1. BIOLOGY
AN OVERVIEW OF PHOTOSYNTHESIS
CONCEPTS & CONNECTIONS
Fourth Edition • Photosynthesis is the process by which
autotrophic organisms use light energy to make
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
sugar and oxygen gas from carbon dioxide and
water
CHAPTER 7
Photosynthesis:
Using Light to Make Food
Carbon Water Glucose Oxygen
Lecture 5 dioxide
PHOTOSYNTHESIS
gas
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
7.2 Photosynthesis occurs in chloroplasts • The location and structure of chloroplasts
Chloroplast
• In most plants, photosynthesis occurs primarily LEAF CROSS SECTION MESOPHYLL CELL
in the leaves, in the chloroplasts LEAF
Mesophyll
• A chloroplast contains:
– stroma, a fluid
– grana, stacks of thylakoids CHLOROPLAST Intermembrane space
Outer
• The thylakoids contain chlorophyll
membrane
– Chlorophyll is the green pigment that captures Granum Inner
membrane
light for photosynthesis Grana Stroma
Stroma Thylakoid
Figure 7.2 Thylakoid compartment
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7.3 Plants produce O2 gas by splitting water
Experiment 1
• The O2 liberated by photosynthesis is made
Not
labeled
Experiment 2
from the oxygen in water
Labeled
Figure 7.3B
Reactants:
Products:
Figure 7.3A Figure 7.3C
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
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2. 7.4 Photosynthesis is a redox process, as is cellular 7.5 Overview: Photosynthesis occurs in two stages
respiration linked by ATP and NADPH
• Water molecules are split apart and electrons • The complete process of photosynthesis
and H+ ions are removed, leaving O2 gas consists of two linked sets of reactions:
– These electrons and H+ ions are transferred to – the light reactions and the Calvin cycle
CO2, producing sugar
• The light reactions convert light energy to
Reduction
chemical energy and produce O2
Oxidation • The Calvin cycle assembles sugar molecules
Figure 7.4A
Oxidation
from CO2 using the energy-carrying products of
the light reactions
Reduction
Figure 7.4B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of photosynthesis THE LIGHT REACTIONS: CONVERTING
SOLAR ENERGY TO CHEMICAL ENERGY
H2 O CO2 7.6 Visible radiation drives the light reactions
Chloroplast
Light
• Certain wavelengths of visible light drive the
NADP+ light reactions of photosynthesis
ADP
+ P
LIGHT CALVIN
REACTIONS CYCLE
(in grana) (in stroma) Gamma Micro- Radio
X-rays UV Infrared
rays waves waves
ATP
Ele
ctro NADPH
ns
Visible light
O2 Sugar
Wavelength (nm)
Figure 7.5 Figure 7.6A
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
7.7 Photosystems capture solar power
Reflected
Light light • Each of the many light-harvesting
photosystems consists of:
Chloroplast
– an “antenna” of chlorophyll and other pigment
molecules that absorb light
– a primary electron acceptor that receives excited
electrons from the reaction-center chlorophyll
Absorbed
light
Transmitted
light
Figure 7.6B
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3. • Excitation of
Primary
electron acceptor Primary
chlorophyll in
electron acceptor
a chloroplast
Other
compounds
PHOTOSYSTEM
Photon
Reaction center
Photon
Chlorophyll
molecule
Pigment
molecules
of antenna
Figure 7.7C Figure 7.7B
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
7.8 In the light reactions, electron transport chains
generate ATP, NADPH, and O2
• Where do the electrons come from that keep
• Two connected photosystems collect photons of the light reactions running?
light and transfer the energy to chlorophyll • In photosystem I, electrons from the bottom of
electrons the cascade pass into its P700 chlorophyll
• The excited electrons are passed from the
primary electron acceptor to electron transport
chains
– Their energy ends up in ATP and NADPH
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• Photosystem II regains electrons by splitting THE CALVIN CYCLE:
CONVERTING CO2 TO SUGARS
water, leaving O2 gas as a by-product
7.10 ATP and NADPH power sugar synthesis in the
El
Primary
ec
tro
n
tra
Calvin cycle
electron acceptor ns
p or
t
• The Calvin cycle occurs
Primary INPUT
electron acceptor El
ec
tro
n
tra
ns
p
in the chloroplast’s
or
tc
ha
in stroma
Photons – This is where carbon CALVIN
CYCLE
fixation takes place and
Energy for sugar is manufactured
synthesis of
PHOTOSYSTEM I
PHOTOSYSTEM II OUTPUT:
by chemiosmosis Figure 7.8 Figure 7.10A
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4. • Details of the
• The Calvin cycle constructs G3P using Calvin cycle INPUT: 3
CO2
In a reaction catalyzed by
rubisco, 3 molecules of CO2
are fixed.
– carbon from atmospheric CO2 Step 1 Carbon
1
fixation.
– electrons and H+ from NADPH
3 P P 6 P
RuBP 3-PGA
6 ATP
3 ADP
– energy from ATP Step 2 Energy
consumption and redox. 6 ADP + P
3 ATP CALVIN 2
4 CYCLE 6 NADPH
• Energy-rich sugar is then converted into 6 NADP+
glucose Step 3 Release of one
molecule of G3P. 5 P 6 P
G3P G3P
3
Step 4 Regeneration
of RuBP. Glucose
OUTPUT: 1 P and other
compounds
G3P
Figure 7.10B
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PHOTOSYNTHESIS REVIEWED AND
EXTENDED
• Many plants make more sugar than they need
7.11 Review: Photosynthesis uses light energy to
make food molecules – The excess is stored in roots, tuber, and fruits
• A summary – These are a major source of food for animals
of the
Chloroplast
Light
chemical
processes Photosystem II
Electron
of photo-
transport CALVIN
chains CYCLE Stroma
Photosystem I
synthesis Ele
ctr ons
Cellular
respiration
Cellulose
Starch
Other
LIGHT REACTIONS CALVIN CYCLE organic
Figure 7.11 compounds
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7.12 C4 and CAM plants have special adaptations
that save water • Leaf cross section
• 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
• Stomata, open and closed
– Photorespiration may then occur
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5. • Photorespiration in a C3 plant • Some plants have special adaptations that
enable them to save water
– Special cells in C4
plants—corn and
sugarcane—incorporate 4-C compound
CALVIN CO2 into a four-carbon
CYCLE
molecule
– This molecule can then
donate CO2 to the CALVIN
2-C compound
Calvin cycle CYCLE
Figure 7.12A Figure 7.12B
3-C sugar
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• The CAM plants—pineapples, most cacti, and
succulents—employ a different mechanism
– They open their
stomata at night and
make a four-carbon
4-C compound
compound Night
– It is used as a CO2 Day
source by the same cell
during the day CALVIN
CYCLE
3-C sugar
Figure 7.12C
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