ch 7 photosynthesis using light to make food
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BIOLOGY CONCEPTS & CONNECTIONS
Fourth Edition
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Neil A. Campbell Jane B. Reece Lawrence G. Mitchell Martha R. Taylor
From PowerPoint® Lectures for Biology: Concepts & Connections
CHAPTER 7Photosynthesis:
Using Light to Make Food
Modules 7.1 ± 7.5
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Light is central to the life of a plant
Photosynthesis is the most important chemicalprocess on Earth
± It provides food for virtually all organisms
Plant cells convert lightinto chemical signalsthat affect a plant¶slife cycle
Life in the Sun
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Light can influence the architecture of a plant
± Plants that get adequate light are often bushy, with deep green leaves
± Without enough light, plants
become tall and spindly withsmall pale leaves
Too much sunlight can
damage a plant± Chloroplasts and carotenoids
help to prevent such damage
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Photosynthesis is the process by whichautotrophic organisms use light energy to makesugar and oxygen gas from carbon dioxide and water
AN OVERVIEW OF PHOTOSYNTHESIS
Carbondioxide
Water Glucose Oxygengas
PHOTOSYNTHESIS
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Plants, some protists, and some bacteria arephotosynthetic autotrophs
± They are the ultimate producers of food
consumed by virtually all organisms
7.1 Autotrophs are the producers of the biosphere
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On land, plants such as oak trees and cacti arethe predominant producers
Figure 7.1A Figure 7.1B
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In aquatic environments, algae andphotosynthetic bacteria are the main foodproducers
Figure 7.1C Figure 7.1D
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In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts
A chloroplast contains:
± stroma, a fluid
± grana, stacks of thylakoids
The thylakoids contain chlorophyll
± Chlorophyll is the green pigment that captureslight for photosynthesis
7.2 Photosynthesis occurs in chloroplasts
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The location and structure of chloroplasts
Figure 7.2
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outer
membrane
Inner membrane
ThylakoidcompartmentThylakoidStroma
Granum
StromaGrana
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Investigating Photosynthesis
y Investigations into photosynthesis began with the
following question:
³When a tiny seedling grows into
a tall tree with a mass of several tons,
where does the tree¶s increase in mass come from?´
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1. ______________ Experiment (1643)
y Put soil in pot and took mass
y Took a seedling and took mass
y Put seed in soil...watered...waited five years...
the seedling became a tree.
y He concluded that
y He determined the
Van Helmont¶s
the mass came from water
the ³hydrate´ in the carbohydrate
portion of photosynthesis
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2. ___________ Experiment (1771)
y Put a lit candle in a bell jar-
y Placed a mint plant in the jar with the candle-
y
Concluded
He determined
Priestly¶s
The flame died out.
Flame lasted longer
plants release a substance needed
for candle burning.
plants release oxygen
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3. ________________ Experiment (1779)
y Put aquatic plants in light...
y Put aquatic plants in dark...
He determined:
4. _______________ (1948)
y He determines
y Known as the
Jan Ingenhousz
produced oxygen
No oxygen
Light is needed to produce oxygen
Melvin Calvin
carbon¶s path to make glucose
Calvin¶s cycle
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The O2 liberated by photosynthesis is madefrom the oxygen in water
7.3 Plants produce O2 gas by splitting water
Figure 7.3A
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Figure 7.3B
Figure 7.3C
Experiment 1
Experiment 2
Notlabeled
Labeled
Reactants:
Products:
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Water molecules are split apart and electronsand H+ ions are removed, leaving O2 gas
± These electrons and H+ ions are transferred to
CO2, producing sugar
7.4 Photosynthesis is a redox process, as is cellularrespiration
Figure 7.4A
Figure 7.4B
Reduction
Oxidation
Oxidation
Reduction
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The complete process of photosynthesisconsists of two linked sets of reactions:
± the light reactions and the Calvin cycle
The light reactions convert light energy tochemical energy and produce O2
The Calvin cycle assembles sugar moleculesfrom CO2 using the energy-carrying products of the light reactions
7.5 Overview: Photosynthesis occurs in two stageslinked by ATP and NADPH
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A n overview of photosynthesis
Figure 7.5
Light
Chloroplast
LIGHTREACTIONS
(in grana)
CALVINCYCLE
(in stroma)
H2O
O2
CO2
NADP+
ADP
+ P
Sugar
ATP
NADPH
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Certain wavelengths of visible light drive thelight reactions of photosynthesis
7.6 Visible radiation drives the light reactions
THE LIGHT REACTIONS: CONVERTINGSOLAR ENERGY TO CHEMICAL ENERGY
Gamma
raysX-rays UV Infrared
Micro-
waves
Radio
waves
Visible light
Wavelength (nm)Figure 7.6A
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Figure 7.6B
Light
Chloroplast
Reflected
light
Absorbed
light
Transmitted
light
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Each of the many light-harvestingphotosystems consists of:
± an ³antenna´ of chlorophyll and other pigment
molecules that absorb light
± a primary electron acceptor that receives excitedelectrons from the reaction-center chlorophyll
7.7 Photosystems capture solar power
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Figure 7.7C
Primary
electron acceptor
Photon
Reaction center
PHOTOSYSTEM
Pigment
molecules
of antenna
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Fluorescence of isolated chlorophyll in solution
Figure 7.7A
Heat
Photon(fluorescence)
PhotonChlorophyll
molecule
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Figure 7.7B
Excitation of
chlorophyll ina chloroplast
Primary
electron acceptor
Other
compounds
Chlorophyll
molecule
Photon
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Two connected photosystems collect photons of light and transfer the energy to chlorophyllelectrons
The excited electrons are passed from theprimary electron acceptor to electron transportchains
± Their energy ends up in A TP and N ADPH
7.8 In the light reactions, electron transport chainsgenerate ATP, NADPH, and O2
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Where do the electrons come from that keep
the light reactions running?
In photosystem I, electrons from the bottom of the cascade pass into its P700 chlorophyll
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Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product
Figure 7.8
Primaryelectron acceptor
Primaryelectron acceptor
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy for synthesis of
by chemiosmosis
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The electron transport chains are arranged withthe photosystems in the thylakoid membranesand pump H+ through that membrane
± The flow of H+ back through the membrane isharnessed by A TP synthase to make A TP
± In the stroma, the H+ ions combine with N ADP+
to form N ADPH
7.9 Chemiosmosis powers ATP synthesis in thelight reactions
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The production of A TP by chemiosmosis inphotosynthesis
Figure 7.9
Thylakoidcompartment(high H+)
Thylakoidmembrane
Stroma(low H+)
Light
Antennamolecules
Light
ELECTRON TRANSPORT
CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
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The Calvin cycle occurs
in the chloroplast¶sstroma
± This is where carbon
fixation takes place andsugar is manufactured
7.10 ATP and NADPH power sugar synthesis in theCalvin cycle
THE CALVIN CYCLE:CONVERTING CO2 TO SUGARS
INPUT
Figure 7.10A OUTPUT:
CALVIN
CYCLE
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The Calvin cycle constructs G3P using
± carbon from atmospheric CO2
± electrons and H+ from N ADPH
± energy from A TP
Energy-rich sugar is then converted intoglucose
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Figure 7.10B
Details of theCalvin cycle INPUT:
Step Carbon
fixation.
In a reaction catalyzed by
rubisco, 3 molecules of CO2
are fixed.
11
Step Energyconsumption and redox.
2
3 P P P6
6
2
ATP
6 ADP + P
6 NADPH
6 NADP+
6 P
G3P
Step Release of one
molecule of G3P.
3
CALVIN
CYCLE
3
OUTPUT: 1 PGlucoseand other compounds
G3P
Step Regeneration
of RuBP.
4
G3P
4
3 ADP
3 ATP
3CO2
5 P
RuBP 3-PGA
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A summary of thechemicalprocessesof photo-
synthesis
7.11 Review: Photosynthesis uses light energy tomake food molecules
PHOTOSYNTHESIS REVIEWED ANDEXTENDED
Figure 7.11
Light
Chloroplast
Photosystem IIElectrontransport
chainsPhotosystem I
CALVINCYCLE Stroma
LIGHT REACTIONS CALVIN CYCLE
Cellular respiration
Cellulose
Starch
Other organiccompounds
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Many plants make more sugar than they need
± The excess is stored in roots, tuber, and fruits
± These are a major source of food for animals
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Most plants are C3 plants, which take CO2
directly from the air and use it in the Calvincycle
± In these types of plants, stomata on the leaf surface close when the weather is hot
± This causes a drop in CO2 and an increase in
O2 in the leaf
± Photorespiration may then occur
7.12 C4 and CAM plants have special adaptationsthat save water
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Photorespiration in a C3 plant
CALVINCYCLE
2-C compound
Figure 7.12A
EXAMPLES: wheat, barley, potatoes and sugar beet.
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Some plants have special adaptations thatenable them to save water
CALVIN
CYCLE
4-C compound
Figure 7.12B
± Special cells in C4
plants²corn, crabgrassand sugarcane²
incorporate CO2 into afour-carbon molecule
± This molecule can then
donate CO2 to theCalvin cycle
3-C sugar
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In C4 plants, the bundle sheath cells contain chloroplasts;
carbon is fixed in mesophyll cells, then transported to bundle
sheath cells where Calvin Cycle reactions occur in the absence
of oxygen.
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The C AM plants²pineapples, most cacti, andsucculents²employ a different mechanism
CALVIN
CYCLE
4-C compound
Figure 7.12C
± They open theirstomata at night andmake a four-carbon
compound± It is used as a CO2
source by the same cellduring the day
3-C sugar
Night
Day
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Due to the increased burning of fossil fuels,
atmospheric CO2 is increasing
± CO2 warms Earth¶s surface by trapping heat inthe atmosphere
± This is called the greenhouse effect
7.13 Human activity is causing global warming;photosynthesis moderates it
PHOTOSYNTHESIS, SOLAR RADIATION, ANDEARTH¶S ATMOSPHERE
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Figure 7.13A & B
Sunlight
ATMOSPHERE
Radiant heat
trapped by CO2
and other gases
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Because photosynthesis removes CO2 from theatmosphere, it moderates the greenhouseeffect
± Unfortunately, deforestation may cause adecline in global photosynthesis
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Mario Molino received aNobel Prize in 1995 forhis work on the ozonelayer
His research focuses onhow certain pollutants(greenhouse gases)damage that layer
7.14 Talking About Science: Mario Molina talksabout Earth¶s protective ozone layer
Figure 7.14A
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The O2 in the atmosphere results from
photosynthesis
± Solar radiation converts O2 high in theatmosphere to ozone (O3)
± Ozone shields organisms on the Earth¶s surfacefrom the damaging effects of UV radiation
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Industrial chemicals called CFCs have hastenedozone breakdown, causing dangerous thinning
of the ozone layer
Figure 7.14B
Sunlight
Southern tip of
South America
International restrictions on these chemicalsare allowing recovery
Antarctica