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BIOLOGYCONCEPTS & 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Light is central to the life of a plant
• Photosynthesis is the most important chemical process on Earth
– It provides food for virtually all organisms
• Plant cells convert light into chemical signals that affect a plant’s life cycle
Life in the Sun
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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 with small pale leaves
• Too much sunlight can damage a plant
– Chloroplasts and carotenoids help to prevent such damage
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Photosynthesis is the process by which autotrophic organisms use light energy to make sugar 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 are photosynthetic autotrophs
– They are the ultimate producers of food consumed by virtually all organisms
7.1 Autotrophs are the producers of the biosphere
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• On land, plants such as oak trees and cacti are the predominant producers
Figure 7.1A Figure 7.1B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• In aquatic environments, algae and photosynthetic bacteria are the main food producers
Figure 7.1C Figure 7.1D
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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 captures light for photosynthesis
7.2 Photosynthesis occurs in chloroplasts
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The location and structure of chloroplasts
Figure 7.2
LEAF CROSS SECTION MESOPHYLL CELL
LEAF
Chloroplast
Mesophyll
CHLOROPLAST Intermembrane space
Outermembrane
Innermembrane
ThylakoidcompartmentThylakoidStroma
Granum
StromaGrana
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Investigating Photosynthesis Investigations into photosynthesis began with the following question:
“When a tiny seedling grows into a tall tree with a mass of several tons, where does the tree’s increase in mass come from?”
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
1. ______________ Experiment (1643)
Put soil in pot and took mass
Took a seedling and took mass
Put seed in soil...watered...waited five years... the seedling became a tree.
He concluded that He determined the
Van Helmont’s
the mass came from water
the “hydrate” in the carbohydrate portion of photosynthesis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
2. ___________ Experiment (1771)
Put a lit candle in a bell jar- Placed a mint plant in the jar with the candle-
Concluded
He determined
Priestly’s
The flame died out.
Flame lasted longer
plants release a substance neededfor candle burning.
plants release oxygen
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
3. ________________Experiment (1779)
Put aquatic plants in light...
Put aquatic plants in dark... He determined:
4. _______________ (1948)
He determines
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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The O2 liberated by photosynthesis is made from the oxygen in water
7.3 Plants produce O2 gas by splitting water
Figure 7.3A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 7.3B
Figure 7.3C
Experiment 1
Experiment 2
Notlabeled
Labeled
Reactants:
Products:
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Water molecules are split apart and electrons and 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 cellular respiration
Figure 7.4A
Figure 7.4B
Reduction
Oxidation
Oxidation
Reduction
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The complete process of photosynthesis consists of two linked sets of reactions:
– the light reactions and the Calvin cycle
• The light reactions convert light energy to chemical energy and produce O2
• The Calvin cycle assembles sugar molecules from CO2 using the energy-carrying products of the light reactions
7.5 Overview: Photosynthesis occurs in two stages linked by ATP and NADPH
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of photosynthesis
Figure 7.5
Light
Chloroplast
LIGHTREACTIONS
(in grana)
CALVINCYCLE
(in stroma)
Electrons
H2O
O2
CO2
NADP+
ADP+ P
Sugar
ATP
NADPH
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Certain wavelengths of visible light drive the light reactions of photosynthesis
7.6 Visible radiation drives the light reactions
THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY
Gammarays
X-rays UV Infrared Micro-waves
Radiowaves
Visible light
Wavelength (nm)Figure 7.6A
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Figure 7.6B
Light
Chloroplast
Reflectedlight
Absorbedlight
Transmittedlight
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Each of the many light-harvesting photosystems consists of:
– an “antenna” of chlorophyll and other pigment molecules that absorb light
– a primary electron acceptor that receives excited electrons from the reaction-center chlorophyll
7.7 Photosystems capture solar power
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Figure 7.7C
Primaryelectron acceptor
Photon
Reaction center
PHOTOSYSTEM
Pigmentmoleculesof antenna
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Fluorescence of isolated chlorophyll in solution
Figure 7.7A
Heat
Photon(fluorescence)Photon
Chlorophyllmolecule
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 7.7B
• Excitation of chlorophyll in a chloroplast
Primaryelectron acceptor
Othercompounds
Chlorophyllmolecule
Photon
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Two connected photosystems collect photons of light and transfer the energy to chlorophyll electrons
• The excited electrons are passed from the primary electron acceptor to electron transport chains
– Their energy ends up in ATP and NADPH
7.8 In the light reactions, electron transport chains generate ATP, NADPH, and O2
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Photosystem II regains electrons by splitting water, leaving O2 gas as a by-product
Figure 7.8
Primaryelectron acceptor
Primaryelectron acceptor
Electron transport chain
Electron transport
Photons
PHOTOSYSTEM I
PHOTOSYSTEM II
Energy forsynthesis of
by chemiosmosis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The electron transport chains are arranged with the photosystems in the thylakoid membranes and pump H+ through that membrane
– The flow of H+ back through the membrane is harnessed by ATP synthase to make ATP
– In the stroma, the H+ ions combine with NADP+ to form NADPH
7.9 Chemiosmosis powers ATP synthesis in the light reactions
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The production of ATP by chemiosmosis in photosynthesis
Figure 7.9
Thylakoidcompartment(high H+)
Thylakoidmembrane
Stroma(low H+)
Light
Antennamolecules
Light
ELECTRON TRANSPORT CHAIN
PHOTOSYSTEM II PHOTOSYSTEM I ATP SYNTHASE
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The Calvin cycle occurs in the chloroplast’s stroma
– This is where carbon fixation takes place and sugar is manufactured
7.10 ATP and NADPH power sugar synthesis in the Calvin cycle
THE CALVIN CYCLE: CONVERTING CO2 TO SUGARS
INPUT
Figure 7.10A OUTPUT:
CALVINCYCLE
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The Calvin cycle constructs G3P using
– carbon from atmospheric CO2
– electrons and H+ from NADPH
– energy from ATP
• Energy-rich sugar is then converted into glucose
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Figure 7.10B
• Details of the Calvin cycle INPUT:
Step Carbon
fixation.
In a reaction catalyzed by rubisco, 3 molecules of CO2 are fixed.
11
Step Energy
consumption 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
CALVINCYCLE
3
OUTPUT: 1 PGlucoseand other compounds
G3P
Step Regeneration
of RuBP.
4
G3P
4
3 ADP
3 ATP
3CO2
5 P
RuBP 3-PGA
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• A summary of the chemical processes of photo-synthesis
7.11 Review: Photosynthesis uses light energy to make food molecules
PHOTOSYNTHESIS REVIEWED AND EXTENDED
Figure 7.11
Light
Chloroplast
Photosystem IIElectron transport
chains Photosystem I
CALVIN CYCLE Stroma
Electrons
LIGHT REACTIONS CALVIN CYCLE
Cellular respiration
Cellulose
Starch
Other organic compounds
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Most plants are C3 plants, which take CO2 directly from the air and use it in the Calvin cycle
– 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 adaptations that save water
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• Photorespiration in a C3 plant
CALVIN CYCLE
2-C compound
Figure 7.12A
EXAMPLES: wheat, barley, potatoes and sugar beet.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Some plants have special adaptations that enable them to save water
CALVIN CYCLE
4-C compound
Figure 7.12B
– Special cells in C4 plants—corn, crabgrass and sugarcane—incorporate CO2 into a four-carbon molecule
– This molecule can then donate CO2 to the Calvin cycle 3-C sugar
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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.
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The CAM plants—pineapples, most cacti, and succulents—employ a different mechanism
CALVIN CYCLE
4-C compound
Figure 7.12C
– They open their stomata at night and make a four-carbon compound
– It is used as a CO2 source by the same cell during the day
3-C sugar
Night
Day
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Due to the increased burning of fossil fuels, atmospheric CO2 is increasing
– CO2 warms Earth’s surface by trapping heat in the atmosphere
– This is called the greenhouse effect
7.13 Human activity is causing global warming; photosynthesis moderates it
PHOTOSYNTHESIS, SOLAR RADIATION, AND EARTH’S ATMOSPHERE
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Figure 7.13A & B
Sunlight
ATMOSPHERE
Radiant heat trapped by CO2 and other gases
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Because photosynthesis removes CO2 from the atmosphere, it moderates the greenhouse effect
– Unfortunately, deforestation may cause a decline in global photosynthesis
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Mario Molino received a Nobel Prize in 1995 for his work on the ozone layer
• His research focuses on how certain pollutants (greenhouse gases) damage that layer
7.14 Talking About Science: Mario Molina talks about Earth’s protective ozone layer
Figure 7.14A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• The O2 in the atmosphere results from photosynthesis
– Solar radiation converts O2 high in the atmosphere to ozone (O3)
– Ozone shields organisms on the Earth’s surface from the damaging effects of UV radiation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• Industrial chemicals called CFCs have hastened ozone breakdown, causing dangerous thinning of the ozone layer
Figure 7.14B
Sunlight
Southern tip of South America
• International restrictions on these chemicals are allowing recovery
Antarctica