The Reactions of
Photosynthesis
Photosynthesis - balanced
summary equation
light
6 CO2 + 6 H2O  C6H12O6 + 6 O2
The carbohydrates synthesized will provide
energy for nearly all living things.
The O2 is used by living things for
respiration.
Chapter 8
Section 8-3
Photosynthesis - overview
Pigments
• Pigments are molecules that absorb
specific wavelengths of light.
p y is the p
primary
yp
plant
• Chlorophyll
pigment
• The other pigments are referred to as
accessory pigments.
• Photosynthesis does 2 things:
–It collects (captures) energy from
the sun.
–It
It makes
k stable
t bl energy storage
t
molecules (sugars).
Photosynthesis - overview
Photosynthesis
• Photosynthesis has 2
parts
– Light dependent
reactions
– Light independent
reactions,
ti
also
l called
ll d
the Calvin cycle.
• These 2 parts are
linked together by the
charging and
discharging of energy
currency molecules.
Capturing energy
from the sun
Making stable
energy storage
molecules (sugars)
• The light dependent reactions take
energy from the sun and transfer it to
energy
gy currency
y molecules that will be
used to power the light independent
reactions (the Calvin cycle).
ATP and NADPH
1
Simplest model of
photosynthesis
Photosynthesis
• The light independent reactions (Calvin
cycle) discharge the energy currency
molecules to make large,
g , high
g energy
gy
storage molecules (sugars, carbohydrates)
out of small, low energy CO2. This is
sometimes referred to as carbon fixation.
sugars
H2 O
chloroplast
O2
CO2
Figure 8-7 Photosynthesis: An Overview
Light
dependent
reaction
provides
energy for
the Calvin
y
Cycle
Light
Chloroplast
NADP
ADP
+P
Light
reactions
Calvin
cycle
Figure 7.4
Light dependent reactions summary
• Require light
• Take place in the thylakoid membrane
of the chloroplasts
reactants
• Use light
light, chlorophyll,
chlorophyll H2O
• Charge NADP+ into NADPH
• Charge ADP into ATP products
• Produce O2 as a byproduct
Light Dependent Reactions (part 1 of 3)
e-
e-
Photosystems
in thylakoid
membrane
2
Light Dependent Reactions (2 of 3)
e-
NADP+
ADP
e-
Light Dependent Reactions (3 of 3)
e-
NADPH
NADP+
ATP
ADP
Photosystems
in thylakoid
membrane
eeUsed to power the
Calvin cycle (lightindependent reactions
NADPH
Photosystems
in thylakoid
membrane
(Replaces ejected e-)
H2O is split
H+
ATP
O2
Important
for us !!
Used to power the
Calvin cycle (lightindependent reactions
Checkpoint
• What are the two parts of photosynthesis?
• Where do the light dependent reactions of
photosynthesis take place?
Light independent reactions of
photosynthesis –the Calvin cycle
• Describe the three events that take place in the
light dependent reactions.
• What are the products of the light dependent
reactions?
Photosynthesis – Recall that…
• Photosynthesis has 2 parts
– Light dependent reactions
– Light independent reactions, also called
the Calvin cycle.
• These 2 parts are linked together by the
charging and discharging of energy
currency molecules.
Calvin cycle
• Plants use NADPH and ATP produced
by the light dependent reactions to
power a complex
p
p
series of reactions
that result in stable, high-energy storage
compounds.
3
Calvin cycle
• A carbon dioxide molecule (CO2) from
the atmosphere is joined with a 5-C
molecule recycled from a previous
Calvin cycle.
• This initial reaction is catalyzed by an
enzyme called Rubisco. This is the
most plentiful protein on the Earth.
Calvin cycle
• The reaction makes two 3-C molecules
out of the short-lived 6-C molecule.
• When 6 cycles
y
have been completed,
p
,
there are enough 3-C molecules to form
1 new 6-C sugar molecule (plus enough
left over to keep the Calvin cycle
running).
6 CO2
Photosynthesis - balanced
summary equation
12 H2O
+
+
light
6 CO2 + 6 H2O  C6H12O6 + 6 O2
6C
24 O
+
1 C6H12O6
Calvin Cycle checkpoint
• What are the main products of the
Calvin cycle?
24 H
+
6 H2O
6 O2
Rates of photosynthesis
• Raw materials
– Water, nutrients
• Temperature
High energy sugars
• 0-35OC
• Light intensity
– Has optimal intensities
– Too much or too little will slow rate
• ..\old lab programs\STARTCEL.EXE
4
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
use
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
NADPH
takes place in
Stroma
In the
O2
Chloroplasts
uses
ATP
NADPH
to produce
High-energy
sugars
Used in the Calvin
Cycle
5