Photosynthesis

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Transcript Photosynthesis

Photosynthesis
State Objectives!
CLE 3210.3.3 Investigate the
relationship between the processes of
photosynthesis and cellular respiration
SPI 3210.3.3 Compare and Contrast
photosynthesis and cellular respiration
in terms of energy transformation.
Introduction:
Overview
6 CO2 + 6 H2O +
light energy → C6H12O6 + 6 O2
Photosynthesis consists of two
independent pathways
light-dependent reaction (light reaction)
the light-independent reaction (dark
reaction).
Introduction
Light Reactions: the energy in sunlight
is trapped, O2 is released, and both
ATP and NADPH + H+ (hydrogencarrier molecule) are formed
Dark Reactions: the ATP and NADPH +
H+ react with CO2 from the atmosphere
and form glucose
The entire process results in the
transformation of light energy from the
sun into energy stored in the bonds of
the glucose molecule.
Structure of a Chloroplast
The light
reactions take
place in the
thylakoid
membrane
The dark
reactions take
place in the
stroma
Structure of a Chloroplast
Electromagnetic Spectrum
Why are
plants
green?
Pigments
Pigments are light-absorbing
compounds.
Pigments appear colored because they
absorb light of certain wavelengths and
reflect that of others.
Chlorophyll a is the primary pigment in
green plants that absorbs red and
blue/violet light and reflects green light.
Structure
of
Chlorophyll
Why aren’t these leaves green??
Accessory Pigments
Chloroplasts also contain other pigments
called accessory pigments.
Accessory pigments trap wavelengths of light
that cannot be absorbed by chlorophyll a and
then transfer the energy to chlorophyll a
molecules for use in photosynthesis. In this
way, accessory pigments enable plants to
use a greater amount of the sun’s energy
than is available to chlorophyll alone.
Light Reaction
Light Reaction
Also called Light Dependent Reaction
Pigments that are in the chloroplasts
intercept light and begin the light reactions of
photosynthesis.
The light reactions occur in two
photosystems (located in the thylakoid
membrane): -photosystem I (PSI)
-photosystem II (PSII)
Photosystem: a unit of several hundred
chlorophyll a molecules and associated
acceptor molecules
Photosystems
Excited Electrons
NADPH
NADP+ is an electron acceptor
NADP+ + 2 e- + 2 H+
NADPH + H+
Primary
Electron
Acceptor
ETC
Proton Pump
PSI
PSII
Lumen
Thylakoid
Water (H2O)
Oxygen (O2)
ATP Synthase
Hydrogen Ion (H+)
Electron
Step 1
Step 2
Step 3
Step 3
Step 3
Step 3
Step 3
Step 3
~
e
low
high
Step 4
Step 4
Step 4
Step 4
Step 4
Step 4
Step 5
Step 5
Step 5
Step 5
Step 5
NADP+
NADPH
+ H+
Step 5
high
low
Step 6
Step 6
Step 6
Step 6
Step 6
ADP + P
~
Step 6
e
ATP
NADP+
ADP + P
Reactants
O2 is
released
into the
atmosphere
NADPH
+ H+
DR
Products
ATP
Dark Reaction
Dark Reaction
The dark reaction is also
known as the Calvin Cycle,
after an American scientist
(Melvin Calvin) who figured
out the pathway.
The dark reaction is also
known as the C3 Cycle
because the first stable
products of this pathway are
molecules that contain three
carbon atoms.
The Calvin Cycle occurs in
the stroma.
6 CO2
C
6 RuBP
C C C C C
6 ATP
C C C
~
12 PGA
e
6 ADP + P
12 ATP
~
e
12 ADP + P
C C C C C C
Glucose
C C C
12 PGAL
C C C
e-
C4
vs.
CAM
WHY??
The End!