinity for CO 2 than
rubisco does; it can fix CO 2 even when CO 2 concentrations are low
These four-carbon compounds are exported to bundle-sheath cells,
where they release CO 2 that is then used in the Calvin cycle
Copyright 2008 Pearson Education, Inc., publishing as Pearson
Benjamin Cummings Slide 49 Fig. 10-19 C 4 leaf anatomy Mesophyll
cell Photosynthetic cells of C 4 plant leaf Bundle- sheath cell
Vein (vascular tissue) Stoma The C 4 pathway Mesophyll cell CO 2
PEP carboxylase Oxaloacetate (4C) Malate (4C) PEP (3C) ADP ATP
Pyruvate (3C) CO 2 Bundle- sheath cell Calvin Cycle Sugar Vascular
tissue Slide 50 CAM Plants Some plants, including succulents, use
crassulacean acid metabolism (CAM) to fix carbon CAM plants open
their stomata at night, incorporating CO 2 into organic acids
Stomata close during the day, and CO 2 is released from organic
acids and used in the Calvin cycle Copyright 2008 Pearson
Education, Inc., publishing as Pearson Benjamin Cummings Slide 51
Fig. 10-20 CO 2 Sugarcane Mesophyll cell CO 2 C4C4 Bundle- sheath
cell Organic acids release CO 2 to Calvin cycle CO 2 incorporated
into four-carbon organic acids (carbon fixation) Pineapple Night
Day CAM Sugar Calvin Cycle Calvin Cycle Organic acid (a) Spatial
separation of steps (b) Temporal separation of steps CO 2 1 2
