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BIOLOGY
A GUIDE TO THE NATURAL WORLD
FOURTH EDITION
DAVID KROGH
The Green World’s Gift:
Photosynthesis
Copyright © 2009 Pearson Education, Inc., publishing as Pearson Benjamin Cummings.
8.1 Photosynthesis and Energy
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Photosynthesis and Energy
• Photosynthesis has made possible life as we
know it on Earth because the organic material
produced in photosynthesis (a sugar) is the
source of food for most of Earth’s living things.
• Photosynthesis also is responsible for the
atmospheric oxygen used by many living things
in cellular respiration.
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Three Types of Photosynthesis
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Figure 8.1
8.2 The Components of Photosynthesis
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The Components of Photosynthesis
• In plants and algae, photosynthesis takes place
in organelles called chloroplasts
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Photosynthesis
• Energy for photosynthesis comes sunlight that
is absorbed by pigments in the chloroplasts.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Electromagnetic Spectrum
high energy
short wavelength
gamma
rays
x-rays
low energy
long wavelength
ultraviolet
infrared
microwaves
radiowaves
visible
light
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Figure 8.2
Stomata
• Plant leaves contain microscopic pores called
stomata that can open and close, letting carbon
dioxide in and water vapor out.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Site of Photosynthesis
1. Leaf
The primary site of photosynthesis in plants,
leaves have a two-part structure: a petiole
(or stalk) and a blade (normally thought of
as the leaf).
petiole
2. Leaf cross section
blade
In cross section, leaves have a sandwichlike structure, with epidermal layers at
top and bottom and mesophyll cells
in between. Most photosynthesis is
performed within mesophyll cells. Leaf
epidermis is pocked with a large number
of microscopic openings, called stomata,
that allow carbon dioxide to pass in
and water vapor to pass out.
epidermis
mesophyll
cells
epidermis
stomata
3. Mesophyll cell
nucleus
A single mesophyll cell within a leaf contains
all the component parts of plant cells in
general, including the organelles—called
chloroplasts—that are the actual sites of
photosynthesis.
chloroplast
cell wall
vacuole
4. Chloroplast
thylakoids
stroma
granum
inner membrane
outer membrane
Energy from
sunlight is
absorbed by
pigments in the
thylakoid
membrane.
thylakoid
thylakoid membrane
thylakoid compartment
Each chloroplast has an outer
membrane at its periphery; then
an inner membrane; then a liquid
material, called the stroma, that
has immersed within it a network
of membranes, the thylakoids.
These thylakoids sometimes
stack on one another to create. . .
5. A Granum
Electrons used in
photosynthesis will come
from water contained in the
thylakoid compartment, and
all the steps of photosynthesis
will take place either within the
thylakoid membrane, or in the
stroma that surrounds the
thylakoids.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 8.3
Stages of Photosynthesis
• There are two primary stages to photosynthesis.
• First stage - light reactions
– electrons derived from water are energetically
boosted by the power of sunlight.
• Second stage - the Calvin cycle
– the electrons are brought together with carbon
dioxide and a sugar.
– The product is a high-energy sugar
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
8.3 Stage 1: The Steps of the Light
Reactions
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The Working Units of Photosynthesis
primary
electron
acceptor
e–
sunlight
reaction
center
antennae
pigments
photosystem
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 8.4
8.4 What Makes the Light Reactions So
Important?
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Two Key Actions in Light Reaction
1. Water is split, yielding both electrons and
oxygen.
–
–
The electrons move through the light reactions.
The oxygen is what organisms such as ourselves
breathe in.
2. The electrons that are derived from the water,
and then given an energy boost by the sun’s
rays, are transferred to a different molecule:
the initial electron acceptor.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Importance of Light Reactions
• Fall of electrons through the ETC also yields
energy that produces ATP,
• ATP used to power the second stage of
photosynthesis.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Collecting Solar Energy
primary
electron
acceptor
primary
electron
acceptor
e–
NADP+
sunlight
sunlight
NADPH
to Calvin
cycle
electrons
photosystem I
photosystem II
electron fall supplies energy that
will lead to ATP synthesis
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Figure 8.5
8.5 Stage 2: The Calvin Cycle
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Stage 2: The Calvin Cycle
• The Calvin Cycle is the second stage of
photosynthesis.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Calvin Cycle
• In the Calvin cycle, carbon dioxide from the
atmosphere is brought together with a sugar
• The resulting compound is energized with
electrons supplied by the first stage of
photosynthesis.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Photosynthesis
Suggested Media Enhancement:
Photosynthesis
To access this animation go to folder C_Animations_and_Video_Files
and open the BioFlix folder.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Calvin Cycle
• The result of the Calvin cycle is the highenergy sugar, which is the product of
photosynthesis.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Calvin Cycle
chloroplast
sunlight
photosystem II
photosystem I
sunlight
e–
NADPH
to Calvin
cycle
thylakoid compartment
thylakoid
membrane
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
stroma
Figure 8.6
The Calvin Cycle
• All these steps are powered by ATP produced in
the light reactions.
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
The Calvin Experiments
PLAY
Animation 8.3: The Calvin Experiments
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.
Different Kinds of Photosynthesis
PLAY
Animation 8.2: Different Kinds of Photosynthesis
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings.