光合作用

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CAMPBELL

BIOLOGY

TENTH EDITION CAMPBELL

BIOLOGY

Reece • Urry • Cain • Wasserman •

Minorsky • Jackson TENTH EDITION

11

Photosynthetic

Processes

Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick 李澤民海洋植物生理暨生質能研究室海洋生物科技暨資源學系國立中山大學高雄台灣

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The Process That Feeds the Biosphere

 Photosynthesis is the process that converts solar

energy into chemical energy

 Directly or indirectly, photosynthesis nourishes

(3)

 Autotrophs sustain themselves without eating anything derived from other organisms

 Autotrophs are the producers of the biosphere,

producing organic molecules from CO₂ and other

inorganic molecules

 Almost all plants are photoautotrophs, using the

(4)

(5)

Figure 11.1a

Other organisms also benefit from photosynthesis.

(6)

 Photosynthesis occurs in plants, algae, certain other unicellular eukaryotes, and some

prokaryotes

 These organisms feed not only themselves but

(7)

(e) Purple sulfur bacteria 40 μm 1 μ m 11 μm

(8)

Figure 11.2a

(9)

Figure 11.2b

(10)

Figure 11.2c

(c) Unicellular eukaryotes

11

μ

(11)

Figure 11.2d

(d) Cyanobacteria

40 μm

(12)

Figure 11.2e

1

μ

m

(e) Purple sulfur bacteria

(13)

 相對於autotrophs

 Heterotrophs obtain their organic material from other organisms

 Heterotrophs are the consumers of the biosphere

 Almost all heterotrophs, including humans, depend

(14)

 Earth’s supply of fossil fuels was formed from the remains of organisms that died hundreds of

millions of years ago

 In a sense, fossil fuels represent stores of solar

(15)

(16)

Concept 11.1: Photosynthesis converts light

energy to the chemical energy of food

 Chloroplasts are structurally similar to and likely

evolved from photosynthetic bacteria 藍綠菌

 The structural organization of these organelles

allows for the chemical reactions of

photosynthesis 基質類囊體

(17)

© 2014 Pearson Education, Inc. Figure 11.4 Stroma Granum Thylakoid Thylakoid space Outer membrane Intermembrane space Inner membrane 20 μm Stomata Chloroplast _Mesophyll cell 1 μm Mesophyll Chloroplasts Vein Leaf cross section

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Chloroplasts: The Sites of Photosynthesis

in Plants

 Leaves are the major locations of photosynthesis

 Chloroplasts are found mainly in cells of the

mesophyll, the interior tissue of the leaf

 Each mesophyll cell contains 30–40 chloroplasts

 CO₂ enters and O₂ exits the leaf through

(19)

Figure 11.4a

Leaf cross section

Stomata Chloroplast Mesophyll Chloroplasts Vein Mesophyll cell 20 μm CO₂ O₂

(20)

Figure 11.4d

20 μm Mesophyll

(21)

 A chloroplast has an envelope of two membranes

surrounding a dense fluid called the stroma

 Thylakoids are connected sacs in the chloroplast which compose a third membrane system

 Thylakoids may be stacked in columns called

grana

 Chlorophyll, the pigment which gives leaves their

(22)

Figure 11.4b Chloroplast Stroma Granum Thylakoid Thylakoid space Outer membrane Intermembrane space Inner membrane 1 μm

(23)

Figure 11.4c

Stroma Granum

(24)

Tracking Atoms Through Photosynthesis:

Scientific Inquiry

 Photosynthesis is a complex series of reactions

that can be summarized as the following equation:

6 CO₂ + 12 H₂O + Light energy → C₆H₁₂O₆ + 6 O₂ + 6 H₂O

 The overall chemical change during

photosynthesis is the reverse of the one that occurs during cellular respiration

(25)

The Splitting of Water

 Chloroplasts split H₂O into hydrogen and oxygen,

incorporating the electrons of hydrogen into sugar molecules and releasing oxygen as a by-product

(26)

Figure 11.5

Reactants:

Products:

6 CO₂ 12 H₂O

(27)

Photosynthesis as a

Redox Process

 Photosynthesis reverses the direction of electron

flow compared to respiration

 Photosynthesis is a redox process in which H₂O is

oxidized and CO₂ is reduced

 Photosynthesis is an endergonic process; the

(28)

Figure 11.UN01

becomes reduced

(29)

The Two Stages of Photosynthesis: A Preview

 Photosynthesis consists of the light reactions

(the photo part) and Calvin cycle (the synthesis

part)

 The light reactions (in the thylakoids)

 Split H₂O

 Release O₂

 Reduce the electron acceptor NADP+ to NADPH

(30)

 The Calvin cycle (in the stroma) forms sugar from

CO₂, using ATP and NADPH

 The Calvin cycle begins with carbon fixation,

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(32)

Figure 11.6-2 Light Thylakoid Stroma Chloroplast LIGHT REACTIONS NADP+ ADP P _i + H₂O NADPH ATP O₂

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© 2014 Pearson Education, Inc. Figure 11.6-3 Light Thylakoid Stroma Chloroplast LIGHT REACTIONS NADP+ ADP P _i + H₂O O₂ CO₂ NADPH ATP CALVIN CYCLE

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Figure 11.6-4 Light Thylakoid Stroma Chloroplast LIGHT REACTIONS NADP+ ADP P _i + H₂O [CH₂O] (sugar) CALVIN CYCLE CO₂ NADPH ATP O₂

(35)

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Concept 11.2: The light reactions convert solar

energy to the chemical energy of ATP and

NADPH

 Chloroplasts are solar-powered chemical factories

 Their thylakoids transform light energy into the chemical energy of ATP and NADPH

(38)

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

(39)

 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

(40)

Figure 11.7

Visible light

Gamma

rays X-rays UV Infrared

Micro-waves Radio waves 380 450 500 550 600 650 700 750 nm Shorter wavelength

Higher energy Lower energy

Longer wavelength

11− 5 nm 11− 3 nm 1 nm 113 nm 116 nm (11 nm)9

1 m

(41)

Photosynthetic

Pigments

: The Light Receptors

 Pigments are substances that absorb visible light

 Different pigments absorb different wavelengths

 Wavelengths that are not absorbed are reflected

or transmitted

 Leaves appear green because chlorophyll reflects

and transmits green light

(42)

Figure 11.8 Light Chloroplast Reflected light Granum Transmitted light Absorbed light

(43)

(44)

 A spectrophotometer measures a pigment’s ability to absorb various wavelengths

 This machine sends light through pigments and

measures the fraction of light transmitted at each wavelength

(45)

The high transmittance (low

absorption) reading indicates that chlorophyll absorbs very

little green light. Slit moves to pass light

of selected wavelength.

Green light

Blue light

The low transmittance (high absorption) reading indicates that chlorophyll absorbs

most blue light.

1

2 3

(46)

Figure 11.10 Chloro-phyll a Chlorophyll b Carotenoids 400 500 600 700 Wavelength of light (nm) (a) Absorption spectra

A bs or pt ion of l ight by c hl or opl a s t pi gme nts Rat e o f p hotos y n the s is (me a s ur e d by O 2 release) 400 500 600 700 400 500 600 700 (b) Action spectrum Aerobic bacteria Filament of alga

(47)

 An absorption spectrum is a graph plotting a pigment’s 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

(48)

Figure 11.10a Chloro-phyll a Chlorophyll b Carotenoids 400 500 600 700 Wavelength of light (nm) (a) Absorption spectra

A bsor pt ion of l ight by c hl or opl ast pi gm ent s

(49)

(50)

 The action spectrum of photosynthesis was first demonstrated in 1883 by Theodor W. Engelmann

 In his experiment, he exposed different segments

of a filamentous alga to different wavelengths

 Areas receiving wavelengths favorable to

photosynthesis produced excess O₂

 He used the growth of aerobic bacteria clustered

(51)

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Why so many chlorophyll pigments?

In response to different wavelength in

the environment!

1. shading

2. under forest

Chl b/Chl a increases (Chl b content

increases)

(53)

 Chlorophyll a is the main photosynthetic pigment

 Chlorophyll b, broaden the spectrum used for photosynthesis

 The difference in the absorption spectrum

between chlorophyll a and b is due to a slight

structural difference between the pigment molecules

 Accessory pigments called carotenoids

absorb excessive light that would damage chlorophyll

(54)

Figure 11.11 Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center Hydrocarbon tail:

interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown CH in chlorophyll a in chlorophyll b 3 CHO CH₃

(55)

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 Accessory pigments called carotenoids function in photoprotection; they absorb excessive light that would damage chlorophyll

(57)

Sun Radiation

Chlorophyll is the main photosynthetic pigment

Photosynthetically active radiation, often

abbreviated PAR,

designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic

organisms are able to use in the process of photosynthesis.

(58)

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Phycobiliprotein: 藻膽蛋白

藍綠藻

紅藻

藻紅素

Phycoerthyrin

藻藍素

Phycocyanin

異藻藍素

Allophycocyanin

(62)

Phycobilisome藻膽蛋白體 in cyanobacteria

These antennae (called "phycobilisomes" in Synechococcus) are composed of pigment-proteins complexes arranged in such a way to capture light with a high

efficiency. Pigments that are bound to antenna systems may have very different colours (such as green, blue, pink or orange) and this will determine the wavelengths of the solar spectrum that cells can efficiently harvest in the oceanic waters.

(63)

(64)

complementary chromatic adaptation (CCA)

The Journal of Biological Chemistry, 276, 11449-11452 (2001)

(65)

Phycobiliproteins, bilin variation, and group III CA regulation.

Kehoe D M PNAS 2010;107:9029-9030

(66)

complementary chromatic

adaptation

Structure of a hemidiscoidal

phycobilisome of Tolypothrix tenuis

under different light conditions. (a) When illuminated by white light, the

phycobilisome contains phycoerythrin, phycocyanin, and allophycocyanin. Energy absorbed by phycoerythrin is transferred to phycocyanin and

allophycocyanin. The allophycocyanin core proteins are attached, via a linker protein, to the photosynthetic membrane, which is not shown. (b) When

illuminated by red light, the phycobilisome undergoes

complementary chromatic adaptation, in which phycoerythrin is no longer

produced but additional phycocyanin is produced. (After R. MacColl and D.

Guard-Friar, Phycobiliproteins, CRC illuminated by white light illuminated by red light

(67)

Excitation of Chlorophyll by Light

 When a pigment absorbs light, it goes from a

ground state to an excited state, which is unstable

 When excited electrons fall back to the ground

state, photons are given off, an afterglow called

fluorescence

 If illuminated, an isolated solution of chlorophyll

(68)

Figure 11.12

Excited state

Heat

(a) Excitation of isolated chlorophyll molecule (b) Fluorescence Ground state Photon (fluorescence) Photon Chlorophyll molecule E n er g y o f el ect ro n e−

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Figure 11.12a

(70)

(71)

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A Photosystem: A Reaction-Center Complex

Associated with Light-Harvesting Complexes

 A photosystem consists of a reaction-center

complex (a type of protein complex) surrounded by light-harvesting complexes

 The light-harvesting complexes=Lhc (pigment

molecules bound to proteins) transfer the energy of photons to the reaction center

(73)

Figure 11.13

(a) How a photosystem harvests light (b) Structure of a photosystem

Chlorophyll STROMA THYLA-KOID SPACE Protein subunits Thy la k oi d m e m bra ne Pigment molecules Primary electron acceptor Reaction-center complex STROMA Photosystem Light-harvesting complexes Photon Transfer

of energy Special pair of chloro-_{phyll a molecules} THYLAKOID SPACE (INTERIOR OF THYLAKOID) Thy la k oi d m e m bra ne e−

(74)

Figure 11.13a

(a) How a photosystem harvests light

Pigment molecules Primary electron acceptor Reaction-center complex STROMA Photosystem Light-harvesting complexes Photon Transfer

of energy Special pair of chloro-_{phyll a molecules} THYLAKOID SPACE (INTERIOR OF THYLAKOID) T h y lako id m em b ran e e−

(75)

(76)

Photosystem II (PSII)

Photosystem II contains chlorophylls a and b and absorbs light at

680nm. This is a large protein complex that is located in the thylakoid membrane.

(77)

LHC-II

 MOST ABUNDANT MEMBRANE PROTEIN IN CHLOROPLASTS OF GREEN PLANTS

 A TRANSMEMBRANE PROTEIN

 BINDS

 ~ 7 CHLOROPHYLL a MOLECULES

 ~ 5 CHLOROPHYLL b MOLECULES

 TWO CAROTENOIDS

 COMPRISES ABOUT 50% OF ALL CHLOROPHYLL IN BIOSPHERE

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 A primary electron acceptor in the reaction

center accepts excited electrons and is reduced as a result

 Solar-powered transfer of an electron from a

chlorophyll a molecule to the primary electron acceptor is the first step of the light reactions

(82)

 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

(83)

 Photosystem I (PS I) is best at absorbing a

wavelength of 700 nm

 The reaction-center chlorophyll a of PS I is called

(84)

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

(85)

 There are 8 steps in linear electron flow:

1. A photon hits a pigment and its energy is passed among pigment molecules until it excites P680

2. An excited electron from P680 is transferred to the primary electron acceptor (we now call it P680+)

(86)

Figure 11.UN02 Light H₂O CO₂ O₂ LIGHT REACTIONS CALVIN CYCLE ATP NADPH ADP NADP+ [CH₂O] (sugar)

(87)

(88)

Figure 11.14-2 Pigment molecules e− 1 2 P680 Light Photosystem II (PS II) Primary acceptor 3 e− e− 2 H+ + O₂ H₂O ½

(89)

© 2014 Pearson Education, Inc. Figure 11.14-3 Pigment molecules e− 1 2 P680 Light Photosystem II (PS II) Primary acceptor 3 e− e− 2 H+ + O₂ H₂O ATP 4 5 Electron transport chain Cytochrome complex Pq Pc ½

(90)

Figure 11.14-4 Pigment molecules e− 1 2 P680 Light Photosystem II (PS II) Primary acceptor 3 e− e− 2 H+ + O₂ H₂O ATP 4 5 Electron transport chain Cytochrome complex Pq Pc P700 Light Photosystem I (PS I) 6 Primary acceptor e− ½

(91)

© 2014 Pearson Education, Inc. Figure 11.14-5 Pigment molecules e− 1 2 P680 Light Photosystem II (PS II) Primary acceptor 3 e− e− 2 H+ + O₂ H₂O ATP 4 5 Electron transport chain Cytochrome complex Pq Pc P700 Light Photosystem I (PS I) 6 Primary acceptor e− e− 7 8 Fd e− Electron transport chain NADP+ reductase NADPH NADP+ + H+ ½

(92)

(93)

3. H₂O is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680

 P680+ is the strongest known biological oxidizing agent

(94)

4. Each electron “falls” down an electron transport chain from the primary electron acceptor of PS II to PS I

5. Energy released by the fall drives the creation of a proton gradient across the thylakoid membrane

 Diffusion of H+ (protons) across the membrane drives ATP synthesis

(95)

6. In PS I (like PS II), transferred light energy excites P700, which loses an electron to an electron

acceptor

 P700+ (P700 that is missing an electron) accepts an electron passed down from PS II via the

(96)

7. Each electron “falls” down an electron transport chain from the primary electron acceptor of PS I to the protein ferredoxin (Fd)

8. The electrons are then transferred to NADP+ and reduce it to NADPH

 The electrons of NADPH are available for the reactions of the Calvin cycle

(97)

 The energy changes of electrons during linear flow

through the light reactions can be shown in a mechanical analogy

(98)

Figure 11.15 Mill makes ATP NADPH Photosystem II Photosystem I ATP e− e− e− e− e− e− e−

(99)

Cyclic Electron Flow

 In cyclic electron flow, electrons cycle back from

Fd to the PS I reaction center

 Cyclic electron flow uses only photosystem I and

produces ATP, but not NADPH

(100)

Figure 11.16 Primary acceptor Primary acceptor Fd Cytochrome complex Pc Pq Photosystem II Photosystem I Fd NADP+ + H+ NADP+ reductase NADPH ATP

(101)

 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

(102)

Cyclic Electron Flow

• Electron in Photosystem I is excited and transferred to ferredoxin that shuttles the electron to the

cytochrome complex.

(103)

(104)

A Comparison of

Chemiosmosis

in Chloroplasts

and Mitochondria

 Chloroplasts and mitochondria generate ATP by

chemiosmosis, but use different sources of energy

 Mitochondria transfer chemical energy from food

to ATP; chloroplasts transform light energy into the chemical energy of ATP

 Spatial organization of chemiosmosis differs

between chloroplasts and mitochondria but also shows similarities

(105)

 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

(106)

Figure 11.17 MITOCHONDRION STRUCTURE CHLOROPLAST STRUCTURE Thylakoid membrane Stroma ATP Thylakoid space Inter-membrane space Inner membrane Matrix Key Diffusion Electron transport chain ATP synthase ADP + H+ H+ Higher [H+] Lower [H+] P_i

(107)

 ATP and NADPH are produced on the side facing

the stroma, where the Calvin cycle takes place

 In summary, light reactions generate ATP and

increase the potential energy of electrons by

(108)

Figure 11.18 Photosystem II Photosystem I Cytochrome complex Light Pq Light 4 H+ +2 H+ 4 H+ O₂ H₂O Pc Fd 3 2 1 NADP+ To Calvin Cycle NADP+ reductase STROMA (low H+ concentration) ATP synthase THYLAKOID SPACE (high H+ concentration) Thylakoid membrane ADP + H+ ATP P_i e−e − NADPH ½ + H+

(109)

© 2014 Pearson Education, Inc. Figure 11.18a STROMA (low H+ concentration) ATP ADP ATP synthase P_i + H+ THYLAKOID SPACE (high H+ concentration) 4 H+ Cytochrome complex Light Photosystem I Pc Pq 4 H+ Light Photosystem II 4 H+ Pc Fd Thylakoid membrane +2 H+ H₂O O₂ ½ e− e− 2 1

(110)

Figure 11.18b Cytochrome complex Light Photosystem I Pc Pq Fd NADP+ reductase NADP+ + H+ NADPH To Calvin Cycle STROMA (low H+ concentration) ATP ADP ATP synthase P + H+ THYLAKOID SPACE (high H+ concentration) 4 H+ 2 3

(111)

Concept 11.3: The Calvin cycle uses the

chemical energy of ATP and NADPH to reduce

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

(112)

 Carbon enters the cycle as CO₂ 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 CO₂

 The Calvin cycle has three phases

1. Carbon fixation (catalyzed by rubisco) 2. Reduction

(113)

(114)

Figure 11.19-1

Input 3 CO₂, entering one per cycle Phase 1: Carbon fixation

Rubisco 3-Phosphoglycerate Calvin Cycle RuBP P P 3 P 3 P P 6

C3 cycle

(115)

Figure 11.19-2

Rubisco 3-Phosphoglycerate 1,3-Bisphosphoglycerate Phase 2: Reduction G3P Calvin Cycle RuBP P P 3 P 3 P P 6 6 6 ADP P 6 P ATP P 6 6 6 NADP+ 6 P_i G3P P 1 Output Glucose and other organic compounds NADPH

(116)

Figure 11.19-3

Rubisco 3-Phosphoglycerate 1,3-Bisphosphoglycerate Phase 2: Reduction G3P Calvin Cycle G3P Phase 3: Regeneration of RuBP ATP 3 ADP 3 5 P RuBP P P 3 P 3 P P 6 6 6 ADP P 6 P ATP P 6 6 6 NADP+ 6 P_i G3P P 1 _{Glucose and} other organic NADPH

(117)

Concept 11.4: 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 H₂O but also limits photosynthesis

 The closing of stomata reduces access to CO₂ and

causes O₂ to build up

 These conditions favor an apparently wasteful

(118)

Rubisco: Ribulose-1,5-bisphosphate

carboxylase/oxygenase

(119)

(120)

(121)

Photorespiration: An Evolutionary Relic?

 In most plants (C₃ plants), initial fixation of CO₂, via rubisco, forms a three-carbon compound

(3-phosphoglycerate)

 In photorespiration, rubisco adds O₂ instead of

CO₂ in the Calvin cycle, producing a two-carbon

compound

 Photorespiration consumes O₂ and organic fuel

(122)

 Photorespiration may be an evolutionary relic

because rubisco first evolved at a time when the

atmosphere had far less O₂ and more CO₂

 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

(123)

C

₄

Plants

 C₄ plants minimize the cost of photorespiration by

incorporating CO₂ into four-carbon compounds

 There are two distinct types of cells in the leaves

of C₄ plants:

 Bundle-sheath cells are arranged in tightly packed

sheaths around the veins of the leaf

 Mesophyll cells are loosely packed between the bundle sheath and the leaf surface

(124)

 Sugar production in C₄ plants occurs in a three-step process:

1. The production of the four carbon precursors is catalyzed by the enzyme PEP carboxylase in the mesophyll cells

 PEP carboxylase has a higher affinity for CO₂ than rubisco does; it can fix CO₂ even when CO₂ concentrations are low

(125)

2. These four-carbon compounds are exported to bundle-sheath cells

3. Within the bundle-sheath cells, they release CO₂ that is then used in the Calvin cycle

(126)

Figure 11.20 Mesophyll cell Bundle-sheath cell Photo-synthetic cells of C₄ plant leaf Vein (vascular tissue) C₄ leaf anatomy Stoma The C₄ pathway Mesophyll

cell _{PEP carboxylase}

Oxaloacetate (4C) Malate (4C) Pyruvate (3C) CO₂ ADP PEP (3C) ATP CO₂ Calvin Cycle Bundle-sheath cell Sugar Vascular tissue

(127)

© 2014 Pearson Education, Inc. Figure 11.20a Mesophyll cell Bundle-sheath cell Photo-synthetic cells of C₄ plant leaf Vein (vascular tissue) C₄ leaf anatomy Stoma

(128)

Figure 11.20b

The C₄ pathway

Mesophyll

cell _{PEP carboxylase}

Oxaloacetate (4C) Malate (4C) Pyruvate (3C) CO₂ ADP PEP (3C) ATP CO₂ Calvin Cycle Bundle-sheath cell Sugar Vascular tissue

(129)

 Since the Industrial Revolution in the 1800s,

CO₂ levels have risen greatly

 Increasing levels of CO₂ may affect C₃ and C₄

plants differently, perhaps changing the relative abundance of these species

 The effects of such changes are unpredictable

(130)

CAM Plants

 Some plants, including succulents, use

crassulacean acid metabolism (CAM) to fix carbon

 CAM plants open their stomata at night,

incorporating CO₂ into organic acids

 Stomata close during the day, and CO₂ is released

(131)

© 2014 Pearson Education, Inc. Figure 11.21 Sugarcane Pineapple C₄ _CO 2 CO2 CAM Organic acid Organic acid Night Day CO₂ CO₂ Calvin Cycle Calvin Cycle Sugar Sugar Bundle-sheath cell

(a) Spatial separation of steps (b) Temporal separation of steps Mesophyll cell 2 1 1 2

(132)

Figure 11.21a

(133)

Figure 11.21b

(134)

The Importance of Photosynthesis: A Review

 The energy entering chloroplasts as sunlight gets

stored as chemical energy in organic compounds

 Sugar made in the chloroplasts supplies chemical

energy and carbon skeletons to synthesize the organic molecules of cells

 Plants store excess sugar as starch in structures

such as roots, tubers, seeds, and fruits

 In addition to food production, photosynthesis

(135)

© 2014 Pearson Education, Inc. Figure 11.22a O₂ CO₂ H₂O Sucrose (export) H₂O Light LIGHT REACTIONS: Photosystem II Electron transport chain Photosystem I Electron transport chain Chloroplast NADP+ ADP + P_i NADPH ATP RuBP G3P CALVIN CYCLE Starch (storage) 3-Phosphoglycerate Sucrose (export) O₂ H2O Mesophyll cell CO₂

(136)

Figure 11.22b

LIGHT REACTIONS CALVIN CYCLE REACTIONS

• Are carried out by molecules

in the thylakoid membranes

• Convert light energy to the

chemical energy of ATP and NADPH

• Split H₂O and release O₂ to the atmosphere

• Take place in the stroma

• Use ATP and NADPH to convert

CO₂ to the sugar G3P

• Return ADP, inorganic phosphate,

(137)

Figure 11.23

Flow of Genetic Information in the Cell:

DNA → RNA → Protein (Chapters 5–7)

Movement Across Cell Membranes (Chapter 7)

Energy Transformations in the Cell: Photosynthesis and Cellular

Respiration (Chapters 8–11) DNA mRNA Nucleus Nuclear pore Protein Ribosome mRNA Protein in vesicle Rough endoplasmic reticulum (ER) Vesicle forming Golgi apparatus _Protein Plasma membrane Cell wall Photosynthesis in chloroplast Organic molecules Transport pump Cellular respiration in mitochondrion ATP ATP ATP ATP CO2 H2O H2O CO2 O2 O2 5 4 3 2 1 7 8 Vacuole 9 11 11 6 MAKE CONNECTIONS The Working Cell

(138)

Figure 11.23a

Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 5–7)

DNA mRNA Nucleus mRNA Nuclear pore Protein Protein in vesicle Rough endoplasmic reticulum (ER) Ribosome 1 2 3

(139)

Flow of Genetic Information in the Cell: DNA → RNA → Protein (Chapters 5–7)

5

(140)

Figure 11.23c Photosynthesis in chloroplast Organic molecules Cellular respiration in mitochondrion Transport pump Movement Across

Cell Membranes (Chapter 7) Energy Transformations in the Cell: Photosynthesis and Cellular Respiration (Chapters 8–11) O₂ O₂ H₂O CO₂ CO₂ H₂O ATP ATP ATP ATP 7 8 11 11 9

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Figure 11.UN04b

Corn plant surrounded by invasive velvetleaf plants

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© 2014 Pearson Education, Inc. Figure 11.UN05 Primary acceptor Primary acceptor Pq Cytochrome complex Photosystem II Photosystem I Pc Fd NADPH NADP+ + H+ NADP+ reductase H₂O O₂

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Figure 11.UN06 Regeneration of CO₂ acceptor Calvin Cycle Carbon fixation Reduction 5 x 3C 3 x 5C _{6 x 3C} 3 CO₂

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Chlorophylls consist of a light-absorbing with a magnesium atom at the center and a long phytol tail that anchors the molecule in a membrane (Figure 1). They absorb light in the blue and red parts of the spectrum, but the green wavelengths are transmitted or reflected.

porphyrin ring