Photosynthesis
Module 2F - Photosynthesis
we saw in the previous module, all
cells can break down organic molecules
and use the energy that is released to
make ATP.
„ In addition, some cells can manufacture
organic molecules from inorganic
substances using energy from light
(photosynthesis)
photosynthesis) or from inorganic
chemicals ((chemosynthesis
chemosynthesis).
).
„ In
this module, we will examine
photosynthesis a process for
manufacturing glucose from CO2
and H2O usingg energy
gy from light.
g
„ During photosynthesis, light
energy is captured and stored in
the chemical bonds of glucose
molecules.
„ As
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Objective # 36
Objective 36
„ Photosynthesis:
6CO2 + 6H2O + light energy →
C6H12O6 + 6O2
Write a summary chemical
equation for photosynthesis and
d
describe
ib the
h origin
i i and
d ffate off
each substance involved.
ƒ During
D i photosynthesis,
h
h i H iis removed
d
from H2O, leaving O2 as a waste
product. The electrons in the removed
H are energized by light, and then used
to reduce CO2 to form glucose.
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Objective # 37
Objective 37
„ All
Explain the role and importance
of photosynthesis for life on
earth,
h and
d id
identify
if the
h main
i
types of cells that carry out this
process.
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living organisms require organic
molecules for survival. Organic
molecules are used as an energy
source, and as structural materials to
build cell components.
„ Photosynthesis is the ultimate source
of almost all organic molecules used by
living organisms. It is also the main
source of O2 in the atmosphere.
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Objective 37
Objective 37
„ Organisms
that can manufacture their
own organic molecules from inorganic
substances are called autotrophs.
autotrophs.
„ Those that must consume organic
g
molecules are called heterotrophs.
heterotrophs.
„ Autotrophs that use photosynthesis to
manufacture organic molecules include
some monerans, some protists, and
almost all plants.
Photosynthesis
ADP+Pi
ATP
photosynthesis and aerobic
respiration form a complex cycle that
is responsible for most of the energy
flow through the biosphere.
„ Photosynthesis uses CO2 + H2O to
produce glucose + O2. Aerobic
respiration uses glucose + O2 to
regenerate CO2 + H2O.
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Objective # 38
Identify the 2 main stages of
photosynthesis and indicate
where
h each
h stage takes
k place
l iin
both prokaryotic and eukaryotic
cells.
Heat
O2
Photosystem
I
NADP+
H2 O
Electron
Transport
System
ATP
ADP+Pi
NAD+
NADPH
NADH
Calvin
Cycle
CO2
Pyruvate
Glucose
ATP
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Aerobic Respiration
Sunlight
Photosystem
II
„ Together,
Krebs
Cycle
ATP
ADP+Pi
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Objective 38
Objective 38
„ In
eukaryotes, photosynthesis occurs
inside chloroplasts.
chloroplasts. Each chloroplast
is surrounded by a double membrane.
„ Inside the inner membrane are
flattened membranous sacs called
thylakoids surrounded by a semi
semi--fluid
material called the stroma.
stroma.
„ The thylakoids are arranged in stacks
called grana:
grana:
Photosynthesis occurs in 2 main stages:
1) The lightlight-dependent reactions, also
g capturing
p
g reactions
called the energy
2) The carbon fixation reactions, also
called the Calvin or C3 cycle
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2
Structure of a Chloroplast
Sunlight
Plant
cell
Inner membrane
Outer membrane
Chloroplast
Photosystem
H2 O
Th l k id
Thylakoid
Thylakoid
Membrane Thylakoid
Light-Dependent
Reactions
ADP+Pi
Granum
O2
ATP
NADP+
NADPH
Stroma
CO2
Calvin
Cycle
Organic
molecules
Stroma
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Copyright
The McGraw-Hill
© The McGraw-Hill
Companies,
Companies,
Inc. Permission
Inc. Permission
required
required
forfor
reproduction
reproduction or
or display.
display.
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Objective 38
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
In eukaryotes, the
light--dependent
light
reactions of
photosynthesis take
place on the surface
of the thylakoid
membranes and the
carbon fixation
reactions (Calvin
cycle) occur in the
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stroma.
The photosynthetic lamellae (membranes) of
this bacterial cell are colored green:
„ In
prokaryotes, which lack chloroplasts:
¾ the lightlight-dependent reactions of
photosynthesis take place on the inner
surface of the p
plasma membrane or on
invaginations of the plasma membrane
called photosynthetic lamellae.
lamellae.
¾ the carbon fixation reactions occur in
the cytoplasm.
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Objective # 39
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Objective 39
Describe the lightlight-dependent (energy capturing)
reactions of photosynthesis with respect to:
a) how pigment molecules in the antenna complexes
are used to capture light energy
b)) how the captured
p
energy
gy is used for the
production of ATP and NADPH during nonnoncyclic photophosphorylation
c) how the captured energy is used for the
production of ATP during cyclic
photophosphorylation
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During the lightlight-dependent
reactions (also called the energy
capturing reactions
reactions)) of
photosynthesis, light energy is
captured
pt r d b
by pi
pigmentt molecules
l l and
d
transferred to electrons. The
molecules used to carry out this
process are organized into
photosystems..
photosystems
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3
Each Photosystem consists of 2 parts:
„ Antenna
The Antenna Complex
complex
¾ Hundreds
„ Also
of accessory pigment
molecules
¾ Gather photons and feed the captured
light energy to the reaction center
„ Reaction
center
¾1
or more chlorophyll a molecules
¾ Passes excited electrons out of the
photosystem
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called lightlight-harvesting complex
„ Captures photons from sunlight and
channels them to the reaction center
chlorophylls
p
„ In chloroplasts, lightlight-harvesting
complexes consist of a web of
chlorophyll molecules linked together
and held tightly in the thylakoid
membrane by a matrix of proteins
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The Reaction Center
A photosystem embedded in the thylakoid
membrane of a chloroplast:
Transmembrane protein
protein––pigment complex
„ When a chlorophyll in the reaction center
absorbs a photon of light, an electron is
excited to a higher energy level
„ LightLight
i h -energized
i d electron
l
can be
b transferred
f
d
to the primary electron acceptor, reducing
it
„ Oxidized chlorophyll then fills its electron
“hole” by oxidizing a donor molecule
„
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Objective 39
Release of
an excited
electron by
the reaction
center
chlorophyll
(shown in
green).
„ High
energy electrons released by
the reaction center chlorophyll can
follow one of 2 pathways:
¾cyclic
photophosphorylation
¾non
non--cyclic photophosphorylation
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Objective 39
¾ In
cyclic photophosphorylation,
photophosphorylation, the
high energy electrons are used to make
ATP by chemiosmosis.
¾ In non
non--cyclic p
photophosphorylation,
photophosphorylation
p p
,
first the high energy electrons are used
to make ATP by chemiosmosis. Next,
they are reenergized by light and used
to reduce NADP+ to form NADPH.
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Objective # 40
Describe the following events of the
carbon fixation reactions (also called the
Calvin or C3 cycle) of photosynthesis:
a) carbon fixation
b) the
h reduction
d i off PGA
GA to fform G
G3P
(also called PGAL)
c) the production of glucose from G3P
d) the regeneration of RuBP from G3P
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Objective 40
¾ During
the carbon fixation reactions
cycle)) of
(also called the Calvin or C3 cycle
photosynthesis, energy from ATP and
h d
hydrogen
ffrom NADPH are used
d to
reduce CO2 in order to form glucose.
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