Lesson Overview
Energy and Life
Chapter 8: Photosynthesis
Lesson Overview
Energy and Life
Section 8.1: Energy and Life
Lesson Overview
Energy and Life
A. Chemical Energy and ATP
a. Adenosine triphosphate (ATP)
i. Used to store and release energy in the cell
ii. Consists of adenine, a 5-carbon sugar, and 3
phosphate groups
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Energy and Life
b. Adenosine diphosphate
(ADP)
i. very similar to ATP
ii. Has 2 phosphate
groups instead of 3
iii. If a phosphate group
is added to ADP, it
produces ATP
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Energy and Life
B. Cells release energy in
ATP by breaking bonds
between the last two
phosphate groups
a. ATP is useful for
short term energy, but
not for long term energy
storage
b. ADP is like a
rechargeable battery in
the cell
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Energy and Life
Section 8.2: Photosynthesis: An
Overview
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Energy and Life
A. Chemical Energy and ATP
a. Light Energy
i. Sunlight is a mixture of different wavelengths
ii. Visible spectrum – red, orange, yellow, green,
blue, indigo, and violet
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Energy and Life
b. Pigments
i. pigments: light-absorbing molecules that gather the sun’s
energy
ii. Chlorophyll: plant’s principle pigment
1. two types of chlorophyll; chlorophyll a and chlorophyll b
2. absorb light in the blue-violet and red regions but not in
the green
3. plants reflect green light, which is why plants look green
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Energy and Life
iii. Carotene: red and orange pigments that absorb light in other
regions of the spectrum
iv. Chlorophyll is primary pigment, but as temperature drops and
chlorophyll breaks down, the red and orange pigments may be
seen
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Energy and Life
c. Chloroplasts
i. Organelle in which photosynthesis takes place
ii. Thylakoids: saclike photosynthetic membranes that are
interconnected and arranged in stacks known as grana
iii. Stroma: fluid portion outside thylakoids
iv. Pigments are located in thylakoid membranes
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Energy and Life
B. High-Energy Electrons
a. Plants use electron carriers to transport high-energy electrons
from chlorophyll to other molecules
b. NADP+ accepts and holds two high-energy electron, along with a
hydrogen ion (H+) and is converted to NADPH
i. NADPH carries the high-energy electrons to chemical reactions
elsewhere in the cell
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Energy and Life
C. An Overview of Photosynthesis
a. Photosynthesis uses the energy of sunlight to convert water
and carbon dioxide into high-energy sugars and oxygen.
In symbols:
6 CO2 + 6 H2O  C6H12O6 + 6 O2
In words:
Carbon dioxide + Water  Sugars + Oxygen
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Energy and Life
i. Plants use the sugars
generated by
photosynthesis to
1. Produce complex
carbohydrates
(starch)
2. Provide energy for
the synthesis of
other compounds
(lipids and proteins)
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Energy and Life
b. Light-Dependent Reactions
i.
Require the direct involvement of light and light-absorbing
pigments
ii. Use energy from sunlight to produce ATP and NADPH
iii. Reactions take place within the thylakoid membranes of the
chloroplast
iv. Water is required as a source of electrons and hydrogen
ions
v. Oxygen is released as a byproduct
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Energy and Life
c. Light-Independent Reactions
i. Plants absorb carbon dioxide from the atmosphere
ii. ATP and NADPH molecules produced in the light-dependent
reactions are used to produce high-energy sugars from carbon
dioxide
iii. No light is required
iv. Reactions take place outside thylakoids in the stroma of the
chloroplast
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Energy and Life
Lesson Overview
Energy and Life
Section 8.3: The Process of
Photosynthesis
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Energy and Life
A. The Light-Dependent Reactions:
Generating ATP and NADPH
a. photosystems: clusters of chlorophyll and proteins in the
thylakoid
i. Absorb sunlight
ii. Generate high-energy electrons that are passed to a series of
electron carriers in the thylakoid membrane
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Energy and Life
b. Photosystem II
i. Light energy is absorbed by
electrons in the pigments
within photosystem II,
increasing the electron’s
energy level
ii. High-energy electrons are
passed to the electron
transport chain
iii. Electron Transport Chain:
series of electron carriers
that shuttle high-energy
electrons during ATPgenerating reactions
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Energy and Life
iv. Thylakoid membrane provides new
electrons to chlorophyll from water
molecules
v. Enzymes break up water molecules
into 2 elecrons, 2 H+ ions, and 1
oxygen atom
vi. The 2 electrons replace the highenergy electrons that have been lost
to the electron transport chain
vii. Oxygen is released into the air
vii. H+ ions are released inside the
thylakoid
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Energy and Life
c. Electron Transport Chain
i. Energy from the electrons is
used by proteins to pump H+
ions from the stroma into the
thylakoid space
i. At the end of the electron
transport chain, electrons
pass to photosytem I
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Energy and Life
d. Photosystem I
i. Pigments in photosystem I
use energy from light to
reenergize electrons
ii. NADP+ molecules in the
stroma pick up high-energy
electrons and H+ ions at the
outer surface of the thylakoid
membrane to become
NADPH
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Energy and Life
e. Hydrogen Ion Movement and ATP
Formation
i.
ii.
iii.
Gradient (difference in both charge and H+ concentration
across the membrane) provide energy to make ATP
ATPsynthase: protein that spans the thylakoid membrane
and allows H+ ions to pass through
ATP synthase binds ADP and a phosphate group to produce
ATP
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Energy and Life
f. Summary of Light-Dependent
Reactions
i. Produce oxygen gas and convert ADP and
NADP+ into ATP and NADPH
ii. ATP and NADPH provide energy needed to build
high-energy sugars from low-energy carbon
dioxide
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Energy and Life
B. The Light-Independent Reactions:
Producing Sugars
a. Also called the Calvin cycle
b. Use energy that ATP and NADPH contain to build stable highenergy carbohydrate compounds that can be stored for a long
time
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Energy and Life
c. Carbon Dioxide Enters the Cycle
i.
Carbon dioxide enters the Calvin cycle from the atmosphere
ii.
An enzyme in the stroma combines carbon dioxide with
5-carbon compounds that are already present
iii.
Produces 3-carbon compounds that continue into the cycle
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Carbon Dioxide Enters the Cycle
iv. For every 6 carbon dioxide
molecules, a total of twelve
3-carbon compounds are
produced
v. Other enzymes convert the
3-carbon compounds into
higher-energy forms, using
energy from ATP and NADPH
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Energy and Life
d. Sugar Production
i. 2 of the twelve 3-carbon
molecules leave the cycle
halfway through
ii. Remaining ten 3-carbon
molecules are converted back
into six 5-carbon molecules
that combine with 6 new
carbon dioxide molecules to
begin the next cycle
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Energy and Life
e. Summary of the Calvin Cycle
i.
6 molecules of carbon
dioxide are used to
produce a single 6carbon sugar molecule
ii.
The energy for the
reactions is supplied by
compounds produced in
the light-dependent
reactions
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Energy and Life
Lesson Overview
Energy and Life
C. Factors Affecting Photosynthesis
a. Temperature, Light, and Water
i. Temperatures above or below 0-35 C may slow
down the rate of photosynthesis or stop it entirely
i. Shortage of water can slow or stop photosynthesis
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Energy and Life
iii. High light intensity increases the rate of
photosynthesis
iv. After reaching a certain level of light intensity, plant
reaches its maximum rate of photosynthesis
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Energy and Life
i. C4 Photosynthesis
1. Have specialized chemical pathways that allow them
to capture even very low levels of carbon dioxide
and pass it to the Calvin cycle
2. Require extra energy in the form of ATP
3. Examples: corn and sugar cane
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Energy and Life
ii. CAM Plants
1. Admit air into their leaves only at night
2. During the daytime, leaves are tightly sealed to
prevent water loss
3. Examples: cacti, succulents and pineapple trees